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• uninitialized constant Active Scaffold rails 2.3.5

  - by Kiva

  Hi guy, I update my rails application 2.0.2 to 2.3.5. I use active scaffold for the administration part. I change nothing in my code but a problem is coming with the update. I have a controller 'admin/user_controller' to manage users. Here is the code of the controller: class Admin::UserController < ApplicationController layout 'admin' active_scaffold :user do |config| config.columns.exclude :content, :historique_content, :user_has_objet, :user_has_arme, :user_has_entrainement, :user_has_mission, :mp, :pvp, :user_salt, :tchat, :notoriete_by_pvp, :invitation config.list.columns = [:user_login, :user_niveau, :user_mail, :user_bloc, :user_valide, :group_id] #:user_description, :race, :group, :user_lastvisited, :user_nextaction, :user_combats_gagner, :user_combats_perdu, :user_combats_nul, :user_password, :user_salt, :user_combats, :user_experience, :user_mana, :user_vie config.create.link.page = true config.update.link.page = true config.create.columns.add :password, :password_confirmation config.update.columns.add :password, :password_confirmation config.create.columns.exclude :user_password, :user_salt config.update.columns.exclude :user_password, :user_salt config.list.sorting = {:user_login => 'ASC'} config.subform.columns = [] end end This code hasn't change with the update, but when I go in this page, I got this error: uninitialized constant Users /Users/Kiva/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:443:in `load_missing_constant' /Users/Kiva/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:80:in `const_missing' /Users/Kiva/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:92:in `const_missing' /Users/Kiva/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/inflector.rb:361:in `constantize' /Users/Kiva/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/inflector.rb:360:in `each' /Users/Kiva/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/inflector.rb:360:in `constantize' /Users/Kiva/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/string/inflections.rb:162:in `constantize' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/extensions/reverse_associations.rb:28:in `reverse_matches_for' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/extensions/reverse_associations.rb:24:in `each' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/extensions/reverse_associations.rb:24:in `reverse_matches_for' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/extensions/reverse_associations.rb:11:in `reverse' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/active_scaffold/data_structures/column.rb:117:in `autolink?' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/active_scaffold.rb:107:in `links_for_associations' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/active_scaffold/data_structures/columns.rb:62:in `each' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/active_scaffold/data_structures/columns.rb:62:in `each' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/active_scaffold.rb:106:in `links_for_associations' /Users/Kiva/Documents/Projet-rpg/jeu/vendor/plugins/active_scaffold/lib/active_scaffold.rb:59:in `active_scaffold' /Users/Kiva/Documents/Projet-rpg/jeu/app/controllers/admin/user_controller.rb:11 I search since 2 days but I don't find the problem, can you help me please.

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• Exception: attempt to acquire a reference on a close SQLiteClosable

  - by CommonsWare

  I posted this back in May on the [android-developers] Google Group. I never heard back and was not able to reproduce the problem until one of my students did last week. I figured I'd post it here and see if it rang any bells for anyone. In one of my code samples, I have the following method: static Cursor getAll(SQLiteDatabase db, String orderBy) { return(db.rawQuery("SELECT * FROM restaurants "+orderBy, null)); } When I run it, sporadically, I get this: 05-01 14:45:05.849: ERROR/AndroidRuntime(1145): java.lang.IllegalStateException: attempt to acquire a reference on a close SQLiteClosable 05-01 14:45:05.849: ERROR/AndroidRuntime(1145): at android.database.sqlite.SQLiteClosable.acquireReference(SQLiteClosable.java:31) 05-01 14:45:05.849: ERROR/AndroidRuntime(1145): at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:56) 05-01 14:45:05.849: ERROR/AndroidRuntime(1145): at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:49) 05-01 14:45:05.849: ERROR/AndroidRuntime(1145): at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:49) 05-01 14:45:05.849: ERROR/AndroidRuntime(1145): at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1118) 05-01 14:45:05.849: ERROR/AndroidRuntime(1145): at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1092) 05-01 14:45:05.849: ERROR/AndroidRuntime(1145): at apt.tutorial.Restaurant.getAll(Restaurant.java:14) This makes no sense to me. The database is definitely open. The SQLiteClosable is the SQLiteQuery created by SQLiteQueryDriver, and I see no evidence that there is an object pool or something going on here that might explain how a "new" SQLiteClosable is already closed. The fact that it is sporadic (meaning the same UI operations sometimes trigger the exception, but not always) suggests some sort of pool, race condition, or something...but I'm not sure where. Thoughts? Thanks! UPDATE: The code in question is from the LunchList tutorials out of my Android Programming Tutorials book. It's a bit spread out and not terribly suitable for posting directly in SO. You can download the code for that book from the above link if you want to take a look at it. I do not recall exactly which edition of the tutorial the student was working on at the time, though it was in the Tutorial 12-Tutorial 16 range. I was mostly hoping to run across somebody who had tripped over this problem before and had a likely culprit. I'm fairly certain my database is open. Thanks again!

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• How do I recover from an unchecked exception?

  - by erickson

  Unchecked exceptions are alright if you want to handle every failure the same way, for example by logging it and skipping to the next request, displaying a message to the user and handling the next event, etc. If this is my use case, all I have to do is catch some general exception type at a high level in my system, and handle everything the same way. But I want to recover from specific problems, and I'm not sure the best way to approach it with unchecked exceptions. Here is a concrete example. Suppose I have a web application, built using Struts2 and Hibernate. If an exception bubbles up to my "action", I log it, and display a pretty apology to the user. But one of the functions of my web application is creating new user accounts, that require a unique user name. If a user picks a name that already exists, Hibernate throws an org.hibernate.exception.ConstraintViolationException (an unchecked exception) down in the guts of my system. I'd really like to recover from this particular problem by asking the user to choose another user name, rather than giving them the same "we logged your problem but for now you're hosed" message. Here are a few points to consider: There a lot of people creating accounts simultaneously. I don't want to lock the whole user table between a "SELECT" to see if the name exists and an "INSERT" if it doesn't. In the case of relational databases, there might be some tricks to work around this, but what I'm really interested in is the general case where pre-checking for an exception won't work because of a fundamental race condition. Same thing could apply to looking for a file on the file system, etc. Given my CTO's propensity for drive-by management induced by reading technology columns in "Inc.", I need a layer of indirection around the persistence mechanism so that I can throw out Hibernate and use Kodo, or whatever, without changing anything except the lowest layer of persistence code. As a matter of fact, there are several such layers of abstraction in my system. How can I prevent them from leaking in spite of unchecked exceptions? One of the declaimed weaknesses of checked exceptions is having to "handle" them in every call on the stack—either by declaring that a calling method throws them, or by catching them and handling them. Handling them often means wrapping them in another checked exception of a type appropriate to the level of abstraction. So, for example, in checked-exception land, a file-system–based implementation of my UserRegistry might catch IOException, while a database implementation would catch SQLException, but both would throw a UserNotFoundException that hides the underlying implementation. How do I take advantage of unchecked exceptions, sparing myself of the burden of this wrapping at each layer, without leaking implementation details?

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• How would you implement this "WorkerChain" functionality in .NET?

  - by Dan Tao

  Sorry for the vague question title -- not sure how to encapsulate what I'm asking below succinctly. (If someone with editing privileges can think of a more descriptive title, feel free to change it.) The behavior I need is this. I am envisioning a worker class that accepts a single delegate task in its constructor (for simplicity, I would make it immutable -- no more tasks can be added after instantiation). I'll call this task T. The class should have a simple method, something like GetToWork, that will exhibit this behavior: If the worker is not currently running T, then it will start doing so right now. If the worker is currently running T, then once it is finished, it will start T again immediately. GetToWork can be called any number of times while the worker is running T; the simple rule is that, during any execution of T, if GetToWork was called at least once, T will run again upon completion (and then if GetToWork is called while T is running that time, it will repeat itself again, etc.). Now, this is pretty straightforward with a boolean switch. But this class needs to be thread-safe, by which I mean, steps 1 and 2 above need to comprise atomic operations (at least I think they do). There is an added layer of complexity. I have need of a "worker chain" class that will consist of many of these workers linked together. As soon as the first worker completes, it essentially calls GetToWork on the worker after it; meanwhile, if its own GetToWork has been called, it restarts itself as well. Logically calling GetToWork on the chain is essentially the same as calling GetToWork on the first worker in the chain (I would fully intend that the chain's workers not be publicly accessible). One way to imagine how this hypothetical "worker chain" would behave is by comparing it to a team in a relay race. Suppose there are four runners, W1 through W4, and let the chain be called C. If I call C.StartWork(), what should happen is this: If W1 is at his starting point (i.e., doing nothing), he will start running towards W2. If W1 is already running towards W2 (i.e., executing his task), then once he reaches W2, he will signal to W2 to get started, immediately return to his starting point and, since StartWork has been called, start running towards W2 again. When W1 reaches W2's starting point, he'll immediately return to his own starting point. If W2 is just sitting around, he'll start running immediately towards W3. If W2 is already off running towards W3, then W2 will simply go again once he's reached W3 and returned to his starting point. The above is probably a little convoluted and written out poorly. But hopefully you get the basic idea. Obviously, these workers will be running on their own threads. Also, I guess it's possible this functionality already exists somewhere? If that's the case, definitely let me know!

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• Using Core Data Concurrently and Reliably

  - by John Topley

  I'm building my first iOS app, which in theory should be pretty straightforward but I'm having difficulty making it sufficiently bulletproof for me to feel confident submitting it to the App Store. Briefly, the main screen has a table view, upon selecting a row it segues to another table view that displays information relevant for the selected row in a master-detail fashion. The underlying data is retrieved as JSON data from a web service once a day and then cached in a Core Data store. The data previous to that day is deleted to stop the SQLite database file from growing indefinitely. All data persistence operations are performed using Core Data, with an NSFetchedResultsController underpinning the detail table view. The problem I am seeing is that if you switch quickly between the master and detail screens several times whilst fresh data is being retrieved, parsed and saved, the app freezes or crashes completely. There seems to be some sort of race condition, maybe due to Core Data importing data in the background whilst the main thread is trying to perform a fetch, but I'm speculating. I've had trouble capturing any meaningful crash information, usually it's a SIGSEGV deep in the Core Data stack. The table below shows the actual order of events that happen when the detail table view controller is loaded: Main Thread Background Thread viewDidLoad Get JSON data (using AFNetworking) Create child NSManagedObjectContext (MOC) Parse JSON data Insert managed objects in child MOC Save child MOC Post import completion notification Receive import completion notification Save parent MOC Perform fetch and reload table view Delete old managed objects in child MOC Save child MOC Post deletion completion notification Receive deletion completion notification Save parent MOC Once the AFNetworking completion block is triggered when the JSON data has arrived, a nested NSManagedObjectContext is created and passed to an "importer" object that parses the JSON data and saves the objects to the Core Data store. The importer executes using the new performBlock method introduced in iOS 5: NSManagedObjectContext *child = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; [child setParentContext:self.managedObjectContext]; [child performBlock:^{ // Create importer instance, passing it the child MOC... }]; The importer object observes its own MOC's NSManagedObjectContextDidSaveNotification and then posts its own notification which is observed by the detail table view controller. When this notification is posted the table view controller performs a save on its own (parent) MOC. I use the same basic pattern with a "deleter" object for deleting the old data after the new data for the day has been imported. This occurs asynchronously after the new data has been fetched by the fetched results controller and the detail table view has been reloaded. One thing I am not doing is observing any merge notifications or locking any of the managed object contexts or the persistent store coordinator. Is this something I should be doing? I'm a bit unsure how to architect this all correctly so would appreciate any advice.

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• waiting for 2 different events in a single thread

  - by João Portela

  component A (in C++) - is blocked waiting for alarm signals (not relevant) and IO signals (1 udp socket). has one handler for each of these. component B (java) - has to receive the same information the component A udp socket receives. periodicaly gives instructions that should be sent through component A udp socket. How to join both components? it is strongly desirable that: the changes to attach component B to component A are minimal (its not my code and it is not very pleasent to mess with). the time taken by the new operations (usually communicating with component B) interfere very little with the usual processing time of component A - this means that if the operations are going to take a "some" time I would rather use a thread or something to do them. note: since component A receives udp packets more frequently that it has component B instructions to forward, if necessary, it can only forward the instructions (when available) from the IO handler. my initial ideia was to develop a component C (in C++) that would sit inside the component A code (is this called an adapter?) that when instanciated starts the java process and makes the necessary connections (that not so little overhead in the initialization is not a problem). It would have 2 stacks, one for the data to give component B (lets call it Bstack) and for the data to give component A (lets call it Astack). It would sit on its thread (lets call it new-thread) waiting for data to be available in Bstack to send it over udp, and listen on the udp socket to put data on the Astack. This means that the changes to component A are only: when it receives a new UDP packet put it on the Bstack, and if there is something on the Astack sent it over its UDP socket (I decided for this because this socket would only be used in the main thread). One of the problems is that I don't know how to wait for both of these events at the same time using only one thread. so my questions are: Do I really need to use the main thread to send the data over component A socket or can I do it from the new-thread? (I think the answer is no, but I'm not sure about race conditions on sockets) how to I wait for both events? boost::condition_variable or something similar seems the solution in the case of the stack and boost::asio::io_service io_service.run() seems like the thing to use for the socket. Is there any other alternative solution for this problem that I'm not aware of? Thanks for reading this long text but I really wanted you to understand the problem.

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• What's the best way to handle modules that use each other?

  - by Axeman

  What's the best way to handle modules that use each other? Let's say I have a module which has functions for hashes: # Really::Useful::Functions::On::Hash.pm use base qw<Exporter>; use strict; use warnings; use Really::Useful::Functions::On::List qw<transform_list>; our @EXPORT_OK = qw<transform_hash transform_hash_as_list ...>; #... sub transform_hash { ... } #... sub transform_hash_as_list { return transform_list( %{ shift() } ); } #... 1 And another module has been segmented out for lists: # Really::Useful::Functions::On::List.pm use base qw<Exporter>; use strict; use warnings; use Really::Useful::Functions::On::Hash qw<transform_hash>; our @EXPORT_OK = qw<transform_list some_func ...>; #... sub transform_list { ... } #... sub some_func { my %params = transform_hash @_; #... } #... 1 Suppose that enough of these utility functions are handy enough that I'll want to use them in BEGIN statements and import functions to process parameter lists or configuration data. I have been putting sub definitions into BEGIN blocks to make sure they are ready to use whenever somebody includes the module. But I have gotten into hairy race conditions where a definition is not completed in a BEGIN block. I put evolving code idioms into modules so that I can reuse any idiom I find myself coding over and over again. For instance: sub list_if { my $condition = shift; return unless $condition; my $more_args = scalar @_; my $arg_list = @_ > 1 ? \@_ : @_ ? shift : $condition; if (( reftype( $arg_list ) || '' ) eq 'ARRAY' ) { return wantarray ? @$arg_list : $arg_list; } elsif ( $more_args ) { return $arg_list; } return; } captures two idioms that I'm kind of tired of typing: @{ func_I_hope_returns_a_listref() || [] } and ( $condition ? LIST : ()) The more I define functions in BEGIN blocks, the more likely I'll use these idiom bricks to express the logic the more likely that bricks are needed in BEGIN blocks. Do people have standard ways of dealing with this sort of language-idiom-brick model? I've been doing mostly Pure-Perl; will XS alleviate some of this?

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• Top 10 Reasons SQL Developer is Perfect for Oracle Beginners

  - by thatjeffsmith

  Learning new technologies can be daunting. If you’ve never used a Mac before, you’ll probably be a bit baffled at first. But, you’re probably at least coming from a desktop computing background (Windows), so you common frame of reference. But what if you’re just now learning to use a relational database? Yes, you’ve played with Access a bit, but now your employer or college instructor has charged you with becoming proficient with Oracle database. Here’s 10 reasons why I think Oracle SQL Developer is the perfect vehicle to help get you started. 1. It’s free No need to break into one of these… No start-up costs, no need to wrangle budget dollars from your company. Students don’t have any money after books and lab fees anyway. And most employees don’t like having to ask for ‘special’ software anyway. So avoid all of that and make sure the free stuff doesn’t suit your needs first. Upgrades are available on a regular base, also at no cost, and support is freely available via our public forums. 2. It will run pretty much anywhere Windows – check. OSX (Apple) – check. Unix – check. Linux – check. No need to start up a windows VM to run your Windows-only software in your lab machine. 3. Anyone can install it There’s no installer, no registry to be updated, no admin privs to be obtained. If you can download and extract files to your machine or USB storage device, you can run it. You can be up and running with SQL Developer in under 5 minutes. Here’s a video tutorial to see how to get started. 4. It’s ubiquitous I admit it, I learned a new word yesterday and I wanted an excuse to use it. SQL Developer’s everywhere. It’s had over 2,500,000 downloads in the past year, and is the one of the most downloaded items from OTN. This means if you need help, there’s someone sitting nearby you that can assist, and since they’re in the same tool as you, they’ll be speaking the same language. 5. Simple User Interface Up-up-down-down-Left-right-left-right-A-B-A-B-START will get you 30 lives, but you already knew that, right? You connect, you see your objects, you click on your objects. Or, you can use the worksheet to write your queries and programs in. There’s only one toolbar, and just a few buttons. If you’re like me, video games became less fun when each button had 6 action items mapped to it. I just want the good ole ‘A’, ‘B’, ‘SELECT’, and ‘START’ controls. If you’re new to Oracle, you shouldn’t have the double-workload of learning a new complicated tool as well. 6. It’s not a ‘black box’ Click through your objects, but also get the SQL that drives the GUI As you use the wizards to accomplish tasks for you, you can view the SQL statement being generated on your behalf. Just because you have a GUI, doesn’t mean you’re ceding your responsibility to learn the underlying code that makes the database work. 7. It’s four tools in one It’s not just a query tool. Maybe you need to design a data model first? Or maybe you need to migrate your Sybase ASE database to Oracle for a new project? Or maybe you need to create some reports? SQL Developer does all of that. So once you get comfortable with one part of the tool, the others will be much easier to pick up as your needs change. 8. Great learning resources available Videos, blogs, hands-on learning labs – you name it, we got it. Why wait for someone to train you, when you can train yourself at your own pace? 9. You can use it to teach yourself SQL Instead of being faced with the white-screen-of-panic, you can visually build your queries by dragging and dropping tables and views into the Query Builder. Yes, ‘just like Access’ – only better. And as you build your query, toggle to the Worksheet panel and see the SQL statement. Again, SQL Developer is not a black box. If you prefer to learn by trial and error, the worksheet will attempt to suggest the next bit of your SQL statement with it’s completion insight feature. And if you have syntax errors, those will be highlighted – just like your misspelled words in your favorite word processor. 10. It scales to match your experience level You won’t be a n00b forever. In 6-8 months, when you’re ready to tackle something a bit more complicated, like XML DB or Oracle Spatial, the tool is already there waiting on you. No need to go out and find the ‘advanced’ tool. 11. Wait, you said this was a ‘Top 10′ list? Yes. Yes, I did. I’m using this ‘trick’ to get you to continue reading because I’m going to say something you might not want to hear. Are you ready? Tools won’t replace experience, failure, hard work, and training. Just because you have the keys to the car, doesn’t mean you’re ready to head out on the race track. While SQL Developer reduces the barriers to entry, it does not completely remove them. Many experienced folks simply do not like tools. Rather, they don’t like the people that pick up tools without the know-how to properly use them. If you don’t understand what ‘TRUNCATE’ means, don’t try it out. Try picking up a book first. Of course, it’s very nice to have your own sandbox to play in, so you don’t upset the other children. That’s why I really like our Dev Days Database Virtual Box image. It’s your own database to learn and experiment with.

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• And What's Your Brand Worth? ...anything?

  - by [email protected]

  100 Best Global Brands from Business Week Story: The Great Trust Offensive Slide Show: Top Brands 2009 Methodology: Picking the Winners The recession has presented marketing executives around the world with the toughest test of their careers. Some brands have prospered amid the hard times--or at least held their own. Others have slipped a surprising number of places on our ninth annual ranking, compiled by consultancy Interbrand. But for seven brands, impressive performances saw them race up the charts to take their place on this year's list. Here are the numbers behind the rankings Rank 2009 Rank 2008 Employer 2009 Brand value($millions) 2008 Brand value($millions) Percent change(%) Country of Ownership 1 1 Coca-Cola  68,734  66,667  3 U.S. 2 2 IBM  60,211  59,031  2 U.S. 3 3 Microsoft  56,647  59,007  -4 U.S. 4 4 GE  47,777  53,086  -10 U.S. 5 5 Nokia  34,864  35,942  -3 Finland 6 8 McDonald's  32,275  31,049  4 U.S. 7 10 Google  31,980  25,590  25 U.S. 8 6 Toyota  31,330  34,050  -8 Japan 9 7 Intel  30,636  31,261  -2 U.S. 10 9 Disney  28,447  29,251  -3 U.S. 11 12 Hewlett-Packard  24,096  23,509  2 U.S. 12 11 Mercedes-Benz  23,867  25,577  -7 Germany 13 14 Gillette  22,841  22,069  4 U.S. 14 17 Cisco  22,030  21,306  3 U.S. 15 13 BMW  21,671  23,298  -7 Germany 16 16 Louis Vuitton  21,120  21,602  -2 France 17 18 Marlboro  19,010  21,300  -11 U.S. 18 20 Honda  17,803  19,079  -7 Japan 19 21 Samsung  17,518  17,689  -1 S. Korea 20 24 Apple  15,443  13,724  12 U.S. 21 22 H&M  15,375  13,840  11 Sweden 22 15 American Express  14,971  21,940  -32 U.S. 23 26 Pepsi  13,706  13,249  3 U.S. 24 23 Oracle  13,699  13,831  -1 U.S. 25 28 Nescafe  13,317  13,055  2 Switzerland 26 29 Nike  13,179  12,672  4 U.S. 27 31 SAP  12,106  12,228  -1 Germany 28 35 Ikea  12,004  10,913  10 Sweden 29 25 Sony  11,953  13,583  -12 Japan 30 33 Budweiser  11,833  11,438  3 Belgium 31 30 UPS  11,594  12,621  -8 U.S. 32 27 HSBC  10,510  13,143  -20 Britain 33 36 Canon  10,441  10,876  -4 Japan 34 39 Kellogg's  10,428  9,710  7 U.S. 35 32 Dell  10,291  11,695  -12 U.S. 36 19 Citi  10,254  20,174  -49 U.S. 37 37 JPMorgan  9,550  10,773  -11 U.S. 38 38 Goldman Sachs  9,248  10,331  -10 U.S. 39 40 Nintendo  9,210  8,772  5 Japan 40 44 Thomson Reuters  8,434  8,313  1 Canada 41 45 Gucci  8,182  8,254  -1 Italy 42 43 Philips  8,121  8,325  -2 Netherlands 43 58 Amazon  7,858  6,434  22 U.S. 44 51 L'Oreal  7,748  7,508  3 France 45 47 Accenture  7,710  7,948  -3 U.S. 46 46 eBay  7,350  7,991  -8 U.S. 47 48 Siemens  7,308  7,943  -8 Germany 48 56 Heinz  7,244  6,646  9 U.S. 49 49 Ford  7,005  7,896  -11 U.S. 50 62 Zara  6,789  5,955  14 Spain   Valuations do not represent a guarantee of future performance of the brands or companies. Data: Interbrand, BusinessWeek

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• More Fun With Math

  - by PointsToShare

  More Fun with Math   The runaway student – three different ways of solving one problem Here is a problem I read in a Russian site: A student is running away. He is moving at 1 mph. Pursuing him are a lion, a tiger and his math teacher. The lion is 40 miles behind and moving at 6 mph. The tiger is 28 miles behind and moving at 4 mph. His math teacher is 30 miles behind and moving at 5 mph. Who will catch him first? Analysis Obviously we have a set of three problems. They are all basically the same, but the details are different. The problems are of the same class. Here is a little excursion into computer science. One of the things we strive to do is to create solutions for classes of problems rather than individual problems. In your daily routine, you call it re-usability. Not all classes of problems have such solutions. If a class has a general (re-usable) solution, it is called computable. Otherwise it is unsolvable. Within unsolvable classes, we may still solve individual (some but not all) problems, albeit with different approaches to each. Luckily the vast majority of our daily problems are computable, and the 3 problems of our runaway student belong to a computable class. So, let’s solve for the catch-up time by the math teacher, after all she is the most frightening. She might even make the poor runaway solve this very problem – perish the thought! Method 1 – numerical analysis. At 30 miles and 5 mph, it’ll take her 6 hours to come to where the student was to begin with. But by then the student has advanced by 6 miles. 6 miles require 6/5 hours, but by then the student advanced by another 6/5 of a mile as well. And so on and so forth. So what are we to do? One way is to write code and iterate it until we have solved it. But this is an infinite process so we’ll end up with an infinite loop. So what to do? We’ll use the principles of numerical analysis. Any calculator – your computer included – has a limited number of digits. A double floating point number is good for about 14 digits. Nothing can be computed at a greater accuracy than that. This means that we will not iterate ad infinidum, but rather to the point where 2 consecutive iterations yield the same result. When we do financial computations, we don’t even have to go that far. We stop at the 10th of a penny.  It behooves us here to stop at a 10th of a second (100 milliseconds) and this will how we will avoid an infinite loop. Interestingly this alludes to the Zeno paradoxes of motion – in particular “Achilles and the Tortoise”. Zeno says exactly the same. To catch the tortoise, Achilles must always first come to where the tortoise was, but the tortoise keeps moving – hence Achilles will never catch the tortoise and our math teacher (or lion, or tiger) will never catch the student, or the policeman the thief. Here is my resolution to the paradox. The distance and time in each step are smaller and smaller, so the student will be caught. The only thing that is infinite is the iterative solution. The race is a convergent geometric process so the steps are diminishing, but each step in the solution takes the same amount of effort and time so with an infinite number of steps, we’ll spend an eternity solving it.  This BTW is an original thought that I have never seen before. But I digress. Let’s simply write the code to solve the problem. To make sure that it runs everywhere, I’ll do it in JavaScript. function LongCatchUpTime(D, PV, FV) // D is Distance; PV is Pursuers Velocity; FV is Fugitive’ Velocity {     var t = 0;     var T = 0;     var d = parseFloat(D);     var pv = parseFloat (PV);     var fv = parseFloat (FV);     t = d / pv;     while (t > 0.000001) //a 10th of a second is 1/36,000 of an hour, I used 1/100,000     {         T = T + t;         d = t * fv;         t = d / pv;     }     return T;     } By and large, the higher the Pursuer’s velocity relative to the fugitive, the faster the calculation. Solving this with the 10th of a second limit yields: 7.499999232000001 Method 2 – Geometric Series. Each step in the iteration above is smaller than the next. As you saw, we stopped iterating when the last step was small enough, small enough not to really matter.  When we have a sequence of numbers in which the ratio of each number to its predecessor is fixed we call the sequence geometric. When we are looking at the sum of sequence, we call the sequence of sums series.  Now let’s look at our student and teacher. The teacher runs 5 times faster than the student, so with each iteration the distance between them shrinks to a fifth of what it was before. This is a fixed ratio so we deal with a geometric series.  We normally designate this ratio as q and when q is less than 1 (0 < q < 1) the sum of  + … +  is  – 1) / (q – 1). When q is less than 1, it is easier to use ) / (1 - q). Now, the steps are 6 hours then 6/5 hours then 6/5*5 and so on, so q = 1/5. And the whole series is multiplied by 6. Also because q is less than 1 , 1/  diminishes to 0. So the sum is just  / (1 - q). or 1/ (1 – 1/5) = 1 / (4/5) = 5/4. This times 6 yields 7.5 hours. We can now continue with some algebra and take it back to a simpler formula. This is arduous and I am not going to do it here. Instead let’s do some simpler algebra. Method 3 – Simple Algebra. If the time to capture the fugitive is T and the fugitive travels at 1 mph, then by the time the pursuer catches him he travelled additional T miles. Time is distance divided by speed, so…. (D + T)/V = T  thus D + T = VT  and D = VT – T = (V – 1)T  and T = D/(V – 1) This “strangely” coincides with the solution we just got from the geometric sequence. This is simpler ad faster. Here is the corresponding code. function ShortCatchUpTime(D, PV, FV) {     var d = parseFloat(D);     var pv = parseFloat (PV);     var fv = parseFloat (FV);     return d / (pv - fv); } The code above, for both the iterative solution and the algebraic solution are actually for a larger class of problems.  In our original problem the student’s velocity (speed) is 1 mph. In the code it may be anything as long as it is less than the pursuer’s velocity. As long as PV > FV, the pursuer will catch up. Here is the really general formula: T = D / (PV – FV) Finally, let’s run the program for each of the pursuers.  It could not be worse. I know he’d rather be eaten alive than suffering through yet another math lesson. See the code run? Select  “Catch Up Time” in www.mgsltns.com/games.htm The host is running on Unix, so the link is case sensitive. That’s All Folks

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• tile_static, tile_barrier, and tiled matrix multiplication with C++ AMP

  - by Daniel Moth

  We ended the previous post with a mechanical transformation of the C++ AMP matrix multiplication example to the tiled model and in the process introduced tiled_index and tiled_grid. This is part 2. tile_static memory You all know that in regular CPU code, static variables have the same value regardless of which thread accesses the static variable. This is in contrast with non-static local variables, where each thread has its own copy. Back to C++ AMP, the same rules apply and each thread has its own value for local variables in your lambda, whereas all threads see the same global memory, which is the data they have access to via the array and array_view. In addition, on an accelerator like the GPU, there is a programmable cache, a third kind of memory type if you'd like to think of it that way (some call it shared memory, others call it scratchpad memory). Variables stored in that memory share the same value for every thread in the same tile. So, when you use the tiled model, you can have variables where each thread in the same tile sees the same value for that variable, that threads from other tiles do not. The new storage class for local variables introduced for this purpose is called tile_static. You can only use tile_static in restrict(direct3d) functions, and only when explicitly using the tiled model. What this looks like in code should be no surprise, but here is a snippet to confirm your mental image, using a good old regular C array // each tile of threads has its own copy of locA, // shared among the threads of the tile tile_static float locA[16][16]; Note that tile_static variables are scoped and have the lifetime of the tile, and they cannot have constructors or destructors. tile_barrier In amp.h one of the types introduced is tile_barrier. You cannot construct this object yourself (although if you had one, you could use a copy constructor to create another one). So how do you get one of these? You get it, from a tiled_index object. Beyond the 4 properties returning index objects, tiled_index has another property, barrier, that returns a tile_barrier object. The tile_barrier class exposes a single member, the method wait. 15: // Given a tiled_index object named t_idx 16: t_idx.barrier.wait(); 17: // more code …in the code above, all threads in the tile will reach line 16 before a single one progresses to line 17. Note that all threads must be able to reach the barrier, i.e. if you had branchy code in such a way which meant that there is a chance that not all threads could reach line 16, then the code above would be illegal. Tiled Matrix Multiplication Example – part 2 So now that we added to our understanding the concepts of tile_static and tile_barrier, let me obfuscate rewrite the matrix multiplication code so that it takes advantage of tiling. Before you start reading this, I suggest you get a cup of your favorite non-alcoholic beverage to enjoy while you try to fully understand the code. 01: void MatrixMultiplyTiled(vector<float>& vC, const vector<float>& vA, const vector<float>& vB, int M, int N, int W) 02: { 03: static const int TS = 16; 04: array_view<const float,2> a(M, W, vA); 05: array_view<const float,2> b(W, N, vB); 06: array_view<writeonly<float>,2> c(M,N,vC); 07: parallel_for_each(c.grid.tile< TS, TS >(), 08: [=] (tiled_index< TS, TS> t_idx) restrict(direct3d) 09: { 10: int row = t_idx.local[0]; int col = t_idx.local[1]; 11: float sum = 0.0f; 12: for (int i = 0; i < W; i += TS) { 13: tile_static float locA[TS][TS], locB[TS][TS]; 14: locA[row][col] = a(t_idx.global[0], col + i); 15: locB[row][col] = b(row + i, t_idx.global[1]); 16: t_idx.barrier.wait(); 17: for (int k = 0; k < TS; k++) 18: sum += locA[row][k] * locB[k][col]; 19: t_idx.barrier.wait(); 20: } 21: c[t_idx.global] = sum; 22: }); 23: } Notice that all the code up to line 9 is the same as per the changes we made in part 1 of tiling introduction. If you squint, the body of the lambda itself preserves the original algorithm on lines 10, 11, and 17, 18, and 21. The difference being that those lines use new indexing and the tile_static arrays; the tile_static arrays are declared and initialized on the brand new lines 13-15. On those lines we copy from the global memory represented by the array_view objects (a and b), to the tile_static vanilla arrays (locA and locB) – we are copying enough to fit a tile. Because in the code that follows on line 18 we expect the data for this tile to be in the tile_static storage, we need to synchronize the threads within each tile with a barrier, which we do on line 16 (to avoid accessing uninitialized memory on line 18). We also need to synchronize the threads within a tile on line 19, again to avoid the race between lines 14, 15 (retrieving the next set of data for each tile and overwriting the previous set) and line 18 (not being done processing the previous set of data). Luckily, as part of the awesome C++ AMP debugger in Visual Studio there is an option that helps you find such races, but that is a story for another blog post another time. May I suggest reading the next section, and then coming back to re-read and walk through this code with pen and paper to really grok what is going on, if you haven't already? Cool. Why would I introduce this tiling complexity into my code? Funny you should ask that, I was just about to tell you. There is only one reason we tiled our extent, had to deal with finding a good tile size, ensure the number of threads we schedule are correctly divisible with the tile size, had to use a tiled_index instead of a normal index, and had to understand tile_barrier and to figure out where we need to use it, and double the size of our lambda in terms of lines of code: the reason is to be able to use tile_static memory. Why do we want to use tile_static memory? Because accessing tile_static memory is around 10 times faster than accessing the global memory on an accelerator like the GPU, e.g. in the code above, if you can get 150GB/second accessing data from the array_view a, you can get 1500GB/second accessing the tile_static array locA. And since by definition you are dealing with really large data sets, the savings really pay off. We have seen tiled implementations being twice as fast as their non-tiled counterparts. Now, some algorithms will not have performance benefits from tiling (and in fact may deteriorate), e.g. algorithms that require you to go only once to global memory will not benefit from tiling, since with tiling you already have to fetch the data once from global memory! Other algorithms may benefit, but you may decide that you are happy with your code being 150 times faster than the serial-version you had, and you do not need to invest to make it 250 times faster. Also algorithms with more than 3 dimensions, which C++ AMP supports in the non-tiled model, cannot be tiled. Also note that in future releases, we may invest in making the non-tiled model, which already uses tiling under the covers, go the extra step and use tile_static memory on your behalf, but it is obviously way to early to commit to anything like that, and we certainly don't do any of that today. Comments about this post by Daniel Moth welcome at the original blog.

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• 5 Best Practices - Laying the Foundation for WebCenter Projects

  - by Kellsey Ruppel

  Today’s guest post comes from Oracle WebCenter expert John Brunswick. John specializes in enterprise portal and content management solutions and actively contributes to the enterprise software business community and has authored a series of articles about optimal business involvement in portal, business process management and SOA development, examining ways of helping organizations move away from monolithic application development. We’re happy to have John join us today! Maximizing success with Oracle WebCenter portal requires a strategic understanding of Oracle WebCenter capabilities.  The following best practices enable the creation of portal solutions with minimal resource overhead, while offering the greatest flexibility for progressive elaboration. They are inherently project agnostic, enabling a strong foundation for future growth and an expedient return on your investment in the platform.  If you are able to embrace even only a few of these practices, you will materially improve your deployment capability with WebCenter. 1. Segment Duties Around 3Cs - Content, Collaboration and Contextual Data "Agility" is one of the most common business benefits touted by modern web platforms.  It sounds good - who doesn't want to be Agile, right?  How exactly IT organizations go about supplying agility to their business counterparts often lacks definition - hamstrung by ambiguity. Ultimately, businesses want to benefit from reduced development time to deliver a solution to a particular constituent, which is augmented by as much self-service as possible to develop and manage the solution directly. All done in the absence of direct IT involvement. With Oracle WebCenter's depth in the areas of content management, pallet of native collaborative services, enterprise mashup capability and delegated administration, it is very possible to execute on this business vision at a technical level. To realize the benefits of the platform depth we can think of Oracle WebCenter's segmentation of duties along the lines of the 3 Cs - Content, Collaboration and Contextual Data.  All three of which can have their foundations developed by IT, then provisioned to the business on a per role basis. Content – Oracle WebCenter benefits from an extremely mature content repository.  Work flow, audit, notification, office integration and conversion capabilities for documents (HTML & PDF) make this a haven for business users to take control of content within external and internal portals, custom applications and web sites.  When deploying WebCenter portal take time to think of areas in which IT can provide the "harness" for content to reside, then allow the business to manage any content items within the site, using the content foundation to ensure compliance with business rules and process.  This frees IT to work on more mission critical challenges and allows the business to respond in short order to emerging market needs. Collaboration – Native collaborative services and WebCenter spaces are a perfect match for business users who are looking to enable document sharing, discussions and social networking.  The ability to deploy the services is granular and on the basis of roles scoped to given areas of the system - much like the first C “content”.  This enables business analysts to design the roles required and IT to provision with peace of mind that users leveraging the collaborative services are only able to do so in explicitly designated areas of a site. Bottom line - business will not need to wait for IT, but cannot go outside of the scope that has been defined based on their roles. Contextual Data – Collaborative capabilities are most powerful when included within the context of business data.  The ability to supply business users with decision shaping data that they can include in various parts of a portal or portals, just as they would with content items, is one of the most powerful aspects of Oracle WebCenter.  Imagine a discussion about new store selection for a retail chain that re-purposes existing information from business intelligence services about various potential locations and or custom backend systems - presenting it directly in the context of the discussion.  If there are some data sources that are preexisting in your enterprise take a look at how they can be made into discrete offerings within the portal, then scoped to given business user roles for inclusion within collaborative activities. 2. Think Generically, Execute Specifically Constructs.  Anyone who has spent much time around me knows that I am obsessed with this word.  Why? Because Constructs offer immense power - more than APIs, Web Services or other technical capability. Constructs offer organizations the ability to leverage a platform's native characteristics to offer substantial business functionality - without writing code.  This concept becomes more powerful with the additional understanding of the concepts from the platform that an organization learns over time.  Let's take a look at an example of where an Oracle WebCenter construct can substantially reduce the time to get a subscription-based site out the door and into the hands of the end consumer. Imagine a site that allows members to subscribe to specific disciplines to access information and application data around that various discipline.  A space is a collection of secured pages within Oracle WebCenter.  Spaces are not only secured, but also default content stored within it to be scoped automatically to that space. Taking this a step further, Oracle WebCenter’s Activity Stream surfaces events, discussions and other activities that are scoped to the given user on the basis of their space affiliations.  In order to have a portal that would allow users to "subscribe" to information around various disciplines - spaces could be used out of the box to achieve this capability and without using any APIs or low level technical work to achieve this. 3. Make Governance Work for You Imagine driving down the street without the painted lines on the road.  The rules of the road are so ingrained in our minds, we often do not think about the process, but seemingly mundane lane markers are critical enablers. Lane markers allow us to travel at speeds that would be impossible if not for the agreed upon direction of flow. Additionally and more importantly, it allows people to act autonomously - going where they please at any given time. The return on the investment for mobility is high enough for people to buy into globally agreed up governance processes. In Oracle WebCenter we can use similar enablers to lane markers.  Our goal should be to enable the flow of information and provide end users with the ability to arrive at business solutions as needed, not on the basis of cumbersome processes that cannot meet the business needs in a timely fashion. How do we do this? Just as with "Segmentation of Duties" Oracle WebCenter technologies offer the opportunity to compartmentalize various business initiatives from each other within the system due to constructs and security that are available to use within the platform. For instance, when a WebCenter space is created, any content added within that space by default will be secured to that particular space and inherits meta data that is associated with a folder created for the space. Oracle WebCenter content uses meta data to support a broad range of rich ECM functionality and can automatically impart retention, workflow and other policies automatically on the basis of what has been defaulted for that space. Depending on your business needs, this paradigm will also extend to sub sections of a space, offering some interesting possibilities to enable automated management around content. An example may be press releases within a particular area of an extranet that require a five year retention period and need to the reviewed by marketing and legal before release.  The underlying content system will transparently take care of this process on the basis of the above rules, enabling peace of mind over unstructured data - which could otherwise become overwhelming. 4. Make Your First Project Your Second Imagine if Michael Phelps was competing in a swimming championship, but told right before his race that he had to use a brand new stroke.  There is no doubt that Michael is an outstanding swimmer, but chances are that he would like to have some time to get acquainted with the new stroke. New technologies should not be treated any differently.  Before jumping into the deep end it helps to take time to get to know the new approach - even though you may have been swimming thousands of times before. To quickly get a handle on Oracle WebCenter capabilities it can be helpful to deploy a sandbox for the team to use to share project documents, discussions and announcements in an effort to help the actual deployment get under way, while increasing everyone’s knowledge of the platform and its functionality that may be helpful down the road. Oracle Technology Network has made a pre-configured virtual machine available for download that can be a great starting point for this exercise. 5. Get to Know the Community If you are reading this blog post you have most certainly faced a software decision or challenge that was solved on the basis of a small piece of missing critical information - which took substantial research to discover.  Chances were also good that somewhere, someone had already come across this information and would have been excited to share it. There is no denying the power of passionate, connected users, sharing key tips around technology.  The Oracle WebCenter brand has a rich heritage that includes industry-leading technology and practitioners.  With the new Oracle WebCenter brand, opportunities to connect with these experts has become easier. Oracle WebCenter Blog Oracle Social Enterprise LinkedIn WebCenter Group Oracle WebCenter Twitter Oracle WebCenter Facebook Oracle User Groups Additionally, there are various Oracle WebCenter related blogs by an excellent grouping of services partners.

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• php script gets two ajax requests, only returns one?

  - by Dan.StackOverflow

  I'll start from the beginning. I'm building a wordpress plugin that does double duty, in that it can be inserted in to a post via a shortcode, or added as a sidebar widget. All it does is output some js to make jquery.post requests to a local php file. The local php file makes a request to a webservice for some data. (I had to do it this way instead of directly querying the web service with jquery.ajax because the url contains a license key that would be public if put in the js). Anyway, When I am viewing a page in the wordpress blog that has both the sidebar widget and the plugin output via shortcode only one of the requests work. I mean it works in that it gets a response back from the php script. Once the page is loaded they both work normally when manually told to. Webpage view - send 2 post requests to my php script - both elements should be filed in, but only one is. My php script is just: <?php if(isset($_POST["zip"])) { // build a curl object, execute the request, // and basically just echo what the curl request returns. } ?> Pretty basic. here is some js some people wanted to see: function widget_getActivities( zip ){ jQuery("#widget_active_list").text(""); jQuery.post("http://localhost/wordpress/wp-content/ActiveAjax.php", { zip: zip}, function(text) { jQuery(text).find("asset").each(function(j, aval){ var html = ""; html += "<a href='" + jQuery(aval).find("trackback").text() + "' target='new'> " + jQuery(aval).find("assetName").text() + "</a><b> at </b>"; jQuery("location", aval).each(function(i, val){ html += jQuery("locationName", val).text() + " <b> on </b>"; }); jQuery("date", aval).each(function(){ html += jQuery("startDate", aval).text(); <!--jQuery("#widget_active_list").append("<div id='ActivityEntry'>" + html + " </div>");--> jQuery("#widget_active_list") .append(jQuery("<div>") .addClass("widget_ActivityEntry") .html(html) .bind("mouseenter", function(){ jQuery(this).animate({ fontSize: "20px", lineHeight: "1.2em" }, 50); }) .bind("mouseleave", function(){ jQuery(this).animate({ fontSize: "10px", lineHeight: "1.2em" }, 50); }) ); }); }); }); } Now imagine there is another function identical to this one except everything that is prepended with 'widget_' isn't prepended. These two functions get called separately via: jQuery(document).ready(function(){ w_zip = jQuery("#widget_zip").val(); widget_getActivities( w_zip ); jQuery("#widget_updateZipLink").click(function() { //start function when any update link is clicked widget_c_zip = jQuery("#widget_zip").val(); if (undefined == widget_c_zip || widget_c_zip == "" || widget_c_zip.length != 5) jQuery("#widget_zipError").text("Bad zip code"); else widget_getActivities( widget_c_zip ); }); }) I can see in my apache logs that both requests are being made. I'm guessing it is some sort of race condition but that doesn't make ANY sense. I'm new to all this, any ideas? EDIT: I've come up with a sub-optimal solution. I have my widget detect if the plugin is also being used on the page, and if so it waits for 3 seconds before performing the request. But I have a feeling this same thing is going to happen if multiple clients perform a page request at the same time that triggers one of the requests to my php script, because I believe the problem is in the php script, which is scary.

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• Need some help with my XML Schema.

  - by Airjoe

  I'm using Qt C++ and am reading in an XML file for data. I want to ensure the XML file contains valid elements, so I began to write an XML Schema to validate against (Qt doesn't support validating against a DTD). The problem is, I'm not sure if my Schema itself is valid, and I can't seem to find an actual XSD validator. I tried using the official w3c validator at http://www.w3.org/2001/03/webdata/xsv, but it's giving me blank output. Would anyone know of a decent XSD validator, or perhaps be willing to look over the following manually? <?xml version="1.0"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified"> <xs:element name="ballot"> <xs:complexType> <xs:sequence> <xs:element name="races"> <xs:complexType> <xs:element name="race" minOccurs="1" maxOccurs="unbounded"> <xs:complexType> <xs:sequence> <xs:element name="rtitle" minOccurs="1" maxOccurs="1" type="xs:string"/> <xs:element name="candidates" minOccurs="1" maxOccurs="1"> <xs:complexType> <xs:element name="candidate" minOccurs="1" maxOccurs="10"> <xs:complexType> <xs:element name="candname" minOccurs="1" maxOccurs="1" type="xs:string"/> <xs:element name="candparty" minOccurs="1" maxOccurs="1" type="xs:string"/> </xs:complexType> </xs:element> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> </xs:element> </xs:complexType> </xs:element> <xs:element name="propositions"> <xs:complexType> <xs:element name="proposition" minOccurs="1" maxOccurs="unbounded"> <xs:complexType> <xs:element name="ptitle" minOccurs="1" maxOccurs="1" type="xs:string"/> <xs:element name="pdesc" minOccurs="1" maxOccurs="1" type="xs:string"/> </xs:complexType> </xs:element> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> </xs:element> </xs:schema> Please let me know what you think, I appreciate it!

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• Unable to launch onscreen keyboard (osk.exe) from a 32-bit process on Win7 x64

  - by Steven Robbins

  90% of the time I am unable to launch osk.exe from a 32bit process on Win7 x64. Originally the code was just using: Process.Launch("osk.exe"); Which won't work on x64 because of the directory virtualization. Not a problem I thought, I'll just disable virtualization, launch the app, and enable it again, which I thought was the correct way to do things. I also added some code to bring the keyboard back up if it has been minimized (which works fine) - the code (in a sample WPF app) now looks as follows: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Windows; using System.Windows.Controls; using System.Windows.Data; using System.Windows.Documents; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Imaging; using System.Windows.Navigation;using System.Diagnostics; using System.Runtime.InteropServices; namespace KeyboardTest { /// <summary> /// Interaction logic for MainWindow.xaml /// </summary> public partial class MainWindow : Window { [DllImport("kernel32.dll", SetLastError = true)] private static extern bool Wow64DisableWow64FsRedirection(ref IntPtr ptr); [DllImport("kernel32.dll", SetLastError = true)] public static extern bool Wow64RevertWow64FsRedirection(IntPtr ptr); private const UInt32 WM_SYSCOMMAND = 0x112; private const UInt32 SC_RESTORE = 0xf120; [DllImport("user32.dll", CharSet = CharSet.Auto)] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam); private string OnScreenKeyboadApplication = "osk.exe"; public MainWindow() { InitializeComponent(); } private void KeyboardButton_Click(object sender, RoutedEventArgs e) { // Get the name of the On screen keyboard string processName = System.IO.Path.GetFileNameWithoutExtension(OnScreenKeyboadApplication); // Check whether the application is not running var query = from process in Process.GetProcesses() where process.ProcessName == processName select process; var keyboardProcess = query.FirstOrDefault(); // launch it if it doesn't exist if (keyboardProcess == null) { IntPtr ptr = new IntPtr(); ; bool sucessfullyDisabledWow64Redirect = false; // Disable x64 directory virtualization if we're on x64, // otherwise keyboard launch will fail. if (System.Environment.Is64BitOperatingSystem) { sucessfullyDisabledWow64Redirect = Wow64DisableWow64FsRedirection(ref ptr); } // osk.exe is in windows/system folder. So we can directky call it without path using (Process osk = new Process()) { osk.StartInfo.FileName = OnScreenKeyboadApplication; osk.Start(); osk.WaitForInputIdle(2000); } // Re-enable directory virtualisation if it was disabled. if (System.Environment.Is64BitOperatingSystem) if (sucessfullyDisabledWow64Redirect) Wow64RevertWow64FsRedirection(ptr); } else { // Bring keyboard to the front if it's already running var windowHandle = keyboardProcess.MainWindowHandle; SendMessage(windowHandle, WM_SYSCOMMAND, new IntPtr(SC_RESTORE), new IntPtr(0)); } } } } But this code, most of the time, throws the following exception on osk.Start(): The specified procedure could not be found at System.Diagnostics.Process.StartWithShellExecuteEx(ProcessStartInfo startInfo) I've tried putting long Thread.Sleep commands in around the osk.Start line, just to make sure it wasn't a race condition, but the same problem persists. Can anyone spot where I'm doing something wrong, or provide an alternative solution for this? It seems to work fine launching Notepad, it just won't play ball with the onscreen keyboard.

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• How might maven's buildNumber metadata become inconsistent across multiple build agents?

  - by Brian Laframboise

  We recently added a second build machine to our build environment and began experiencing very odd occasional build failures. I have two separate Maven build machines, A and B, each running Maven 2.2.1 and communicating to a shared Nexus 1.5.0 repository manager. My problem is that builds on B will occasionally fail because it refuses to download a newer version of a common dependency 'acme-1.0.0-SNAPSHOT' previously built by A and uploaded to Nexus. Looking inside the local repositories on both machines I noticed some oddities in the repository metadata. Machine A's acme\1.0.0-SNAPSHOT\maven-metadata-nexus.xml: <metadata> <groupId>acme</groupId> <artifactId>acme</artifactId> <version>1.0.0-SNAPSHOT</version> <versioning> <snapshot> <buildNumber>1</buildNumber> </snapshot> <lastUpdated>20100525173546</lastUpdated> </versioning> </metadata> Machine B's acme\1.0.0-SNAPSHOT\maven-metadata-nexus.xml: <metadata> <groupId>acme</groupId> <artifactId>acme</artifactId> <version>1.0.0-SNAPSHOT</version> <versioning> <snapshot> <buildNumber>2</buildNumber> </snapshot> <lastUpdated>20100519232317</lastUpdated> </versioning> </metadata> In Nexus's acme/1.0.0-SNAPSHOT/maven-metadata.xml: <metadata> <groupId>acme</groupId> <artifactId>acme</artifactId> <version>1.0.0-SNAPSHOT</version> <versioning /> </metadata> If I'm interpreting the metadata files correctly (documentation online is scant), it appears machine B believes it has a newer version of the acme dependency (based on buildNumber) despite the fact that machine A last built it 6 days after machine B did (based on timestamp). Nexus also appears to be unaware of a universally correct buildNumber. How could this situation possibly arise? What could I do to prevent my builds from failing due to inconsistent metadata? Have you experienced anything similar? Important notes: Both build machines have settings.xml files where the updatePolicy is "always". Nexus does indeed have the newer version of acme that was built by A. B simply refuses to download it. A and B are the only machines uploading to Nexus. Both servers share the same system time. All processes involved have write privileges to the metadata files so that they can be updated as necessary. I was unable to find any open Maven or Nexus issues describing this behaviour. Our CI server (Atlassian Bamboo) prevents builds of the same artifact from happening concurrently, so some race condition while uploading to Nexus is rather unlikely.

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• what's wrong with my producer-consumer queue design?

  - by toasteroven

  I'm starting with the C# code example here. I'm trying to adapt it for a couple reasons: 1) in my scenario, all tasks will be put in the queue up-front before consumers will start, and 2) I wanted to abstract the worker into a separate class instead of having raw Thread members within the WorkerQueue class. My queue doesn't seem to dispose of itself though, it just hangs, and when I break in Visual Studio it's stuck on the _th.Join() line for WorkerThread #1. Also, is there a better way to organize this? Something about exposing the WaitOne() and Join() methods seems wrong, but I couldn't think of an appropriate way to let the WorkerThread interact with the queue. Also, an aside - if I call q.Start(#) at the top of the using block, only some of the threads every kick in (e.g. threads 1, 2, and 8 process every task). Why is this? Is it a race condition of some sort, or am I doing something wrong? using System; using System.Collections.Generic; using System.Text; using System.Messaging; using System.Threading; using System.Linq; namespace QueueTest { class Program { static void Main(string[] args) { using (WorkQueue q = new WorkQueue()) { q.Finished += new Action(delegate { Console.WriteLine("All jobs finished"); }); Random r = new Random(); foreach (int i in Enumerable.Range(1, 10)) q.Enqueue(r.Next(100, 500)); Console.WriteLine("All jobs queued"); q.Start(8); } } } class WorkQueue : IDisposable { private Queue _jobs = new Queue(); private int _job_count; private EventWaitHandle _wh = new AutoResetEvent(false); private object _lock = new object(); private List _th; public event Action Finished; public WorkQueue() { } public void Start(int num_threads) { _job_count = _jobs.Count; _th = new List(num_threads); foreach (int i in Enumerable.Range(1, num_threads)) { _th.Add(new WorkerThread(i, this)); _th[_th.Count - 1].JobFinished += new Action(WorkQueue_JobFinished); } } void WorkQueue_JobFinished(int obj) { lock (_lock) { _job_count--; if (_job_count == 0 && Finished != null) Finished(); } } public void Enqueue(int job) { lock (_lock) _jobs.Enqueue(job); _wh.Set(); } public void Dispose() { Enqueue(Int32.MinValue); _th.ForEach(th = th.Join()); _wh.Close(); } public int GetNextJob() { lock (_lock) { if (_jobs.Count 0) return _jobs.Dequeue(); else return Int32.MinValue; } } public void WaitOne() { _wh.WaitOne(); } } class WorkerThread { private Thread _th; private WorkQueue _q; private int _i; public event Action JobFinished; public WorkerThread(int i, WorkQueue q) { _i = i; _q = q; _th = new Thread(DoWork); _th.Start(); } public void Join() { _th.Join(); } private void DoWork() { while (true) { int job = _q.GetNextJob(); if (job != Int32.MinValue) { Console.WriteLine("Thread {0} Got job {1}", _i, job); Thread.Sleep(job * 10); // in reality would to actual work here if (JobFinished != null) JobFinished(job); } else { Console.WriteLine("Thread {0} no job available", _i); _q.WaitOne(); } } } } }

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• php, mySQL & AJAX: Unable to use sessions across the scripts in the same domain

  - by Devner

  Hi all, I have the following pages: page1.php, page2.php and page3.php. Code in each of them is as below CODE: page1.php <script type="text/javascript"> $(function(){ $('#imgID').upload({ submit_to_url: "page2.php", file_name: 'myfile1', description : "Image", limit : 1, file_types : "*.jpg", }) }); </script> <body> <form action="page3.php" method="post" enctype="multipart/form-data" name="frm1" id="frm1"> //Some other text fields <input type="submit" name="submit" id="submit" value="Submit" /> </form> </body> page2.php <?php session_start(); $a = $_SESSION['a']; $b = $_SESSION['b']; $c = $_SESSION['c']; $res = mysql_query("SELECT col FROM table WHERE col1 = $a AND col2 = $b AND col3 = $c LIMIT 1"); $num_rows = mysql_num_rows($res); echo $num_rows; //echos 0 when in fact it should have been 1 because the data in the Session exists. //Ok let's proceed further //... Do some stuff... //Store some more values and create new session variables (and assume that page1.php is going to be able to use it) $_SESSION['d'] = 'd'; $_SESSION['e'] = 'e'; $_SESSION['f'] = 'f'; if (move_uploaded_file($_FILES['file']['tmp_name'], $file)) { echo "success"; } else { echo "error ".$_FILES['file']['error']; } ?> page3.php <?php session_start(); if( isset($_POST['submit']) ) { //These sessions are non-existent although the AJAX request //to page2.php may have created them when called via AJAX from within page1.php echo $_SESSION['d'].$_SESSION['e'].$_SESSION['f']; ?> } ?> As the code says it I am posting some info via AJAX call from page1.php to page2.php. page2.php is supposed to be able to use the session values from page1.php i.e. $_SESSION['a'], $_SESSION['b'] and $_SESSION['c'] but it does not. Why? How can I fix this? page2.php is creating some more sessions after some processing is done and a response is sent back to page1.php. The submit button of the form on page1.php is hit and the page gets POST'ed to page3.php. But when the SESSION info that gets created in page2.php is echoed, it's blank signifying that SESSIONS from page2.php are not used. How can I fix this? I looked over a lot of information and have spent about 50 hours trying to do different things with my scripts before arriving at the above conclusions. My app. is custom made using function (not OOPS) and does not use any PHP frameworks & I am not even about to use any as my knowledge of OOP concepts is limited any many frameworks are object oriented. I came across race conditions, but the solutions provided don't help too much. One more solution of using DB to hold sessions and seek and retrieve from DB is the last thing on my mind and I really want to avoid creating table, coding and maintaining code for a task as simple as just keeping sessions across pages in the same domain. So my request is: Is there a way that I can solve the above problem(s) via simple coding in present conditions? Any help is appreciated. Thank you.

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• Recommended integration mechanism for bi-directional, authenticated, encrypted connection in C clien

  - by rcampbell

  Let me first give an example. Imagine you have a single server running a JVM application. This server keeps a collection of N equations, once for each client: Client #1: 2x Client #2: 1 + y Client #3: z/4 This server includes an HTTP interface so that random visitors can type https://www.acme.com/client/3 int their browsers and see the latest evaluated result of z/4. The tricky part is that either the client or the server may change the variable value at any time, informing the other party immediately. More specifically, Client #3 - a C app - can initially tell the server that z = 20. An hour later that same client informs the server that z = 23. Likewise the server can later inform the client that z = 28. As caf pointed out in the comments, there can be a race condition when values are changed by the client and server simultaneously. The solution would be for both client and server to send the operation performed in their message, which would need to be executed by the other party. To keep things simple, let's limit the operations to (commutative) addition, allowing us to disregard message ordering. For example, the client seeds the server with z = 20: server:z=20, client:z=20 server sends {+3} message (so z=23 locally) & client sends {-2} message (so z=18 locally) at the exact same time server receives {-2} message at some point, adds to his local copy so z=21 client receives {+3} message at some point, adds to his local copy so z=21 As long as all messages are eventually evaluated by both parties, the correct answer will eventually be given to the users of the client and server since we limited ourselves to commutative operations (addition of 3 and -2). This does mean that both client and server can be returning incorrect answers in the time it takes for messages to be exchanged and processed. While undesirable, I believe this is unavoidable. Some possible implementations of this idea include: Open an encrypted, always on TCP socket connection for communication Pros: no additional infrastructure needed, client and server know immediately if there is a problem (disconnect) with the other party, fairly straightforward (except the the encryption), native support from both JVM and C platforms Cons: pretty low-level so you end up writing a lot yourself (protocol, delivery verification, retry-on-failure logic), probably have a lot of firewall headaches during client app installation Asynchronous messaging (ex: ActiveMQ) Pros: transactional, both C & Java integration, free up the client and server apps from needing retry logic or delivery verification, pretty straightforward encryption, easy extensibility via message filters/routers/etc Cons: need additional infrastructure (message server) which must never fail, Database or file system as asynchronous integration point Same pros/cons as above but messier RESTful Web Service Pros: simple, possible reuse of the server's existing REST API, SSL figures out the encryption problem for you (maybe use RSA key a la GitHub for authentication?) Cons: Client now needs to run a C HTTP REST server w/SSL, client and server need retry logic. Axis2 has both a Java and C version, but you may be limited to SOAP. What other techniques should I be evaluating? What real world experiences have you had with these mechanisms? Which do you recommend for this problem and why?

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• HTML 5 <video> tag vs Flash video. What are the pros and cons?

  - by Vilx-

  Seems like the new <video> tag is all the hype these days, especially since Firefox now supports it. News of this are popping up in blogs all over the place, and everyone seems to be excited. But what about? As much as I searched I could not find anything that would make it better than the good old Flash video. In fact, I see only problems with it: It will still be some time before all the browsers start supporting it, and much more time before most people upgrade; Flash is available already and everyone has it; You can couple Flash with whatever fancy UI you want for controlling the playback. I gather that the tag will be controllable as well (via JavaScript probably), but will it be able to go fullscreen? The only two pros for a <video> tag that I can see are: It is more "semantic" - which probably holds no importance to a whole lot of people, including me; It is not dependent on a single commercial 3rd party entity (Adobe) - which I also don't see as a compelling reason to switch, because free players and video converters are already available, and Adobe is not hindering the whole process in any way (it's not in their interests even). So... what's the big deal? Added: OK, so there is one more Pro... maybe. Support for mobile devices. Hard to say though. A number of thoughts race through my head about the subject: How many mobile devices are actually able to decode video at a decent speed anyway, Flash or otherwise? How long until mainstream mobile devices get the <video> support? Even if it is available through updates, how many people actually do that? How many people watch videos on web pages on their mobile phones at all? As for the semantics part - I understand that search engines might be able to detect videos better now, but... what will they do with them anyway? OK, so they know that there is a video in the page. And? They can't index a video! I'd like some more arguments here. Added: Just thought of another Cons. This opens up a whole new area of cross-browser incompatibility. HTML and CSS is quite messy already in this aspect. Flash at least is the same everywhere. But it's enough for at least one major browser vendor to decide against the <video> tag (can anyone say "Internet Explorer"?) and we have a nice new area of hell to explore. Added: A Pro just came in. More competition = more innovation. That's true. Giving Adobe more competition will probably force them to improve Flash in areas it has been lacking so far. Linux seems to be a weak spot for it, cited by many.

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• CodePlex Daily Summary for Wednesday, February 24, 2010

  CodePlex Daily Summary for Wednesday, February 24, 2010New ProjectsADO.Net DataSets to ExtJs.data.Store: A JavaScript (and C#) based project to reduce the amount of client-side code necessary to consume ADO.Net / ASP.Net web services when using ExtJS.AMP.Net Wrapper: AMP is a platform to build on-line marketplaces (http://www.poweredbyamp.com). AMP.Net provided Object-Like interaction with AMP's restful service...ArkSwitch: ArkSwitch is an easy to use, finger-friendly task manager for Windows Mobile 6.5.3 (with a WM6.5 compatibility mode). It is developed mainly in C#,...Biffen: Cinema-booking project in Computer Science at University College Nordjylland, Denmark.Braintree Client Library: Client library for integrating with the Braintree Gateway.Business Framework: A framework which helps building business applications. It provides business rules, validation rules and a text-based language for writing rules. I...Camp Araminta: This project will be used to coordinate development efforts on the Camp Araminta website.ChoServiceHost: Simple and easy way to create and host Windows Service Applications in .NET 3.5/Visual Studio 2008Delta College Game Development Project: Project site for cs 16 game development classDotNetNuke® Labs: DotNetNuke Labs is a collection of "research & development" type projects for the DotNetNuke platform.Generic web part for hosting Silverlight content on SharePoint sites (WSS,MOSS): This is a generic web part for hosting Silverlight content on WSS 30 and MOSS 2007 sites. The objective of this web part was to make it easy for us...GpTiming: GpTiming is a simple "lab" application related to race events, based on a Domain Model.HTML Forms in Windows Forms: As the names suggests this code library is designed to introduce HTML code (primarily form code) into Windows Forms. It was created because standar...imgur uploader - .net open source uploader for image sharing site imgur: Imgur uploader strives to be an easy to use uploader for images you would like to share with friends and family. It is written in c#.kuuy static system: kuuy static system is a full static publish website system!LaTeX Grapher: The goal of this project is to make a tool that facilitates making high quality two dimensional vector graphic function plots with a minimal amount...LightREST: A .NET library to consume REST-based HTTP services.Machiavelli: Machiavelli is Stackoverflow inspired project that I am working on following Andrew Siemer's article on DotNetSlackers. Mover: Mover makes it easier for developers to create programmatic animations in Silverlight. It provides an expressive API to the platform's underlying S...MVC Presenter: ASP.NET MVC 2で作るプレゼンビューアーnHibernate Attribute mapping: How to use Attibute mapping with a ManyToMany Relationship with nHibernateNIPO Data Processing Component Framework: NIPO is a general purpose component framework for data processing applications (that follow the IPO-principle). Its plugin-based architecture makes...PowerShell Remote File Explorer: This project intends to develop a Windows forms based file explorer to browse/transfer files over PowerShell 2.0 remoting channel. The file transfe...Process Flow Tracking of Biomass Distribution Project (University of Mumbai): At Larsen & Toubro Infotech India Ltd., my team worked on a SCM (Supply Chain Management) based project titled 'Process Flow Tracking of Biomass Di...VS2010 Rc1 Fix: Illustrates a fix for working with the ASAP.NET Wizard control with VS2010 RC1Yicker: a microblog program devolep by c#.New ReleasesADO.Net DataSets to ExtJs.data.Store: Ext.net: This is the first version of Ext.net. This version contains a single class, Ext.net.Store which extends the Ext.data.Store class to consume ADO.Ne...AMP.Net Wrapper: AMP.Net v1.0: Provides abstraction for all the product search functionality offered by AMP.ArkSwitch: ArkSwitch legacy versions: Old versions - no need to download themArkSwitch: ArkSwitch v1.1.0: ArkSwitch v1.1.0Braintree Client Library: Braintree 1.0.0: Braintree .NET client library 1.0.0Business Framework: BusinessFramework preview: Early preview bits. See Rules for a sample.Business Framework: Samples: SamplesCC.Votd: CC.Votd 1.0.10.224: This is the initial release of CC.Votd. Marking as beta since I'm the only one who has used it up to this point.ChoServiceHost: ChoServiceHost.msi: Easy way to develop Windows Service applications in .NET 3.5/VS.NET 2008. (Installer)ChoServiceHost: ChoServiceHost-Src.zip: Easy way to develop Windows Service applications in .NET 3.5/VS.NET 2008. (Source Files)CHS Extranet: Beta 2.4: Beta 2.4 Release: Change Log: Added HTML preview options for XLS, XLSX, DOCX File Changes: ~/MyComputer.aspx ~/mycomputer.css ~/basestyle.css...Composure: AvalonDock-55751-VS2010.NET4: This is a "convenience build" of AvalonDock (drop 55751) for VIsual Studio 2010 and .NET 4.0. Nothing has been altered in the source code (which ...Data Access Component: Version 2.6: Add LINQ support.Desktop Google Reader: 1.3 Beta 1: New features: Read it Later included (see http://readitlaterlist.com/) Liking added (working: see number of liking users, see if liking yourself,...Explorer Plus: Explorer Plus v0.3: Amazon Locales AddedFree Silverlight & WPF Chart Control - Visifire: Visifire SL and WPF Charts 3.0.3 Released: Hi, Today we have released the final version of Visifire v3.0.3 which contains the following major features: * DataBinding. * IndicatorEn...Generic web part for hosting Silverlight content on SharePoint sites (WSS,MOSS): CTP: The objective of this release was to gather feedback from the wider community. I intend to pursue further development and make fixes wherever appro...HTML Forms in Windows Forms: HTMLForms 1.0: First Release.imgur uploader - .net open source uploader for image sharing site imgur: Release 2010-02-23-01: This is the first codeplex release! Let mayhem commence...Jeremi Stadler: Stick Tops 2.5: Sticktops is a very light program that makes it easy to paste stuff on small notes on the screen. All notes you have is saved on a server so you ca...kuuy static system: kss_v1.0beta sql: kss_v1.0beta sql scripts sourceMDownloader: MDownloader-0.15.2.55998: Fixed detecting uploading.com dead links; Added hiding rss entries without files;Mover: MoverLib for Silverlight 3: A first version of MoverLib for Silverlight 3.nHibernate Attribute mapping: 1.0: Source CodenHibernate Attribute mapping: Download 1: Zip fileNodeXL: Network Overview, Discovery and Exploration for Excel: NodeXL Class Libraries, version 1.0.1.113: The NodeXL class libraries can be used to display network graphs in .NET applications. To include a NodeXL network graph in a WPF desktop or Windo...NodeXL: Network Overview, Discovery and Exploration for Excel: NodeXL Excel 2007 Template, version 1.0.1.113: The NodeXL Excel 2007 template displays a network graph using edge and vertex lists stored in an Excel 2007 workbook. What's NewThis version inclu...OAuthLib: OAuthLib (1.6.0.0): Difference between previous version is as next. 7079 Make it possible to pass factory method of request in ObtainUnauthorizedRequestToken and Reque...patterns & practices SharePoint Guidance: SPG2010 Drop 5: SharePoint Guidance Drop Notes Microsoft patterns and practices ****************************************** ***************************************...PowerShell Remote File Explorer: PSRemoteExplorer 0.1: This release is the initial release of PowerShell remote file explorer. This enables the basic functionality of a remote file explorer. This also p...Reusable Library: v1.0.3: A collection of reusable abstractions for enterprise application developer.SharePoint Outlook Connector: Version 1.0.2.4: Version 1.0.2.4 Minor bugs have been fixed.Silverlight Server File Manager: First production release: This release is in production. Release on change set 37268.SIMD Detector: 2nd Release: Released C/CLI assembly project for use in CSharp and VB. Tested in CSharp console application. A Windows Form application coming soon. Projects ma...Source Analysis Policy: Source Analysis Policy v1.1 SP1: This release contains the compiled, and signed binaries in an installation package. This package also registers the policy with Microsoft Visual St...SpecExpress : A Fluent Validation Framework: SpecExpress 1.1: UpdatesAdded Validation Contexts feature Fixed bug with handling for Bool Types and Required MessageStore now allows for overriding individual ...VCC: Latest build, v2.1.30223.0: Automatic drop of latest buildVS2010 Rc1 Fix: RC1Fix01: This is a very simple project implementing a Microsoft Walkthrough at http://msdn.microsoft.com/en-us/library/wdb4eb30%28VS.100%29.aspx and the man...WPF AutoComplete TextBox Control: version 1.0: Initial releaseMost Popular ProjectsASP.NET Ajax LibraryManaged Extensibility FrameworkAccelerators for Microsoft Dynamics CRMWindows 7 USB/DVD Download ToolDotNetZip LibraryMDownloaderVirtual Router - Wifi Hot Spot for Windows 7 / 2008 R2MFCMAPIDroid ExplorerUseful Sharepoint Designer Custom Workflow ActivitiesMost Active ProjectsDinnerNow.netRawrBlogEngine.NETInfoServiceNB_Store - Free DotNetNuke Ecommerce Catalog ModuleRapid Entity Framework. (ORM). CTP 2SharpMap - Geospatial Application Framework for the CLRjQuery Library for SharePoint Web Servicespatterns & practices – Enterprise LibraryXcoordination Application Space

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• The How-To Geek Holiday Gift Guide (Geeky Stuff We Like)

  - by The Geek

  Welcome to the very first How-To Geek Holiday Gift Guide, where we’ve put together a list of our absolute favorites to help you weed through all of the junk out there to pick the perfect gift for anybody. Though really, it’s just a list of the geeky stuff we want. We’ve got a whole range of items on the list, from cheaper gifts that most anybody can afford, to the really expensive stuff that we’re pretty sure nobody is giving us. Stocking Stuffers Here’s a couple of ideas for items that won’t break the bank. LED Keychain Micro-Light   Magcraft 1/8-Inch Rare Earth Cube Magnets Best little LED keychain light around. If they don’t need the penknife of the above item this is the perfect gift. I give them out by the handfuls and nobody ever says anything but good things about them. I’ve got ones that are years old and still running on the same battery.  Price: $8   Geeks cannot resist magnets. Jason bought this pack for his fridge because he was sick of big clunky magnets… these things are amazing. One tiny magnet, smaller than an Altoid mint, can practically hold a clipboard right to the fridge. Amazing. I spend more time playing with them on the counter than I do actually hanging stuff.  Price: $10 Lots of Geeky Mugs   Astronomy Powerful Green Laser Pointer There’s loads of fun, geeky mugs you can find on Amazon or anywhere else—and they are great choices for the geek who loves their coffee. You can get the Caffeine mug pictured here, or go with an Atari one, Canon Lens, or the Aperture mug based on Portal. Your choice. Price: $7   No, it’s not a light saber, but it’s nearly bright enough to be one—you can illuminate low flying clouds at night or just blind some aliens on your day off. All that for an extremely low price. Loads of fun. Price: $15       Geeky TV Shows and Books Sometimes you just want to relax and enjoy a some TV or a good book. Here’s a few choices. The IT Crowd Fourth Season   Doctor Who, Complete Fifth Series Ridiculous, funny show about nerds in the IT department, loved by almost all the geeks here at HTG. Justin even makes this required watching for new hires in his office so they’ll get his jokes. You can pre-order the fourth season, or pick up seasons one, two, or three for even cheaper. Price: $13   It doesn’t get any more nerdy than Eric’s pick, the fifth all-new series of Doctor Who, where the Daleks are hatching a new master plan from the heart of war-torn London. There’s also alien vampires, humanoid reptiles, and a lot more. Price: $52 Battlestar Galactica Complete Series   MAKE: Electronics: Learning Through Discovery Watch the epic fight to save the human race by finding the fabled planet Earth while being hunted by the robotic Cylons. You can grab the entire series on DVD or Blu-ray, or get the seasons individually. This isn’t your average sci-fi TV show. Price: $150 for Blu-ray.   Want to learn the fundamentals of electronics in a fun, hands-on way? The Make:Electronics book helps you build the circuits and learn how it all works—as if you had any more time between all that registry hacking and loading software on your new PC. Price: $21       Geeky Gadgets for the Gadget-Loving Geek Here’s a few of the items on our gadget list, though lets be honest: geeks are going to love almost any gadget, especially shiny new ones. Klipsch Image S4i Premium Noise-Isolating Headset with 3-Button Apple Control   GP2X Caanoo MAME/Console Emulator If you’re a real music geek looking for some serious quality in the headset for your iPhone or iPod, this is the pair that Alex recommends. They aren’t terribly cheap, but you can get the less expensive S3 earphones instead if you prefer. Price: $50-100   Eric says: “As an owner of an older version, I can say the GP2X is one of my favorite gadgets ever. Touted a “Retro Emulation Juggernaut,” GP2X runs Linux and may be the only open source software console available. Sounds too good to be true, but isn’t.” Price: $150 Roku XDS Streaming Player 1080p   Western Digital WD TV Live Plus HD Media Player If you do a lot of streaming over Netflix, Hulu Plus, Amazon’s Video on Demand, Pandora, and others, the Roku box is a great choice to get your content on your TV without paying a lot of money.  It’s also got Wireless-N built in, and it supports full 1080P HD. Price: $99   If you’ve got a home media collection sitting on a hard drive or a network server, the Western Digital box is probably the cheapest way to get that content on your TV, and it even supports Netflix streaming too. It’ll play loads of formats in full HD quality. Price: $99 Fujitsu ScanSnap S300 Color Mobile Scanner   Doxie, the amazing scanner for documents Trevor said: “This wonderful little scanner has become absolutely essential to me. My desk used to just be a gigantic pile of papers that I didn’t need at the moment, but couldn’t throw away ‘just in case.’ Now, every few weeks, I’ll run that paper pile through this and then happily shred the originals!” Price: $300   If you don’t scan quite as often and are looking for a budget scanner you can throw into your bag, or toss into a drawer in your desk, the Doxie scanner is a great alternative that I’ve been using for a while. It’s half the price, and while it’s not as full-featured as the Fujitsu, it might be a better choice for the very casual user. Price: $150       (Expensive) Gadgets Almost Anybody Will Love If you’re not sure that one of the more geeky presents is gonna work, here’s some gadgets that just about anybody is going to love, especially if they don’t have one already. Of course, some of these are a bit on the expensive side—but it’s a wish list, right? Amazon Kindle       The Kindle weighs less than a paperback book, the screen is amazing and easy on the eyes, and get ready for the kicker: the battery lasts at least a month. We aren’t kidding, either—it really lasts that long. If you don’t feel like spending money for books, you can use it to read PDFs, and if you want to get really geeky, you can hack it for custom screensavers. Price: $139 iPod Touch or iPad       You can’t go wrong with either of these presents—the iPod Touch can do almost everything the iPhone can do, including games, apps, and music, and it has the same Retina display as the iPhone, HD video recording, and a front-facing camera so you can use FaceTime. Price: $229+, depending on model. The iPad is a great tablet for playing games, browsing the web, or just using on your coffee table for guests. It’s well worth buying one—but if you’re buying for yourself, keep in mind that the iPad 2 is probably coming out in 3 months. Price: $500+ MacBook Air  The MacBook Air comes in 11” or 13” versions, and it’s an amazing little machine. It’s lightweight, the battery lasts nearly forever, and it resumes from sleep almost instantly. Since it uses an SSD drive instead of a hard drive, you’re barely going to notice any speed problems for general use. So if you’ve got a lot of money to blow, this is a killer gift. Price: $999 and up. Stuck with No Idea for a Present? Gift Cards! Yeah, you’re not going to win any “thoughtful present” awards with these, but you might just give somebody what they really want—the new Angry Birds HD for their iPad, Cut the Rope, or anything else they want. ITunes Gift Card   Amazon.com Gift Card Somebody in your circle getting a new iPod, iPhone, or iPad? You can get them an iTunes gift card, which they can use to buy music, games or apps. Yep, this way you can gift them a copy of Angry Birds if they don’t already have it. Or even Cut the Rope.   No clue what to get somebody on your list? Amazon gift cards let them buy pretty much anything they want, from organic weirdberries to big screen TVs. Yeah, it’s not as thoughtful as getting them a nice present, but look at the bright side: maybe they’ll get you an Amazon gift card and it’ll balance out. That’s the highlights from our lists—got anything else to add? Share your geeky gift ideas in the comments. Latest Features How-To Geek ETC The How-To Geek Holiday Gift Guide (Geeky Stuff We Like) LCD? LED? Plasma? The How-To Geek Guide to HDTV Technology The How-To Geek Guide to Learning Photoshop, Part 8: Filters Improve Digital Photography by Calibrating Your Monitor Our Favorite Tech: What We’re Thankful For at How-To Geek The How-To Geek Guide to Learning Photoshop, Part 7: Design and Typography Happy Snow Bears Theme for Chrome and Iron [Holiday] Download Full Command and Conquer: Tiberian Sun Game for Free Scorched Cometary Planet Wallpaper Quick Fix: Add the RSS Button Back to the Firefox Awesome Bar Dropbox Desktop Client 1.0.0 RC for Windows, Linux, and Mac Released Hang in There Scrat! – Ice Age Wallpaper

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• What You Need to Know About Windows 8.1

  - by Chris Hoffman

  Windows 8.1 is available to everyone starting today, October 19. The latest version of Windows improves on Windows 8 in every way. It’s a big upgrade, whether you use the desktop or new touch-optimized interface. The latest version of Windows has been dubbed “an apology” by some — it’s definitely more at home on a desktop PC than Windows 8 was. However, it also offers a more fleshed out and mature tablet experience. How to Get Windows 8.1 For Windows 8 users, Windows 8.1 is completely free. It will be available as a download from the Windows Store — that’s the “Store” app in the Modern, tiled interface. Assuming upgrading to the final version will be just like upgrading to the preview version, you’ll likely see a “Get Windows 8.1″ pop-up that will take you to the Windows Store and guide you through the download process. You’ll also be able to download ISO images of Windows 8.1, so can perform a clean install to upgrade. On any new computer, you can just install Windows 8.1 without going through Windows 8. New computers will start to ship with Windows 8.1 and boxed copies of Windows 8 will be replaced by boxed copies of Windows 8.1. If you’re using Windows 7 or a previous version of Windows, the update won’t be free. Getting Windows 8.1 will cost you the same amount as a full copy of Windows 8 — $120 for the standard version. If you’re an average Windows 7 user, you’re likely better off waiting until you buy a new PC with Windows 8.1 included rather than spend this amount of money to upgrade. Improvements for Desktop Users Some have dubbed Windows 8.1 “an apology” from Microsoft, although you certainly won’t see Microsoft referring to it this way. Either way, Steven Sinofsky, who presided over Windows 8′s development, left the company shortly after Windows 8 was released. Coincidentally, Windows 8.1 contains many features that Steven Sinofsky and Microsoft refused to implement. Windows 8.1 offers the following big improvements for desktop users: Boot to Desktop: You can now log in directly to the desktop, skipping the tiled interface entirely. Disable Top-Left and Top-Right Hot Corners: The app switcher and charms bar won’t appear when you move your mouse to the top-left or top-right corners of the screen if you enable this option. No more intrusions into the desktop. The Start Button Returns: Windows 8.1 brings back an always-present Start button on the desktop taskbar, dramatically improving discoverability for new Windows 8 users and providing a bigger mouse target for remote desktops and virtual machines. Crucially, the Start menu isn’t back — clicking this button will open the full-screen Modern interface. Start menu replacements will continue to function on Windows 8.1, offering more traditional Start menus. Show All Apps By Default: Luckily, you can hide the Start screen and its tiles almost entirely. Windows 8.1 can be configured to show a full-screen list of all your installed apps when you click the Start button, with desktop apps prioritized. The only real difference is that the Start menu is now a full-screen interface. Shut Down or Restart From Start Button: You can now right-click the Start button to access Shut down, Restart, and other power options in just as many clicks as you could on Windows 7. Shared Start Screen and Desktop Backgrounds; Windows 8 limited you to just a few Steven Sinofsky-approved background images for your Start screen, but Windows 8.1 allows you to use your desktop background on the Start screen. This can make the transition between the Start screen and desktop much less jarring. The tiles or shortcuts appear to be floating above the desktop rather than off in their own separate universe. Unified Search: Unified search is back, so you can start typing and search your programs, settings, and files all at once — no more awkwardly clicking between different categories when trying to open a Control Panel screen or search for a file. These all add up to a big improvement when using Windows 8.1 on the desktop. Microsoft is being much more flexible — the Start menu is full screen, but Microsoft has relented on so many other things and you’d never have to see a tile if you didn’t want to. For more information, read our guide to optimizing Windows 8.1 for a desktop PC. These are just the improvements specifically for desktop users. Windows 8.1 includes other useful features for everyone, such as deep SkyDrive integration that allows you to store your files in the cloud without installing any additional sync programs. Improvements for Touch Users If you have a Windows 8 or Windows RT tablet or another touch-based device you use the interface formerly known as Metro on, you’ll see many other noticeable improvements. Windows 8′s new interface was half-baked when it launched, but it’s now much more capable and mature. App Updates: Windows 8′s included apps were extremely limited in many cases. For example, Internet Explorer 10 could only display ten tabs at a time and the Mail app was a barren experience devoid of features. In Windows 8.1, some apps — like Xbox Music — have been redesigned from scratch, Internet Explorer allows you to display a tab bar on-screen all the time, while apps like Mail have accumulated quite a few useful features. The Windows Store app has been entirely redesigned and is less awkward to browse. Snap Improvements: Windows 8′s Snap feature was a toy, allowing you to snap one app to a small sidebar at one side of your screen while another app consumed most of your screen. Windows 8.1 allows you to snap two apps side-by-side, seeing each app’s full interface at once. On larger displays, you can even snap three or four apps at once. Windows 8′s ability to use multiple apps at once on a tablet is compelling and unmatched by iPads and Android tablets. You can also snap two of the same apps side-by-side — to view two web pages at once, for example. More Comprehensive PC Settings: Windows 8.1 offers a more comprehensive PC settings app, allowing you to change most system settings in a touch-optimized interface. You shouldn’t have to use the desktop Control Panel on a tablet anymore — or at least not as often. Touch-Optimized File Browsing: Microsoft’s SkyDrive app allows you to browse files on your local PC, finally offering a built-in, touch-optimized way to manage files without using the desktop. Help & Tips: Windows 8.1 includes a Help+Tips app that will help guide new users through its new interface, something Microsoft stubbornly refused to add during development. There’s still no “Modern” version of Microsoft Office apps (aside from OneNote), so you’ll still have to head to use desktop Office apps on tablets. It’s not perfect, but the Modern interface doesn’t feel anywhere near as immature anymore. Read our in-depth look at the ways Microsoft’s Modern interface, formerly known as Metro, is improved in Windows 8.1 for more information. In summary, Windows 8.1 is what Windows 8 should have been. All of these improvements are on top of the many great desktop features, security improvements, and all-around battery life and performance optimizations that appeared in Windows 8. If you’re still using Windows 7 and are happy with it, there’s probably no reason to race out and buy a copy of Windows 8.1 at the rather high price of $120. But, if you’re using Windows 8, it’s a big upgrade no matter what you’re doing. If you buy a new PC and it comes with Windows 8.1, you’re getting a much more flexible and comfortable experience. If you’re holding off on buying a new computer because you don’t want Windows 8, give Windows 8.1 a try — yes, it’s different, but Microsoft has compromised on the desktop while making a lot of improvements to the new interface. You just might find that Windows 8.1 is now a worthwhile upgrade, even if you only want to use the desktop.     

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• Inside the Concurrent Collections: ConcurrentBag

  - by Simon Cooper

  Unlike the other concurrent collections, ConcurrentBag does not really have a non-concurrent analogy. As stated in the MSDN documentation, ConcurrentBag is optimised for the situation where the same thread is both producing and consuming items from the collection. We'll see how this is the case as we take a closer look. Again, I recommend you have ConcurrentBag open in a decompiler for reference. Thread Statics ConcurrentBag makes heavy use of thread statics - static variables marked with ThreadStaticAttribute. This is a special attribute that instructs the CLR to scope any values assigned to or read from the variable to the executing thread, not globally within the AppDomain. This means that if two different threads assign two different values to the same thread static variable, one value will not overwrite the other, and each thread will see the value they assigned to the variable, separately to any other thread. This is a very useful function that allows for ConcurrentBag's concurrency properties. You can think of a thread static variable: [ThreadStatic] private static int m_Value; as doing the same as: private static Dictionary<Thread, int> m_Values; where the executing thread's identity is used to automatically set and retrieve the corresponding value in the dictionary. In .NET 4, this usage of ThreadStaticAttribute is encapsulated in the ThreadLocal class. Lists of lists ConcurrentBag, at its core, operates as a linked list of linked lists: Each outer list node is an instance of ThreadLocalList, and each inner list node is an instance of Node. Each outer ThreadLocalList is owned by a particular thread, accessible through the thread local m_locals variable: private ThreadLocal<ThreadLocalList<T>> m_locals It is important to note that, although the m_locals variable is thread-local, that only applies to accesses through that variable. The objects referenced by the thread (each instance of the ThreadLocalList object) are normal heap objects that are not specific to any thread. Thinking back to the Dictionary analogy above, if each value stored in the dictionary could be accessed by other means, then any thread could access the value belonging to other threads using that mechanism. Only reads and writes to the variable defined as thread-local are re-routed by the CLR according to the executing thread's identity. So, although m_locals is defined as thread-local, the m_headList, m_nextList and m_tailList variables aren't. This means that any thread can access all the thread local lists in the collection by doing a linear search through the outer linked list defined by these variables. Adding items So, onto the collection operations. First, adding items. This one's pretty simple. If the current thread doesn't already own an instance of ThreadLocalList, then one is created (or, if there are lists owned by threads that have stopped, it takes control of one of those). Then the item is added to the head of that thread's list. That's it. Don't worry, it'll get more complicated when we account for the other operations on the list! Taking & Peeking items This is where it gets tricky. If the current thread's list has items in it, then it peeks or removes the head item (not the tail item) from the local list and returns that. However, if the local list is empty, it has to go and steal another item from another list, belonging to a different thread. It iterates through all the thread local lists in the collection using the m_headList and m_nextList variables until it finds one that has items in it, and it steals one item from that list. Up to this point, the two threads had been operating completely independently. To steal an item from another thread's list, the stealing thread has to do it in such a way as to not step on the owning thread's toes. Recall how adding and removing items both operate on the head of the thread's linked list? That gives us an easy way out - a thread trying to steal items from another thread can pop in round the back of another thread's list using the m_tail variable, and steal an item from the back without the owning thread knowing anything about it. The owning thread can carry on completely independently, unaware that one of its items has been nicked. However, this only works when there are at least 3 items in the list, as that guarantees there will be at least one node between the owning thread performing operations on the list head and the thread stealing items from the tail - there's no chance of the two threads operating on the same node at the same time and causing a race condition. If there's less than three items in the list, then there does need to be some synchronization between the two threads. In this case, the lock on the ThreadLocalList object is used to mediate access to a thread's list when there's the possibility of contention. Thread synchronization In ConcurrentBag, this is done using several mechanisms: Operations performed by the owner thread only take out the lock when there are less than three items in the collection. With three or greater items, there won't be any conflict with a stealing thread operating on the tail of the list. If a lock isn't taken out, the owning thread sets the list's m_currentOp variable to a non-zero value for the duration of the operation. This indicates to all other threads that there is a non-locked operation currently occuring on that list. The stealing thread always takes out the lock, to prevent two threads trying to steal from the same list at the same time. After taking out the lock, the stealing thread spinwaits until m_currentOp has been set to zero before actually performing the steal. This ensures there won't be a conflict with the owning thread when the number of items in the list is on the 2-3 item borderline. If any add or remove operations are started in the meantime, and the list is below 3 items, those operations try to take out the list's lock and are blocked until the stealing thread has finished. This allows a thread to steal an item from another thread's list without corrupting it. What about synchronization in the collection as a whole? Collection synchronization Any thread that operates on the collection's global structure (accessing anything outside the thread local lists) has to take out the collection's global lock - m_globalListsLock. This single lock is sufficient when adding a new thread local list, as the items inside each thread's list are unaffected. However, what about operations (such as Count or ToArray) that need to access every item in the collection? In order to ensure a consistent view, all operations on the collection are stopped while the count or ToArray is performed. This is done by freezing the bag at the start, performing the global operation, and unfreezing at the end: The global lock is taken out, to prevent structural alterations to the collection. m_needSync is set to true. This notifies all the threads that they need to take out their list's lock irregardless of what operation they're doing. All the list locks are taken out in order. This blocks all locking operations on the lists. The freezing thread waits for all current lockless operations to finish by spinwaiting on each m_currentOp field. The global operation can then be performed while the bag is frozen, but no other operations can take place at the same time, as all other threads are blocked on a list's lock. Then, once the global operation has finished, the locks are released, m_needSync is unset, and normal concurrent operation resumes. Concurrent principles That's the essence of how ConcurrentBag operates. Each thread operates independently on its own local list, except when they have to steal items from another list. When stealing, only the stealing thread is forced to take out the lock; the owning thread only has to when there is the possibility of contention. And a global lock controls accesses to the structure of the collection outside the thread lists. Operations affecting the entire collection take out all locks in the collection to freeze the contents at a single point in time. So, what principles can we extract here? Threads operate independently Thread-static variables and ThreadLocal makes this easy. Threads operate entirely concurrently on their own structures; only when they need to grab data from another thread is there any thread contention. Minimised lock-taking Even when two threads need to operate on the same data structures (one thread stealing from another), they do so in such a way such that the probability of actually blocking on a lock is minimised; the owning thread always operates on the head of the list, and the stealing thread always operates on the tail. Management of lockless operations Any operations that don't take out a lock still have a 'hook' to force them to lock when necessary. This allows all operations on the collection to be stopped temporarily while a global snapshot is taken. Hopefully, such operations will be short-lived and infrequent. That's all the concurrent collections covered. I hope you've found it as informative and interesting as I have. Next, I'll be taking a closer look at ThreadLocal, which I came across while analyzing ConcurrentBag. As you'll see, the operation of this class deserves a much closer look.

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• C#/.NET Little Wonders: The EventHandler and EventHandler&lt;TEventArgs&gt; delegates

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. In the last two weeks, we examined the Action family of delegates (and delegates in general), and the Func family of delegates and how they can be used to support generic, reusable algorithms and classes. So this week, we are going to look at a handy pair of delegates that can be used to eliminate the need for defining custom delegates when creating events: the EventHandler and EventHandler<TEventArgs> delegates. Events and delegates Before we begin, let’s quickly consider events in .NET.  According to the MSDN: An event in C# is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object. So, basically, you can create an event in a type so that users of that type can subscribe to notifications of things of interest.  How is this different than some of the delegate programming that we talked about in the last two weeks?  Well, you can think of an event as a special access modifier on a delegate.  Some differences between the two are: Events are a special access case of delegates They behave much like delegates instances inside the type they are declared in, but outside of that type they can only be (un)subscribed to. Events can specify add/remove behavior explicitly If you want to do additional work when someone subscribes or unsubscribes to an event, you can specify the add and remove actions explicitly. Events have access modifiers, but these only specify the access level of those who can (un)subscribe A public event, for example, means anyone can (un)subscribe, but it does not mean that anyone can raise (invoke) the event directly.  Events can only be raised by the type that contains them In contrast, if a delegate is visible, it can be invoked outside of the object (not even in a sub-class!). Events tend to be for notifications only, and should be treated as optional Semantically speaking, events typically don’t perform work on the the class directly, but tend to just notify subscribers when something of note occurs. My basic rule-of-thumb is that if you are just wanting to notify any listeners (who may or may not care) that something has happened, use an event.  However, if you want the caller to provide some function to perform to direct the class about how it should perform work, make it a delegate. Declaring events using custom delegates To declare an event in a type, we simply use the event keyword and specify its delegate type.  For example, let’s say you wanted to create a new TimeOfDayTimer that triggers at a given time of the day (as opposed to on an interval).  We could write something like this: 1: public delegate void TimeOfDayHandler(object source, ElapsedEventArgs e); 2:  3: // A timer that will fire at time of day each day. 4: public class TimeOfDayTimer : IDisposable 5: { 6: // Event that is triggered at time of day. 7: public event TimeOfDayHandler Elapsed; 8:  9: // ... 10: } The first thing to note is that the event is a delegate type, which tells us what types of methods may subscribe to it.  The second thing to note is the signature of the event handler delegate, according to the MSDN: The standard signature of an event handler delegate defines a method that does not return a value, whose first parameter is of type Object and refers to the instance that raises the event, and whose second parameter is derived from type EventArgs and holds the event data. If the event does not generate event data, the second parameter is simply an instance of EventArgs. Otherwise, the second parameter is a custom type derived from EventArgs and supplies any fields or properties needed to hold the event data. So, in a nutshell, the event handler delegates should return void and take two parameters: An object reference to the object that raised the event. An EventArgs (or a subclass of EventArgs) reference to event specific information. Even if your event has no additional information to provide, you are still expected to provide an EventArgs instance.  In this case, feel free to pass the EventArgs.Empty singleton instead of creating new instances of EventArgs (to avoid generating unneeded memory garbage). The EventHandler delegate Because many events have no additional information to pass, and thus do not require custom EventArgs, the signature of the delegates for subscribing to these events is typically: 1: // always takes an object and an EventArgs reference 2: public delegate void EventHandler(object sender, EventArgs e) It would be insane to recreate this delegate for every class that had a basic event with no additional event data, so there already exists a delegate for you called EventHandler that has this very definition!  Feel free to use it to define any events which supply no additional event information: 1: public class Cache 2: { 3: // event that is raised whenever the cache performs a cleanup 4: public event EventHandler OnCleanup; 5:  6: // ... 7: } This will handle any event with the standard EventArgs (no additional information).  But what of events that do need to supply additional information?  Does that mean we’re out of luck for subclasses of EventArgs?  That’s where the generic for of EventHandler comes into play… The generic EventHandler<TEventArgs> delegate Starting with the introduction of generics in .NET 2.0, we have a generic delegate called EventHandler<TEventArgs>.  Its signature is as follows: 1: public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e) 2: where TEventArgs : EventArgs This is similar to EventHandler except it has been made generic to support the more general case.  Thus, it will work for any delegate where the first argument is an object (the sender) and the second argument is a class derived from EventArgs (the event data). For example, let’s say we wanted to create a message receiver, and we wanted it to have a few events such as OnConnected that will tell us when a connection is established (probably with no additional information) and OnMessageReceived that will tell us when a new message arrives (probably with a string for the new message text). So for OnMessageReceived, our MessageReceivedEventArgs might look like this: 1: public sealed class MessageReceivedEventArgs : EventArgs 2: { 3: public string Message { get; set; } 4: } And since OnConnected needs no event argument type defined, our class might look something like this: 1: public class MessageReceiver 2: { 3: // event that is called when the receiver connects with sender 4: public event EventHandler OnConnected; 5:  6: // event that is called when a new message is received. 7: public event EventHandler<MessageReceivedEventArgs> OnMessageReceived; 8:  9: // ... 10: } Notice, nowhere did we have to define a delegate to fit our event definition, the EventHandler and generic EventHandler<TEventArgs> delegates fit almost anything we’d need to do with events. Sidebar: Thread-safety and raising an event When the time comes to raise an event, we should always check to make sure there are subscribers, and then only raise the event if anyone is subscribed.  This is important because if no one is subscribed to the event, then the instance will be null and we will get a NullReferenceException if we attempt to raise the event. 1: // This protects against NullReferenceException... or does it? 2: if (OnMessageReceived != null) 3: { 4: OnMessageReceived(this, new MessageReceivedEventArgs(aMessage)); 5: } The above code seems to handle the null reference if no one is subscribed, but there’s a problem if this is being used in multi-threaded environments.  For example, assume we have thread A which is about to raise the event, and it checks and clears the null check and is about to raise the event.  However, before it can do that thread B unsubscribes to the event, which sets the delegate to null.  Now, when thread A attempts to raise the event, this causes the NullReferenceException that we were hoping to avoid! To counter this, the simplest best-practice method is to copy the event (just a multicast delegate) to a temporary local variable just before we raise it.  Since we are inside the class where this event is being raised, we can copy it to a local variable like this, and it will protect us from multi-threading since multicast delegates are immutable and assignments are atomic: 1: // always make copy of the event multi-cast delegate before checking 2: // for null to avoid race-condition between the null-check and raising it. 3: var handler = OnMessageReceived; 4: 5: if (handler != null) 6: { 7: handler(this, new MessageReceivedEventArgs(aMessage)); 8: } The very slight trade-off is that it’s possible a class may get an event after it unsubscribes in a multi-threaded environment, but this is a small risk and classes should be prepared for this possibility anyway.  For a more detailed discussion on this, check out this excellent Eric Lippert blog post on Events and Races. Summary Generic delegates give us a lot of power to make generic algorithms and classes, and the EventHandler delegate family gives us the flexibility to create events easily, without needing to redefine delegates over and over.  Use them whenever you need to define events with or without specialized EventArgs.   Tweet Technorati Tags: .NET, C#, CSharp, Little Wonders, Generics, Delegates, EventHandler

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