ReaderWriterLock ReaderWriterLock ReaderWriterLock ReaderWriterLock Class

Definição

Define um bloqueio que dá suporte a autores únicos e múltiplos leitores.Defines a lock that supports single writers and multiple readers.

public ref class ReaderWriterLock sealed : System::Runtime::ConstrainedExecution::CriticalFinalizerObject
[System.Runtime.InteropServices.ComVisible(true)]
public sealed class ReaderWriterLock : System.Runtime.ConstrainedExecution.CriticalFinalizerObject
type ReaderWriterLock = class
    inherit CriticalFinalizerObject
Public NotInheritable Class ReaderWriterLock
Inherits CriticalFinalizerObject
Herança
ReaderWriterLockReaderWriterLockReaderWriterLockReaderWriterLock
Atributos

Exemplos

O exemplo a seguir demonstra como usar um ReaderWriterLock para proteger um recurso compartilhado, um valor inteiro chamado resource, que é lido simultaneamente e gravado exclusivamente por vários threads.The following example demonstrates how to use a ReaderWriterLock to protect a shared resource, an integer value named resource, that is read concurrently and written exclusively by multiple threads. Observe que o ReaderWriterLock é declarado no nível de classe para que fique visível para todos os threads.Note that the ReaderWriterLock is declared at the class level so that it is visible to all threads.

// 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;
   static Random^ rnd = gcnew Random;

   // Statistics.
   static int readerTimeouts = 0;
   static int writerTimeouts = 0;
   static int reads = 0;
   static int writes = 0;
   static void ThreadProc()
   {
      
      // 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( 50 );
         else
         if ( action < .90 )
                  UpgradeDowngrade( 100 );
         else
                  WriteToResource( 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( 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( 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( 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;
   static Random rnd = new Random();

   // 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(Convert.ToChar(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()
   {
      // 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(50);
         else if (action < .90)
            UpgradeDowngrade(100);
         else
            WriteToResource(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(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(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(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
   Private rnd As New Random()
   
   ' 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()
      ' 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(50)
         ElseIf action < 0.9 Then
            UpgradeDowngrade(100)
         Else
            WriteToResource(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(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(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(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

Comentários

Importante

O .NET Framework.NET Framework tem dois bloqueios de leitor-gravador, ReaderWriterLockSlim e ReaderWriterLock.The .NET Framework.NET Framework has two reader-writer locks, ReaderWriterLockSlim and ReaderWriterLock. O ReaderWriterLockSlim é recomendado para todos os novos desenvolvimentos.ReaderWriterLockSlim is recommended for all new development. O ReaderWriterLockSlim é semelhante ao ReaderWriterLock, mas tem regras simplificadas para recursão e para atualização e downgrade de estado de bloqueio.ReaderWriterLockSlim is similar to ReaderWriterLock, but it has simplified rules for recursion and for upgrading and downgrading lock state. ReaderWriterLockSlim evita muitos casos potenciais de deadlock.ReaderWriterLockSlim avoids many cases of potential deadlock. Além disso, o desempenho de ReaderWriterLockSlim é significativamente melhor que o de ReaderWriterLock.In addition, the performance of ReaderWriterLockSlim is significantly better than ReaderWriterLock.

ReaderWriterLocké usado para sincronizar o acesso a um recurso.ReaderWriterLock is used to synchronize access to a resource. A qualquer momento, ele permite o acesso de leitura simultâneo para vários threads ou acesso de gravação para um único thread.At any given time, it allows either concurrent read access for multiple threads, or write access for a single thread. Em uma situação em que um recurso é alterado com pouca frequência ReaderWriterLock , um fornece uma taxa de transferência melhor do que um bloqueio simples de um único tempo Monitor, como.In a situation where a resource is changed infrequently, a ReaderWriterLock provides better throughput than a simple one-at-a-time lock, such as Monitor.

ReaderWriterLockfunciona melhor quando a maioria dos acessos são leituras, enquanto as gravações são infrequentes e de duração curta.ReaderWriterLock works best where most accesses are reads, while writes are infrequent and of short duration. Vários leitores alternam com gravadores únicos, para que nem leitores nem gravadores sejam bloqueados por longos períodos.Multiple readers alternate with single writers, so that neither readers nor writers are blocked for long periods.

Observação

A retenção de bloqueios de leitor ou bloqueios de gravador por longos períodos deixará de usar outros threads.Holding reader locks or writer locks for long periods will starve other threads. Para obter o melhor desempenho, considere reestruturar seu aplicativo para minimizar a duração das gravações.For best performance, consider restructuring your application to minimize the duration of writes.

Um thread pode manter um bloqueio de leitor ou um bloqueio de gravador, mas não ambos ao mesmo tempo.A thread can hold a reader lock or a writer lock, but not both at the same time. Em vez de liberar um bloqueio de leitor a fim de adquirir o bloqueio do gravador, UpgradeToWriterLock você DowngradeFromWriterLockpode usar e.Instead of releasing a reader lock in order to acquire the writer lock, you can use UpgradeToWriterLock and DowngradeFromWriterLock.

As solicitações de bloqueio recursivas aumentam a contagem de bloqueios em um bloqueio.Recursive lock requests increase the lock count on a lock.

Leitores e gravadores são colocados em fila separadamente.Readers and writers are queued separately. Quando um thread libera o bloqueio do gravador, todos os threads aguardando na fila do leitor no momento são concedidos bloqueios de leitor; Quando todos os bloqueios de leitor forem liberados, o próximo Thread aguardando na fila de gravador, se houver, receberá o bloqueio do gravador e assim por diante.When a thread releases the writer lock, all threads waiting in the reader queue at that instant are granted reader locks; when all of those reader locks have been released, the next thread waiting in the writer queue, if any, is granted the writer lock, and so on. Em outras palavras, ReaderWriterLock alterna entre uma coleção de leitores e um escritor.In other words, ReaderWriterLock alternates between a collection of readers, and one writer.

Embora um thread na fila de gravador esteja aguardando a liberação de bloqueios de leitor ativos, os threads solicitando novos bloqueios de leitor se acumulam na fila do leitor.While a thread in the writer queue is waiting for active reader locks to be released, threads requesting new reader locks accumulate in the reader queue. Suas solicitações não são concedidas, mesmo que possam compartilhar o acesso simultâneo com os detentores de bloqueio de leitor existentes; Isso ajuda a proteger gravadores contra o bloqueio indefinido pelos leitores.Their requests are not granted, even though they could share concurrent access with existing reader-lock holders; this helps protect writers against indefinite blockage by readers.

A maioria dos métodos para adquirir bloqueios ReaderWriterLock em valores de tempo limite de aceitação.Most methods for acquiring locks on a ReaderWriterLock accept time-out values. Use os tempos limite para evitar deadlocks em seu aplicativo.Use time-outs to avoid deadlocks in your application. Por exemplo, um thread pode adquirir o bloqueio do gravador em um recurso e, em seguida, solicitar um bloqueio de leitor em um segundo recurso; Enquanto isso, outro thread pode adquirir o bloqueio do gravador no segundo recurso e solicitar um bloqueio de leitor no primeiro.For example, a thread might acquire the writer lock on one resource and then request a reader lock on a second resource; in the meantime, another thread might acquire the writer lock on the second resource, and request a reader lock on the first. A menos que os tempos limite sejam usados, os threads são bloqueados.Unless time-outs are used, the threads deadlock.

Se o intervalo de tempo limite expirar e a solicitação de bloqueio não tiver sido concedida, o método retornará o controle para o thread de chamada ApplicationExceptionlançando um.If the time-out interval expires and the lock request has not been granted, the method returns control to the calling thread by throwing an ApplicationException. Um thread pode capturar essa exceção e determinar a ação a ser tomada em seguida.A thread can catch this exception and determine what action to take next.

Os tempos limite são expressos em milissegundos.Time-outs are expressed in milliseconds. Se você usar um System.TimeSpan para especificar o tempo limite, o valor usado será o número total de milissegundos inteiros representados TimeSpanpelo.If you use a System.TimeSpan to specify the time-out, the value used is the total number of whole milliseconds represented by the TimeSpan. A tabela a seguir mostra os valores de tempo limite válidos em milissegundos.The following table shows the valid time-out values in milliseconds.

ValorValue DescriçãoDescription
-1-1 O thread aguarda até que o bloqueio seja adquirido, independentemente do tempo necessário.The thread waits until the lock is acquired, regardless of how long it takes. Para métodos que especificam o tempo limite de inteiros, Infinite a constante pode ser usada.For methods that specify integer time-outs, the constant Infinite can be used.
00 O thread não espera adquirir o bloqueio.The thread does not wait to acquire the lock. Se o bloqueio não puder ser adquirido imediatamente, o método retornará.If the lock cannot be acquired immediately, the method returns.
>0>0 O número de milissegundos a aguardar.The number of milliseconds to wait.

Com a exceção de-1, valores de tempo limite negativos não são permitidos.With the exception of -1, negative time-out values are not allowed. Se você especificar um inteiro negativo diferente de-1, um valor de tempo limite igual a zero será usado em seu lugar.If you specify a negative integer other than -1, a time-out value of zero is used instead. (Ou seja, o método retorna sem espera, se o bloqueio não puder ser adquirido imediatamente.) Se você especificar um TimeSpan que representa um número negativo de milissegundos diferente de-1, ArgumentOutOfRangeException será lançado.(That is, the method returns without waiting, if the lock cannot be acquired immediately.) If you specify a TimeSpan that represents a negative number of milliseconds other than -1, ArgumentOutOfRangeException is thrown.

Construtores

ReaderWriterLock() ReaderWriterLock() ReaderWriterLock() ReaderWriterLock()

Inicializa uma nova instância da classe ReaderWriterLock.Initializes a new instance of the ReaderWriterLock class.

Propriedades

IsReaderLockHeld IsReaderLockHeld IsReaderLockHeld IsReaderLockHeld

Obtém um valor que indica se o thread atual mantém um bloqueio de leitor.Gets a value indicating whether the current thread holds a reader lock.

IsWriterLockHeld IsWriterLockHeld IsWriterLockHeld IsWriterLockHeld

Obtém um valor que indica se o thread atual mantém um bloqueio de gravador.Gets a value indicating whether the current thread holds the writer lock.

WriterSeqNum WriterSeqNum WriterSeqNum WriterSeqNum

Obtém o número de sequência atual.Gets the current sequence number.

Métodos

AcquireReaderLock(Int32) AcquireReaderLock(Int32) AcquireReaderLock(Int32) AcquireReaderLock(Int32)

Adquire um bloqueio de leitor, usando um valor Int32 para o tempo limite.Acquires a reader lock, using an Int32 value for the time-out.

AcquireReaderLock(TimeSpan) AcquireReaderLock(TimeSpan) AcquireReaderLock(TimeSpan) AcquireReaderLock(TimeSpan)

Adquire um bloqueio de leitor, usando um valor TimeSpan para o tempo limite.Acquires a reader lock, using a TimeSpan value for the time-out.

AcquireWriterLock(Int32) AcquireWriterLock(Int32) AcquireWriterLock(Int32) AcquireWriterLock(Int32)

Adquire um bloqueio de gravador, usando um valor Int32 para o tempo limite.Acquires the writer lock, using an Int32 value for the time-out.

AcquireWriterLock(TimeSpan) AcquireWriterLock(TimeSpan) AcquireWriterLock(TimeSpan) AcquireWriterLock(TimeSpan)

Adquire um bloqueio de gravador, usando um valor TimeSpan para o tempo limite.Acquires the writer lock, using a TimeSpan value for the time-out.

AnyWritersSince(Int32) AnyWritersSince(Int32) AnyWritersSince(Int32) AnyWritersSince(Int32)

Indica se o bloqueio de gravador foi concedido a qualquer thread desde que o número de sequência foi obtido.Indicates whether the writer lock has been granted to any thread since the sequence number was obtained.

DowngradeFromWriterLock(LockCookie) DowngradeFromWriterLock(LockCookie) DowngradeFromWriterLock(LockCookie) DowngradeFromWriterLock(LockCookie)

Restaura o status de bloqueio do thread para o status prévio antes de UpgradeToWriterLock(Int32) ser chamado.Restores the lock status of the thread to what it was before UpgradeToWriterLock(Int32) was called.

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Determina se o objeto especificado é igual ao objeto atual.Determines whether the specified object is equal to the current object.

(Inherited from Object)
Finalize() Finalize() Finalize() Finalize()

Garante que os recursos são liberados e outras operações de limpeza são executadas quando o coletor de lixo recupera o objeto ReaderWriterLock.Ensures that resources are freed and other cleanup operations are performed when the garbage collector reclaims the ReaderWriterLock object.

GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Serve como a função de hash padrão.Serves as the default hash function.

(Inherited from Object)
GetType() GetType() GetType() GetType()

Obtém o Type da instância atual.Gets the Type of the current instance.

(Inherited from Object)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Cria uma cópia superficial do Object atual.Creates a shallow copy of the current Object.

(Inherited from Object)
ReleaseLock() ReleaseLock() ReleaseLock() ReleaseLock()

Libera o bloqueio, independentemente do número de vezes que o thread adquiriu o bloqueio.Releases the lock, regardless of the number of times the thread acquired the lock.

ReleaseReaderLock() ReleaseReaderLock() ReleaseReaderLock() ReleaseReaderLock()

Diminui a contagem de bloqueio.Decrements the lock count.

ReleaseWriterLock() ReleaseWriterLock() ReleaseWriterLock() ReleaseWriterLock()

Diminui a contagem de bloqueio no bloqueio de gravador.Decrements the lock count on the writer lock.

RestoreLock(LockCookie) RestoreLock(LockCookie) RestoreLock(LockCookie) RestoreLock(LockCookie)

Restaura o status de bloqueio do thread para o que era antes de chamar ReleaseLock().Restores the lock status of the thread to what it was before calling ReleaseLock().

ToString() ToString() ToString() ToString()

Retorna uma cadeia de caracteres que representa o objeto atual.Returns a string that represents the current object.

(Inherited from Object)
UpgradeToWriterLock(Int32) UpgradeToWriterLock(Int32) UpgradeToWriterLock(Int32) UpgradeToWriterLock(Int32)

Atualiza um bloqueio de leitor para o bloqueio de gravador, usando um valor Int32 para o tempo limite.Upgrades a reader lock to the writer lock, using an Int32 value for the time-out.

UpgradeToWriterLock(TimeSpan) UpgradeToWriterLock(TimeSpan) UpgradeToWriterLock(TimeSpan) UpgradeToWriterLock(TimeSpan)

Faz o upgrade de um bloqueio de leitor para o bloqueio de gravador usando um valor TimeSpan para o tempo limite.Upgrades a reader lock to the writer lock, using a TimeSpan value for the time-out.

Aplica-se a

Acesso thread-safe

Este tipo é thread-safe.This type is thread safe.

Veja também