.NET並行計算和並發8-QueueUserWorkItem非同步

標籤：been   return   led   none   sleep   ecif   space   sse   set   

QueueUserWorkItem方法將非常簡單的任務排入隊列

下面這個簡單的代碼，涉及到資源競爭問題，如果主線程先爭取到資源，如果沒有等待

一段時間，那麼QueueUserWorkItem申請的線程沒有機會執行。

  1     using System;  2     using System.Threading;  3   4 public static void Main()  5     {  6         // Queue the task.  7         ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc));  8   9         Console.WriteLine("Main thread does some work, then sleeps."); 10         // If you comment out the Sleep, the main thread exits before 11         // the thread pool task runs.  The thread pool uses background 12         // threads, which do not keep the application running.  (This 13         // is a simple example of a race condition.) 14         Thread.Sleep(1000); 15  16         Console.WriteLine("Main thread exits."); 17     } 18  19     // This thread procedure performs the task. 20     static void ThreadProc(Object stateInfo) 21     { 22         // No state object was passed to QueueUserWorkItem, so 23         // stateInfo is null. 24         Console.WriteLine("Hello from the thread pool."); 25     } 26 

View Code

下面的程式碼範例使用 QueueUserWorkItem 方法將任務排入隊列，並為該任務提供資料。

  1 using System;  2 using System.Threading;  3   4 // TaskInfo holds state information for a task that will be  5 // executed by a ThreadPool thread.  6 public class TaskInfo  7 {  8     // State information for the task.  These members  9     // can be implemented as read-only properties, read/write 10     // properties with validation, and so on, as required. 11     public string Boilerplate; 12     public int Value; 13  14     // Public constructor provides an easy way to supply all 15     // the information needed for the task. 16     public TaskInfo(string text, int number) 17     { 18         Boilerplate = text; 19         Value = number; 20     } 21 } 22  23 public class Example 24 { 25     public static void Main() 26     { 27         // Create an object containing the information needed 28         // for the task. 29         TaskInfo ti = new TaskInfo("This report displays the number {0}.", 42); 30  31         // Queue the task and data. 32         if (ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc), ti)) 33         { 34             Console.WriteLine("Main thread does some work, then sleeps."); 35  36             // If you comment out the Sleep, the main thread exits before 37             // the ThreadPool task has a chance to run.  ThreadPool uses 38             // background threads, which do not keep the application 39             // running.  (This is a simple example of a race condition.) 40             Thread.Sleep(1000); 41  42             Console.WriteLine("Main thread exits."); 43         } 44         else 45         { 46             Console.WriteLine("Unable to queue ThreadPool request."); 47         } 48     } 49  50     // The thread procedure performs the independent task, in this case 51     // formatting and printing a very simple report. 52     // 53     static void ThreadProc(Object stateInfo) 54     { 55         TaskInfo ti = (TaskInfo)stateInfo; 56         Console.WriteLine(ti.Boilerplate, ti.Value); 57     } 58 } 59 

View Code

使用 RegisterWaitForSingleObject

下面的樣本展示多種線程處理功能。

• 使用 RegisterWaitForSingleObject 方法，將任務排入隊列，以便由 ThreadPool 線程執行。

• 使用 AutoResetEvent 發出要執行的任務的訊號。 請參閱 EventWaitHandle, AutoResetEvent, CountdownEvent, ManualResetEvent。

• 使用 WaitOrTimerCallback 委託處理逾時和訊號。

• 使用 RegisteredWaitHandle 清除佇列的任務。

注意：
在Main方法的最後有一句：

        If you start a thread yourself, you can wait for it to end by calling Thread.Join.  This option is not available with thread pool threads.
       

 

  1 using System;  2 using System.Threading;  3   4 // TaskInfo contains data that will be passed to the callback  5 // method.  6 public class TaskInfo  7 {  8     public RegisteredWaitHandle Handle = null;  9     public string OtherInfo = "default"; 10 } 11  12 public class Example 13 { 14     public static void Main(string[] args) 15     { 16         // The main thread uses AutoResetEvent to signal the 17         // registered wait handle, which executes the callback 18         // method. 19         AutoResetEvent ev = new AutoResetEvent(false); 20  21         TaskInfo ti = new TaskInfo(); 22         ti.OtherInfo = "First task"; 23         // The TaskInfo for the task includes the registered wait 24         // handle returned by RegisterWaitForSingleObject.  This 25         // allows the wait to be terminated when the object has 26         // been signaled once (see WaitProc). 27         ti.Handle = ThreadPool.RegisterWaitForSingleObject( 28             ev, 29             new WaitOrTimerCallback(WaitProc), 30             ti, 31             1000, 32             false); 33  34         // The main thread waits three seconds, to demonstrate the 35         // time-outs on the queued thread, and then signals. 36         Thread.Sleep(3100); 37         Console.WriteLine("Main thread signals."); 38         ev.Set(); 39  40         // The main thread sleeps, which should give the callback 41         // method time to execute.  If you comment out this line, the 42         // program usually ends before the ThreadPool thread can execute. 43         Thread.Sleep(1000); 44         // If you start a thread yourself, you can wait for it to end 45         // by calling Thread.Join.  This option is not available with 46         // thread pool threads. 47     } 48  49     // The callback method executes when the registered wait times out, 50     // or when the WaitHandle (in this case AutoResetEvent) is signaled. 51     // WaitProc unregisters the WaitHandle the first time the event is 52     // signaled. 53     public static void WaitProc(object state, bool timedOut) 54     { 55         // The state object must be cast to the correct type, because the 56         // signature of the WaitOrTimerCallback delegate specifies type 57         // Object. 58         TaskInfo ti = (TaskInfo)state; 59  60         string cause = "TIMED OUT"; 61         if (!timedOut) 62         { 63             cause = "SIGNALED"; 64             // If the callback method executes because the WaitHandle is 65             // signaled, stop future execution of the callback method 66             // by unregistering the WaitHandle. 67             if (ti.Handle != null) 68                 ti.Handle.Unregister(null); 69         } 70  71         Console.WriteLine("WaitProc( {0} ) executes on thread {1}; cause = {2}.", 72             ti.OtherInfo, 73             Thread.CurrentThread.GetHashCode().ToString(), 74             cause 75         ); 76     } 77 } 78 

View Code

.NET並行計算和並發8-QueueUserWorkItem非同步