ReaderWriterLock クラス

定義

public ref class ReaderWriterLock sealed : System::Runtime::ConstrainedExecution::CriticalFinalizerObject

public ref class ReaderWriterLock sealed

public sealed class ReaderWriterLock : System.Runtime.ConstrainedExecution.CriticalFinalizerObject

public sealed class ReaderWriterLock

[System.Runtime.InteropServices.ComVisible(true)]
public sealed class ReaderWriterLock : System.Runtime.ConstrainedExecution.CriticalFinalizerObject

type ReaderWriterLock = class
    inherit CriticalFinalizerObject

type ReaderWriterLock = class

[<System.Runtime.InteropServices.ComVisible(true)>]
type ReaderWriterLock = class
    inherit CriticalFinalizerObject

Public NotInheritable Class ReaderWriterLock
Inherits CriticalFinalizerObject

Public NotInheritable Class ReaderWriterLock

継承

Object

CriticalFinalizerObject

ReaderWriterLock

継承

Object

ReaderWriterLock

属性

ComVisibleAttribute

例

次の例では、 を使用 ReaderWriterLock して共有リソース (という名前 resourceの整数値) を保護する方法を示します。これは、同時に読み取られ、複数のスレッドによって排他的に書き込まれます。 ReaderWriterLockはクラス レベルで宣言され、すべてのスレッドに表示されることに注意してください。

// This example shows a ReaderWriterLock protecting a shared
// resource that is read concurrently and written exclusively
// by multiple threads.
// 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;

   literal int numThreads = 26;
   static bool running = true;

   // Statistics.
   static int readerTimeouts = 0;
   static int writerTimeouts = 0;
   static int reads = 0;
   static int writes = 0;
   static void ThreadProc()
   {
      Random^ rnd = gcnew Random;

      // As long as a thread runs, it randomly selects
      // various ways to read and write from the shared
      // resource. Each of the methods demonstrates one
      // or more features of ReaderWriterLock.
      while ( running )
      {
         double action = rnd->NextDouble();
         if ( action < .8 )
                  ReadFromResource( 10 );
         else
         if ( action < .81 )
                  ReleaseRestore( rnd, 50 );
         else
         if ( action < .90 )
                  UpgradeDowngrade( rnd, 100 );
         else
                  WriteToResource( rnd, 100 );
      }
   }


   // Shows how to request and release a reader lock, and
   // how to handle time-outs.
   static void ReadFromResource( 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 );
         }
         finally
         {

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

      }
      catch ( ApplicationException^ )
      {

         // The reader lock request timed out.
         Interlocked::Increment( readerTimeouts );
      }

   }


   // Shows how to request and release the writer lock, and
   // how to handle time-outs.
   static void WriteToResource( Random^ rnd, int timeOut )
   {
      try
      {
         rwl->AcquireWriterLock( 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->ReleaseWriterLock();
         }

      }
      catch ( ApplicationException^ )
      {

         // The writer lock request timed out.
         Interlocked::Increment( writerTimeouts );
      }

   }


   // 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( Random^ rnd, 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 );
      }

   }


   // 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 );
      }

   }


   // Helper method briefly displays the most recent
   // thread action. Comment out calls to Display to
   // get a better idea of throughput.
   static void Display( String^ msg )
   {
      Console::Write( "Thread {0} {1}.       \r", Thread::CurrentThread->Name, msg );
   }

};


int main()
{
   array<String^>^args = Environment::GetCommandLineArgs();

   // Start a series of threads. Each thread randomly
   // performs reads and writes on the shared resource.
   array<Thread^>^t = gcnew array<Thread^>(Test::numThreads);
   for ( int i = 0; i < Test::numThreads; i++ )
   {
      t[ i ] = gcnew Thread( gcnew ThreadStart( Test::ThreadProc ) );
      t[ i ]->Name = gcnew String( Convert::ToChar( i + 65 ),1 );
      t[ i ]->Start();
      if ( i > 10 )
            Thread::Sleep( 300 );

   }

   // Tell the threads to shut down, then wait until they all
   // finish.
   Test::running = false;
   for ( int i = 0; i < Test::numThreads; i++ )
   {
      t[ i ]->Join();

   }

   // Display statistics.
   Console::WriteLine( "\r\n {0} reads, {1} writes, {2} reader time-outs, {3} writer time-outs.", Test::reads, Test::writes, Test::readerTimeouts, Test::writerTimeouts );
   Console::WriteLine( "Press ENTER to exit." );
   Console::ReadLine();
   return 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;

   const int numThreads = 26;
   static bool running = true;

   // Statistics.
   static int readerTimeouts = 0;
   static int writerTimeouts = 0;
   static int reads = 0;
   static int writes = 0;

   public static void Main()
   {
      // Start a series of threads to randomly read from and
      // write to the shared resource.
      Thread[] t = new Thread[numThreads];
      for (int i = 0; i < numThreads; i++){
         t[i] = new Thread(new ThreadStart(ThreadProc));
         t[i].Name = new String((char)(i + 65), 1);
         t[i].Start();
         if (i > 10)
            Thread.Sleep(300);
      }

      // Tell the threads to shut down and wait until they all finish.
      running = false;
      for (int i = 0; i < numThreads; i++)
         t[i].Join();

      // Display statistics.
      Console.WriteLine("\n{0} reads, {1} writes, {2} reader time-outs, {3} writer time-outs.",
            reads, writes, readerTimeouts, writerTimeouts);
      Console.Write("Press ENTER to exit... ");
      Console.ReadLine();
   }

   static void ThreadProc()
   {
      Random rnd = new Random();

      // Randomly select a way for the thread to read and write from the shared
      // resource.
      while (running) {
         double action = rnd.NextDouble();
         if (action < .8)
            ReadFromResource(10);
         else if (action < .81)
            ReleaseRestore(rnd, 50);
         else if (action < .90)
            UpgradeDowngrade(rnd, 100);
         else
            WriteToResource(rnd, 100);
      }
   }

   // Request and release a reader lock, and handle time-outs.
   static void ReadFromResource(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);
         }
         finally {
            // Ensure that the lock is released.
            rwl.ReleaseReaderLock();
         }
      }
      catch (ApplicationException) {
         // The reader lock request timed out.
         Interlocked.Increment(ref readerTimeouts);
      }
   }

   // Request and release the writer lock, and handle time-outs.
   static void WriteToResource(Random rnd, int timeOut)
   {
      try {
         rwl.AcquireWriterLock(timeOut);
         try {
            // It's safe for this thread to access 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.ReleaseWriterLock();
         }
      }
      catch (ApplicationException) {
         // The writer lock request timed out.
         Interlocked.Increment(ref writerTimeouts);
      }
   }

   // Requests a reader lock, upgrades the reader lock to the writer
   // lock, and downgrades it to a reader lock again.
   static void UpgradeDowngrade(Random rnd, int timeOut)
   {
      try {
         rwl.AcquireReaderLock(timeOut);
         try {
            // It's safe for this thread to read from the shared resource.
            Display("reads resource value " + resource);
            Interlocked.Increment(ref reads);

            // To write to the resource, either release the reader lock and
            // request the writer lock, or upgrade the reader lock. 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's 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);
            }

            // If the lock was downgraded, it's 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);
      }
   }

   // 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);
      }
   }

   // Helper method briefly displays the most recent thread action.
   static void Display(string msg)
   {
      Console.Write("Thread {0} {1}.       \r", Thread.CurrentThread.Name, msg);
   }
}

' 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

   Const numThreads As Integer = 26
   Private running As Boolean = True
   
   ' Statistics.
   Private readerTimeouts As Integer = 0
   Private writerTimeouts As Integer = 0
   Private reads As Integer = 0
   Private writes As Integer = 0
  
   Public Sub Main()
      ' Start a series of threads to randomly read from and
      ' write to the shared resource.
      Dim t(numThreads - 1) As Thread
      Dim i As Integer
      For i = 0 To numThreads - 1
         t(i) = New Thread(New ThreadStart(AddressOf ThreadProc))
         t(i).Name = Chr(i + 65)
         t(i).Start()
         If i > 10 Then
            Thread.Sleep(300)
         End If
      Next

      ' Tell the threads to shut down and wait until they all finish.
      running = False
      For i = 0 To numThreads - 1
         t(i).Join()
      Next
      
      ' Display statistics.
      Console.WriteLine(vbCrLf & "{0} reads, {1} writes, {2} reader time-outs, {3} writer time-outs.",
                        reads, writes, readerTimeouts, writerTimeouts)
      Console.Write("Press ENTER to exit... ")
      Console.ReadLine()
   End Sub

   Sub ThreadProc()
      Dim rnd As New Random

      ' Randomly select a way for the thread to read and write from the shared
      ' resource.
      While running
         Dim action As Double = rnd.NextDouble()
         If action < 0.8 Then
            ReadFromResource(10)
         ElseIf action < 0.81 Then
            ReleaseRestore(rnd, 50)
         ElseIf action < 0.9 Then
            UpgradeDowngrade(rnd, 100)
         Else
            WriteToResource(rnd, 100)
         End If
      End While
   End Sub
    
   ' Request and release a reader lock, and handle time-outs.
   Sub ReadFromResource(timeOut As Integer)
      Try
         rwl.AcquireReaderLock(timeOut)
         Try
            ' It's safe for this thread to read from the shared 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

   ' Request and release the writer lock, and handle time-outs.
   Sub WriteToResource(rnd As Random, timeOut As Integer)
      Try
         rwl.AcquireWriterLock(timeOut)
         Try
            ' It's 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.ReleaseWriterLock()
         End Try
      Catch ex As ApplicationException
         ' The writer lock request timed out.
         Interlocked.Increment(writerTimeouts)
      End Try
   End Sub

   ' Requests a reader lock, upgrades the reader lock to the writer
   ' lock, and downgrades it to a reader lock again.
   Sub UpgradeDowngrade(rnd As Random, timeOut As Integer)
      Try
         rwl.AcquireReaderLock(timeOut)
         Try
            ' It's safe for this thread to read from the shared resource.
            Display("reads resource value " & resource)
            Interlocked.Increment(reads)
            
            ' To write to the resource, either release the reader lock and
            ' request the writer lock, or upgrade the reader lock. 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's 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
            
            ' If the lock was downgraded, it's 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

   ' 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

   ' Helper method briefly displays the most recent thread action.
   Sub Display(msg As String)
      Console.Write("Thread {0} {1}.       " & vbCr, Thread.CurrentThread.Name, msg)
   End Sub
End Module

注釈

ReaderWriterLock は、リソースへのアクセスを同期するために使用されます。 任意の時点で、複数のスレッドに対する同時読み取りアクセスまたは単一スレッドの書き込みアクセスを許可します。 リソースが頻繁に変更されない状況では、 ReaderWriterLock のように Monitor、単純な一度に 1 回限りのロックよりもスループットが向上します。

ReaderWriterLock は、ほとんどのアクセスが読み取りであるのに対し、書き込みの頻度が低く、期間が短い場合に最適です。 複数のリーダーは単一のライターと交互に使用されるため、リーダーもライターも長期間ブロックされません。

スレッドはリーダー ロックまたはライター ロックを保持できますが、両方を同時に保持することはできません。 ライター ロックを取得するためにリーダー ロックを解放する代わりに、 と DowngradeFromWriterLockを使用UpgradeToWriterLockできます。

再帰的なロック要求は、ロックのロック数を増やします。

リーダーとライターは個別にキューに入れられます。 スレッドがライター ロックを解放すると、その時点でリーダー キューで待機しているすべてのスレッドにリーダー ロックが付与されます。これらのすべてのリーダー ロックが解放されると、ライター キューで待機している次のスレッド (存在する場合) にライター ロックが付与されます。 つまり、 ReaderWriterLock はリーダーのコレクションと 1 つのライターの間で交互に行われます。

ライター キュー内のスレッドがアクティブなリーダー ロックの解放を待機している間に、新しいリーダー ロックを要求するスレッドがリーダー キューに蓄積されます。 既存のリーダー ロック 所有者と同時アクセスを共有できる場合でも、要求は許可されません。これは、読者による無期限の封じ込めからライターを保護するのに役立ちます。

タイムアウト値を受け入れるロックを ReaderWriterLock 取得するためのほとんどの方法。 タイムアウトを使用して、アプリケーションのデッドロックを回避します。 たとえば、スレッドが 1 つのリソースに対してライター ロックを取得し、2 つ目のリソースに対してリーダー ロックを要求する場合があります。その間、別のスレッドが 2 番目のリソースのライター ロックを取得し、最初のリソースに対してリーダー ロックを要求する可能性があります。 タイムアウトが使用されていない限り、スレッドはデッドロックします。

タイムアウト間隔が切れ、ロック要求が許可されていない場合、 メソッドは をスローして呼び出し元のスレッドに制御を ApplicationException返します。 スレッドは、この例外をキャッチし、次に実行するアクションを決定できます。

タイムアウトはミリ秒単位で表されます。 を System.TimeSpan 使用してタイムアウトを指定する場合、使用される値は、 で TimeSpan表されるミリ秒単位の合計数です。 次の表は、有効なタイムアウト値をミリ秒単位で示しています。

-1 を除き、負のタイムアウト値は使用できません。 -1 以外の負の整数を指定すると、代わりにタイムアウト値 0 が使用されます。 (つまり、ロックをすぐに取得できない場合、メソッドは待機せずに を返します)。-1 以外の負のミリ秒数を表す を指定 TimeSpan すると、 ArgumentOutOfRangeException がスローされます。

コンストラクター

プロパティ

メソッド

適用対象

スレッド セーフ

この型はスレッド セーフです。

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• マネージド スレッド処理
• ReaderWriterLock