ReaderWriterLock.DowngradeFromWriterLock メソッド

.NET Framework クラス ライブラリ リファレンス

ReaderWriterLock.DowngradeFromWriterLock メソッド

スレッドのロック ステータスを、UpgradeToWriterLock を呼び出す前の状態に復元します。

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

Visual Basic (宣言)

Public Sub DowngradeFromWriterLock ( _
    ByRef lockCookie As LockCookie _
)

Visual Basic (使用法)

Dim instance As ReaderWriterLock
Dim lockCookie As LockCookie

instance.DowngradeFromWriterLock(lockCookie)

C#

public void DowngradeFromWriterLock (
    ref LockCookie lockCookie
)

C++

public:
void DowngradeFromWriterLock (
    LockCookie% lockCookie
)

J#

public void DowngradeFromWriterLock (
    /** @ref */ LockCookie lockCookie
)

JScript

JScript では、値型の引数は参照渡しされません。

パラメータ

lockCookie

UpgradeToWriterLock から返される LockCookie。

例外

例外の種類	条件
ApplicationException	スレッドがライタ ロックを保持していません。
NullReferenceException	lockCookie のアドレスが null ポインタです。

解説

DowngradeFromWriterLock を呼び出すと、再帰的なロック カウントに関係なく、ライタ ロックが解放され、ライタ ロックにアップグレードする前にスレッドが保持していたリーダー ロックが復元されます。リーダー ロックのロック カウントも復元されます。

メモ
DowngradeFromWriterLock は、UpgradeToWriterLock の呼び出しで取得した LockCookie を受け取ります。ReleaseLock から返される LockCookie は使用しないでください。

ライタ ロックが解放されたときにリーダー ロックの要求はすべて許可されるため、他のスレッドがライタ ロックを待機している場合でも、ライタ ロックからダウングレードしたときスレッドがブロックすることはありません。

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 request a reader lock, upgrade the
    ' reader lock to the writer lock, and downgrade to a
    ' reader lock again.
    Shared Sub UpgradeDowngrade(timeOut As
 Integer)
        Try
            rwl.AcquireReaderLock(timeOut)
            Try
                ' It is safe for this thread to read from
                ' the shared resource.
                Display("reads resource value " &
 resource)
                Interlocked.Increment(reads)
            
                ' If it is necessary to write to the resource,
                ' you must either release the reader lock and 
                ' then request the writer lock, or upgrade the
                ' reader lock. Note that 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 is 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
            
                ' When the lock has been downgraded, it is 
                ' 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 'UpgradeDowngrade
<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 request a reader lock, upgrade the
    // reader lock to the writer lock, and downgrade to a
    // reader lock again.
    static void UpgradeDowngrade(int
 timeOut)
    {
        try
        {
            rwl.AcquireReaderLock(timeOut);
            try
            {
                // It is safe for this thread to read from
                // the shared resource.
                Display("reads resource value " + resource); 
                Interlocked.Increment(ref reads);

                // If it is necessary to write to the resource,
                // you must either release the reader lock and 
                // then request the writer lock, or upgrade the
                // reader lock. Note that 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 is 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);
                }

                // When the lock has been downgraded, it is 
                // 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);
        }
    }
<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 request a reader lock, upgrade the
   // reader lock to the writer lock, and downgrade to a
   // reader lock again.
   static void UpgradeDowngrade( int
 timeOut )
   {
      try
      {
         rwl->AcquireReaderLock( timeOut );
         try
         {
            
            // It is safe for this thread to read from
            // the shared resource.
            Display( String::Format( "reads resource value {0}", resource
 ) );
            Interlocked::Increment( reads );
            
            // If it is necessary to write to the resource,
            // you must either release the reader lock and 
            // then request the writer lock, or upgrade the
            // reader lock. Note that 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 is safe for this thread to read or write
                  // from the shared resource.
                  resource = rnd->Next( 500 );
                  Display( String::Format( "writes resource value {0}",
 resource ) );
                  Interlocked::Increment( writes );
               }
               finally
               {
                  
                  // Ensure that the lock is released.
                  rwl->DowngradeFromWriterLock( lc );
               }

            }
            catch ( ApplicationException^ ) 
            {
               
               // The upgrade request timed out.
               Interlocked::Increment( writerTimeouts );
            }

            
            // When the lock has been downgraded, it is 
            // still safe to read from the resource.
            Display( String::Format( "reads resource value {0}", resource
 ) );
            Interlocked::Increment( reads );
         }
         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 request a reader lock, upgrade the
    // reader lock to the writer lock, and downgrade to a
    // reader lock again.
    static void UpgradeDowngrade(int
 timeOut)
    {
        try {
            rwl.AcquireReaderLock(timeOut);
            try {
                // It is safe for this thread to read from
                // the shared resource.
                Display(("reads resource value " + resource));
                Interlocked.Increment(reads);

                // If it is necessary to write to the resource,
                // you must either release the reader lock and 
                // then request the writer lock, or upgrade the
                // reader lock. Note that 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 is 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);
                    }
                }
                catch (ApplicationException exp) {
                    // The upgrade request timed out.
                    Interlocked.Increment(writerTimeouts);
                }

                // When the lock has been downgraded, it is 
                // still safe to read from the resource.
                Display(("reads resource value " + resource));
                Interlocked.Increment(reads);
            }
            finally {
                // Ensure that the lock is released.
                rwl.ReleaseReaderLock();
            }
        }
        catch (ApplicationException exp) {
            // The reader lock request timed out.
            Interlocked.Increment(readerTimeouts);
        }
    } //UpgradeDowngrade
<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