ReaderWriterLock.DowngradeFromWriterLock(LockCookie) Metoda

Definicja

Przestrzeń nazw:

System.Threading

Zestawy:

netstandard.dll, System.Threading.dll

Źródło:

ReaderWriterLock.cs

Przywraca stan blokady wątku do tego, co było wcześniej UpgradeToWriterLock(Int32) wywoływane.

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)

Parametry

lockCookie

LockCookie

Zwracany LockCookie przez element UpgradeToWriterLock(Int32).

Wyjątki

ApplicationException

Wątek nie ma blokady modułu zapisywania.

NullReferenceException

Adres to lockCookie wskaźnik o wartości null.

Przykłady

W poniższym przykładzie kodu pokazano, jak zażądać blokady czytnika, uaktualnić blokadę czytnika do blokady modułu zapisywania i ponownie obniżyć jej poziom do blokady czytnika.

Ten kod jest częścią większego przykładu udostępnionego ReaderWriterLock dla klasy.

// 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

Uwagi

DowngradeFromWriterLock zwalnia blokadę modułu zapisywania, niezależnie od cyklicznej liczby blokad i przywraca blokadę czytnika, która była przechowywana przez wątek przed uaktualnieniem do blokady modułu zapisywania. Liczba blokad w blokadzie czytnika jest przywracana.

Uwaga

DowngradeFromWriterLock LockCookie akceptuje uzyskany przez wywołanie metody UpgradeToWriterLock. Nie używaj zwracanego LockCookie przez ReleaseLockelement .

Wątek nie blokuje się podczas obniżania poziomu z blokady modułu zapisywania, nawet jeśli inne wątki czekają na blokadę modułu zapisywania, ponieważ wszystkie żądania blokady czytnika są przyznawane po zwolnieniu blokady modułu zapisywania.

Zobacz też

• Zarządzane wątki
• Readerwriterlock