ReaderWriterLock.DowngradeFromWriterLock(LockCookie) Metoda

Definice

Obor názvů:

System.Threading

Sestavení:

netstandard.dll, System.Threading.dll

Zdroj:

ReaderWriterLock.cs

Obnoví stav zámku vlákna na to, co bylo dříve UpgradeToWriterLock(Int32) volána.

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

A LockCookie vráceno .UpgradeToWriterLock(Int32)

Výjimky

ApplicationException

Vlákno nemá zámek zapisovače.

NullReferenceException

Adresa lockCookie je ukazatel null.

Příklady

Následující příklad kódu ukazuje, jak požádat o zámek čtečky, upgradovat zámek čtečky na zámek zapisovače a downgradovat na zámek čtečky znovu.

Tento kód je součástí většího příkladu poskytovaného ReaderWriterLock pro třídu.

// 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

Poznámky

DowngradeFromWriterLock uvolní zámek zapisovače bez ohledu na počet rekurzivních zámků a obnoví zámek čtečky uchovávané vláknem před upgradem na zámek zapisovače. Počet zámků na zámek čtečky se obnoví.

Note

DowngradeFromWriterLock přijme získanou LockCookie voláním UpgradeToWriterLock. Nepoužívejte LockCookie vrácené ReleaseLock.

Vlákno při downgradu zámku zapisovače neblokuje, i když na zámek zapisovače čekají další vlákna, protože při uvolnění zámku zapisovače jsou uděleny všechny žádosti o uzamčení čtečky.

Viz také

• spravovaných vláken