ReaderWriterLock.DowngradeFromWriterLock(LockCookie) Метод

Определение

Пространство имен:

System.Threading

Сборки:

netstandard.dll, System.Threading.dll

Исходный код:

ReaderWriterLock.cs

Восстанавливает состояние блокировки потока до UpgradeToWriterLock(Int32) вызова.

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

public void DowngradeFromWriterLock(ref System.Threading.LockCookie lockCookie);

member this.DowngradeFromWriterLock : LockCookie -> unit

Public Sub DowngradeFromWriterLock (ByRef lockCookie As LockCookie)

Параметры

lockCookie

LockCookie

Возвращается LockCookieUpgradeToWriterLock(Int32).

Исключения

ApplicationException

Поток не имеет блокировки записи.

NullReferenceException

Адрес lockCookie является указателем null.

Примеры

В следующем примере кода показано, как запросить блокировку чтения, обновить блокировку чтения до блокировки записи и снова перейти на блокировку чтения.

Этот код является частью более крупного примера, предоставленного ReaderWriterLock для класса.

// 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

// Requests a reader lock, upgrades the reader lock to the writer
// lock, and downgrades it to a reader lock again.
static void UpgradeDowngrade(Random rnd, int timeOut)
{
   try {
      rwl.AcquireReaderLock(timeOut);
      try {
         // It's safe for this thread to read from the shared resource.
         Display("reads resource value " + resource);
         Interlocked.Increment(ref reads);

         // To write to the resource, either release the reader lock and
         // request the writer lock, or upgrade the reader lock. Upgrading
         // the reader lock puts the thread in the write queue, behind any
         // other threads that might be waiting for the writer lock.
         try {
            LockCookie lc = rwl.UpgradeToWriterLock(timeOut);
            try {
               // It's safe for this thread to read or write from the shared resource.
               resource = rnd.Next(500);
               Display("writes resource value " + resource);
               Interlocked.Increment(ref writes);
            }
            finally {
               // Ensure that the lock is released.
               rwl.DowngradeFromWriterLock(ref lc);
            }
         }
         catch (ApplicationException) {
            // The upgrade request timed out.
            Interlocked.Increment(ref writerTimeouts);
         }

         // If the lock was downgraded, it's still safe to read from the resource.
         Display("reads resource value " + resource);
         Interlocked.Increment(ref reads);
      }
      finally {
         // Ensure that the lock is released.
         rwl.ReleaseReaderLock();
      }
   }
   catch (ApplicationException) {
      // The reader lock request timed out.
      Interlocked.Increment(ref readerTimeouts);
   }
}

' Requests a reader lock, upgrades the reader lock to the writer
' lock, and downgrades it to a reader lock again.
Sub UpgradeDowngrade(rnd As Random, timeOut As Integer)
   Try
      rwl.AcquireReaderLock(timeOut)
      Try
         ' It's safe for this thread to read from the shared resource.
         Display("reads resource value " & resource)
         Interlocked.Increment(reads)
         
         ' To write to the resource, either release the reader lock and
         ' request the writer lock, or upgrade the reader lock. Upgrading
         ' the reader lock puts the thread in the write queue, behind any
         ' other threads that might be waiting for the writer lock.
         Try
            Dim lc As LockCookie = rwl.UpgradeToWriterLock(timeOut)
            Try
               ' It's safe for this thread to read or write from the shared resource.
               resource = rnd.Next(500)
               Display("writes resource value " & resource)
               Interlocked.Increment(writes)
            Finally
               ' Ensure that the lock is released.
               rwl.DowngradeFromWriterLock(lc)
            End Try
         Catch ex As ApplicationException
            ' The upgrade request timed out.
            Interlocked.Increment(writerTimeouts)
         End Try
         
         ' If the lock was downgraded, it's still safe to read from the resource.
         Display("reads resource value " & resource)
         Interlocked.Increment(reads)
      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

Комментарии

DowngradeFromWriterLock освобождает блокировку записи независимо от рекурсивного количества блокировок и восстанавливает блокировку чтения, которая была проведена потоком перед обновлением до блокировки записи. Счетчик блокировки на блокировке чтения восстанавливается.

Note

DowngradeFromWriterLock LockCookie принимает полученный путем вызоваUpgradeToWriterLock. Не используйте LockCookie возвращаемый ReleaseLockобъект.

Поток не блокируется при понижении от блокировки записи, даже если другие потоки ожидают блокировки записи, так как все запросы на блокировку чтения предоставляются при освобождении блокировки записи.

См. также раздел

• Управляемая многопоточность