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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)

static bool WaitAll (
	array<WaitHandle^>^ waitHandles
public static boolean WaitAll (
	WaitHandle[] waitHandles
public static function WaitAll (
	waitHandles : WaitHandle[]
) : boolean



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

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

Exception typeCondition


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

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


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


The waitHandles array contains elements that are duplicates.


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


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


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


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 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.


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 namespace System;
using namespace System::IO;
using namespace System::Security::Permissions;
using namespace System::Threading;

// Request permission to create and write files to C:\TestTest.
// Maintain state to pass to WriteToFile.

ref class State
   String^ fileName;
   ManualResetEvent^ manualEvent;
   State( String^ fileName, array<Byte>^byteArray, ManualResetEvent^ manualEvent )
      : fileName( fileName ), byteArray( byteArray ), manualEvent( manualEvent )


ref class Writer
   static int workItemCount = 0;

   static void WriteToFile( Object^ state )
      int workItemNumber = workItemCount;
      Interlocked::Increment( workItemCount );
      Console::WriteLine( "Starting work item {0}.", workItemNumber.ToString() );
      State^ stateInfo = dynamic_cast<State^>(state);
      FileStream^ fileWriter;
      // Create and write to the file.
         fileWriter = gcnew FileStream( stateInfo->fileName,FileMode::Create );
         fileWriter->Write( stateInfo->byteArray, 0, stateInfo->byteArray->Length );
         if ( fileWriter != nullptr )
         // Signal main() that the work item has finished.
         Console::WriteLine( "Ending work item {0}.", workItemNumber.ToString() );



void main()
   const int numberOfFiles = 5;
   String^ dirName =  "C:\\TestTest";
   String^ fileName;
   Random^ randomGenerator = gcnew Random;
   array<ManualResetEvent^>^manualEvents = gcnew array<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 = gcnew array<Byte>(1000000);
      randomGenerator->NextBytes( byteArray );
      manualEvents[ i ] = gcnew ManualResetEvent( false );
      stateInfo = gcnew State( fileName,byteArray,manualEvents[ i ] );
      ThreadPool::QueueUserWorkItem( gcnew 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." );

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

// 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))) {

        // 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),

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

        // Since ThreadPool threads are background threads, 
        // wait for the work items to signal before exiting.
        Console.WriteLine("Files written - 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

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

        Console.WriteLine("Starting work item {0}.",

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

        // Create and write to the file.
            fileWriter = new FileStream(stateInfo.fileName, FileMode.Create);
            fileWriter.Write(stateInfo.byteArray, 0, 
        finally {
            if ( fileWriter  != null  ) {
            // Signal Main that the work item has finished.
            Console.WriteLine("Ending work item {0}.", 
    } //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