.NET并行计算和并发8-QueueUserWorkItem异步

QueueUserWorkItem方法将非常简单的任务排入队列

下面这个简单的代码，涉及到资源竞争问题，如果主线程先争取到资源，如果没有等待

一段时间，那么QueueUserWorkItem申请的线程没有机会执行。

    using System;
    using System.Threading;

public static void Main()
    {
        // Queue the task.
        ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc));

        Console.WriteLine("Main thread does some work, then sleeps.");
        // If you comment out the Sleep, the main thread exits before
        // the thread pool task runs.  The thread pool uses background
        // threads, which do not keep the application running.  (This
        // is a simple example of a race condition.)
        Thread.Sleep(1000);

        Console.WriteLine("Main thread exits.");
    }

    // This thread procedure performs the task.
    static void ThreadProc(Object stateInfo)
    {
        // No state object was passed to QueueUserWorkItem, so
        // stateInfo is null.
        Console.WriteLine("Hello from the thread pool.");
    }

下面的代码示例使用 QueueUserWorkItem 方法将任务排入队列，并为该任务提供数据。

using System;
using System.Threading;

// TaskInfo holds state information for a task that will be
// executed by a ThreadPool thread.
public class TaskInfo
{
    // State information for the task.  These members
    // can be implemented as read-only properties, read/write
    // properties with validation, and so on, as required.
    public string Boilerplate;
    public int Value;

    // Public constructor provides an easy way to supply all
    // the information needed for the task.
    public TaskInfo(string text, int number)
    {
        Boilerplate = text;
        Value = number;
    }
}

public class Example
{
    public static void Main()
    {
        // Create an object containing the information needed
        // for the task.
        TaskInfo ti = new TaskInfo("This report displays the number {0}.", 42);

        // Queue the task and data.
        if (ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc), ti))
        {
            Console.WriteLine("Main thread does some work, then sleeps.");

            // If you comment out the Sleep, the main thread exits before
            // the ThreadPool task has a chance to run.  ThreadPool uses
            // background threads, which do not keep the application
            // running.  (This is a simple example of a race condition.)
            Thread.Sleep(1000);

            Console.WriteLine("Main thread exits.");
        }
        else
        {
            Console.WriteLine("Unable to queue ThreadPool request.");
        }
    }

    // The thread procedure performs the independent task, in this case
    // formatting and printing a very simple report.
    //
    static void ThreadProc(Object stateInfo)
    {
        TaskInfo ti = (TaskInfo)stateInfo;
        Console.WriteLine(ti.Boilerplate, ti.Value);
    }
}

使用 RegisterWaitForSingleObject

下面的示例展示多种线程处理功能。

• 使用 RegisterWaitForSingleObject 方法，将任务排入队列，以便由 ThreadPool 线程执行。

• 使用 AutoResetEvent 发出要执行的任务的信号。 请参阅 EventWaitHandle, AutoResetEvent, CountdownEvent, ManualResetEvent。

• 使用 WaitOrTimerCallback 委托处理超时和信号。

• 使用 RegisteredWaitHandle 取消排队的任务。

注意：
在Main方法的最后有一句：

        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.
       

 

using System;
using System.Threading;

// TaskInfo contains data that will be passed to the callback
// method.
public class TaskInfo
{
    public RegisteredWaitHandle Handle = null;
    public string OtherInfo = "default";
}

public class Example
{
    public static void Main(string[] args)
    {
        // The main thread uses AutoResetEvent to signal the
        // registered wait handle, which executes the callback
        // method.
        AutoResetEvent ev = new AutoResetEvent(false);

        TaskInfo ti = new TaskInfo();
        ti.OtherInfo = "First task";
        // The TaskInfo for the task includes the registered wait
        // handle returned by RegisterWaitForSingleObject.  This
        // allows the wait to be terminated when the object has
        // been signaled once (see WaitProc).
        ti.Handle = ThreadPool.RegisterWaitForSingleObject(
            ev,
            new WaitOrTimerCallback(WaitProc),
            ti,
            1000,
            false);

        // The main thread waits three seconds, to demonstrate the
        // time-outs on the queued thread, and then signals.
        Thread.Sleep(3100);
        Console.WriteLine("Main thread signals.");
        ev.Set();

        // The main thread sleeps, which should give the callback
        // method time to execute.  If you comment out this line, the
        // program usually ends before the ThreadPool thread can execute.
        Thread.Sleep(1000);
        // 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.
    }

    // The callback method executes when the registered wait times out,
    // or when the WaitHandle (in this case AutoResetEvent) is signaled.
    // WaitProc unregisters the WaitHandle the first time the event is
    // signaled.
    public static void WaitProc(object state, bool timedOut)
    {
        // The state object must be cast to the correct type, because the
        // signature of the WaitOrTimerCallback delegate specifies type
        // Object.
        TaskInfo ti = (TaskInfo)state;

        string cause = "TIMED OUT";
        if (!timedOut)
        {
            cause = "SIGNALED";
            // If the callback method executes because the WaitHandle is
            // signaled, stop future execution of the callback method
            // by unregistering the WaitHandle.
            if (ti.Handle != null)
                ti.Handle.Unregister(null);
        }

        Console.WriteLine("WaitProc( {0} ) executes on thread {1}; cause = {2}.",
            ti.OtherInfo,
            Thread.CurrentThread.GetHashCode().ToString(),
            cause
        );
    }
}