WaitHandle.WaitAll Method (WaitHandle[])

Waits for all the elements in the specified array to receive a signal.

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

public static bool WaitAll(
	WaitHandle[] waitHandles
)

Parameters

waitHandles
Type: System.Threading.WaitHandle[]

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

Return Value

Type: System.Boolean
true when every element in waitHandles has received a signal; otherwise the method never returns.

ExceptionCondition
ArgumentNullException

The waitHandles parameter is null. -or-

One or more of the objects in the waitHandles array are null.

-or-

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

DuplicateWaitObjectException
NoteNote

In the .NET for Windows Store apps or the Portable Class Library, catch the base class exception, ArgumentException, instead.

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.

AbandonedMutexException

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

InvalidOperationException

The waitHandles array contains a transparent proxy for a WaitHandle in another application domain.

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 often indicates a serious coding error. In the case of a system-wide mutex, it might indicate that an application has been terminated abruptly (for example, by using Windows Task Manager). The exception contains information useful for debugging.

The WaitAll method returns when all the handles are signaled. On some implementations, if more than 64 handles are passed, a NotSupportedException is thrown. If the array contains duplicates, the call fails with a DuplicateWaitObjectException.

NoteNote

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

Calling this method overload is equivalent to calling the WaitAll(WaitHandle[], Int32, Boolean) method overload and specifying -1 (or Timeout.Infinite) for millisecondsTimeout and true for exitContext.

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;

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.
        WaitHandle.WaitAll(manualEvents);
        Console.WriteLine("Files written - 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();
        }
    }
}

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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