ReaderWriterLock.WriterSeqNum プロパティ

.NET Framework クラス ライブラリ リファレンス

ReaderWriterLock.WriterSeqNum プロパティ

現在のシーケンス番号を取得します。

名前空間: System.Threading
アセンブリ: mscorlib (mscorlib.dll 内)
構文

Visual Basic (宣言)

Public ReadOnly Property
 WriterSeqNum As Integer

Visual Basic (使用法)

Dim instance As ReaderWriterLock
Dim value As Integer

value = instance.WriterSeqNum

C#

public int WriterSeqNum { get;
 }

C++

public:
property int WriterSeqNum {
    int get ();
}

J#

/** @property */
public int get_WriterSeqNum ()

JScript

public function get WriterSeqNum
 () : int

プロパティ値
現在のシーケンス番号。

解説

シーケンス番号は、ライタ ロックをスレッドが取得するたびに増分されます。シーケンス番号を保存しておき、後で AnyWritersSince に渡すことによって、その間にライタ ロックを取得した別のスレッドがあったかどうかを知ることができます。

WriterSeqNum は、アプリケーションのパフォーマンス向上に役立てることができます。たとえば、リーダー ロックの保持中に取得した情報をキャッシュに格納しておきます。ロックを解放した後、再度リーダー ロックを取得した場合は、AnyWritersSince を呼び出すことによって、別のスレッドがこのリソースに対して書き込みを行ったかどうかを確認します。書き込みを行ったリソースがなかった場合は、キャッシュに格納した情報を使用できます。この手法は、データベース クエリの実行など、ロックで保護された情報の読み取りの負荷が大きい場合に有効です。

シーケンス番号を使用するときは、呼び出し元はリーダー ロックまたはライタ ロックを保持している必要があります。

使用例

Visual Basic

' The complete code is located in the ReaderWriterLock
' class topic.
Imports System
Imports System.Threading
Imports Microsoft.VisualBasic

Public Class Test
    ' Declaring the ReaderWriterLock at the class level
    ' makes it visible to all threads.
    Private Shared rwl As
 New ReaderWriterLock()
    ' For this example, the shared resource protected by the
    ' ReaderWriterLock is just an integer.
    Private Shared resource As
 Integer = 0
<br /><span space="preserve">...</span><br
 />    ' 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.
    Shared Sub ReleaseRestore(timeOut As
 Integer)
        Dim lastWriter As Integer
      
        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.)
                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 (up to a 
                ' quarter of a second), and then restore
                ' the previous state of the lock. Note that
                ' there is no time-out 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) 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 'ReleaseRestore
<br /><span space="preserve">...</span><br
 />End Class 'Test 

C#

// The complete code is located in the ReaderWriterLock
// class topic.
using System;
using System.Threading;

public class Test
{
    // Declaring the ReaderWriterLock at the class level
    // makes it visible to all threads.
    static ReaderWriterLock rwl = new ReaderWriterLock();
    // For this example, the shared resource protected by the
    // ReaderWriterLock is just an integer.
    static int resource = 0;
<br /><span space="preserve">...</span><br /> 
   // 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(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("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 (up to a 
                // quarter of a second), and then restore
                // the previous state of the lock. Note that
                // there is no time-out on the Restore method.
                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);
        }
    }
<br /><span space="preserve">...</span><br />}

C++

// 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;

<br /><span space="preserve">...</span><br /> 
  // 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( 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 );
      }

   }


<br /><span space="preserve">...</span><br />};

J#

// The complete code is located in the ReaderWriterLock
// class topic.
import System.*;
import System.Threading.*;
import System.Threading.Thread;    

public class Test
{
    // Declaring the ReaderWriterLock at the class level
    // makes it visible to all threads.
    private static ReaderWriterLock rwl = new
 ReaderWriterLock();

    // For this example, the shared resource protected by the
    // ReaderWriterLock is just an integer.
    private static int resource
 = 0;
<br /><span space="preserve">...</span><br />
    // 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(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(("reads resource value " + resourceValue));
                Interlocked.Increment(reads);

                // Save the current writer sequence number.
                lastWriter = rwl.get_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 time-out 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(("resource has changed " + resourceValue));
                }
                else {
                    Display(("resource has not changed " + resourceValue));
                }
            }
            finally {
                // Ensure that the lock is released.
                rwl.ReleaseReaderLock();
            }
        }
        catch (ApplicationException exp) {
            // The reader lock request timed out.
            Interlocked.Increment(readerTimeouts);
        }
    } //ReleaseRestore
<br /><span space="preserve">...</span><br />}

プラットフォーム

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

開発プラットフォームの中には、.NET Framework によってサポートされていないバージョンがあります。サポートされているバージョンについては、「システム要件」を参照してください。

バージョン情報

.NET Framework
サポート対象 : 2.0、1.1、1.0

参照

関連項目
ReaderWriterLock クラス
ReaderWriterLock メンバ
System.Threading 名前空間
その他の技術情報
マネージ スレッド処理
読み取り/書き込みロック