ReaderWriterLock.AcquireWriterLock Method

Definition

Namespace:

System.Threading

Assembly:

System.Threading.dll

Acquires the writer lock.

Overloads

AcquireWriterLock(Int32)	Acquires the writer lock, using an Int32 value for the time-out.
AcquireWriterLock(TimeSpan)	Acquires the writer lock, using a TimeSpan value for the time-out.

AcquireWriterLock(Int32)

Source:

ReaderWriterLock.cs

Acquires the writer lock, using an Int32 value for the time-out.

public:
 void AcquireWriterLock(int millisecondsTimeout);

public void AcquireWriterLock (int millisecondsTimeout);

member this.AcquireWriterLock : int -> unit

Public Sub AcquireWriterLock (millisecondsTimeout As Integer)

Parameters

millisecondsTimeout

Int32

The time-out in milliseconds.

Exceptions

ApplicationException

timeout expires before the lock request is granted.

Examples

The following code example shows how to acquire and release a writer lock, and how to handle the exception thrown when a request times out.

This code is part of a larger example provided for the ReaderWriterLock class.

// 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;

// 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;

' 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

// 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 );
   }

}

// 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);
   }
}

' 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

};

}

End Module

Remarks

This method blocks if another thread has a reader lock or writer lock. For a description of the way the writer lock alternates with multiple concurrent reader locks, see the ReaderWriterLock class.

A thread that already has a reader lock can acquire the writer lock in one of two ways: by releasing the reader lock before calling AcquireWriterLock, or by calling UpgradeToWriterLock.

Caution

If a thread calls AcquireWriterLock while it still has a reader lock, it will block on its own reader lock; if an infinite time-out is specified, the thread will deadlock. To avoid such deadlocks, use IsReaderLockHeld to determine whether the current thread already has a reader lock.

AcquireWriterLock supports recursive writer-lock requests. That is, a thread can call AcquireWriterLock multiple times, which increments the lock count each time. You must call ReleaseWriterLock once for each time you call AcquireWriterLock. Alternatively, you can call ReleaseLock to reduce the lock count to zero immediately.

Recursive lock requests are always granted immediately, without placing the requesting thread in the writer queue.

For valid time-out values, see ReaderWriterLock.

See also

• Managed Threading
• ReaderWriterLock

AcquireWriterLock(TimeSpan)

Source:

ReaderWriterLock.cs

Acquires the writer lock, using a TimeSpan value for the time-out.

public:
 void AcquireWriterLock(TimeSpan timeout);

public void AcquireWriterLock (TimeSpan timeout);

member this.AcquireWriterLock : TimeSpan -> unit

Public Sub AcquireWriterLock (timeout As TimeSpan)

Parameters

timeout

TimeSpan

The TimeSpan specifying the time-out period.

Exceptions

ApplicationException

timeout expires before the lock request is granted.

ArgumentOutOfRangeException

timeout specifies a negative value other than -1 milliseconds.

Remarks

This method blocks if another thread has a reader lock or writer lock. For a description of the way the writer lock alternates with multiple concurrent reader locks, see the ReaderWriterLock class.

A thread that already has a reader lock can acquire the writer lock in one of two ways: by releasing the reader lock before calling AcquireWriterLock, or by calling UpgradeToWriterLock.

Caution

If a thread calls AcquireWriterLock while it still has a reader lock, it will block on its own reader lock; if an infinite time-out is specified, the thread will deadlock. To avoid such deadlocks, use IsReaderLockHeld to determine whether the current thread already has a reader lock.

AcquireWriterLock supports recursive writer-lock requests. That is, a thread can call AcquireWriterLock multiple times, which increments the lock count each time. You must call ReleaseWriterLock once for each time you call AcquireWriterLock. Alternatively, you can call ReleaseLock to reduce the lock count to zero immediately.

Recursive lock requests are always granted immediately, without placing the requesting thread in the writer queue.

For valid time-out values, see ReaderWriterLock.

See also

• Managed Threading
• ReaderWriterLock