ReaderWriterLock.AnyWritersSince(Int32) 方法

定義

指示取得序號之後有無將寫入器鎖定授與至任何執行緒。Indicates whether the writer lock has been granted to any thread since the sequence number was obtained.

public:
 bool AnyWritersSince(int seqNum);
public bool AnyWritersSince (int seqNum);
member this.AnyWritersSince : int -> bool
Public Function AnyWritersSince (seqNum As Integer) As Boolean

參數

seqNum
Int32

序號。The sequence number.

傳回

如果取得序號之後有將寫入器鎖定授與至任何執行緒,則為 true,否則為 falsetrue if the writer lock has been granted to any thread since the sequence number was obtained; otherwise, false.

範例

下列程式碼範例示範如何使用 AnyWritersSince 方法和 WriterSeqNum 屬性,判斷另一個執行緒是否取得受保護資源的寫入器鎖定,因為目前的執行緒上次持有寫入器鎖定。The following code example shows how to use the AnyWritersSince method and the WriterSeqNum property to determine whether another thread acquired the writer lock on the protected resource since the current thread last held the writer lock.

此程式碼是為 ReaderWriterLock 類別提供的較大範例的一部分。This code is part of a larger example provided for the ReaderWriterLock class.

// The complete code is located in the ReaderWriterLock
// class topic.
using namespace System;
using namespace System::Threading;
public ref class Test
{
public:

   // Declaring the ReaderWriterLock at the class level
   // makes it visible to all threads.
   static ReaderWriterLock^ rwl = gcnew ReaderWriterLock;

   // For this example, the shared resource protected by the
   // ReaderWriterLock is just an integer.
   static int resource = 0;

// 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
// Shows how to release all locks and later restore
// the lock state. Shows how to use 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 is safe for this thread to read from
         // the shared resource. Cache the value. (You
         // might do this if reading the resource is
         // an expensive operation.)
         int resourceValue = resource;
         Display( String::Format( "reads resource value {0}", 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.
         LockCookie lc = rwl->ReleaseLock();

         // Wait for a random interval (up to a
         // quarter of a second), and then restore
         // the previous state of the lock. Note that
         // there is no timeout on the Restore method.
         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 ) )
         {
            resourceValue = resource;
            Interlocked::Increment( reads );
            Display( String::Format( "resource has changed {0}", resourceValue ) );
         }
         else
         {
            Display( String::Format( "resource has not changed {0}", resourceValue ) );
         }
      }
      finally
      {

         // Ensure that the lock is released.
         rwl->ReleaseReaderLock();
      }

   }
   catch ( ApplicationException^ )
   {

      // The reader lock request timed out.
      Interlocked::Increment( 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.
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

備註

您可以使用 WriterSeqNumAnyWritersSince 來改善應用程式效能。You can use WriterSeqNum and AnyWritersSince to improve application performance. 例如,執行緒可能會快取在持有讀取器鎖定時所取得的資訊。For example, a thread might cache the information it obtains while holding a reader lock. 釋放並于稍後 reacquiring 鎖定之後,執行緒可以使用 AnyWritersSince 來判斷其他執行緒是否已在過渡期間寫入資源;如果不是,則可以使用快取的資訊。After releasing and later reacquiring the lock, the thread can use AnyWritersSince to determine whether other threads have written to the resource in the interim; if not, the cached information can be used. 這項技術非常有用,因為讀取鎖定保護的資訊相當耗費資源;例如,執行資料庫查詢。This technique is useful where reading the information protected by the lock is expensive; for example, running a database query.

呼叫端必須持有讀取器鎖定或寫入器鎖定,序號才會很有用。The caller must be holding a reader lock or a writer lock in order for the sequence number to be useful.

適用於

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