ReaderWriterLock Klasse

Definition

Definiert eine Sperre, die einen Writer und mehrere Reader unterstützt.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
Vererbung
ReaderWriterLock
Attribute

Beispiele

Im folgenden Beispiel wird veranschaulicht, wie ein ReaderWriterLock verwendet wird, um eine freigegebene Ressource, einen ganzzahligen Wert mit dem Namen resourcezu schützen, der gleichzeitig gelesen und exklusiv von mehreren Threads geschrieben wird.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. Beachten Sie, dass die ReaderWriterLock auf Klassenebene deklariert ist, sodass Sie für alle Threads sichtbar ist.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

Hinweise

Wichtig

.NET Framework.NET Framework verfügt über zwei Lese-/Schreibsperren, ReaderWriterLockSlim und ReaderWriterLock.The .NET Framework.NET Framework has two reader-writer locks, ReaderWriterLockSlim and ReaderWriterLock. ReaderWriterLockSlim wird für alle Neuentwicklungen empfohlen.ReaderWriterLockSlim is recommended for all new development. ReaderWriterLockSlim ähnelt ReaderWriterLock, verfügt aber über vereinfachte Regeln für Rekursion sowie für Upgrade und Downgrade des Sperrstatus.ReaderWriterLockSlim is similar to ReaderWriterLock, but it has simplified rules for recursion and for upgrading and downgrading lock state. ReaderWriterLockSlim vermeidet viele potenzielle Deadlocks.ReaderWriterLockSlim avoids many cases of potential deadlock. Darüber hinaus ist die Leistung von ReaderWriterLockSlim wesentlich besser als die von ReaderWriterLock.In addition, the performance of ReaderWriterLockSlim is significantly better than ReaderWriterLock.

ReaderWriterLock wird zum Synchronisieren des Zugriffs auf eine Ressource verwendet.ReaderWriterLock is used to synchronize access to a resource. Es ermöglicht zu einem beliebigen Zeitpunkt entweder gleichzeitigen Lesezugriff auf mehrere Threads oder Schreibzugriff für einen einzelnen Thread.At any given time, it allows either concurrent read access for multiple threads, or write access for a single thread. In einer Situation, in der eine Ressource nur selten geändert wird, bietet eine ReaderWriterLock einen besseren Durchsatz als eine einfache einmalige Sperre, z. b. Monitor.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.

ReaderWriterLock funktioniert am besten, wenn die meisten Zugriffe Lesevorgänge sind, während Schreibvorgänge selten und kurze Zeit dauern.ReaderWriterLock works best where most accesses are reads, while writes are infrequent and of short duration. Mehrere Leser wechseln mit einzelnen Writern, sodass weder Leser noch Writer für lange Zeiträume blockiert werden.Multiple readers alternate with single writers, so that neither readers nor writers are blocked for long periods.

Hinweis

Wenn Sie Lese-und Schreib Sperren für lange Zeiträume halten, werden andere Threads nicht mehr verwendet.Holding reader locks or writer locks for long periods will starve other threads. Um eine optimale Leistung zu erzielen, sollten Sie eine Umstrukturierung ihrer Anwendung in Erwägung gezogen habenFor best performance, consider restructuring your application to minimize the duration of writes.

Ein Thread kann eine Lesesperre oder eine Writer-Sperre enthalten, jedoch nicht beides gleichzeitig.A thread can hold a reader lock or a writer lock, but not both at the same time. Anstatt eine Lesesperre freizugeben, um die Writer-Sperre zu erhalten, können Sie UpgradeToWriterLock und DowngradeFromWriterLockverwenden.Instead of releasing a reader lock in order to acquire the writer lock, you can use UpgradeToWriterLock and DowngradeFromWriterLock.

Rekursive Sperr Anforderungen erhöhen die Sperrenanzahl für eine Sperre.Recursive lock requests increase the lock count on a lock.

Reader und Writer werden separat in die Warteschlange eingereiht.Readers and writers are queued separately. Wenn ein Thread die Schreibsperre freigibt, erhalten alle Threads, die zu diesem Zeitpunkt in der Leser Warteschlange warten, Lese sperren. Wenn alle diese Leser Sperren freigegeben wurden, erhält der nächste Thread, der in der Writer-Warteschlange wartet, ggf. die Schreibsperre, usw.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. Mit anderen Worten: ReaderWriterLock wechselt zwischen einer Auflistung von Lesern und einem Writer.In other words, ReaderWriterLock alternates between a collection of readers, and one writer.

Während ein Thread in der Writer-Warteschlange darauf wartet, dass aktive Lese Sperren freigegeben werden, werden Threads, die neue Leser Sperren anfordern, in der Leser Warteschlange gesammelt.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. Ihre Anforderungen werden nicht erteilt, auch wenn Sie gleichzeitigen Zugriff auf vorhandene Reader-Lock-Inhaber haben können. Dies trägt dazu bei, Writer vor unbegrenzter Blockierung hin durch Leser zu schützen.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.

Die meisten Methoden zum Abrufen von Sperren für eine ReaderWriterLock die Timeout Werte akzeptieren.Most methods for acquiring locks on a ReaderWriterLock accept time-out values. Verwenden Sie Timeouts, um Deadlocks in der Anwendung zu vermeiden.Use time-outs to avoid deadlocks in your application. Ein Thread kann z. b. die Schreibsperre für eine Ressource abrufen und dann eine Lesesperre für eine zweite Ressource anfordern. in der Zwischenzeit kann ein anderer Thread die Schreibsperre für die zweite Ressource abrufen und eine Lesesperre für die erste anfordern.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. Wenn Timeouts nicht verwendet werden, Deadlock der Threads.Unless time-outs are used, the threads deadlock.

Wenn das Timeout Intervall abläuft und die Sperranforderung nicht erteilt wurde, gibt die Methode die Steuerung an den aufrufenden Thread zurück, indem eine ApplicationExceptionausgelöst wird.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. Ein Thread kann diese Ausnahme abfangen und ermitteln, welche Aktion als nächstes ausgeführt werden soll.A thread can catch this exception and determine what action to take next.

Timeouts werden in Millisekunden angegeben.Time-outs are expressed in milliseconds. Wenn Sie ein System.TimeSpan verwenden, um das Timeout anzugeben, entspricht der verwendete Wert der Gesamtzahl ganzer Millisekunden, die durch die TimeSpandargestellt wird.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. In der folgenden Tabelle werden die gültigen Timeout Werte in Millisekunden angezeigt.The following table shows the valid time-out values in milliseconds.

WertValue BeschreibungDescription
-1-1 Der Thread wartet, bis die Sperre abgerufen wird, unabhängig davon, wie lange es dauert.The thread waits until the lock is acquired, regardless of how long it takes. Bei Methoden, die ganzzahlige Timeouts angeben, kann die Konstante Infinite verwendet werden.For methods that specify integer time-outs, the constant Infinite can be used.
00 Der Thread wartet nicht darauf, die Sperre abzurufen.The thread does not wait to acquire the lock. Wenn die Sperre nicht sofort abgerufen werden kann, gibt die Methode zurück.If the lock cannot be acquired immediately, the method returns.
>0>0 Die Anzahl der Millisekunden, die gewartet werden soll.The number of milliseconds to wait.

Mit der Ausnahme-1 sind keine negativen Timeout Werte zulässig.With the exception of -1, negative time-out values are not allowed. Wenn Sie eine negative ganze Zahl ungleich-1 angeben, wird stattdessen ein Timeout Wert von 0 (null) verwendet.If you specify a negative integer other than -1, a time-out value of zero is used instead. (Das heißt, die Methode gibt zurück, ohne zu warten, wenn die Sperre nicht sofort abgerufen werden kann.) Wenn Sie eine TimeSpan angeben, die eine negative Anzahl von Millisekunden darstellt, die nicht-1 ist, wird ArgumentOutOfRangeException ausgelöst.(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.

Konstruktoren

ReaderWriterLock()

Initialisiert eine neue Instanz der ReaderWriterLock-Klasse.Initializes a new instance of the ReaderWriterLock class.

Eigenschaften

IsReaderLockHeld

Ruft einen Wert ab, der angibt, ob der aktuelle Thread eine Lesesperre besitzt.Gets a value indicating whether the current thread holds a reader lock.

IsWriterLockHeld

Ruft einen Wert ab, der angibt, ob der aktuelle Thread die Schreibsperre enthält.Gets a value indicating whether the current thread holds the writer lock.

WriterSeqNum

Ruft die aktuelle Sequenznummer ab.Gets the current sequence number.

Methoden

AcquireReaderLock(Int32)

Erhält eine Lesesperre unter Verwendung eines Int32-Werts für das Timeout.Acquires a reader lock, using an Int32 value for the time-out.

AcquireReaderLock(TimeSpan)

Erhält eine Lesesperre unter Verwendung eines TimeSpan-Werts für das Timeout.Acquires a reader lock, using a TimeSpan value for the time-out.

AcquireWriterLock(Int32)

Erhält die Schreibsperre unter Verwendung eines Int32-Werts für das Timeout.Acquires the writer lock, using an Int32 value for the time-out.

AcquireWriterLock(TimeSpan)

Erhält die Schreibsperre unter Verwendung eines TimeSpan-Werts für das Timeout.Acquires the writer lock, using a TimeSpan value for the time-out.

AnyWritersSince(Int32)

Gibt an, ob einem Thread die Schreibsperre erteilt wurde, seitdem die Sequenznummer erhalten wurde.Indicates whether the writer lock has been granted to any thread since the sequence number was obtained.

DowngradeFromWriterLock(LockCookie)

Stellt den Sperrstatus des Threads mit dem Status vor dem Aufruf von UpgradeToWriterLock(Int32) wieder her.Restores the lock status of the thread to what it was before UpgradeToWriterLock(Int32) was called.

Equals(Object)

Ermittelt, ob das angegebene Objekt und das aktuelle Objekt gleich sind.Determines whether the specified object is equal to the current object.

(Geerbt von Object)
Finalize()

Stellt das Freigeben von Ressourcen und das Ausführen anderer Garbage Collector-Vorgänge sicher, wenn der Garbage Collector das ReaderWriterLock-Objekt verarbeitet.Ensures that resources are freed and other cleanup operations are performed when the garbage collector reclaims the ReaderWriterLock object.

GetHashCode()

Dient als die Standard-HashfunktionServes as the default hash function.

(Geerbt von Object)
GetType()

Ruft den Type der aktuellen Instanz ab.Gets the Type of the current instance.

(Geerbt von Object)
MemberwiseClone()

Erstellt eine flache Kopie des aktuellen Object.Creates a shallow copy of the current Object.

(Geerbt von Object)
ReleaseLock()

Hebt die Sperre unabhängig davon auf, wie oft dem Thread die Sperre zugewiesen wurde.Releases the lock, regardless of the number of times the thread acquired the lock.

ReleaseReaderLock()

Verringert die Sperrenanzahl.Decrements the lock count.

ReleaseWriterLock()

Verringert die Sperrenanzahl für die Schreibsperre.Decrements the lock count on the writer lock.

RestoreLock(LockCookie)

Stellt den Sperrstatus des Threads mit dem Status vor dem Aufruf von ReleaseLock() wieder her.Restores the lock status of the thread to what it was before calling ReleaseLock().

ToString()

Gibt eine Zeichenfolge zurück, die das aktuelle Objekt darstellt.Returns a string that represents the current object.

(Geerbt von Object)
UpgradeToWriterLock(Int32)

Wandelt eine Lesesperre unter Verwendung eines Int32-Werts für das Timeout in eine Schreibsperre um.Upgrades a reader lock to the writer lock, using an Int32 value for the time-out.

UpgradeToWriterLock(TimeSpan)

Wandelt eine Lesesperre unter Verwendung eines TimeSpan-Werts für das Timeout in eine Schreibsperre um.Upgrades a reader lock to the writer lock, using a TimeSpan value for the time-out.

Gilt für:

Threadsicherheit

Dieser Typ ist threadsicher.This type is thread safe.

Siehe auch