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  • C#/.NET Little Wonders: Interlocked CompareExchange()

    - 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. Two posts ago, I discussed the Interlocked Add(), Increment(), and Decrement() methods (here) for adding and subtracting values in a thread-safe, lightweight manner.  Then, last post I talked about the Interlocked Read() and Exchange() methods (here) for safely and efficiently reading and setting 32 or 64 bit values (or references).  This week, we’ll round out the discussion by talking about the Interlocked CompareExchange() method and how it can be put to use to exchange a value if the current value is what you expected it to be. Dirty reads can lead to bad results Many of the uses of Interlocked that we’ve explored so far have centered around either reading, setting, or adding values.  But what happens if you want to do something more complex such as setting a value based on the previous value in some manner? Perhaps you were creating an application that reads a current balance, applies a deposit, and then saves the new modified balance, where of course you’d want that to happen atomically.  If you read the balance, then go to save the new balance and between that time the previous balance has already changed, you’ll have an issue!  Think about it, if we read the current balance as $400, and we are applying a new deposit of $50.75, but meanwhile someone else deposits $200 and sets the total to $600, but then we write a total of $450.75 we’ve lost $200! Now, certainly for int and long values we can use Interlocked.Add() to handles these cases, and it works well for that.  But what if we want to work with doubles, for example?  Let’s say we wanted to add the numbers from 0 to 99,999 in parallel.  We could do this by spawning several parallel tasks to continuously add to a total: 1: double total = 0; 2:  3: Parallel.For(0, 10000, next => 4: { 5: total += next; 6: }); Were this run on one thread using a standard for loop, we’d expect an answer of 4,999,950,000 (the sum of all numbers from 0 to 99,999).  But when we run this in parallel as written above, we’ll likely get something far off.  The result of one of my runs, for example, was 1,281,880,740.  That is way off!  If this were banking software we’d be in big trouble with our clients.  So what happened?  The += operator is not atomic, it will read in the current value, add the result, then store it back into the total.  At any point in all of this another thread could read a “dirty” current total and accidentally “skip” our add.   So, to clean this up, we could use a lock to guarantee concurrency: 1: double total = 0.0; 2: object locker = new object(); 3:  4: Parallel.For(0, count, next => 5: { 6: lock (locker) 7: { 8: total += next; 9: } 10: }); Which will give us the correct result of 4,999,950,000.  One thing to note is that locking can be heavy, especially if the operation being locked over is trivial, or the life of the lock is a high percentage of the work being performed concurrently.  In the case above, the lock consumes pretty much all of the time of each parallel task – and the task being locked on is relatively trivial. Now, let me put in a disclaimer here before we go further: For most uses, lock is more than sufficient for your needs, and is often the simplest solution!    So, if lock is sufficient for most needs, why would we ever consider another solution?  The problem with locking is that it can suspend execution of your thread while it waits for the signal that the lock is free.  Moreover, if the operation being locked over is trivial, the lock can add a very high level of overhead.  This is why things like Interlocked.Increment() perform so well, instead of locking just to perform an increment, we perform the increment with an atomic, lockless method. As with all things performance related, it’s important to profile before jumping to the conclusion that you should optimize everything in your path.  If your profiling shows that locking is causing a high level of waiting in your application, then it’s time to consider lighter alternatives such as Interlocked. CompareExchange() – Exchange existing value if equal some value So let’s look at how we could use CompareExchange() to solve our problem above.  The general syntax of CompareExchange() is: T CompareExchange<T>(ref T location, T newValue, T expectedValue) If the value in location == expectedValue, then newValue is exchanged.  Either way, the value in location (before exchange) is returned. Actually, CompareExchange() is not one method, but a family of overloaded methods that can take int, long, float, double, pointers, or references.  It cannot take other value types (that is, can’t CompareExchange() two DateTime instances directly).  Also keep in mind that the version that takes any reference type (the generic overload) only checks for reference equality, it does not call any overridden Equals(). So how does this help us?  Well, we can grab the current total, and exchange the new value if total hasn’t changed.  This would look like this: 1: // grab the snapshot 2: double current = total; 3:  4: // if the total hasn’t changed since I grabbed the snapshot, then 5: // set it to the new total 6: Interlocked.CompareExchange(ref total, current + next, current); So what the code above says is: if the amount in total (1st arg) is the same as the amount in current (3rd arg), then set total to current + next (2nd arg).  This check and exchange pair is atomic (and thus thread-safe). This works if total is the same as our snapshot in current, but the problem, is what happens if they aren’t the same?  Well, we know that in either case we will get the previous value of total (before the exchange), back as a result.  Thus, we can test this against our snapshot to see if it was the value we expected: 1: // if the value returned is != current, then our snapshot must be out of date 2: // which means we didn't (and shouldn't) apply current + next 3: if (Interlocked.CompareExchange(ref total, current + next, current) != current) 4: { 5: // ooops, total was not equal to our snapshot in current, what should we do??? 6: } So what do we do if we fail?  That’s up to you and the problem you are trying to solve.  It’s possible you would decide to abort the whole transaction, or perhaps do a lightweight spin and try again.  Let’s try that: 1: double current = total; 2:  3: // make first attempt... 4: if (Interlocked.CompareExchange(ref total, current + i, current) != current) 5: { 6: // if we fail, go into a spin wait, spin, and try again until succeed 7: var spinner = new SpinWait(); 8:  9: do 10: { 11: spinner.SpinOnce(); 12: current = total; 13: } 14: while (Interlocked.CompareExchange(ref total, current + i, current) != current); 15: } 16:  This is not trivial code, but it illustrates a possible use of CompareExchange().  What we are doing is first checking to see if we succeed on the first try, and if so great!  If not, we create a SpinWait and then repeat the process of SpinOnce(), grab a fresh snapshot, and repeat until CompareExchnage() succeeds.  You may wonder why not a simple do-while here, and the reason it’s more efficient to only create the SpinWait until we absolutely know we need one, for optimal efficiency. Though not as simple (or maintainable) as a simple lock, this will perform better in many situations.  Comparing an unlocked (and wrong) version, a version using lock, and the Interlocked of the code, we get the following average times for multiple iterations of adding the sum of 100,000 numbers: 1: Unlocked money average time: 2.1 ms 2: Locked money average time: 5.1 ms 3: Interlocked money average time: 3 ms So the Interlocked.CompareExchange(), while heavier to code, came in lighter than the lock, offering a good compromise of safety and performance when we need to reduce contention. CompareExchange() - it’s not just for adding stuff… So that was one simple use of CompareExchange() in the context of adding double values -- which meant we couldn’t have used the simpler Interlocked.Add() -- but it has other uses as well. If you think about it, this really works anytime you want to create something new based on a current value without using a full lock.  For example, you could use it to create a simple lazy instantiation implementation.  In this case, we want to set the lazy instance only if the previous value was null: 1: public static class Lazy<T> where T : class, new() 2: { 3: private static T _instance; 4:  5: public static T Instance 6: { 7: get 8: { 9: // if current is null, we need to create new instance 10: if (_instance == null) 11: { 12: // attempt create, it will only set if previous was null 13: Interlocked.CompareExchange(ref _instance, new T(), (T)null); 14: } 15:  16: return _instance; 17: } 18: } 19: } So, if _instance == null, this will create a new T() and attempt to exchange it with _instance.  If _instance is not null, then it does nothing and we discard the new T() we created. This is a way to create lazy instances of a type where we are more concerned about locking overhead than creating an accidental duplicate which is not used.  In fact, the BCL implementation of Lazy<T> offers a similar thread-safety choice for Publication thread safety, where it will not guarantee only one instance was created, but it will guarantee that all readers get the same instance.  Another possible use would be in concurrent collections.  Let’s say, for example, that you are creating your own brand new super stack that uses a linked list paradigm and is “lock free”.  We could use Interlocked.CompareExchange() to be able to do a lockless Push() which could be more efficient in multi-threaded applications where several threads are pushing and popping on the stack concurrently. Yes, there are already concurrent collections in the BCL (in .NET 4.0 as part of the TPL), but it’s a fun exercise!  So let’s assume we have a node like this: 1: public sealed class Node<T> 2: { 3: // the data for this node 4: public T Data { get; set; } 5:  6: // the link to the next instance 7: internal Node<T> Next { get; set; } 8: } Then, perhaps, our stack’s Push() operation might look something like: 1: public sealed class SuperStack<T> 2: { 3: private volatile T _head; 4:  5: public void Push(T value) 6: { 7: var newNode = new Node<int> { Data = value, Next = _head }; 8:  9: if (Interlocked.CompareExchange(ref _head, newNode, newNode.Next) != newNode.Next) 10: { 11: var spinner = new SpinWait(); 12:  13: do 14: { 15: spinner.SpinOnce(); 16: newNode.Next = _head; 17: } 18: while (Interlocked.CompareExchange(ref _head, newNode, newNode.Next) != newNode.Next); 19: } 20: } 21:  22: // ... 23: } Notice a similar paradigm here as with adding our doubles before.  What we are doing is creating the new Node with the data to push, and with a Next value being the original node referenced by _head.  This will create our stack behavior (LIFO – Last In, First Out).  Now, we have to set _head to now refer to the newNode, but we must first make sure it hasn’t changed! So we check to see if _head has the same value we saved in our snapshot as newNode.Next, and if so, we set _head to newNode.  This is all done atomically, and the result is _head’s original value, as long as the original value was what we assumed it was with newNode.Next, then we are good and we set it without a lock!  If not, we SpinWait and try again. Once again, this is much lighter than locking in highly parallelized code with lots of contention.  If I compare the method above with a similar class using lock, I get the following results for pushing 100,000 items: 1: Locked SuperStack average time: 6 ms 2: Interlocked SuperStack average time: 4.5 ms So, once again, we can get more efficient than a lock, though there is the cost of added code complexity.  Fortunately for you, most of the concurrent collection you’d ever need are already created for you in the System.Collections.Concurrent (here) namespace – for more information, see my Little Wonders – The Concurent Collections Part 1 (here), Part 2 (here), and Part 3 (here). Summary We’ve seen before how the Interlocked class can be used to safely and efficiently add, increment, decrement, read, and exchange values in a multi-threaded environment.  In addition to these, Interlocked CompareExchange() can be used to perform more complex logic without the need of a lock when lock contention is a concern. The added efficiency, though, comes at the cost of more complex code.  As such, the standard lock is often sufficient for most thread-safety needs.  But if profiling indicates you spend a lot of time waiting for locks, or if you just need a lock for something simple such as an increment, decrement, read, exchange, etc., then consider using the Interlocked class’s methods to reduce wait. Technorati Tags: C#,CSharp,.NET,Little Wonders,Interlocked,CompareExchange,threading,concurrency

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  • Performance of Silverlight Datagrid in Silverlight 3 vs Silverlight 4 on a mac

    - by Simon
    I'm using Silverlight Beta 4 for a LOB application. After finding out today that I'll have to wait perhaps 4 months to be able to develop with SL4 on Visual Studio 2010 I'm thinking I need to downgrade my application to SL3 but thats another question. The problem is I'm noticing absolutely abismal performance for simple datagrids that work just fine on a PC when I'm running on a Mac. These grids contain only 5-10 columns and maybe 50 rows. Paging up and down takes about 1-2 seconds sometimes. I would appreciate anybody's experience in which of the following is the best solution: reverting to Silverlight 3 and hoping DataGrid is faster switching to 3rd party datagrid such as Telerik forgetting silverlight altogether I was hoping that possibly SL4 runtime might be updated but that won't happen probably for 3-4 months. Just a reminder - this is specifically a mac issue. Performance on my PC while slightly slow to populate the grid initially is fine.

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  • Creating a Cross-Process EventWaitHandle c#

    - by Navaneeth
    Hello all, I have two windows application, one is a windows service which create EventWaitHandle and wait for it .Second application is a windows gui which open it by calling EventWaitHandle.OpenExisting() and try to Set the event .But I am getting an exception in OpenExisting .The Exception is "Access to the path is denied". windows Service code EventWaitHandle wh = new EventWaitHandle(false, EventResetMode.AutoReset, "MyEventName"); wh.WaitOne(); Windows GUI code try { EventWaitHandle wh = EventWaitHandle.OpenExisting("MyEventName"); wh.Set(); } catch (Exception ex) { MessageBox.Show(ex.Message); } I tried the same code with two sample console application ,it was working fine. Looking forward to hearing from you

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  • vir-install virtual machine hang on Probbing EDD

    - by user2256235
    I'm using vir-stall virtual machine, and my command is virt-install --name=gust --vcpus=4 --ram=8192 --network bridge:br0 --cdrom=/opt/rhel-server-6.2-x86_64-dvd.iso --disk path=/opt/as1/as1.img,size=50 --accelerate After running the command, it hangs on probing EDD, - Press the <ENTER> key to begin the installation process. +----------------------------------------------------------+ | Welcome to Red Hat Enterprise Linux 6.2! | |----------------------------------------------------------| | Install or upgrade an existing system | | Install system with basic video driver | | Rescue installed system | | Boot from local drive | | Memory test | | | | | | | | | | | | | | | +----------------------------------------------------------+ Press [Tab] to edit options Automatic boot in 57 seconds... Loading vmlinuz...... Loading initrd.img...............................ready. Probing EDD (edd=off to disable)... ok ÿ Previously, I wait a long time, it seems no marching. After I press ctrl + ] and stop it. I find it was running using virsh list, but I cannot console it using virsh concole gust. Any problem and how should I do. Many Thanks

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  • Is LINQ to SQL deprecated?

    - by Mayo
    Back in late 2008 there was alot of debate about the future of LINQ to SQL. Many suggested that Microsoft's investments in the Entity Framework in .NET 4.0 were a sign that LINQ to SQL had no future. I figured I'd wait before making my own decision since folks were not in agreement. Fast-forward 18 months and I've got vendors providing solutions that rely on LINQ to SQL and I have personally given it a try and really enjoyed working with it. I figured it was here to stay. But I'm reading a new book (C# 4.0 How-To by Ben Watson) and in chapter 21 (LINQ), he suggests that it "has been more or less deprecated by Microsoft" and suggests using LINQ to Entity Framework. My question to you is whether or not LINQ to SQL is officially deprecated and/or if authoritative entities (Microsoft, Scott Gu, etc.) officially suggest using LINQ to Entities instead of LINQ to SQL.

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  • MSDeploy: error using runCommand provider to call remote .cmd file (timeout)

    - by mjw.
    We are running into an error when trying to use the MSDeploy "runCommand" provider to execute a .cmd file on a remote machine. The expected run time should be about 10 seconds, but MSDeploy only runs it for about 2-3 seconds, after which time error details are returned. Here is the complete MSDeploy "runCommand" command line text I am using: msdeploy.exe -verb:sync -source:runCommand="D:\web deploy tester\test_cmd.cmd",dontUseCommandExe=false,waitAttempts=5,waitInterval=1000 -dest:auto,computername=http://test-machine:89/MsDeployAgentService/,userName=aaa,password=bbb Here are the error details returned: Error 'Error: (4/21/2010 12:19:25 PM) An error occurred when the request was processed on the remote computer. Error: The process 'C:\WINDOWS\system32\cmd.exe' (command line '/c "D:\web deploy tester\test_cmd.cmd"') was terminated because it exceeded the wait time. Error count: 1. ' occurred in call to RunCommand Any ideas as to why this is happening and how to resolve it?

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  • WPF Delay Refresh of UI Elements in ItemsControl

    - by Wonko the Sane
    Hello All, The short question is - how can I prevent (delay) a bound UI element from refreshing until I want it to? The longer explanation: I have a process that adds a number of items to an ItemsControl, and then performs some additional calculations on those items using a background thread. This (correctly) updates the items as it goes along. However, I would like to prevent the ItemsControl from updating during a particular calculation, as it performs some reordering of the items before it does additional calculations based on that order, and then returns the items to their original order. I do show a "Please Wait" animation on top of the ItemsControl, with the ItemsControl dimmed down as it is working, but I'd rather not hide the ItemsControl entirely because it gives the user an indication that progress is being made. Thanks, wTs

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  • How to handle screen orientation change when progress dialog and background thread active?

    - by Heikki Toivonen
    My program does some network activity in a background thread. Before starting, it pops up a progress dialog. The dialog is dismissed on the handler. This all works fine, except when screen orientation changes while the dialog is up (and the background thread is going). At this point the app either crashes, or deadlocks, or gets into a weird stage where the app does not work at all until all the threads have been killed. How can I handle the screen orientation change gracefully? The sample code below matches roughly what my real program does: public class MyAct extends Activity implements Runnable { public ProgressDialog mProgress; // UI has a button that when pressed calls send public void send() { mProgress = ProgressDialog.show(this, "Please wait", "Please wait", true, true); Thread thread = new Thread(this); thread.start(); } public void run() { Thread.sleep(10000); Message msg = new Message(); mHandler.sendMessage(msg); } private final Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { mProgress.dismiss(); } }; } Stack: E/WindowManager( 244): Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@433b7150 that was originally added here E/WindowManager( 244): android.view.WindowLeaked: Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@433b7150 that was originally added here E/WindowManager( 244): at android.view.ViewRoot.<init>(ViewRoot.java:178) E/WindowManager( 244): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:147) E/WindowManager( 244): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:90) E/WindowManager( 244): at android.view.Window$LocalWindowManager.addView(Window.java:393) E/WindowManager( 244): at android.app.Dialog.show(Dialog.java:212) E/WindowManager( 244): at android.app.ProgressDialog.show(ProgressDialog.java:103) E/WindowManager( 244): at android.app.ProgressDialog.show(ProgressDialog.java:91) E/WindowManager( 244): at MyAct.send(MyAct.java:294) E/WindowManager( 244): at MyAct$4.onClick(MyAct.java:174) E/WindowManager( 244): at android.view.View.performClick(View.java:2129) E/WindowManager( 244): at android.view.View.onTouchEvent(View.java:3543) E/WindowManager( 244): at android.widget.TextView.onTouchEvent(TextView.java:4664) E/WindowManager( 244): at android.view.View.dispatchTouchEvent(View.java:3198) E/WindowManager( 244): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:857) E/WindowManager( 244): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:857) E/WindowManager( 244): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:857) E/WindowManager( 244): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:857) E/WindowManager( 244): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:857) E/WindowManager( 244): at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1593) E/WindowManager( 244): at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1089) E/WindowManager( 244): at android.app.Activity.dispatchTouchEvent(Activity.java:1871) E/WindowManager( 244): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1577) E/WindowManager( 244): at android.view.ViewRoot.handleMessage(ViewRoot.java:1140) E/WindowManager( 244): at android.os.Handler.dispatchMessage(Handler.java:88) E/WindowManager( 244): at android.os.Looper.loop(Looper.java:123) E/WindowManager( 244): at android.app.ActivityThread.main(ActivityThread.java:3739) E/WindowManager( 244): at java.lang.reflect.Method.invokeNative(Native Method) E/WindowManager( 244): at java.lang.reflect.Method.invoke(Method.java:515) E/WindowManager( 244): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739) E/WindowManager( 244): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:497) E/WindowManager( 244): at dalvik.system.NativeStart.main(Native Method) and: W/dalvikvm( 244): threadid=3: thread exiting with uncaught exception (group=0x4000fe68) E/AndroidRuntime( 244): Uncaught handler: thread main exiting due to uncaught exception E/AndroidRuntime( 244): java.lang.IllegalArgumentException: View not attached to window manager E/AndroidRuntime( 244): at android.view.WindowManagerImpl.findViewLocked(WindowManagerImpl.java:331) E/AndroidRuntime( 244): at android.view.WindowManagerImpl.removeView(WindowManagerImpl.java:200) E/AndroidRuntime( 244): at android.view.Window$LocalWindowManager.removeView(Window.java:401) E/AndroidRuntime( 244): at android.app.Dialog.dismissDialog(Dialog.java:249) E/AndroidRuntime( 244): at android.app.Dialog.access$000(Dialog.java:59) E/AndroidRuntime( 244): at android.app.Dialog$1.run(Dialog.java:93) E/AndroidRuntime( 244): at android.app.Dialog.dismiss(Dialog.java:233) E/AndroidRuntime( 244): at MyAct$1.handleMessage(MyAct.java:321) E/AndroidRuntime( 244): at android.os.Handler.dispatchMessage(Handler.java:88) E/AndroidRuntime( 244): at android.os.Looper.loop(Looper.java:123) E/AndroidRuntime( 244): at android.app.ActivityThread.main(ActivityThread.java:3739) E/AndroidRuntime( 244): at java.lang.reflect.Method.invokeNative(Native Method) E/AndroidRuntime( 244): at java.lang.reflect.Method.invoke(Method.java:515) E/AndroidRuntime( 244): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739) E/AndroidRuntime( 244): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:497) E/AndroidRuntime( 244): at dalvik.system.NativeStart.main(Native Method) I/Process ( 46): Sending signal. PID: 244 SIG: 3 I/dalvikvm( 244): threadid=7: reacting to signal 3 I/dalvikvm( 244): Wrote stack trace to '/data/anr/traces.txt' I/Process ( 244): Sending signal. PID: 244 SIG: 9 I/ActivityManager( 46): Process MyAct (pid 244) has died. I have tried to dismiss the progress dialog in onSaveInstanceState, but that just prevents an immediate crash. The background thread is still going, and the UI is in partially drawn state. Need to kill the whole app before it starts working again.

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  • Improve WPF Rendering Performance (WrapPanel in ItemsControl)

    - by Wonko the Sane
    Hello All, I have an ItemsSource that appears to have poor performance when adding even a fairly small ObservableCollection to it. The ItemsPanel is a WrapPanel, and the ItemTemplate is essentially a Border containing another Border painted with an ImageBrush. The ItemsControl is wrapped inside a ScrollViewer. After some investigation using WpfPerf, it would appear that most of the "what the heck is it doing?" time is spent on WrapPanel.Measure after creating the collection that is being bound. As I've mentioned, it's a fairly small collection - generally less than 100 items. If nothing else, I'd like to be able to put a "Please Wait" on the screen (during the collection creation portion as well), but I am not sure how to know when the rendering is complete. Any thoughts would be greatly appreciated! Thanks, wTs

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  • Error TF31004 when connecting to TFS2008

    - by Ben
    I'm trying to connect to a TFS2008 server through Visual Studio 2008 (Tools\Connect to Team Foundation Server) and get this error when trying to add our server: TF31004: Team Foundation encountered an unexpected error while connecting to Team Foundation Server . Wait a few minutes and try again. If the problem persists, contact your Team Foundation Server administrator. Needless to say, waiting doesn't help. I've tried using the ip address instead of the hostname but get the same error. I can log in via a browser, in fact IE and Chrome both SSO me straight in. The server is only used for testing one of our TFS plugins, so doesn't get much real use.

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  • Seamless jQuery Marquee?

    - by Pez Cuckow
    Is it possible to create a 100% seamless marquee in jQuery (or just javascript but jQuery prefered)? I've made a simple marquee that moves left until it is off the screen then simply jumps (when out of view) to the right and starts again. However I would love it to not have the wait. The only way I could think of doing this would be to duplicate the text and put it after the first text, then swap them round again. However I have no idea how to implement this in jQuery. Any ideas?

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  • C# Sleep for 500 milliseconds

    - by ikurtz
    could you please tell me how do i go about pausing my program for 500 milliseconds and then continue? i read thread.sleep(50) is not good as it holds up the GUI thread. using a timer it fires a callback .. i just want to wait 500 and then continue to the next statement. please advise. EDIT: i need to display a status bar message for 500 and then update the message with a different one. sorry i meant 500 not 50.

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  • Delay rendering or force re-rendering in Flex

    - by Tereno
    Hi there, In my Flex application, using a custom control, I am making a JSON request to grab some data from the server. My rendering depends on this data such as knowing how many boxes to draw. How can I either force the rendering to wait until I've got the data before drawing to screen or have the boxes draw once we receive the data? I have an event listener for Event.COMPLETE for my JSON request and in there, I call methods that add to the control. I've tried invalidateDisplayList but that doesn't seem to do anything for me?

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  • jQuery: Dynamic image handling (waiting for load)

    - by dclowd9901
    I'm trying to write a plugin that has a built in function to wait until all images that are on the page to be loaded before it executes itself. $(window).load() only works if it's the initial load of the page, but if someone wants to pull down some HTML through AJAX that contains images, it doesn't work. Is there any good way of doing this AND implementing it so that it can be self-contained in the plug-in? I've tried looping over $('img').complete, and I know that doesn't work (the images never load, and the browser crashes under a "script takes too long to complete" bug). For an example of what I'm trying to do, visit the page I'm looking to house the plugin at: http://www.simplesli.de If you go to the "more uses" section (click it on the nav bar), you'll see that the image slideshow won't load properly. I know the current code doesn't work, but it's just holding place until I figure something out.

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  • SQL Server deadlocks between select/update or multiple selects

    - by RobW
    All of the documentation on SQL Server deadlocks talks about the scenario in which operation 1 locks resource A then attempts to access resource B and operation 2 locks resource B and attempts to access resource A. However, I quite often see deadlocks between a select and an update or even between multiple selects in some of our busy applications. I find some of the finer points of the deadlock trace output pretty impenetrable but I would really just like to understand what can cause a deadlock between two single operations. Surely if a select has a read lock the update should just wait before obtaining an exclusive lock and vice versa? This is happening on SQL Server 2005 not that I think this makes a difference.

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  • HttpClient automatically retires before the response is received from server

    - by RD
    Hi all, I'm come upon a wierd problem with java HttpClient library. Specifically the library automatically retries my request (POST requests) even before the response is received from the server. Moreover the weirder problem is that this only happens on specific hosts (machines). So the end result is if a post request succeeds, then there may be an exact same post request coming to the server which the server can't handle. Now, I do want the retry behavior, but it should behave intuitively. Anyone faced this kind of problem before, or is there a way to configure http client to wait for a specific time before retrying. I'm not sure what going wrong here.

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  • AdMob ads on Android app are not rotating / refreshing

    - by Ben Mc
    Has anyone else had this problem? I have a game, and the Ads show at the top of the phone above my game view. When I'm tapping away on the game, the ads just stay the same. BUT, if I don't touch anything and wait the 15 seconds, as is set in my Interval, THEN the ad changes (usually). I don't get any error reports. There's nothing to indicate that this shouldn't be working just fine, but I have no idea why my ads aren't refreshing or rotating while I'm interacting with the other View in my application. Any direction or thoughts would be helpful, thank you!

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  • WatiN File Upload

    - by James Jeffery
    I've hit a snag. I am trying to use WatiN to upload a file. I can load the upload box, but it quickly disappears. The last line of my code at the moment is: ie.FileUpload(Find.ById("profile_file")).Click(); It loads the dialog to select a picture but disappears. Is it possible to set the path of the box automatically example, load "C:/Desktop/image.jpg"? Also, is it possible to wait for the upload to complete before continuing? Help is much appreciated. Thanks.

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  • callback execution order in jQuery getJSON

    - by lau
    I'm trying to implement a iGoogle like dashboard interface using widgets that get their content from other sites using JSONP calls. The problem is that if the first widget that calls the "$.ajax" takes 8 seconds to get the content back, it seems that the callbacks of the other widgets will only be called after the callback of the first widget gets executed. For the user experience, it would be better if the widgets could be displayed as soon as they get the content back from the remote sites, and not wait for those that were scheduled before to complete. Is there a way I can do that?

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  • Thrift client-server multiple roles

    - by dexter
    Hi, this is my first question, so sorry if the form is wrong! I'm trying to make thrift server (python) and client (c++). However I need to exchange messages in both direction. Client should register (call server's function and wait), and server should listen on same port for N (N- 100k) incoming connections (clients). After some conditions are satisfied, server needs to call functions on each client and collect results and interpret them. I'm little confused, and first questions is "can this be done in Thrift"? Second question is related to mechanism that will allow me bidirectional communication. I guess that I will need two services. One with client's functions other with server's. But I'm confused with calling code. I understand one way communication (calling functions from server), but with calling functions from client side I have a problem. Any suggestions??? Thanks!

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  • Problem with room/screen/menu controller in python game: old rooms are not removed from memory

    - by Jordan Magnuson
    I'm literally banging my head against a wall here (as in, yes, physically, at my current location, I am damaging my cranium). Basically, I've got a Python/Pygame game with some typical game "rooms", or "screens." EG title screen, high scores screen, and the actual game room. Something bad is happening when I switch between rooms: the old room (and its various items) are not removed from memory, or from my event listener. Not only that, but every time I go back to a certain room, my number of event listeners increases, as well as the RAM being consumed! (So if I go back and forth between the title screen and the "game room", for instance, the number of event listeners and the memory usage just keep going up and up. The main issue is that all the event listeners start to add up and really drain the CPU. I'm new to Python, and don't know if I'm doing something obviously wrong here, or what. I will love you so much if you can help me with this! Below is the relevant source code. Complete source code at http://www.necessarygames.com/my_games/betraveled/betraveled_src0328.zip MAIN.PY class RoomController(object): """Controls which room is currently active (eg Title Screen)""" def __init__(self, screen, ev_manager): self.room = None self.screen = screen self.ev_manager = ev_manager self.ev_manager.register_listener(self) self.room = self.set_room(config.room) def set_room(self, room_const): #Unregister old room from ev_manager if self.room: self.room.ev_manager.unregister_listener(self.room) self.room = None #Set new room based on const if room_const == config.TITLE_SCREEN: return rooms.TitleScreen(self.screen, self.ev_manager) elif room_const == config.GAME_MODE_ROOM: return rooms.GameModeRoom(self.screen, self.ev_manager) elif room_const == config.GAME_ROOM: return rooms.GameRoom(self.screen, self.ev_manager) elif room_const == config.HIGH_SCORES_ROOM: return rooms.HighScoresRoom(self.screen, self.ev_manager) def notify(self, event): if isinstance(event, ChangeRoomRequest): if event.game_mode: config.game_mode = event.game_mode self.room = self.set_room(event.new_room) #Run game def main(): pygame.init() screen = pygame.display.set_mode(config.screen_size) ev_manager = EventManager() spinner = CPUSpinnerController(ev_manager) room_controller = RoomController(screen, ev_manager) pygame_event_controller = PyGameEventController(ev_manager) spinner.run() EVENT_MANAGER.PY class EventManager: #This object is responsible for coordinating most communication #between the Model, View, and Controller. def __init__(self): from weakref import WeakKeyDictionary self.last_listeners = {} self.listeners = WeakKeyDictionary() self.eventQueue= [] self.gui_app = None #---------------------------------------------------------------------- def register_listener(self, listener): self.listeners[listener] = 1 #---------------------------------------------------------------------- def unregister_listener(self, listener): if listener in self.listeners: del self.listeners[listener] #---------------------------------------------------------------------- def clear(self): del self.listeners[:] #---------------------------------------------------------------------- def post(self, event): # if isinstance(event, MouseButtonLeftEvent): # debug(event.name) #NOTE: copying the list like this before iterating over it, EVERY tick, is highly inefficient, #but currently has to be done because of how new listeners are added to the queue while it is running #(eg when popping cards from a deck). Should be changed. See: http://dr0id.homepage.bluewin.ch/pygame_tutorial08.html #and search for "Watch the iteration" print 'Number of listeners: ' + str(len(self.listeners)) for listener in list(self.listeners): #NOTE: If the weakref has died, it will be #automatically removed, so we don't have #to worry about it. listener.notify(event) def notify(self, event): pass #------------------------------------------------------------------------------ class PyGameEventController: """...""" def __init__(self, ev_manager): self.ev_manager = ev_manager self.ev_manager.register_listener(self) self.input_freeze = False #---------------------------------------------------------------------- def notify(self, incoming_event): if isinstance(incoming_event, UserInputFreeze): self.input_freeze = True elif isinstance(incoming_event, UserInputUnFreeze): self.input_freeze = False elif isinstance(incoming_event, TickEvent) or isinstance(incoming_event, BoardCreationTick): #Share some time with other processes, so we don't hog the cpu pygame.time.wait(5) #Handle Pygame Events for event in pygame.event.get(): #If this event manager has an associated PGU GUI app, notify it of the event if self.ev_manager.gui_app: self.ev_manager.gui_app.event(event) #Standard event handling for everything else ev = None if event.type == QUIT: ev = QuitEvent() elif event.type == pygame.MOUSEBUTTONDOWN and not self.input_freeze: if event.button == 1: #Button 1 pos = pygame.mouse.get_pos() ev = MouseButtonLeftEvent(pos) elif event.type == pygame.MOUSEBUTTONDOWN and not self.input_freeze: if event.button == 2: #Button 2 pos = pygame.mouse.get_pos() ev = MouseButtonRightEvent(pos) elif event.type == pygame.MOUSEBUTTONUP and not self.input_freeze: if event.button == 2: #Button 2 Release pos = pygame.mouse.get_pos() ev = MouseButtonRightReleaseEvent(pos) elif event.type == pygame.MOUSEMOTION: pos = pygame.mouse.get_pos() ev = MouseMoveEvent(pos) #Post event to event manager if ev: self.ev_manager.post(ev) # elif isinstance(event, BoardCreationTick): # #Share some time with other processes, so we don't hog the cpu # pygame.time.wait(5) # # #If this event manager has an associated PGU GUI app, notify it of the event # if self.ev_manager.gui_app: # self.ev_manager.gui_app.event(event) #------------------------------------------------------------------------------ class CPUSpinnerController: def __init__(self, ev_manager): self.ev_manager = ev_manager self.ev_manager.register_listener(self) self.clock = pygame.time.Clock() self.cumu_time = 0 self.keep_going = True #---------------------------------------------------------------------- def run(self): if not self.keep_going: raise Exception('dead spinner') while self.keep_going: time_passed = self.clock.tick() fps = self.clock.get_fps() self.cumu_time += time_passed self.ev_manager.post(TickEvent(time_passed, fps)) if self.cumu_time >= 1000: self.cumu_time = 0 self.ev_manager.post(SecondEvent(fps=fps)) pygame.quit() #---------------------------------------------------------------------- def notify(self, event): if isinstance(event, QuitEvent): #this will stop the while loop from running self.keep_going = False EXAMPLE CLASS USING EVENT MANAGER class Timer(object): def __init__(self, ev_manager, time_left): self.ev_manager = ev_manager self.ev_manager.register_listener(self) self.time_left = time_left self.paused = False def __repr__(self): return str(self.time_left) def pause(self): self.paused = True def unpause(self): self.paused = False def notify(self, event): #Pause Event if isinstance(event, Pause): self.pause() #Unpause Event elif isinstance(event, Unpause): self.unpause() #Second Event elif isinstance(event, SecondEvent): if not self.paused: self.time_left -= 1

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  • nsthread in iphone xcode

    - by BibiBuBu
    Good Day! i want to use nsthreads in a project of xcode that will call a function which is for the network access and will check that if the network is there or not, so i need to have a thread which will execute after lets say 1 minutes to check the connectivity. and will continue run unless the app is closed. [NSThread detachNewThreadSelector:@selector(startTheBackgroundJob) toTarget:self withObject:nil]; startTheBackgroundJob NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; // wait for 3 seconds before starting the thread, you don't have to do that. This is just an example how to stop the NSThread for some time [NSThread sleepForTimeInterval:5]; //[self performSelectorInBackground:@selector(checkNet) withObject:nil]; [self performSelectorOnMainThread:@selector(checkNet) withObject:nil waitUntilDone:YES]; [pool release]; it works only for the first time but not any other, i mean only 1 loop it makes can somebody help me in this regard. Thanks

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  • Marquee Text When Text Overflows

    - by Mike Stanford
    Hi all, well heres my problem. Lets say i have 3 div tags, all are 100pixels wide: <--- DIV WIDTH ---> Text in div 1 Text in div two, it overflows Text in div three <--- DIV WIDTH ---> Now, currently i have this css for the divs: width:100px; overflow:hidden; What i want to do is if the text overflows, it scrolls like a marquee so all the text can be seen if you wait a little bit. But i only want the marquee to show if the text overflows. How would i do this? Thx, Tony

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  • Elusive race condition in Java

    - by nasufara
    I am creating a graphing calculator. In an attempt to squeeze some more performance out of it, I added some multithreaded to the line calculator. Essentially what my current implementation does is construct a thread-safe Queue of X values, then start however many threads it needs, each one calculating a point on the line using the queue to get its values, and then ordering the points using a HashMap when the calculations are done. This implementation works great, and that's not where my race condition is (merely some background info). In examining the performance results from this, I found that the HashMap is a performance bottleneck, since I do that synchronously on one thread. So I figured that ordering each point as its calculated would work best. I tried a PriorityQueue, but that was slower than the HashMap. I ended up creating an algorithm that essentially works like this: I construct a list of X values to calculate, like in my current algorithm. I then copy that list of values into another class, unimaginatively and temporarily named BlockingList, which is responsible for ordering the points as they are calculated. BlockingList contains a put() method, which takes in two BigDecimals as parameters, the first the X value, the second the calculated Y value. put() will only accept a value if the X value is the next one on the list to be accepted in the list of X values, and will block until another thread gives it the next excepted value. For example, since that can be confusing, say I have two threads, Thread-1 and Thread-2. Thread-2 gets the X value 10.0 from the values queue, and Thread-1 gets 9.0. However, Thread-1 completes its calculations first, and calls put() before Thread-2 does. Because BlockingList is expecting to get 10.0 first, and not 9.0, it will block on Thread-1 until Thread-2 finishes and calls put(). Once Thread-2 gives BlockingList 10.0, it notify()s all waiting threads, and expects 9.0 next. This continues until BlockingList gets all of its expected values. (I apologise if that was hard to follow, if you need more clarification, just ask.) As expected by the question title, there is a race condition in here. If I run it without any System.out.printlns, it will sometimes lock because of conflicting wait() and notifyAll()s, but if I put a println in, it will run great. A small implementation of this is included below, and exhibits the same behavior: import java.math.BigDecimal; import java.util.concurrent.ConcurrentLinkedQueue; public class Example { public static void main(String[] args) throws InterruptedException { // Various scaling values, determined based on the graph size // in the real implementation BigDecimal xMax = new BigDecimal(10); BigDecimal xStep = new BigDecimal(0.05); // Construct the values list, from -10 to 10 final ConcurrentLinkedQueue<BigDecimal> values = new ConcurrentLinkedQueue<BigDecimal>(); for (BigDecimal i = new BigDecimal(-10); i.compareTo(xMax) <= 0; i = i.add(xStep)) { values.add(i); } // Contains the calculated values final BlockingList list = new BlockingList(values); for (int i = 0; i < 4; i++) { new Thread() { public void run() { BigDecimal x; // Keep looping until there are no more values while ((x = values.poll()) != null) { PointPair pair = new PointPair(); pair.realX = x; try { list.put(pair); } catch (Exception ex) { ex.printStackTrace(); } } } }.start(); } } private static class PointPair { public BigDecimal realX; } private static class BlockingList { private final ConcurrentLinkedQueue<BigDecimal> _values; private final ConcurrentLinkedQueue<PointPair> _list = new ConcurrentLinkedQueue<PointPair>(); public BlockingList(ConcurrentLinkedQueue<BigDecimal> expectedValues) throws InterruptedException { // Copy the values into a new queue BigDecimal[] arr = expectedValues.toArray(new BigDecimal[0]); _values = new ConcurrentLinkedQueue<BigDecimal>(); for (BigDecimal dec : arr) { _values.add(dec); } } public void put(PointPair item) throws InterruptedException { while (item.realX.compareTo(_values.peek()) != 0) { synchronized (this) { // Block until someone enters the next desired value wait(); } } _list.add(item); _values.poll(); synchronized (this) { notifyAll(); } } } } My question is can anybody help me find the threading error? Thanks!

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  • How to unit test asynchronous APIs?

    - by Ben Clayton
    Hi all. I have installed Google Toolbox for Mac (http://code.google.com/p/google-toolbox-for-mac/) into Xcode and followed the instructions to set up unit testing found here (http://code.google.com/p/google-toolbox-for-mac/wiki/iPhoneUnitTesting). It all works great, and I can test my synchronous methods on all my objects absolutely fine. However, most of the complex APIs I actually want to test return results asynchronously via calling a method on a delegate - for example a call to a file download and update system will return immediately and then run a -fileDownloadDidComplete: method when the file finishes downloading. How would I test this as a unit test? It seems like I'd want to the testDownload function, or at least the test framework to 'wait' for fileDownloadDidComplete: method to run. Any ideas much appreciated!

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