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Mutex.ReleaseMutex Method

Releases the Mutex once.

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

'Declaration
Public Sub ReleaseMutex
'Usage
Dim instance As Mutex

instance.ReleaseMutex
public void ReleaseMutex ()
public function ReleaseMutex ()
Not applicable.

Exception typeCondition

ApplicationException

The calling thread does not own the mutex.

A thread that owns a mutex can specify the same mutex in repeated wait function calls without blocking its execution. The number of calls is kept by the common language runtime. The thread must call ReleaseMutex the same number of times to release ownership of the mutex.

If a thread terminates while owning a mutex, the mutex is said to be abandoned. The state of the mutex is set to signaled and the next waiting thread gets ownership. If no one owns the mutex, the state of the mutex is signaled. Beginning in version 2.0 of the .NET Framework, an AbandonedMutexException is thrown in the next thread that acquires the mutex. Prior to version 2.0 of the .NET Framework, no exception was thrown.

Caution noteCaution:

An abandoned mutex often indicates a serious error in the code. When a thread exits without releasing the mutex, the data structures protected by the mutex might not be in a consistent state. The next thread to request ownership of the mutex can handle this exception and proceed, if the integrity of the data structures can be verified.

In the case of a system-wide mutex, an abandoned mutex might indicate that an application has been terminated abruptly (for example, by using Windows Task Manager).

The following example shows how a local Mutex object is used to synchronize access to a protected resource. The thread that creates the mutex does not own it initially. The ReleaseMutex method is used to release the mutex when it is no longer needed.

' This example shows how a Mutex is used to synchronize access
' to a protected resource. Unlike Monitor, Mutex can be used with
' WaitHandle.WaitAll and WaitAny, and can be passed across
' AppDomain boundaries.
 
Imports System
Imports System.Threading
Imports Microsoft.VisualBasic

Class Test
    ' Create a new Mutex. The creating thread does not own the
    ' Mutex.
    Private Shared mut As New Mutex()
    Private Const numIterations As Integer = 1
    Private Const numThreads As Integer = 3

    <MTAThread> _
    Shared Sub Main()
        ' Create the threads that will use the protected resource.
        Dim i As Integer
        For i = 1 To numThreads
            Dim myThread As New Thread(AddressOf MyThreadProc)
            myThread.Name = [String].Format("Thread{0}", i)
            myThread.Start()
        Next i

        ' The main thread exits, but the application continues to
        ' run until all foreground threads have exited.

    End Sub 'Main

    Private Shared Sub MyThreadProc()
        Dim i As Integer
        For i = 1 To numIterations
            UseResource()
        Next i
    End Sub 'MyThreadProc

    ' This method represents a resource that must be synchronized
    ' so that only one thread at a time can enter.
    Private Shared Sub UseResource()
        ' Wait until it is safe to enter.
        mut.WaitOne()

        Console.WriteLine("{0} has entered protected area", _
            Thread.CurrentThread.Name)

        ' Place code to access non-reentrant resources here.

        ' Simulate some work
        Thread.Sleep(500)

        Console.WriteLine("{0} is leaving protected area" & vbCrLf, _
            Thread.CurrentThread.Name)

        ' Release Mutex.
        mut.ReleaseMutex()
    End Sub 'UseResource
End Class 'MyMainClass

// This example shows how a Mutex is used to synchronize access
// to a protected resource. Unlike Monitor, Mutex can be used with
// WaitHandle.WaitAll and WaitAny, and can be passed across
// AppDomain boundaries.

import System.*;
import System.Threading.*;
import System.Threading.Thread;

class Test
{
    // Create a new Mutex. The creating thread does not own the
    // Mutex.
    private static Mutex mut = new Mutex();
    private static int numIterations = 1;
    private static int numThreads = 3;

    public static void main(String[] args)
    {
        // Create the threads that will use the protected resource.
        for (int i = 0; i < numThreads; i++) {
            Thread myThread = new Thread(new ThreadStart(MyThreadProc));
            myThread.set_Name(String.Format("Thread{0}", 
                String.valueOf(i + 1)));
            myThread.Start();
        }
    } //main

    // The main thread exits, but the application continues to
    // run until all foreground threads have exited.
    private static void MyThreadProc()
    {
        for (int i = 0; i < numIterations; i++) {
            UseResource();
        }
    } //MyThreadProc

    // This method represents a resource that must be synchronized
    // so that only one thread at a time can enter.
    private static void UseResource()
    {
        // Wait until it is safe to enter.
        mut.WaitOne();
        Console.WriteLine("{0} has entered the protected area", 
            Thread.get_CurrentThread().get_Name());

        // Place code to access non-reentrant resources here.
        // Simulate some work.
        Thread.Sleep(500);
        Console.WriteLine("{0} is leaving the protected area\r\n", 
            Thread.get_CurrentThread().get_Name());

        // Release the Mutex.
        mut.ReleaseMutex();
    } //UseResource
} //Test

Windows 98, Windows Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0

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