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  • extendible hashing

    - by Phenom
    I need to make a program that shows the hash value of a given key, using extendible hashing. In extendible hashing, I know that the buckets split and directories change. So if I make my program, do I have to already know things like if the bucket it hashes to is filled, or do I not have to worry about those things and just compute a hash value based on the key?

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  • Java: JButton actionListener explantation

    - by MrDoctorProfessorTyler
    I am extremely confused as to how a JButton works. I have read over the oracle documents of the JButton, but I have failed to see how a JButton can have an actionlistener added to it. I have really always wondered how things like JFrames and all that can have things like .addMouseListener and all that. Can anyone explain how a JButton can have an actionListener added to it like the .addActionListener(...) syntax?

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  • Drawbacks of using an integer as a bitfield?

    - by Mark
    I have a bunch of boolean options for things like "accepted payment types" which can include things like cash, credit card, cheque, paypal, etc. Rather than having a half dozen booleans in my DB, I can just use an integer and assign each payment method an integer, like so PAYMENT_METHODS = ( (1<<0, 'Cash'), (1<<1, 'Credit Card'), (1<<2, 'Cheque'), (1<<3, 'Other'), ) and then query the specific bit in python to retrieve the flag. I know this means the database can't index by specific flags, but are there any other drawbacks?

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  • What doesn't MySQL do? [closed]

    - by sean riley
    When using MySQL 5.1 Enterprise after years of using other database products like Sybase, Infomix, DB2; I run into things that MySQL just doesn't do. For example, it can only generate an EXPLAIN query plan for SELECT queries. What are the other things I should watch out for?

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  • can i perform xml operations in XMLLITE with the same features of MSXML?

    - by Rajakumar
    Hi , I know something about MSXML parser ,to create an xml with native code ..Msxml depends COM..So I want to create xml without com and dom ,so i wish to choose XMLLITE..but i dont know full details about xmllite ,when i was read the xmllite documentation in msdn ,i gathered some points ,they will provide only 2 things (IXMLReader & IxmlWriter).Here in msxml ,i had many functions to do xml operations ,such as selectsinglenode,appendchild ..Now can i perform the same things with XMLLITE?..please give me the right choice towards this ...

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  • How to emulate OOP with C?

    - by Francisco Garcia
    I would like to know which articles or books are good to use OOP concepts in C. I mean things like using function pointers to emulate classes, strict naming conventions to emulate namespaces, and things like that. Also a reference about how to code in C different types of UML diagrams would be great.

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  • Rails-like console for PHP?

    - by Chad Johnson
    Every so often, things work in my local PHP development environment, while in my test environment on my server, things do not. It's a nightmare to debug this. If I had a console like Rails provides, debugging would be much much simpler. Is there anything like the Rails console but for PHP? I should mention that I am using a home-brewn PHP application.

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  • Can I use a filehandle instead of a filename for creating DBM files?

    - by Dancrumb
    I'm using MLDBM to persist some Perl data structures and I'm wondering if there's an alternative to the following: tie %hash, "MLDBM", $dbm_file, O_CREAT | O_RDWR, 0644; Primarily, I'd like to be able to use STDOUT, rather than a known file name. This could then be redirected to a file on the shell-side. I've been searching with keywords like "tie", "DBM" and "filehandle", but the hits tend to talk about tying filehandles to things, as opposed to things to filehandles. Any suggestions?

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  • using Hibernate to loading 20K products, modifying the entity and updating to db

    - by Blankman
    I am using hibernate to update 20K products in my database. As of now I am pulling in the 20K products, looping through them and modifying some properties and then updating the database. so: load products foreach products session begintransaction productDao.MakePersistant(p); session commit(); As of now things are pretty slow compared to your standard jdbc, what can I do to speed things up? I am sure I am doing something wrong here.

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  • Moving from php to rails

    - by piemesons
    While moving from php to rails (Means procedural language to Object oriented language), what are the various things you should keep in mind. How to think in world of object oriented programming? What are thinks i should kept in mind before starting the things. Any tips?

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  • C++ finding pointer errors

    - by Tony
    Hello! I am currently on a project which has been buggy for a long while, now I suspect, among other things, that there is pointer errors in the code. The program is written in native C++ using COM and uses out-of-process COM servers. Can anybody give me some tips as how one would go about finding these errors? Is there specific things to keep in mind, ways to do it, etc...

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  • What exactly is SEO friendly site?

    - by Tom
    Hey, So, I've seen web developers writing in their CV that they create "SEO friendly sites. ". Also I heard that Wordpress is SEO friendly site and other CMSs. So, what does SEO friendly site mean? I understand, that titles and URLs are probably the most important things for making good positions in google, but is there any other things which I should know? Thanks

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  • need help while working on a website

    - by EqEdi
    I'm working for a website where i need to sum functionality related to sales I'm very new to the website stuff and found many things on net but don't knew what to follow. Can anybody suggest me some good tutorials which i can follow to create my website The things which i am going to work on as: saving customer information to data base using saved customer information, placing order generating bills and invoices and downloading it in pdf file format sending mails to customer with those invoice as attachments

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  • WPF Application with Database.

    - by mike
    Hi, i would like to or need to use a database for my wpf project. It has to store "person" "team" "goals" and maybe 2 more things, nothing very big. Ive already used (worked) with databases in java / php (postgresql), but is there maybe an "easier" way to store the things.. i mean if the db is going to be big than i could use (postgre or mysql), but this one would be small.

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  • Would Python make a good substitute for the Windows command-line/batch scripts?

    - by Lawrence Johnston
    I've got some experience with Bash, which I don't mind, but now that I'm doing a lot of Windows development I'm needing to do basic stuff/write basic scripts using the Windows command-line language. For some reason said language really irritates me, so I was considering learning Python and using that instead. Is Python suitable for such things? Moving files around, creating scripts to do things like unzipping a backup and restoring a SQL database, etc.

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  • Alternative for execCommand('underline');

    - by Phil
    The Underline-Tag are removed on HTML5… But the execCommand creates that Tag… Is there any alternative working like the execCommand? (An Alternative who prevents also things like nicetestString, things like that will happen if i use only the surroundContents Methode of the Range… it throws a BAD_BOUNDARYPOINTS_ERR)

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  • The Product Owner

    - by Robert May
    In a previous post, I outlined the rules of Scrum.  This post details one of those rules. Picking a most important part of Scrum is difficult.  All of the rules are required, but if there were one rule that is “more” required that every other rule, its having a good Product Owner.  Simply put, the Product Owner can make or break the project. Duties of the Product Owner A Product Owner has many duties and responsibilities.  I’ll talk about each of these duties in detail below. A Product Owner: Discovers and records stories for the backlog. Prioritizes stories in the Product Backlog, Release Backlog and Iteration Backlog. Determines Release dates and Iteration Dates. Develops story details and helps the team understand those details. Helps QA to develop acceptance tests. Interact with the Customer to make sure that the product is meeting the customer’s needs. Discovers and Records Stories for the Backlog When I do Scrum, I always use User Stories as the means for capturing functionality that’s required in the system.  Some people will use Use Cases, but the same rule applies.  The Product Owner has the ultimate responsibility for figuring out what functionality will be in the system.  Many different mechanisms for capturing this input can be used.  User interviews are great, but all sources should be considered, including talking with Customer Support types.  Often, they hear what users are struggling with the most and are a great source for stories that can make the application easier to use. Care should be taken when soliciting user stories from technical types such as programmers and the people that manage them.  They will almost always give stories that are very technical in nature and may not have a direct benefit for the end user.  Stories are about adding value to the company.  If the stories don’t have direct benefit to the end user, the Product Owner should question whether or not the story should be implemented.  In general, technical stories should be included as tasks in User Stories.  Technical stories are often needed, but the ultimate value to the user is in user based functionality, so technical stories should be considered nothing more than overhead in providing that user functionality. Until the iteration prior to development, stories should be nothing more than short, one line placeholders. An exercise called Story Planning can be used to brainstorm and come up with stories.  I’ll save the description of this activity for another blog post. For more information on User Stories, please read the book User Stories Applied by Mike Cohn. Prioritizes Stories in the Product Backlog, Release Backlog and Iteration Backlog Prioritization of stories is one of the most difficult tasks that a Product Owner must do.  A key concept of Scrum done right is the need to have the team working from a single set of prioritized stories.  If the team does not have a single set of prioritized stories, Scrum will likely fail at your organization.  The Product Owner is the ONLY person who has the responsibility to prioritize that list.  The Product Owner must be very diplomatic and sincerely listen to the people around him so that he can get the priorities correct. Just listening will still not yield the proper priorities.  Care must also be taken to ensure that Return on Investment is also considered.  Ultimately, determining which stories give the most value to the company for the least cost is the most important factor in determining priorities.  Product Owners should be willing to look at cold, hard numbers to determine the order for stories.  Even when many people want a feature, if that features is costly to develop, it may not have as high of a return on investment as features that are cheaper, but not as popular. The act of prioritization often causes conflict in an environment.  Customer Service thinks that feature X is the most important, because it will stop people from calling.  Operations thinks that feature Y is the most important, because it will stop servers from crashing.  Developers think that feature Z is most important because it will make writing software much easier for them.  All of these are useful goals, but the team can have only one list of items, and each item must have a priority that is different from all other stories.  The Product Owner will determine which feature gives the best return on investment and the other features will have to wait their turn, which means that someone will not have their top priority feature implemented first. A weak Product Owner will refuse to do prioritization.  I’ve heard from multiple Product Owners the following phrase, “Well, it’s all got to be done, so what does it matter what order we do it in?”  If your product owner is using this phrase, you need a new Product Owner.  Order is VERY important.  In Scrum, every release is potentially shippable.  If the wrong priority items are developed, then the value added in each release isn’t what it should be.  Additionally, the Product Owner with this mindset doesn’t understand Agile.  A product is NEVER finished, until the company has decided that it is no longer a going concern and they are no longer going to sell the product.  Therefore, prioritization isn’t an event, its something that continues every day.  The logical extension of the phrase “It’s all got to be done” is that you will never ship your product, since a product is never “done.”  Once stories have been prioritized, assigning them to the Release Backlog and the Iteration Backlog becomes relatively simple.  The top priority items are copied into the respective backlogs in order and the task is complete.  The team does have the right to shuffle things around a little in the iteration backlog.  For example, they may determine that working on story C with story A is appropriate because they’re related, even though story B is technically a higher priority than story C.  Or they may decide that story B is too big to complete in the time available after Story A has tasks created, so they’ll work on Story C since it’s smaller.  They can’t, however, go deep into the backlog to pick stories to implement.  The team and the Product Owner should work together to determine what’s best for the company. Prioritization is time consuming, but its one of the most important things a Product Owner does. Determines Release Dates and Iteration Dates Product owners are responsible for determining release dates for a product.  A common misconception that Product Owners have is that every “release” needs to correspond with an actual release to customers.  This is not the case.  In general, releases should be no more than 3 months long.  You  may decide to release the product to the customers, and many companies do release the product to customers, but it may also be an internal release. If a release date is too far away, developers will fall into the trap of not feeling a sense of urgency.  The date is far enough away that they don’t need to give the release their full attention.  Additionally, important tasks, such as performance tuning, regression testing, user documentation, and release preparation, will not happen regularly, making them much more difficult and time consuming to do.  The more frequently you do these tasks, the easier they are to accomplish. The Product Owner will be a key participant in determining whether or not a release should be sent out to the customers.  The determination should be made on whether or not the features contained in the release are valuable enough  and complete enough that the customers will see real value in the release.  Often, some features will take more than three months to get them to a state where they qualify for a release or need additional supporting features to be released.  The product owner has the right to make this determination. In addition to release dates, the Product Owner also will help determine iteration dates.  In general, an iteration length should be chosen and the team should follow that iteration length for an extended period of time.  If the iteration length is changed every iteration, you’re not doing Scrum.  Iteration lengths help the team and company get into a rhythm of developing quality software.  Iterations should be somewhere between 2 and 4 weeks in length.  Any shorter, and significant software will likely not be developed.  Any longer, and the team won’t feel urgency and planning will become very difficult. Iterations may not be extended during the iteration.  Companies where Scrum isn’t really followed will often use this as a strategy to complete all stories.  They don’t want to face the harsh reality of what their true performance is, and looking good is more important than seeking visibility and improving the process and team.  Companies like this typically don’t allow failure.  This is unhealthy.  Failure is part of life and unless we learn from it, we can’t improve.  I would much rather see a team push out stories to the next iteration and then have healthy discussions about why they failed rather than extend the iteration and not deal with the core problems. If iteration length varies, retrospectives become more difficult.  For example, evaluating the performance of the team’s estimation efforts becomes much more difficult if the iteration length varies.  Also, the team must have a velocity measurement.  If the iteration length varies, measuring velocity becomes impossible and upper management no longer will have the ability to evaluate the teams performance.  People external to the team will no longer have the ability to determine when key features are likely to be developed.  Variable iterations cause the entire company to fail and likely cause Scrum to fail at an organization. Develops Story Details and Helps the Team Understand Those Details A key concept in Scrum is that the stories are nothing more than a placeholder for a conversation.  Stories should be nothing more than short, one line statements about the functionality.  The team will then converse with the Product Owner about the details about that story.  The product owner needs to have a very good idea about what the details of the story are and needs to be able to help the team understand those details. Too often, we see this requirement as being translated into the need for comprehensive documentation about the story, including old fashioned requirements documentation.  The team should only develop the documentation that is required and should not develop documentation that is only created because their is a process to do so. In general, what we see that works best is the iteration before a team starts development work on a story, the Product Owner, with other appropriate business analysts, will develop the details of that story.  They’ll figure out what business rules are required, potentially make paper prototypes or other light weight mock-ups, and they seek to understand the story and what is implied.  Note that the time allowed for this task is deliberately short.  The Product Owner only has a single iteration to develop all of the stories for the next iteration. If more than one iteration is used, I’ve found that teams will end up with Big Design Up Front and traditional requirements documents.  This is a waste of time, since the team will need to then have discussions with the Product Owner to figure out what the requirements document says.  Instead of this, skip making the pretty pictures and detailing the nuances of the requirements and build only what is minimally needed by the team to do development.  If something comes up during development, you can address it at that time and figure out what you want to do.  The goal is to keep things as light weight as possible so that everyone can move as quickly as possible. Helps QA to Develop Acceptance Tests In Scrum, no story can be counted until it is accepted by QA.  Because of this, acceptance tests are very important to the team.  In general, acceptance tests need to be developed prior to the iteration or at the very beginning of the iteration so that the team can make sure that the tasks that they develop will fulfill the acceptance criteria. The Product Owner will help the team, including QA, understand what will make the story acceptable.  Note that the Product Owner needs to be careful about specifying that the feature will work “Perfectly” at the end of the iteration.  In general, features are developed a little bit at a time, so only the bit that is being developed should be considered as necessary for acceptance. A weak Product Owner will make statements like “Do it right the first time.”  Not only are these statements damaging to the team (like they would try to do it WRONG the first time . . .), they’re also ignoring the iterative nature of Scrum.  Additionally, a weak product owner will seek to add scope in the acceptance testing.  For example, they will refuse to determine acceptance at the beginning of the iteration, and then, after the team has planned and committed to the iteration, they will expand scope by defining acceptance.  This often causes the team to miss the iteration because scope that wasn’t planned on is included.  There are ways that the team can mitigate this problem.  For example, include extra “Product Owner” time to deal with the uncertainty that you know will be introduced by the Product Owner.  This will slow the perceived velocity of the team and is not ideal, since they’ll be doing more work than they get credit for. Interact with the Customer to Make Sure that the Product is Meeting the Customer’s Needs Once development is complete, what the team has worked on should be put in front of real live people to see if it meets the needs of the customer.  One of the great things about Agile is that if something doesn’t work, we can revisit it in a future iteration!  This frees up the team to make the best decision now and know that if that decision proves to be incorrect, the team can revisit it and change that decision. Features are about adding value to the customer, so if the customer doesn’t find them useful, then having the team make tweaks is valuable.  In general, most software will be 80 to 90 percent “right” after the initial round and only minor tweaks are required.  If proper coding standards are followed, these tweaks are usually minor and easy to accomplish.  Product Owners that are doing a good job will encourage real users to see and use the software, since they know that they are trying to add value to the customer. Poor product owners will think that they know the answers already, that their customers are silly and do stupid things and that they don’t need customer input.  If you have a product owner that is afraid to show the team’s work to real customers, you probably need a different product owner. Up Next, “Who Makes a Good Product Owner.” Followed by, “Messing with the Team.” Technorati Tags: Scrum,Product Owner

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  • You should NOT be writing jQuery in SharePoint if&hellip;

    - by Mark Rackley
    Yes… another one of these posts. What can I say? I’m a pot stirrer.. a rabble rouser *rabble rabble* jQuery in SharePoint seems to be a fairly polarizing issue with one side thinking it is the most awesome thing since Princess Leia as the slave girl in Return of the Jedi and the other half thinking it is the worst idea since Mannequin 2: On the Move. The correct answer is OF COURSE “it depends”. But what are those deciding factors that make jQuery an awesome fit or leave a bad taste in your mouth? Let’s see if I can drive the discussion here with some polarizing comments of my own… I know some of you are getting ready to leave your comments even now before reading the rest of the blog, which is great! Iron sharpens iron… These discussions hopefully open us up to understanding the entire process better and think about things in a different way. You should not be writing jQuery in SharePoint if you are not a developer… Let’s start off with my most polarizing and rant filled portion of the blog post. If you don’t know what you are doing or you don’t have a background that helps you understand the implications of what you are writing then you should not be writing jQuery in SharePoint! I truly believe that one of the biggest reasons for the jQuery haters is because of all the bad jQuery out there. If you don’t know what you are doing you can do some NASTY things! One of the best stories I’ve heard about this is from my good friend John Ferringer (@ferringer). John tells this story during our Mythbusters session we do together. One of his clients was undergoing a Denial of Service attack and they couldn’t figure out what was going on! After much searching they found that some genius jQuery developer wrote some code for an image rotator, but did not take into account what happens when there are no images to load! The code just kept hitting the servers over and over and over again which prevented anything else from getting done! Now, I’m NOT saying that I have not done the same sort of thing in the past or am immune from such mistakes. My point is that if you don’t know what you are doing, there are very REAL consequences that can have a major impact on your organization AND they will be hard to track down.  Think how happy your boss will be after you copy and pasted some jQuery from a blog without understanding what it does, it brings down the farm, AND it takes them 3 days to track it back to you.  :/ Good times will not be had. Like it or not JavaScript/jQuery is a programming language. While you .NET people sit on your high horses because your code is compiled and “runs faster” (also debatable), the rest of us will be actually getting work done and delivering solutions while you are trying to figure out why your widget won’t deploy. I can pick at that scab because I write .NET code too and speak from experience. I can do both, and do both well. So, I am not speaking from ignorance here. In JavaScript/jQuery you have variables, loops, conditionals, functions, arrays, events, and built in methods. If you are not a developer you just aren’t going to take advantage of all of that and use it correctly. Ahhh.. but there is hope! There is a lot of jQuery resources out there to help you learn and learn well! There are many experts on the subject that will gladly tell you when you are smoking crack. I just this minute saw a tweet from @cquick with a link to: “jQuery Fundamentals”. I just glanced through it and this may be a great primer for you aspiring jQuery devs. Take advantage of all the resources and become a developer! Hey, it will look awesome on your resume right? You should not be writing jQuery in SharePoint if it depends too much on client resources for a good user experience I’ve said it once and I’ll say it over and over until you understand. jQuery is executed on the client’s computer. Got it? If you are looping through hundreds of rows of data, searching through an enormous DOM, or performing many calculations it is going to take some time! AND if your user happens to be sitting on some old PC somewhere that they picked up at a garage sale their experience will be that much worse! If you can’t give the user a good experience they will not use the site. So, if jQuery is causing the user to have a bad experience, don’t use it. I sometimes go as far to say that you should NOT go to jQuery as a first option for external facing web sites because you have ZERO control over what the end user’s computer will be. You just can’t guarantee an awesome user experience all of the time. Ahhh… but you have no choice? (where have I heard that before?). Well… if you really have no choice, here are some tips to help improve the experience: Avoid screen scraping This is not 1999 and SharePoint is not an old green screen from a mainframe… so why are you treating it like it is? Screen scraping is time consuming and client intensive. Take advantage of tools like SPServices to do your data retrieval when possible. Fine tune your DOM searches A lot of time can be eaten up just searching the DOM and ignoring table rows that you don’t need. Write better jQuery to only loop through tables rows that you need, or only access specific elements you need. Take advantage of Element ID’s to return the one element you are looking for instead of looping through all the DOM over and over again. Write better jQuery Remember this is development. Think about how you can write cleaner, faster jQuery. This directly relates to the previous point of improving your DOM searches, but also when using arrays, variables and loops. Do you REALLY need to loop through that array 3 times? How can you knock it down to 2 times or even 1? When you have lots of calculations and data that you are manipulating every operation adds up. Think about how you can streamline it. Back in the old days before RAM was abundant, Cores were plentiful and dinosaurs roamed the earth, us developers had to take performance into account in everything we did. It’s a lost art that really needs to be used here. You should not be writing jQuery in SharePoint if you are sending a lot of data over the wire… Developer:  “Awesome… you can easily call SharePoint’s web services to retrieve and write data using SPServices!” Administrator: “Crap! you can easily call SharePoint’s web services to retrieve and write data using SPServices!” SPServices may indeed be the best thing that happened to SharePoint since the invention of SharePoint Saturdays by Godfather Lotter… BUT you HAVE to use it wisely! (I REFUSE to make the Spiderman reference). If you do not know what you are doing your code will bring back EVERY field and EVERY row from a list and push that over the internet with all that lovely XML wrapped around it. That can be a HUGE amount of data and will GREATLY impact performance! Calling several web service methods at the same time can cause the same problem and can negatively impact your SharePoint servers. These problems, thankfully, are not difficult to rectify if you are careful: Limit list data retrieved Use CAML to reduce the number of rows returned and limit the fields returned using ViewFields.  You should definitely be doing this regardless. If you aren’t I hope your admin thumps you upside the head. Batch large list updates You may or may not have noticed that if you try to do large updates (hundreds of rows) that the performance is either completely abysmal or it fails over half the time. You can greatly improve performance and avoid timeouts by breaking up your updates into several smaller updates. I don’t know if there is a magic number for best performance, it really depends on how much data you are sending back more than the number of rows. However, I have found that 200 rows generally works well.  Play around and find the right number for your situation. Delay Web Service calls when possible One of the cool things about jQuery and SPServices is that you can delay queries to the server until they are actually needed instead of doing them all at once. This can lead to performance improvements over DataViewWebParts and even .NET code in the right situations. So, don’t load the data until it’s needed. In some instances you may not need to retrieve the data at all, so why retrieve it ALL the time? You should not be writing jQuery in SharePoint if there is a better solution… jQuery is NOT the silver bullet in SharePoint, it is not the answer to every question, it is just another tool in the developers toolkit. I urge all developers to know what options exist out there and choose the right one! Sometimes it will be jQuery, sometimes it will be .NET,  sometimes it will be XSL, and sometimes it will be some other choice… So, when is there a better solution to jQuery? When you can’t get away from performance problems Sometimes jQuery will just give you horrible performance regardless of what you do because of unavoidable obstacles. In these situations you are going to have to figure out an alternative. Can I do it with a DVWP or do I have to crack open Visual Studio? When you need to do something that jQuery can’t do There are lots of things you can’t do in jQuery like elevate privileges, event handlers, workflows, or interact with back end systems that have no web service interface. It just can’t do everything. When it can be done faster and more efficiently another way Why are you spending time to write jQuery to do a DataViewWebPart that would take 5 minutes? Or why are you trying to implement complicated logic that would be simple to do in .NET? If your answer is that you don’t have the option, okay. BUT if you do have the option don’t reinvent the wheel! Take advantage of the other tools. The answer is not always jQuery… sorry… the kool-aid tastes good, but sweet tea is pretty awesome too. You should not be using jQuery in SharePoint if you are a moron… Let’s finish up the blog on a high note… Yes.. it’s true, I sometimes type things just to get a reaction… guess this section title might be a good example, but it feels good sometimes just to type the words that a lot of us think… So.. don’t be that guy! Another good buddy of mine that works for Microsoft told me. “I loved jQuery in SharePoint…. until I had to support it.”. He went on to explain that some user was making several web service calls on a page using jQuery and then was calling Microsoft and COMPLAINING because the page took so long to load… DUH! What do you expect to happen when you are pushing that much data over the wire and are making that many web service calls at once!! It’s one thing to write that kind of code and accept it’s just going to take a while, it’s COMPLETELY another issue to do that and then complain when it’s not lightning fast!  Someone’s gene pool needs some chlorine. So, I think this is a nice summary of the blog… DON’T be that guy… don’t be a moron. How can you stop yourself from being a moron? Ah.. glad you asked, here are some tips: Think Is jQuery the right solution to my problem? Is there a better approach? What are the implications and pitfalls of using jQuery in this situation? Search What are others doing? Does someone have a better solution? Is there a third party library that does the same thing I need? Plan Write good jQuery. Limit calculations and data sent over the wire and don’t reinvent the wheel when possible. Test Okay, it works well on your machine. Try it on others ESPECIALLY if this is for an external site. Test with empty data. Test with hundreds of rows of data. Test as many scenarios as possible. Monitor those server resources to see the impact there as well. Ask the experts As smart as you are, there are people smarter than you. Even the experts talk to each other to make sure they aren't doing something stupid. And for the MOST part they are pretty nice guys. Marc Anderson and Christophe Humbert are two guys who regularly keep me in line. Make sure you aren’t doing something stupid. Repeat So, when you think you have the best solution possible, repeat the steps above just to be safe.  Conclusion jQuery is an awesome tool and has come in handy on many occasions. I’m even teaching a 1/2 day SharePoint & jQuery workshop at the upcoming SPTechCon in Boston if you want to berate me in person. However, it’s only as awesome as the developer behind the keyboard. It IS development and has its pitfalls. Knowledge and experience are invaluable to giving the user the best experience possible.  Let’s face it, in the end, no matter our opinions, prejudices, or ego providing our clients, customers, and users with the best solution possible is what counts. Period… end of sentence…

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  • .NET Code Evolution

    - by Alois Kraus
    Originally posted on: http://geekswithblogs.net/akraus1/archive/2013/07/24/153504.aspxAt my day job I do look at a lot of code written by other people. Most of the code is quite good and some is even a masterpiece. And there is also code which makes you think WTF… oh it was written by me. Hm not so bad after all. There are many excuses reasons for bad code. Most often it is time pressure followed by not enough ambition (who cares) or insufficient training. Normally I do care about code quality quite a lot which makes me a (perceived) slow worker who does write many tests and refines the code quite a lot because of the design deficiencies. Most of the deficiencies I do find by putting my design under stress while checking for invariants. It does also help a lot to step into the code with a debugger (sometimes also Windbg). I do this much more often when my tests are red. That way I do get a much better understanding what my code really does and not what I think it should be doing. This time I do want to show you how code can evolve over the years with different .NET Framework versions. Once there was  time where .NET 1.1 was new and many C++ programmers did switch over to get rid of not initialized pointers and memory leaks. There were also nice new data structures available such as the Hashtable which is fast lookup table with O(1) time complexity. All was good and much code was written since then. At 2005 a new version of the .NET Framework did arrive which did bring many new things like generics and new data structures. The “old” fashioned way of Hashtable were coming to an end and everyone used the new Dictionary<xx,xx> type instead which was type safe and faster because the object to type conversion (aka boxing) was no longer necessary. I think 95% of all Hashtables and dictionaries use string as key. Often it is convenient to ignore casing to make it easy to look up values which the user did enter. An often followed route is to convert the string to upper case before putting it into the Hashtable. Hashtable Table = new Hashtable(); void Add(string key, string value) { Table.Add(key.ToUpper(), value); } This is valid and working code but it has problems. First we can pass to the Hashtable a custom IEqualityComparer to do the string matching case insensitive. Second we can switch over to the now also old Dictionary type to become a little faster and we can keep the the original keys (not upper cased) in the dictionary. Dictionary<string, string> DictTable = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase); void AddDict(string key, string value) { DictTable.Add(key, value); } Many people do not user the other ctors of Dictionary because they do shy away from the overhead of writing their own comparer. They do not know that .NET has for strings already predefined comparers at hand which you can directly use. Today in the many core area we do use threads all over the place. Sometimes things break in subtle ways but most of the time it is sufficient to place a lock around the offender. Threading has become so mainstream that it may sound weird that in the year 2000 some guy got a huge incentive for the idea to reduce the time to process calibration data from 12 hours to 6 hours by using two threads on a dual core machine. Threading does make it easy to become faster at the expense of correctness. Correct and scalable multithreading can be arbitrarily hard to achieve depending on the problem you are trying to solve. Lets suppose we want to process millions of items with two threads and count the processed items processed by all threads. A typical beginners code might look like this: int Counter; void IJustLearnedToUseThreads() { var t1 = new Thread(ThreadWorkMethod); t1.Start(); var t2 = new Thread(ThreadWorkMethod); t2.Start(); t1.Join(); t2.Join(); if (Counter != 2 * Increments) throw new Exception("Hmm " + Counter + " != " + 2 * Increments); } const int Increments = 10 * 1000 * 1000; void ThreadWorkMethod() { for (int i = 0; i < Increments; i++) { Counter++; } } It does throw an exception with the message e.g. “Hmm 10.222.287 != 20.000.000” and does never finish. The code does fail because the assumption that Counter++ is an atomic operation is wrong. The ++ operator is just a shortcut for Counter = Counter + 1 This does involve reading the counter from a memory location into the CPU, incrementing value on the CPU and writing the new value back to the memory location. When we do look at the generated assembly code we will see only inc dword ptr [ecx+10h] which is only one instruction. Yes it is one instruction but it is not atomic. All modern CPUs have several layers of caches (L1,L2,L3) which try to hide the fact how slow actual main memory accesses are. Since cache is just another word for redundant copy it can happen that one CPU does read a value from main memory into the cache, modifies it and write it back to the main memory. The problem is that at least the L1 cache is not shared between CPUs so it can happen that one CPU does make changes to values which did change in meantime in the main memory. From the exception you can see we did increment the value 20 million times but half of the changes were lost because we did overwrite the already changed value from the other thread. This is a very common case and people do learn to protect their  data with proper locking.   void Intermediate() { var time = Stopwatch.StartNew(); Action acc = ThreadWorkMethod_Intermediate; var ar1 = acc.BeginInvoke(null, null); var ar2 = acc.BeginInvoke(null, null); ar1.AsyncWaitHandle.WaitOne(); ar2.AsyncWaitHandle.WaitOne(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Intermediate did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Intermediate() { for (int i = 0; i < Increments; i++) { lock (this) { Counter++; } } } This is better and does use the .NET Threadpool to get rid of manual thread management. It does give the expected result but it can result in deadlocks because you do lock on this. This is in general a bad idea since it can lead to deadlocks when other threads use your class instance as lock object. It is therefore recommended to create a private object as lock object to ensure that nobody else can lock your lock object. When you read more about threading you will read about lock free algorithms. They are nice and can improve performance quite a lot but you need to pay close attention to the CLR memory model. It does make quite weak guarantees in general but it can still work because your CPU architecture does give you more invariants than the CLR memory model. For a simple counter there is an easy lock free alternative present with the Interlocked class in .NET. As a general rule you should not try to write lock free algos since most likely you will fail to get it right on all CPU architectures. void Experienced() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Experienced); t1.Wait(); t2.Wait(); if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Experienced did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Experienced() { for (int i = 0; i < Increments; i++) { Interlocked.Increment(ref Counter); } } Since time does move forward we do not use threads explicitly anymore but the much nicer Task abstraction which was introduced with .NET 4 at 2010. It is educational to look at the generated assembly code. The Interlocked.Increment method must be called which does wondrous things right? Lets see: lock inc dword ptr [eax] The first thing to note that there is no method call at all. Why? Because the JIT compiler does know very well about CPU intrinsic functions. Atomic operations which do lock the memory bus to prevent other processors to read stale values are such things. Second: This is the same increment call prefixed with a lock instruction. The only reason for the existence of the Interlocked class is that the JIT compiler can compile it to the matching CPU intrinsic functions which can not only increment by one but can also do an add, exchange and a combined compare and exchange operation. But be warned that the correct usage of its methods can be tricky. If you try to be clever and look a the generated IL code and try to reason about its efficiency you will fail. Only the generated machine code counts. Is this the best code we can write? Perhaps. It is nice and clean. But can we make it any faster? Lets see how good we are doing currently. Level Time in s IJustLearnedToUseThreads Flawed Code Intermediate 1,5 (lock) Experienced 0,3 (Interlocked.Increment) Master 0,1 (1,0 for int[2]) That lock free thing is really a nice thing. But if you read more about CPU cache, cache coherency, false sharing you can do even better. int[] Counters = new int[12]; // Cache line size is 64 bytes on my machine with an 8 way associative cache try for yourself e.g. 64 on more modern CPUs void Master() { var time = Stopwatch.StartNew(); Task t1 = Task.Factory.StartNew(ThreadWorkMethod_Master, 0); Task t2 = Task.Factory.StartNew(ThreadWorkMethod_Master, Counters.Length - 1); t1.Wait(); t2.Wait(); Counter = Counters[0] + Counters[Counters.Length - 1]; if (Counter != 2 * Increments) throw new Exception(String.Format("Hmm {0:N0} != {1:N0}", Counter, 2 * Increments)); Console.WriteLine("Master did take: {0:F1}s", time.Elapsed.TotalSeconds); } void ThreadWorkMethod_Master(object number) { int index = (int) number; for (int i = 0; i < Increments; i++) { Counters[index]++; } } The key insight here is to use for each core its own value. But if you simply use simply an integer array of two items, one for each core and add the items at the end you will be much slower than the lock free version (factor 3). Each CPU core has its own cache line size which is something in the range of 16-256 bytes. When you do access a value from one location the CPU does not only fetch one value from main memory but a complete cache line (e.g. 16 bytes). This means that you do not pay for the next 15 bytes when you access them. This can lead to dramatic performance improvements and non obvious code which is faster although it does have many more memory reads than another algorithm. So what have we done here? We have started with correct code but it was lacking knowledge how to use the .NET Base Class Libraries optimally. Then we did try to get fancy and used threads for the first time and failed. Our next try was better but it still had non obvious issues (lock object exposed to the outside). Knowledge has increased further and we have found a lock free version of our counter which is a nice and clean way which is a perfectly valid solution. The last example is only here to show you how you can get most out of threading by paying close attention to your used data structures and CPU cache coherency. Although we are working in a virtual execution environment in a high level language with automatic memory management it does pay off to know the details down to the assembly level. Only if you continue to learn and to dig deeper you can come up with solutions no one else was even considering. I have studied particle physics which does help at the digging deeper part. Have you ever tried to solve Quantum Chromodynamics equations? Compared to that the rest must be easy ;-). Although I am no longer working in the Science field I take pride in discovering non obvious things. This can be a very hard to find bug or a new way to restructure data to make something 10 times faster. Now I need to get some sleep ….

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  • How to get full control of umask/PAM/permissions?

    - by plua
    OUR SITUATION Several people from our company log in to a server and upload files. They all need to be able to upload and overwrite the same files. They have different usernames, but are all part of the same group. However, this is an internet server, so the "other" users should have (in general) just read-only access. So what I want to have is these standard permissions: files: 664 directories: 771 My goal is that all users do not need to worry about permissions. The server should be configured in such a way that these permissions apply to all files and directories, newly created, copied, or over-written. Only when we need some special permissions we'd manually change this. We upload files to the server by SFTP-ing in Nautilus, by mounting the server using sshfs and accessing it in Nautilus as if it were a local folder, and by SCP-ing in the command line. That basically covers our situation and what we aim to do. Now, I have read many things about the beautiful umask functionality. From what I understand umask (together with PAM) should allow me to do exactly what I want: set standard permissions for new files and directories. However, after many many hours of reading and trial-and-error, I still do not get this to work. I get many unexpected results. I really like to get a solid grasp of umask and have many question unanswered. I will post these questions below, together with my findings and an explanation of my trials that led to these questions. Given that many things appear to go wrong, I think that I am doing several things wrong. So therefore, there are many questions. NOTE: I am using Ubuntu 9.10 and therefore can not change the sshd_config to set the umask for the SFTP server. Installed SSH OpenSSH_5.1p1 Debian-6ubuntu2 < required OpenSSH 5.4p1. So here go the questions. 1. DO I NEED TO RESTART FOR PAM CHANGS TO TAKE EFFECT? Let's start with this. There were so many files involved and I was unable to figure out what does and what does not affect things, also because I did not know whether or not I have to restart the whole system for PAM changes to take effect. I did do so after not seeing the expected results, but is this really necessary? Or can I just log out from the server and log back in, and should new PAM policies be effective? Or is there some 'PAM' program to reload? 2. IS THERE ONE SINGLE FILE TO CHANGE THAT AFFECTS ALL USERS FOR ALL SESSIONS? So I ended up changing MANY files, as I read MANY different things. I ended up setting the umask in the following files: ~/.profile -> umask=0002 ~/.bashrc -> umask=0002 /etc/profile -> umask=0002 /etc/pam.d/common-session -> umask=0002 /etc/pam.d/sshd -> umask=0002 /etc/pam.d/login -> umask=0002 I want this change to apply to all users, so some sort of system-wide change would be best. Can it be achieved? 3. AFTER ALL, THIS UMASK THING, DOES IT WORK? So after changing umask to 0002 at every possible place, I run tests. ------------SCP----------- TEST 1: scp testfile (which has 777 permissions for testing purposes) server:/home/ testfile 100% 4 0.0KB/s 00:00 Let's check permissions: user@server:/home$ ls -l total 4 -rwx--x--x 1 user uploaders 4 2011-02-05 17:59 testfile (711) ---------SSH------------ TEST 2: ssh server user@server:/home$ touch anotherfile user@server:/home$ ls -l total 4 -rw-rw-r-- 1 user uploaders 0 2011-02-05 18:03 anotherfile (664) --------SFTP----------- Nautilus: sftp://server/home/ Copy and paste newfile from client to server (777 on client) TEST 3: user@server:/home$ ls -l total 4 -rwxrwxrwx 1 user uploaders 3 2011-02-05 18:05 newfile (777) Create a new file through Nautilus. Check file permissions in terminal: TEST 4: user@server:/home$ ls -l total 4 -rw------- 1 user uploaders 0 2011-02-05 18:06 newfile (600) I mean... WHAT just happened here?! We should get 644 every single time. Instead I get 711, 777, 600, and then once 644. And the 644 is only achieved when creating a new, blank file through SSH, which is the least probable scenario. So I am asking, does umask/pam work after all? 4. SO WHAT DOES IT MEAN TO UMASK SSHFS? Sometimes we mount a server locally, using sshfs. Very useful. But again, we have permissions issues. Here is how we mount: sshfs -o idmap=user -o umask=0113 user@server:/home/ /mnt NOTE: we use umask = 113 because apparently, sshfs starts from 777 instead of 666, so with 113 we get 664 which is the desired file permission. But what now happens is that we see all files and directories as if they are 664. We browse in Nautilus to /mnt and: Right click - New File (newfile) --- TEST 5 Right click - New Folder (newfolder) --- TEST 6 Copy and paste a 777 file from our local client --- TEST 7 So let's check on the command line: user@client:/mnt$ ls -l total 8 -rw-rw-r-- 1 user 1007 3 Feb 5 18:05 copyfile (664) -rw-rw-r-- 1 user 1007 0 Feb 5 18:15 newfile (664) drw-rw-r-- 1 user 1007 4096 Feb 5 18:15 newfolder (664) But hey, let's check this same folder on the server-side: user@server:/home$ ls -l total 8 -rwxrwxrwx 1 user uploaders 3 2011-02-05 18:05 copyfile (777) -rw------- 1 user uploaders 0 2011-02-05 18:15 newfile (600) drwx--x--x 2 user uploaders 4096 2011-02-05 18:15 newfolder (711) What?! The REAL file permissions are very different from what we see in Nautilus. So does this umask on sshfs just create a 'filter' that shows unreal file permissions? And I tried to open a file from another user but the same group that had real 600 permissions but 644 'fake' permissions, and I could still not read this, so what good is this filter?? 5. UMASK IS ALL ABOUT FILES. BUT WHAT ABOUT DIRECTORIES? From my tests I can see that the umask that is being applied also somehow influences the directory permissions. However, I want my files to be 664 (002) and my directories to be 771 (006). So is it possible to have a different umask for directories? 6. PERHAPS UMASK/PAM IS REALLY COOL, BUT UBUNTU IS JUST BUGGY? On the one hand, I have read topics of people that have had success with PAM/UMASK and Ubuntu. On the other hand, I have found many older and newer bugs regarding umask/PAM/fuse on Ubuntu: https://bugs.launchpad.net/ubuntu/+source/gdm/+bug/241198 https://bugs.launchpad.net/ubuntu/+source/fuse/+bug/239792 https://bugs.launchpad.net/ubuntu/+source/pam/+bug/253096 https://bugs.launchpad.net/ubuntu/+source/sudo/+bug/549172 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=314796 So I do not know what to believe anymore. Should I just give up? Would ACL solve all my problems? Or do I have again problems using Ubuntu? One word of caution with backups using tar. Red Hat /Centos distributions support acls in the tar program but Ubuntu does not support acls when backing up. This means that all acls will be lost when you create a backup. I am very willing to upgrade to Ubuntu 10.04 if that would solve my problems too, but first I want to understand what is happening.

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