TryEnterWriteLock Method (Int32)
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ReaderWriterLockSlim.TryEnterWriteLock Method (Int32)


Tries to enter the lock in write mode, with an optional time-out.

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

public bool TryEnterWriteLock(
	int millisecondsTimeout


Type: System.Int32

The number of milliseconds to wait, or -1 (Timeout.Infinite) to wait indefinitely.

Return Value

Type: System.Boolean

true if the calling thread entered write mode, otherwise, false.

Exception Condition

The RecursionPolicy property is LockRecursionPolicy.NoRecursion and the current thread has already entered the lock.


The current thread initially entered the lock in read mode, and therefore trying to enter write mode would create the possibility of a deadlock.


The recursion number would exceed the capacity of the counter. The limit is so large that applications should never encounter it.


The value of millisecondsTimeout is negative, but it is not equal to Timeout.Infinite (-1), which is the only negative value allowed.


The ReaderWriterLockSlim object has been disposed.

If millisecondsTimeout is 0 (zero), this method checks the lock state and returns false immediately if the desired state is unavailable.

If other threads have entered the lock in read mode, a thread that calls the TryEnterWriteLock method blocks until those threads have exited read mode or until the time-out interval has elapsed. While threads are blocked waiting to enter write mode, additional threads that try to enter read mode or upgradeable mode block until all the threads waiting to enter write mode have either timed out or entered write mode and then exited from it.


If a lock allows recursion, a thread that has entered the lock in write mode can enter write mode recursively, even if other threads are waiting to enter write mode.

The following example shows how to use the TryEnterWriteLock method to enter the lock in write mode, with a time-out. The method shown in the example adds a new key/value pair to the synchronized cache. If the specified time-out interval elapses before the thread enters the lock, the method returns false. The method returns true if the key/value pair is added.

If the key is already in the cache, the exception thrown by the inner Dictionary<TKey, TValue> is allowed to terminate the method. A finally block is used to execute the ExitWriteLock method, ensuring that the caller exits the lock.

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

private ReaderWriterLockSlim cacheLock = new ReaderWriterLockSlim();
private Dictionary<int, string> innerCache = new Dictionary<int, string>();
public bool AddWithTimeout(int key, string value, int timeout)
    if (cacheLock.TryEnterWriteLock(timeout))
            innerCache.Add(key, value);
        return true;
        return false;

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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