ReaderWriterLock.RestoreLock(LockCookie) Método

Definição

Namespace:

System.Threading

Assembly:

System.Threading.dll

Origem:

ReaderWriterLock.cs

Restaura o status de bloqueio do thread para o que era antes de chamar ReleaseLock().

public:
 void RestoreLock(System::Threading::LockCookie % lockCookie);

[System.Runtime.Versioning.UnsupportedOSPlatform("browser")]
public void RestoreLock (ref System.Threading.LockCookie lockCookie);

[<System.Runtime.Versioning.UnsupportedOSPlatform("browser")>]
member this.RestoreLock : LockCookie -> unit

Public Sub RestoreLock (ByRef lockCookie As LockCookie)

Parâmetros

lockCookie

LockCookie

Um LockCookie retornado por ReleaseLock().

Atributos

UnsupportedOSPlatformAttribute

Exceções

NullReferenceException

O endereço de lockCookie é um ponteiro nulo.

Exemplos

O exemplo de código a seguir mostra como usar o ReleaseLock método para liberar o bloqueio, independentemente de quantas vezes ele foi adquirido pelo thread e como restaurar o estado do bloqueio posteriormente.

Esse código faz parte de um exemplo maior fornecido para a ReaderWriterLock classe .

// The complete code is located in the ReaderWriterLock
// class topic.
using namespace System;
using namespace System::Threading;
public ref class Test
{
public:

   // Declaring the ReaderWriterLock at the class level
   // makes it visible to all threads.
   static ReaderWriterLock^ rwl = gcnew ReaderWriterLock;

   // For this example, the shared resource protected by the
   // ReaderWriterLock is just an integer.
   static int resource = 0;

// The complete code is located in the ReaderWriterLock class topic.
using System;
using System.Threading;

public class Example
{
   static ReaderWriterLock rwl = new ReaderWriterLock();
   // Define the shared resource protected by the ReaderWriterLock.
   static int resource = 0;

' The complete code is located in the ReaderWriterLock class topic.
Imports System.Threading

Public Module Example
   Private rwl As New ReaderWriterLock()
   ' Define the shared resource protected by the ReaderWriterLock.
   Private resource As Integer = 0

// Shows how to release all locks and later restore
// the lock state. Shows how to use sequence numbers
// to determine whether another thread has obtained
// a writer lock since this thread last accessed the
// resource.
static void ReleaseRestore( Random^ rnd, int timeOut )
{
   int lastWriter;
   try
   {
      rwl->AcquireReaderLock( timeOut );
      try
      {

         // It is safe for this thread to read from
         // the shared resource. Cache the value. (You
         // might do this if reading the resource is
         // an expensive operation.)
         int resourceValue = resource;
         Display( String::Format( "reads resource value {0}", resourceValue ) );
         Interlocked::Increment( reads );

         // Save the current writer sequence number.
         lastWriter = rwl->WriterSeqNum;

         // Release the lock, and save a cookie so the
         // lock can be restored later.
         LockCookie lc = rwl->ReleaseLock();

         // Wait for a random interval (up to a
         // quarter of a second), and then restore
         // the previous state of the lock. Note that
         // there is no timeout on the Restore method.
         Thread::Sleep( rnd->Next( 250 ) );
         rwl->RestoreLock( lc );

         // Check whether other threads obtained the
         // writer lock in the interval. If not, then
         // the cached value of the resource is still
         // valid.
         if ( rwl->AnyWritersSince( lastWriter ) )
         {
            resourceValue = resource;
            Interlocked::Increment( reads );
            Display( String::Format( "resource has changed {0}", resourceValue ) );
         }
         else
         {
            Display( String::Format( "resource has not changed {0}", resourceValue ) );
         }
      }
      finally
      {

         // Ensure that the lock is released.
         rwl->ReleaseReaderLock();
      }

   }
   catch ( ApplicationException^ )
   {

      // The reader lock request timed out.
      Interlocked::Increment( readerTimeouts );
   }

}

// Release all locks and later restores the lock state.
// Uses sequence numbers to determine whether another thread has
// obtained a writer lock since this thread last accessed the resource.
static void ReleaseRestore(Random rnd, int timeOut)
{
   int lastWriter;

   try {
      rwl.AcquireReaderLock(timeOut);
      try {
         // It's safe for this thread to read from the shared resource,
         // so read and cache the resource value.
         int resourceValue = resource;     // Cache the resource value.
         Display("reads resource value " + resourceValue);
         Interlocked.Increment(ref reads);

         // Save the current writer sequence number.
         lastWriter = rwl.WriterSeqNum;

         // Release the lock and save a cookie so the lock can be restored later.
         LockCookie lc = rwl.ReleaseLock();

         // Wait for a random interval and then restore the previous state of the lock.
         Thread.Sleep(rnd.Next(250));
         rwl.RestoreLock(ref lc);

         // Check whether other threads obtained the writer lock in the interval.
         // If not, then the cached value of the resource is still valid.
         if (rwl.AnyWritersSince(lastWriter)) {
            resourceValue = resource;
            Interlocked.Increment(ref reads);
            Display("resource has changed " + resourceValue);
         }
         else {
            Display("resource has not changed " + resourceValue);
         }
      }
      finally {
         // Ensure that the lock is released.
         rwl.ReleaseReaderLock();
      }
   }
   catch (ApplicationException) {
      // The reader lock request timed out.
      Interlocked.Increment(ref readerTimeouts);
   }
}

' Release all locks and later restores the lock state.
' Uses sequence numbers to determine whether another thread has
' obtained a writer lock since this thread last accessed the resource.
Sub ReleaseRestore(rnd As Random ,timeOut As Integer)
   Dim lastWriter As Integer
   
   Try
      rwl.AcquireReaderLock(timeOut)
      Try
         ' It's safe for this thread to read from the shared resource,
         ' so read and cache the resource value.
         Dim resourceValue As Integer = resource
         Display("reads resource value " & resourceValue)
         Interlocked.Increment(reads)
         
         ' Save the current writer sequence number.
         lastWriter = rwl.WriterSeqNum
         
         ' Release the lock and save a cookie so the lock can be restored later.
         Dim lc As LockCookie = rwl.ReleaseLock()
         
         ' Wait for a random interval and then restore the previous state of the lock.
         Thread.Sleep(rnd.Next(250))
         rwl.RestoreLock(lc)
        
         ' Check whether other threads obtained the writer lock in the interval.
         ' If not, then the cached value of the resource is still valid.
         If rwl.AnyWritersSince(lastWriter) Then
            resourceValue = resource
            Interlocked.Increment(reads)
            Display("resource has changed " & resourceValue)
         Else
            Display("resource has not changed " & resourceValue)
         End If
      Finally
         ' Ensure that the lock is released.
         rwl.ReleaseReaderLock()
      End Try
   Catch ex As ApplicationException
      ' The reader lock request timed out.
      Interlocked.Increment(readerTimeouts)
   End Try
End Sub

};

}

End Module

Comentários

O estado restaurado por RestoreLock inclui a contagem de bloqueios recursivos.

Um thread será bloqueado se tentar restaurar um bloqueio de leitor depois que outro thread tiver adquirido o bloqueio de gravador ou se tentar restaurar o bloqueio do gravador depois que outro thread tiver adquirido um bloqueio de leitor ou bloqueio de gravador. Como RestoreLock não aceita um tempo limite, você deve tomar cuidado para evitar possíveis deadlocks.

Cuidado

Antes de chamar RestoreLock, certifique-se de ter liberado todos os bloqueios adquiridos desde a chamada para ReleaseLock. Por exemplo, um thread será bloqueado se adquirir um bloqueio de leitor e tentar restaurar um bloqueio de gravador anterior. Use IsReaderLockHeld e IsWriterLockHeld para detectar esses bloqueios adicionais.

Não use um LockCookie retornado de UpgradeToWriterLock.

Confira também

• Threading gerenciado
• Readerwriterlock