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Mutex::ReleaseMutex Method ()

 

Releases the Mutex once.

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

public:
void ReleaseMutex()

Exception Condition
ApplicationException

The calling thread does not own the mutex.

ObjectDisposedException

The current instance has already been disposed.

Whenever a thread acquires a mutex (for example, by calling its WaitOne method), it must subsequently call ReleaseMutex to relinquish ownership of the mutex and unblock other threads that are trying to gain ownership of the mutex. If the attempt to get ownership of the mutex fails (for example, when a call to the WaitOne method with a millisecondsTimeout or a timeout parameter returns false because the request times out), the thread shouldn't call ReleaseMutex, In this case, the thread should also not be allowed to access the resource protected by the mutex, as the following example shows.

No code example is currently available or this language may not be supported.

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.

System_CAPS_cautionCaution

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.
using namespace System;
using namespace System::Threading;
const int numIterations = 1;
const int numThreads = 3;
ref class Test
{
public:

   // Create a new Mutex. The creating thread does not own the
   // Mutex.
   static Mutex^ mut = gcnew Mutex;
   static void MyThreadProc()
   {
      for ( int i = 0; i < numIterations; i++ )
      {
         UseResource();

      }
   }


private:

   // This method represents a resource that must be synchronized
   // so that only one thread at a time can enter.
   static void UseResource()
   {

      //Wait until it is OK to enter.
      mut->WaitOne();
      Console::WriteLine( "{0} has entered protected the area", Thread::CurrentThread->Name );

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

      // Release the Mutex.
      mut->ReleaseMutex();
   }

};

int main()
{

   // Create the threads that will use the protected resource.
   for ( int i = 0; i < numThreads; i++ )
   {
      Thread^ myThread = gcnew Thread( gcnew ThreadStart( Test::MyThreadProc ) );
      myThread->Name = String::Format( "Thread {0}", i + 1 );
      myThread->Start();

   }

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

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
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