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WaitHandle.WaitAll Method (WaitHandle[], TimeSpan, Boolean)

Waits for all the elements in the specified array to receive a signal, using a TimeSpan value to measure the time interval, and specifying whether to exit the synchronization domain before the wait.

Namespace: System.Threading
Assembly: mscorlib (in mscorlib.dll)

public static bool WaitAll (
	WaitHandle[] waitHandles,
	TimeSpan timeout,
	bool exitContext
)
public static boolean WaitAll (
	WaitHandle[] waitHandles, 
	TimeSpan timeout, 
	boolean exitContext
)
public static function WaitAll (
	waitHandles : WaitHandle[], 
	timeout : TimeSpan, 
	exitContext : boolean
) : boolean

Parameters

waitHandles

A WaitHandle array containing the objects for which the current instance will wait. This array cannot contain multiple references to the same object.

timeout

A TimeSpan that represents the number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds, to wait indefinitely.

exitContext

true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it afterward; otherwise, false.

Return Value

true when every element in waitHandles has received a signal; otherwise false.

Exception typeCondition

ArgumentNullException

The waitHandles parameter is a null reference (Nothing in Visual Basic).

-or-

One or more of the objects in the waitHandles array is a null reference (Nothing in Visual Basic).

-or-

waitHandles is an array with no elements, and the .NET Framework version is 2.0.

DuplicateWaitObjectException

The waitHandles array contains elements that are duplicates.

NotSupportedException

The number of objects in waitHandles is greater than the system permits.

-or-

The STAThreadAttribute attribute is applied to the thread procedure for the current thread, and waitHandles contains more than one element.

ApplicationException

waitHandles is an array with no elements, and the .NET Framework version is 1.0 or 1.1.

ArgumentOutOfRangeException

timeout is a negative number other than -1 milliseconds, which represents an infinite time-out.

AbandonedMutexException

The wait terminated because a thread exited without releasing a mutex. This exception is not thrown on Windows 98 or Windows Millennium Edition.

AbandonedMutexException is new in the .NET Framework version 2.0. In previous versions, the WaitAll method returns true when a mutex is abandoned. An abandoned mutex indicates a serious coding error. The exception contains information useful for debugging.

The WaitAll method returns when the wait terminates, which means either all the handles are signaled or a time-out occurs. On some implementations, if more than 64 handles are passed, a NotSupportedException is thrown. If the array contains duplicates, the call will fail.

NoteNote

The WaitAll method is not supported on threads that have STAThreadAttribute.

Notes on Exiting the Context

The exitContext parameter has no effect unless the WaitAll method is called from inside a nondefault managed context. This can happen if your thread is inside a call to an instance of a class derived from ContextBoundObject. Even if you are currently executing a method on a class that is not derived from ContextBoundObject, like String, you can be in a nondefault context if a ContextBoundObject is on your stack in the current application domain.

When your code is executing in a nondefault context, specifying true for exitContext causes the thread to exit the nondefault managed context (that is, to transition to the default context) before executing the WaitAll method. It returns to the original nondefault context after the call to the WaitAll method completes.

This can be useful when the context-bound class has SynchronizationAttribute. In that case, all calls to members of the class are automatically synchronized, and the synchronization domain is the entire body of code for the class. If code in the call stack of a member calls the WaitAll method and specifies true for exitContext, the thread exits the synchronization domain, allowing a thread that is blocked on a call to any member of the object to proceed. When the WaitAll method returns, the thread that made the call must wait to reenter the synchronization domain.

The following code example shows how to use the thread pool to asynchronously create and write to a group of files. Each write operation is queued as a work item and signals when it is finished. The main thread waits for all the items to signal and then exits.

using System;
using System.IO;
using System.Security.Permissions;
using System.Threading;

// Request permission to create and write files to C:\TestTest.
[assembly: FileIOPermissionAttribute(SecurityAction.RequestMinimum, 
     All = @"C:\TestTest")]

class Test
{
    static void Main()
    {
        const int numberOfFiles = 5;
        string dirName = @"C:\TestTest";
        string fileName;

        byte[] byteArray;
        Random randomGenerator = new Random();

        ManualResetEvent[] manualEvents = 
            new ManualResetEvent[numberOfFiles];
        State stateInfo;

        if(!Directory.Exists(dirName))
        {
            Directory.CreateDirectory(dirName);
        }

        // Queue the work items that create and write to the files.
        for(int i = 0; i < numberOfFiles; i++)
        {
            fileName = string.Concat(
                dirName, @"\Test", i.ToString(), ".dat");

            // Create random data to write to the file.
            byteArray = new byte[1000000];
            randomGenerator.NextBytes(byteArray);

            manualEvents[i] = new ManualResetEvent(false);

            stateInfo = 
                new State(fileName, byteArray, manualEvents[i]);

            ThreadPool.QueueUserWorkItem(new WaitCallback(
                Writer.WriteToFile), stateInfo);
        }
    
        // Since ThreadPool threads are background threads, 
        // wait for the work items to signal before exiting.
        if(WaitHandle.WaitAll(
            manualEvents, new TimeSpan(0, 0, 5), false))
        {
            Console.WriteLine("Files written - main exiting.");
        }
        else
        {
            // The wait operation times out.
            Console.WriteLine("Error writing files - main exiting.");
        }
    }
}

// Maintain state to pass to WriteToFile.
class State
{
    public string fileName;
    public byte[] byteArray;
    public ManualResetEvent manualEvent;

    public State(string fileName, byte[] byteArray, 
        ManualResetEvent manualEvent)
    {
        this.fileName = fileName;
        this.byteArray = byteArray;
        this.manualEvent = manualEvent;
    }
}

class Writer
{
    static int workItemCount = 0;
    Writer() {}

    public static void WriteToFile(object state)
    {
        int workItemNumber = workItemCount;
        Interlocked.Increment(ref workItemCount);
        Console.WriteLine("Starting work item {0}.",
            workItemNumber.ToString());
        State stateInfo = (State)state;
        FileStream fileWriter = null;

        // Create and write to the file.
        try
        {
            fileWriter = new FileStream(
                stateInfo.fileName, FileMode.Create);
            fileWriter.Write(stateInfo.byteArray, 
                0, stateInfo.byteArray.Length);
        }
        finally
        {
            if(fileWriter != null)
            {
                fileWriter.Close();
            }

            // Signal Main that the work item has finished.
            Console.WriteLine("Ending work item {0}.", 
                workItemNumber.ToString());
            stateInfo.manualEvent.Set();
        }
    }
}

import System.*;
import System.IO.*;
import System.Security.Permissions.*;
import System.Threading.*;

// Request permission to create and write files to C:\TestTest.
/** @assembly FileIOPermissionAttribute(SecurityAction.RequestMinimum,
    All = "C:\\TestTest")
 */

class Test
{
    public static void main(String[] args)
    {
        final int numberOfFiles = 5;
        String dirName = "C:\\TestTest";
        String fileName;
        ubyte byteArray[];
        Random randomGenerator = new Random();
        ManualResetEvent manualEvents[] = new ManualResetEvent[numberOfFiles];
        State stateInfo;

        if (!(Directory.Exists(dirName))) {
            Directory.CreateDirectory(dirName);
        }

        // Queue the work items that create and write to the files.
        for (int i = 0; i < numberOfFiles; i++) {
            fileName = String.Concat(dirName, "\\Test",
                String.valueOf(i),".dat");

            // Create random data to write to the file.
            byteArray = new ubyte[1000000];
            randomGenerator.NextBytes(byteArray);
            manualEvents[i] = new ManualResetEvent(false);
            stateInfo = new State(fileName, byteArray, manualEvents[i]);
            ThreadPool.QueueUserWorkItem(new WaitCallback(Writer.WriteToFile), 
                stateInfo);
        }

        // Since ThreadPool threads are background threads, 
        // wait for the work items to signal before exiting.
        if (WaitHandle.WaitAll(manualEvents, new TimeSpan(0, 0, 5), false)) {
            Console.WriteLine("Files written - main exiting.");
        }
        else {
            // The wait operation times out.
            Console.WriteLine("Error writing files - main exiting.");
        }
    } //main
} //Test

// Maintain state to pass to WriteToFile.
class State
{
    public String fileName;
    public ubyte byteArray[];
    public ManualResetEvent manualEvent;

    public State(String fileName, ubyte byteArray[],
            ManualResetEvent manualEvent)
    {
        this.fileName = fileName;
        this.byteArray = byteArray;
        this.manualEvent = manualEvent;
    } //State
} //State

class Writer
{
    private static int workItemCount = 0;

    Writer()
    {
    } //Writer

    public static void WriteToFile(Object state)
    {
        int workItemNumber = workItemCount;

        Interlocked.Increment(workItemCount);
        Console.WriteLine("Starting work item {0}.", 
            String.valueOf(workItemNumber));

        State stateInfo = ((State)(state));
        FileStream fileWriter = null;

        // Create and write to the file.
        try {
            fileWriter = new FileStream(stateInfo.fileName, FileMode.Create);
            fileWriter.Write(stateInfo.byteArray, 0,
                stateInfo.byteArray.length);
        }
        finally {
            if ( fileWriter  != null  ) {
                fileWriter.Close();
            }
         
            // Signal Main that the work item has finished.
            Console.WriteLine("Ending work item {0}.",
                String.valueOf(workItemNumber));
            stateInfo.manualEvent.Set();
        }
    } //WriteToFile
} //Writer

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

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