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ReaderWriterLock.AcquireWriterLock Method (Int32)

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

Namespace:  System.Threading
Assembly:  mscorlib (in mscorlib.dll)

public void AcquireWriterLock(
	int millisecondsTimeout


Type: System.Int32

The time-out in milliseconds.


timeout expires before the lock request is granted.

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 noteCaution

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.

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 System;
using System.Threading;

public class Test
    // Declaring the ReaderWriterLock at the class level 
    // makes it visible to all threads. 
    static ReaderWriterLock rwl = new ReaderWriterLock();
    // For this example, the shared resource protected by the 
    // ReaderWriterLock is just an integer. 
    static int resource = 0;


// Shows how to request and release the writer lock, and 
// how to handle time-outs. 
static void WriteToResource(int timeOut)
            // It is safe for this thread to read or write 
            // from the shared resource.
            resource = rnd.Next(500);
            Display("writes resource value " + resource);
            Interlocked.Increment(ref writes);
            // Ensure that the lock is released.
    catch (ApplicationException)
        // The writer lock request timed out.
        Interlocked.Increment(ref writerTimeouts);



.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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