Mutex.ReleaseMutex Método
Definição
Importante
Algumas informações se referem a produtos de pré-lançamento que podem ser substancialmente modificados antes do lançamento. A Microsoft não oferece garantias, expressas ou implícitas, das informações aqui fornecidas.
Libera uma Mutex vez.
public:
void ReleaseMutex();public void ReleaseMutex();member this.ReleaseMutex : unit -> unitPublic Sub ReleaseMutex ()Exceções
O thread de chamada não possui o mutex.
A instância atual já foi descartada.
Exemplos
O exemplo a seguir mostra como um objeto local Mutex é usado para sincronizar o acesso a um recurso protegido. O thread que cria o mutex não o possui inicialmente. O ReleaseMutex método é usado para liberar o mutex quando ele não é mais necessário.
// 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 System;
using System.Threading;
class Test13
{
// Create a new Mutex. The creating thread does not own the
// Mutex.
private static Mutex mut = new Mutex();
private const int numIterations = 1;
private const int numThreads = 3;
static void Main()
{
// Create the threads that will use the protected resource.
for(int i = 0; i < numThreads; i++)
{
Thread myThread = new Thread(new ThreadStart(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.
}
private static void MyThreadProc()
{
for(int i = 0; i < numIterations; i++)
{
UseResource();
}
}
// 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.CurrentThread.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.CurrentThread.Name);
// Release the Mutex.
mut.ReleaseMutex();
}
}
' 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.Threading
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
Private Shared Sub MyThreadProc()
Dim i As Integer
For i = 1 To numIterations
UseResource()
Next i
End Sub
' 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
End Class
Comentários
Sempre que um thread adquire um mutex (por exemplo, chamando seu WaitOne método), ele deve chamar ReleaseMutex posteriormente para renunciar à propriedade do mutex e desbloquear outros threads que estão tentando obter a propriedade do mutex. Se a tentativa de obter a propriedade do mutex falhar (por exemplo, quando uma chamada para o WaitOne método com um millisecondsTimeout ou um timeout parâmetro retorna false porque a solicitação atinge o tempo limite), o thread não deve chamar ReleaseMutex, nesse caso, o thread também não deve ter permissão para acessar o recurso protegido pelo mutex, como mostra o exemplo a seguir.
using System;
using System.Threading;
class Example
{
// Create a new Mutex. The creating thread does not own the mutex.
private static Mutex mut = new Mutex();
private const int numIterations = 1;
private const int numThreads = 3;
static void Main()
{
Example ex = new Example();
ex.StartThreads();
}
private void StartThreads()
{
// Create the threads that will use the protected resource.
for(int i = 0; i < numThreads; i++)
{
Thread newThread = new Thread(new ThreadStart(ThreadProc));
newThread.Name = String.Format("Thread{0}", i + 1);
newThread.Start();
}
// The main thread returns to Main and exits, but the application continues to
// run until all foreground threads have exited.
}
private static void ThreadProc()
{
for(int i = 0; i < numIterations; i++)
{
UseResource();
}
}
// 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, and do not enter if the request times out.
Console.WriteLine("{0} is requesting the mutex", Thread.CurrentThread.Name);
if (mut.WaitOne(1000)) {
Console.WriteLine("{0} has entered the protected area",
Thread.CurrentThread.Name);
// Place code to access non-reentrant resources here.
// Simulate some work.
Thread.Sleep(5000);
Console.WriteLine("{0} is leaving the protected area",
Thread.CurrentThread.Name);
// Release the Mutex.
mut.ReleaseMutex();
Console.WriteLine("{0} has released the mutex",
Thread.CurrentThread.Name);
}
else {
Console.WriteLine("{0} will not acquire the mutex",
Thread.CurrentThread.Name);
}
}
~Example()
{
mut.Dispose();
}
}
// The example displays output like the following:
// Thread1 is requesting the mutex
// Thread1 has entered the protected area
// Thread2 is requesting the mutex
// Thread3 is requesting the mutex
// Thread2 will not acquire the mutex
// Thread3 will not acquire the mutex
// Thread1 is leaving the protected area
// Thread1 has released the mutex
Imports System.Threading
Class Example
' Create a new Mutex. The creating thread does not own the mutex.
Private mut As New Mutex()
Private Const numIterations As Integer = 1
Private Const numThreads As Integer = 3
Public Shared Sub Main()
Dim ex As New Example()
ex.StartThreads()
End Sub
Private Sub StartThreads()
' Create the threads that will use the protected resource.
For i As Integer = 0 To numThreads - 1
Dim newThread As New Thread(AddressOf ThreadProc)
newThread.Name = String.Format("Thread{0}", i + 1)
newThread.Start()
Next
' The main thread returns to Main and exits, but the application continues to
' run until all foreground threads have exited.
End Sub
Private Sub ThreadProc()
For i As Integer = 0 To numIterations - 1
UseResource()
Next
End Sub
' This method represents a resource that must be synchronized
' so that only one thread at a time can enter.
Private Sub UseResource()
' Wait until it is safe to enter.
Console.WriteLine("{0} is requesting the mutex",
Thread.CurrentThread.Name)
If mut.WaitOne(1000) Then
Console.WriteLine("{0} has entered the protected area",
Thread.CurrentThread.Name)
' Place code to access non-reentrant resources here.
' Simulate some work.
Thread.Sleep(5000)
Console.WriteLine("{0} is leaving the protected area",
Thread.CurrentThread.Name)
' Release the Mutex.
mut.ReleaseMutex()
Console.WriteLine("{0} has released the mutex",
Thread.CurrentThread.Name)
Else
Console.WriteLine("{0} will not acquire the mutex",
Thread.CurrentThread.Name)
End If
End Sub
Protected Overrides Sub Finalize()
mut.Dispose()
End Sub
End Class
' The example displays output like the following:
' Thread1 is requesting the mutex
' Thread1 has entered the protected area
' Thread2 is requesting the mutex
' Thread3 is requesting the mutex
' Thread2 will not acquire the mutex
' Thread3 will not acquire the mutex
' Thread1 is leaving the protected area
' Thread1 has released the mutex
Um thread que possui um mutex pode especificar o mesmo mutex em chamadas de função de espera repetidas sem bloquear sua execução. O número de chamadas é mantido pelo common language runtime. O thread deve chamar ReleaseMutex o mesmo número de vezes para liberar a propriedade do mutex.
Se um thread terminar enquanto tiver um mutex, o mutex será abandonado. O estado do mutex é definido como sinalizado e o próximo thread de espera obtém a propriedade. Se ninguém tiver o mutex, o estado do mutex será sinalizado. A partir da versão 2.0 do .NET Framework, um AbandonedMutexException é lançado no próximo thread que adquire o mutex. Antes da versão 2.0 do .NET Framework, nenhuma exceção era gerada.
Caution
Um mutex abandonado geralmente indica um erro grave no código. Quando um thread é encerrado sem liberar o mutex, as estruturas de dados protegidas pelo mutex podem não estar em um estado consistente. O próximo thread a solicitar a propriedade do mutex poderá lidar com essa exceção e continuar, se a integridade das estruturas de dados puder ser verificada.
No caso de um mutex de todo o sistema, um mutex abandonado pode indicar que um aplicativo foi finalizado abruptamente (por exemplo, usando o Gerenciador de Tarefas do Windows).
