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• Converting a constantly changing scalar value to a changing interval or frequency

  - by eco_bach

  Although I'm coding in Objective C, this is more of a general programming question. What is the best way to convert a constantly changing scalar value to a changing interval or frequency? Right now every time the scalar value changes I am destroying the NSInterval ie [self.myTimer invalidate]; self.myTimer = nil; and creating a new one, but this seems like a VERY expensive way to achieve my goal, since the changing scalar value in my case represents the horizontal velocity of a swipe. For a rough analogy, think of the speed of a swipe being reflected in a visual metronome, the faster you swipe, the higher(shorter interval) the frequency of the metronome.

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• In Javascript, by what mechanism does setting an Image src property trigger an image load?

  - by brainjam

  One of the things you learn early on when manipulating a DOM using Javascript is the following pattern: var img = new Image(); // Create new Image object img.onload = function(){ // execute drawImage statements here } img.src = 'myImage.png'; // Set source path As far as I know, in general when you set an object property there are no side effects. So what is the mechanism for triggering an image load? Is it just magic? Or can I use a similar mechanism to implement a class Foo that supports a parallel pattern? var foo = new Foo(); // Create new object foo.barchanged = function(){ // execute something after side effect has completed } foo.bar = 'whatever'; // Assign something to 'bar' property I'm vaguely aware of Javascript getters and setters. Is this how Image.src triggers a load?

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• Ideas for Computer Science related Microteaching

  - by Roman Stolper

  This semester, I will be a TA for an introductory computer science course at my university. As part of TA training, I'll be doing something called Microteaching, which is where I teach for 5-7 minutes in front of a small audience (4-5 people) and I am reviewed on my teaching style. Among being critiqued on my personal things like confidence and eye contact, I will be critiqued on how well I know the subject material, as well as how interesting it is to the audience. So my question is: Can you offer me any suggestions of computer science related topics that: I can begin and finish teaching in a span of 5-7 minutes Are fun to learn about Are accessible to a general engineering (but not necessarily computer science) audience Some topics I have considered: Teaching how to write Hello World in some simple language Introducing a synchronization problem like dining philosophers

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• Is re-using a Command and Connection object in ado.net a legitimate way of reducing new object creat

  - by Neil Trodden

  The current way our application is written, involves creating a new connection and command object in every method that access our sqlite db. Considering we need it to run on a WM5 device, that is leading to hideous performance. Our plan is to use just one connection object per-thread but it's also occurred to us to use one global command object per-thread too. The benefit of this is it reduces the overhead on the garbage collector created by instantiating objects all over the place. I can't find any advice against doing this but wondered if anyone can answer definitively if this is a good or bad thing to do, and why?

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• Where is a good Address Parser

  - by Brig Lamoreaux

  I'm looking for a good tool that can take a full mailing address, formatted for display or use with a mailing label, and convert it into a structured object. So for instance: // Start with a formatted address in a single string string f = "18698 E. Main Street\r\nBig Town, AZ, 86011"; // Parse into address Address addr = new Address(f); addr.Street; // 18698 E. Main Street addr.Locality; // Big Town addr.Region; // AZ addr.PostalCode; // 86011 Now I could do this using RegEx. But the tricky part is keeping it general enough to handle any address in the world! I'm sure there has to be something out there that can do it. If anyone noticed, this is actually the format of the opensocial.address object.

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• How can I synchronize database access between a write-thread and a read-thread?

  - by Runcible

  My program has two threads: Main execution thread that handles user input and queues up database writes A utility thread that wakes up every second and flushes the writes to the database Inside the main thread, I occasionally need to make reads on the database. When this happens, performance is not important, but correctness is. (In a perfect world, I would be reading from a cache, not making a round-trip to the database - but let's put that aside for the sake of discussion.) How do I make sure that the main thread sees a correct / quiescent database? A standard mutex won't work, since I run the risk of having the main thread grab the mutex before the data gets flushed to the database. This would be a big race condition. What I really want is some sort of mutex that lets the main thread of execution proceed only AFTER the mutex has been grabbed and released once. Does such a thing exist? What's the best way to solve this problem?

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• NSMutableSet addObject question

  - by Jacob Relkin

  I've got a class that wraps around an NSMutableSet object, and I have an instance method that adds objects (using the addObject: method) to the NSMutableSet. This works well, but I'm smelling a performance hitch because inside the method i'm explicitly calling containsObject: before adding the object to the set. Three part question: Do I need to be calling containsObject: before I add an object to the set? If so, then what actual method should I be using, containsObject or containsObjectIdenticalTo:? If that is not so, what contains method gets invoked under the hood of addObject:? This is important to me because if I pass an object to containsObject: it would return true, but if I pass it to containsObjectIdenticalTo: it would return false.

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• Are the built-in images in iPhone documented, and is there a list of their names somewhere?

  - by Alex Gosselin

  I discovered somewhat by accident that if you make a UIButton in Interface Builder and type in Plus in the image field, a + image appears for the button. A similar result comes from typing Minus. I am wondering if this is a bug, or if there is some way the poor programmers can access the built-in general GUI images from other apple apps, such as the green +, the red -, the detail disclosure chevron, the big red "Delete Contact" or similarly styled button, etc. Has anyone else encountered this, or know where to access these things in Xcode? It makes sense to me that they should be usable, cause the Apple HIG seems to be all about making things recognizable and intuitive, and using them the way other apps use them.

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• SDL versus GLFW?

  - by user697111

  What are the pros and cons to each? It seems they serve the same purpose. I have a few demos with each and they seem about the same. Performance or cross platform wise, is one better than the other? The only thing I notice is that SDL seems to have more "helper" libraries (fonts, images, mixer, built in sound support, etc). On its site, GLFW claims to be more "OpenGL" focused, but still have to use a GLEW to get any newer OpenGL features (same with SDL). I guess I'm leaning towards using SDL now (more mature, more features, more community). Are there any reasons I've missed why GLFW stands out and I should use it instead of SDL?

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• starting 64 Bit Windows Application Development

  - by user173438

  I intend to start writing a 64 Bit Scientific Computing Application (signal processing) for Windows using Microsoft Visual Studio 2008. What should I have ready as far as a development platform is concerned? How would it be different from 32 Bit development? What could be the porting issues for a 32 Bit version that I already have (ok - this might too early to ask.. even before I start compiling)? As you might have guessed, I am looking for general directions. All pointers would be much appreciated! :) Thanks in advance..

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• foreign key constraints on primary key columns - issues ?

  - by zzzeek

  What are the pros/cons from a performance/indexing/data management perspective of creating a one-to-one relationship between tables using the primary key on the child as foreign key, versus a pure surrogate primary key on the child? The first approach seems to reduce redundancy and nicely constrains the one-to-one implicitly, while the second approach seems to be favored by DBAs, even though it creates a second index: create table parent ( id integer primary key, data varchar(50) ) create table child ( id integer primary key references parent(id), data varchar(50) ) pure surrogate key: create table parent ( id integer primary key, data varchar(50) ) create table child ( id integer primary key, parent_id integer unique references parent(id), data varchar(50) ) the platforms of interest here are Postgresql, Microsoft SQL Server.

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• Which package from CPAN should I use to send mail?

  - by Uri

  Which package from CPAN should I use to send mail? Sometime the timtowtdi approach is very tiring. For me, especially when it comes to package selection. So all I want is to send email, potentially HTML emails. Between Mail-Sendmail, Mail-Sender, NET-SMTP (by the way - not available in PPM), Mail-SendEasy, and the 80 or so other packages that have 'Mail' in their package name - which one should I choose? And while in this subject, what is your general apprach to choose the "canonical" package for a jog. I.e. the package that "everybody is using". Is there any rating or popularity billboard somewhere?

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• How sql server evaluates the multiple different joins?

  - by ziang

  Hi, i have a general question about how sql server evaluates the joins.The query is SELECT * FROM TableA INNER JOIN TableB ON TableB.id = TableA.id LEFT JOIN TABLEC ON TABLEC.id = TABLEB.id Q1: What tables is the left join based on? I know it will based on the TABLEC but what is the other one? Is it the result of the first inner join or the TABLEB specified in the left join condition? Q2: Is "LEFT JOIN TABLEC ON TABLEC.id = TABLEB.id" equivalent to "LEFT JOIN TABLEC ON TABLEB.id = TABLEC.id" Q3: Is the query equivalent to the following one? (with TABLEB.id replaced by TABLEA.id?) SELECT * FROM TableA INNER JOIN TableB ON TableB.id = TableA.id LEFT JOIN TABLEC ON TABLEC.id = TABLEA.id Thank you!

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• Algorithms for modern hardware?

  - by Jurily

  Once again, I find myself with a set of broken assumptions. The article itself is about a 10x performance gain by modifying a proven-optimal algorithm to account for virtual memory: What good is an O(log2(n)) algorithm if those operations cause page faults and slow disk operations? For most relevant datasets an O(n) or even an O(n^2) algorithm, which avoids page faults, will run circles around it. Are there more such algorithms around? Should we re-examine all those fundamental building blocks of our education? What else do I need to watch out for when writing my own?

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• Validation errors from Google App Engine Logout link

  - by goggin13

  I am making a web page using the Google App Engine. I am validating my pages, and found that the logout link that is generated by the call to the users api (in python) users.create_logout_url(request.uri) does not validate as XHTML 1.0 Strict. The href in the anchor tag looks like this: /_ah/login?continue=http%3A//localhost%3A8080/&action=Logout Including a link with this anchor text throws three different validation errors: *general entity "action" not defined and no default entity *reference to entity "action" for which no system identifier could be generated *EntityRef: expecting ';' Here is a dummy page with the anchor tag in it, if you want to try it on w3c validator.Dummy Page. The logout link wont work, but you can see how the page is valid without it, but the actual text inside the href tag breaks the validation. Any thoughts on whats going on? Thank you!

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• What should I do if a IOException is thrown?

  - by Roman

  I have the following 3 lines of the code: ServerSocket listeningSocket = new ServerSocket(earPort); Socket serverSideSocket = listeningSocket.accept(); BufferedReader in = new BufferedReader(new InputStreamReader(serverSideSocket.getInputStream())); The compiler complains about all of these 3 lines and its complain is the same for all 3 lines: unreported exception java.io.IOException; In more details, these exception are thrown by new ServerSocket, accept() and getInputStream(). I know I need to use try ... catch .... But for that I need to know what this exceptions mean in every particular case (how should I interpret them). When they happen? I mean, not in general, but in these 3 particular cases.

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• How do I confirm a pdf loaded correctly with Watir webdriver testing

  - by Mike Rose

  This is a general type question that I dont know what code I could post that would help get an answer. So I apologize in advance, but if some piece of code would help, please let me know and Ill add it. The question is, how do I confirm that a pdf loaded in a web browser when using Ruby/Cucumber/Watir Webdriver? My test clicks on a random link that should load a pdf in a new browser window, so I cant check the url because it will vary with each test. Any ideas how I can make sure the correct pdf loads after clicking the link that should load it?

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• Which data structure for List of objects + datagrid wiev

  - by Martin

  Hi, I have to develop a code which will store a list of objects, as example below 101, value 11, value 12, value 13 ...etc 102, value 21, value 22, value 23 ...etc 103, value 31, value 32, value 33 ...etc 104, value 41, value 42, value 43 ...etc Now, the difficulty is, that first column is an identifier, and whole table should always be sorted by it. Easy access to each element is required. Additionally, list should be easily updated, and extended by adding element at the end as well as in front and still keep being sorted by first column. Finally, I would like to be able to display values of the above in datagridview. What is most important is a performance of the implementation, as rows will be updated many times per second, and datagridview should be able to display all changes immediately. I was thinking about creating class for the values, and then a Dictionary but encountered a problem with displaying values in gridview. What would be the most optimal way of implementing the code? Thanks in advance Martin

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• Is there an easy way to replace a deprecated method call in Xcode?

  - by Alex Basson

  So iOS 6 deprecates presentModalViewController:animated: and dismissModalViewControllerAnimated:, and it replaces them with presentViewController:animated:completion: and dismissViewControllerAnimated:completion:, respectively. I suppose I could use find-replace to update my app, although it would be awkward with the present* methods, since the controller to be presented is different every time. I know I could handle that situation with a regex, but I don't feel comfortable enough with regex to try using it with my 1000+-files-big app. So I'm wondering: Does Xcode have some magic "update deprecated methods" command or something? I mean, I've described my particular situation above, but in general, deprecations come around with every OS release. Is there a better way to update an app than simply to use find-replace?

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• Thread.sleep vs Monitor.Wait vs RegisteredWaitHandle?

  - by Royi Namir

  (the following items has different goals , but im interesting knowing how they "PAUSEd") questions Thread.sleep - Does it impact performance on a system ?does it tie up a thread with its wait ? what about Monitor.Wait ? what is the difference in the way they "wait"? do they tie up a thread with their wait ? what aboutRegisteredWaitHandle ? This method accepts a delegate that is executed when a wait handle is signaled. While it’s waiting, it doesn’t tie up a thread. so some thread are paused and can be woken by a delegate , while others just wait ? spin ? can someone please make things clearer ? edit http://www.albahari.com/threading/part2.aspx

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• Can any JavaScript library perform as well as the Cut The Rope JavaScript implementation?

  - by joe

  Now that the canvas tag is starting to get hardware execration [acceleration - thanks guys!] by many browsers, developing casual games in HTML5 is becoming more feasible. ZeptoLabs did a great job porting Cut The Rope to HTML5 for use as a Windows 8 Metro App. You can find some of the details here but they do not get into specifics. I was wondering if anyone knew if they used a library (such as Impact or Crafty) or if you need to write all custom and optimized JavaScript code in order to get this type of performance. Thanks!

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• NSUserDefaults and default language used for I18N

  - by fedmest

  I have searched around a lot for this and found some answers that sounded quite like what I wanted but never worked. I simply need to have my iPhone app load NIBs and Localizable.strings that I decide (through user selection) rather than the ones that are established through the global iPhone/iPad settings. General consensus seems to be that this line [[NSUserDefaults standardUserDefaults] setObject:[NSArray arrayWithObject:@"ro"] forKey:@"AppleLanguages"]; would do the trick (in this specific case, load the NIBs and Localizable.strings in ro.lproj) but I have not had such luck. It keeps on looking for the files in en.lproj or whatever language I chose in the Settings app. I have then tried adding this line [[NSUserDefaults standardUserDefaults] setObject:[NSArray arrayWithObject:@"ro_RO"] forKey:@"AppleLocale"]; and to my great surprise, it worked! ...only once :-( then back to the same issue. Has anyone got any idea how to solve this issue? The aforementioned code was added at the very start of applicationDidFinishLaunching, which is before any NIBs or strings files should be loaded.

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• Self-Configuring Classes W/ Command Line Args: Pattern or Anti-Pattern?

  - by dsimcha

  I've got a program where a lot of classes have really complicated configuration requirements. I've adopted the pattern of decentralizing the configuration and allowing each class to take and parse the command line/configuration file arguments in its c'tor and do whatever it needs with them. (These are very coarse-grained classes that are only instantiated a few times, so there is absolutely no performance issue here.) This avoids having to do shotgun surgery to plumb new options I add through all the levels they need to be passed through. It also avoids having to specify each configuration option in multiple places (where it's parsed and where it's used). What are some advantages/disadvantages of this style of programming? It seems to reduce separation of concerns in that every class is now doing configuration stuff, and to make programs less self-documenting because what parameters a class takes becomes less explicit. OTOH, it seems to increase encapsulation in that it makes each class more self-contained because no other part of the program needs to know exactly what configuration parameters a class might need.

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• How to model dependency injection in UML ?

  - by hjo1620

  I have a Contract class. The contract is valid 1 Jan 2010 - 31 Dec 2010. It can be in state Active or Passive, depending on which date I ask the instance for it's state. ex. if I ask 4 July 2010, it's in state Active, but if I ask 1 Jan 2011, it's in state Passive. Instances are created using constructor dependency injection, i.e. they are either Active or Passive already when created, null is not allowed as a parameter for the internal state member. One initial/created vertex is drawn in UML. I have two arrows, leading out from the initial vertex, one leading to state Active and the other to state Passive. Is this a correct representation of dependency injection in UML ? This is related to http://stackoverflow.com/questions/2779922/how-model-statemachine-when-state-is-dependent-on-a-function which initiated the question on how to model DI in general, in UML.

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• How to pull a RANDOM and UNIQUE record from SQL via LINQ.

  - by Jeremy H

  Okay, I found lots of posts on SO about how to pull a RANDOM item from the database when using LINQ. There seems to be a couple of differnet ways to handle this. What I need to do though is pull a RANDOM item from the database that the user has not seen before. The data I am pulling from the database is very small. Is there any way I can just hit the database once for 1000 records and then randomly scroll through those? Should I put a cookie on the users system recording the IDs of which items they have seen, pull a random record, check to see if it is seen and if so, pull from the database again? That seems like performance issues just waiting to happen. I don't expect anyone to code it for me, I am just looking for concepts and pointing in the right direction of how I should go about this. Need more details? Just let me know!

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