ReaderWriterLock.AnyWritersSince(Int32) Metode

Definisi

Ruang nama:

System.Threading

Rakitan:

netstandard.dll, System.Threading.dll

Sumber:

ReaderWriterLock.cs

Menunjukkan apakah kunci penulis telah diberikan ke utas apa pun sejak nomor urut diperoleh.

public:
 bool AnyWritersSince(int seqNum);

public bool AnyWritersSince(int seqNum);

member this.AnyWritersSince : int -> bool

Public Function AnyWritersSince (seqNum As Integer) As Boolean

Parameter

seqNum

Int32

Nomor urut.

Mengembalikan

Boolean

true jika kunci penulis telah diberikan ke utas apa pun sejak nomor urut diperoleh; jika tidak, false.

Contoh

Contoh kode berikut menunjukkan cara menggunakan AnyWritersSince metode dan WriterSeqNum properti untuk menentukan apakah utas lain memperoleh kunci penulis pada sumber daya yang dilindungi sejak utas saat ini terakhir kali memegang kunci penulis.

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

Anda dapat menggunakan WriterSeqNum dan AnyWritersSince untuk meningkatkan performa aplikasi. Misalnya, utas mungkin menyimpan cache informasi yang diperolehnya saat memegang kunci pembaca. Setelah merilis dan kemudian mengambil kunci, utas dapat digunakan AnyWritersSince untuk menentukan apakah utas lain telah menulis ke sumber daya di sementara; jika tidak, informasi yang di-cache dapat digunakan. Teknik ini berguna di mana membaca informasi yang dilindungi oleh kunci mahal; misalnya, menjalankan kueri database.

Pemanggil harus memegang kunci pembaca atau kunci penulis agar nomor urutan berguna.

Lihat juga

• Managed Threading
• ReaderWriterLock