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WaitHandle.WaitAny Method (WaitHandle[], Int32, Boolean)

Waits for any of the elements in the specified array to receive a signal, using a 32-bit signed integer 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 int WaitAny (
	WaitHandle[] waitHandles,
	int millisecondsTimeout,
	bool exitContext
)
public static int WaitAny (
	WaitHandle[] waitHandles, 
	int millisecondsTimeout, 
	boolean exitContext
)
public static function WaitAny (
	waitHandles : WaitHandle[], 
	millisecondsTimeout : int, 
	exitContext : boolean
) : int

Parameters

waitHandles

A WaitHandle array containing the objects for which the current instance will wait.

millisecondsTimeout

The number of milliseconds to wait, or Timeout.Infinite (-1) 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

The array index of the object that satisfied the wait, or WaitTimeout if no object satisfied the wait and a time interval equivalent to millisecondsTimeout has passed.

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).

NotSupportedException

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

ApplicationException

waitHandles is an array with no elements.

ArgumentOutOfRangeException

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

AbandonedMutexException

The wait completed 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 WaitAny method returns true if the wait completes because a mutex is abandoned. An abandoned mutex indicates a serious coding error. The exception contains information useful for debugging.

The WaitAny method throws an AbandonedMutexException only when the wait completes because of an abandoned mutex. If waitHandles contains a released mutex with a lower index number than the abandoned mutex, the WaitAny method completes normally and the exception is not thrown.

NoteNote

In versions of the .NET Framework earlier than version 2.0, if a thread exits or aborts without explicitly releasing a Mutex, and that Mutex is at index 0 (zero) in a WaitAny array on another thread, the index returned by WaitAny is 128 instead of 0.

This method returns when the wait terminates, either when any of the handles are signaled or when a timeout occurs. If more than one object becomes signaled during the call, the return value is the array index of the signaled object with the smallest index value of all the signaled objects. On some implementations, if more that 64 handles are passed, a NotSupportedException is thrown.

Notes on Exiting the Context

The exitContext parameter has no effect unless the WaitAny 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 does not derive 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 WaitAny method. The thread returns to the original nondefault context after the call to the WaitAny 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 WaitAny 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 WaitAny method returns, the thread that made the call must wait to reenter the synchronization domain.

The following code example demonstrates how to use the thread pool to simultaneously search for a file on multiple disks. For space considerations, only the root directory of each disk is searched.

using System;
using System.IO;
using System.Threading;

class Test
{
    static void Main()
    {
        Search search = new Search();
        search.FindFile("SomeFile.dat");
    }
}

class Search
{
    // Maintain state information to pass to FindCallback.
    class State
    {
        public AutoResetEvent autoEvent;
        public string         fileName;

        public State(AutoResetEvent autoEvent, string fileName)
        {
            this.autoEvent    = autoEvent;
            this.fileName     = fileName;
        }
    }

    AutoResetEvent[] autoEvents;
    String[] diskLetters;

    public Search()
    {
        // Retrieve an array of disk letters.
        diskLetters = Environment.GetLogicalDrives();

        autoEvents = new AutoResetEvent[diskLetters.Length];
        for(int i = 0; i < diskLetters.Length; i++)
        {
            autoEvents[i] = new AutoResetEvent(false);
        }
    }

    // Search for fileName in the root directory of all disks.
    public void FindFile(string fileName)
    {
        for(int i = 0; i < diskLetters.Length; i++)
        {
            Console.WriteLine("Searching for {0} on {1}.",
                fileName, diskLetters[i]);
            ThreadPool.QueueUserWorkItem(
                new WaitCallback(FindCallback), 
                new State(autoEvents[i], diskLetters[i] + fileName));
        }

        // Wait for the first instance of the file to be found.
        int index = WaitHandle.WaitAny(autoEvents, 3000, false);
        if(index == WaitHandle.WaitTimeout)
        {
            Console.WriteLine("\n{0} not found.", fileName);
        }
        else
        {
            Console.WriteLine("\n{0} found on {1}.", fileName,
                diskLetters[index]);
        }
    }

    // Search for stateInfo.fileName.
    void FindCallback(object state)
    {
        State stateInfo = (State)state;

        // Signal if the file is found.
        if(File.Exists(stateInfo.fileName))
        {
            stateInfo.autoEvent.Set();
        }
    }
}

import System.*;
import System.IO.*;
import System.Threading.*;

class Test
{
    public static void main(String[] args)
    {
        Search search = new Search();
        search.FindFile("SomeFile.dat");
    } //main
} //Test

class Search
{
    // Maintain state information to pass to FindCallback.
    class State
    {
        public AutoResetEvent autoEvent;
        public String fileName;

        public State(AutoResetEvent autoEvent, String fileName)
        {
            this.autoEvent = autoEvent;
            this.fileName = fileName;
        } //State
    } //State

    private AutoResetEvent autoEvents[];
    private String diskLetters[];

    public Search()
    {
        // Retrieve an array of disk letters.
        diskLetters = Environment.GetLogicalDrives();
        autoEvents = new AutoResetEvent[diskLetters.length];
        for (int i = 0; i < diskLetters.length; i++) {
            autoEvents[i] = new AutoResetEvent(false);
        }
    } //Search

    // Search for fileName in the root directory of all disks.
    public void FindFile(String fileName)
    {
        for (int i = 0; i < diskLetters.length; i++) {
            Console.WriteLine("Searching for {0} on {1}.", fileName,
                diskLetters.get_Item(i));
            ThreadPool.QueueUserWorkItem(new WaitCallback(FindCallback), 
                new State(autoEvents[i], diskLetters[i] + fileName));
        }

        // Wait for the first instance of the file to be found.
        int index = WaitHandle.WaitAny(autoEvents, 3000, false);

        if (index == WaitHandle.WaitTimeout) {
            Console.WriteLine("\n{0} not found.", fileName);
        }
        else {
            Console.WriteLine("\n{0} found on {1}.", fileName,
                diskLetters.get_Item(index));
        }
    } //FindFile

    // Search for stateInfo.fileName.
    void FindCallback(Object state)
    {
        State stateInfo = ((State)(state));

        // Signal if the file is found.
        if (File.Exists(stateInfo.fileName)) {
            stateInfo.autoEvent.Set();
        }
    } //FindCallback
} //Search

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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