ReaderWriterLock.RestoreLock(LockCookie) Metode

Definisi

Ruang nama:

System.Threading

Rakitan:

netstandard.dll, System.Threading.dll

Sumber:

ReaderWriterLock.cs

Memulihkan status kunci utas ke panggilan sebelum memanggil 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)

Parameter

lockCookie

LockCookie

Yang LockCookie dikembalikan oleh ReleaseLock().

Atribut

UnsupportedOSPlatformAttribute

Pengecualian

NullReferenceException

Alamat adalah lockCookie penunjuk null.

Contoh

Contoh kode berikut menunjukkan cara menggunakan ReleaseLock metode untuk melepaskan kunci, terlepas dari berapa kali telah diperoleh oleh utas, dan cara memulihkan status kunci nanti.

Kode ini adalah bagian dari contoh yang lebih besar yang disediakan untuk ReaderWriterLock kelas .

// 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

// 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

Keterangan

Status yang dipulihkan dengan RestoreLock menyertakan jumlah kunci rekursif.

Utas memblokir jika mencoba memulihkan kunci pembaca setelah utas lain memperoleh kunci penulis, atau jika mencoba memulihkan kunci penulis setelah utas lain memperoleh kunci pembaca atau kunci penulis. Karena RestoreLock tidak menerima waktu habis, Anda harus berhati-hati untuk menghindari kemungkinan kebuntuan.

Perhatian

Sebelum memanggil RestoreLock, pastikan Anda telah merilis semua kunci yang diperoleh sejak panggilan ke ReleaseLock. Misalnya, utas mengalami kebuntuan jika memperoleh kunci pembaca, lalu mencoba memulihkan kunci penulis sebelumnya. Gunakan IsReaderLockHeld dan IsWriterLockHeld untuk mendeteksi kunci tambahan tersebut.

Jangan gunakan yang LockCookie dikembalikan dari UpgradeToWriterLock.

Lihat juga

• Managed Threading
• ReaderWriterLock