ReaderWriterLockSlim.TryEnterUpgradeableReadLock Method (Int32)


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

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

public bool TryEnterUpgradeableReadLock(
	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 upgradeable 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 upgradeable 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.

Use upgradeable mode when a thread usually accesses the resource that is protected by the ReaderWriterLockSlim in read mode, but may need to enter write mode if certain conditions are met. A thread in upgradeable mode can upgrade to write mode or downgrade to read mode.

Only one thread can enter a lock in upgradeable mode at any given time. If a thread is in upgradeable mode, and there are no threads waiting to enter write mode, any number of other threads can enter read mode, even if there are threads waiting to enter upgradeable mode.

If one or more threads are waiting to enter write mode, a thread that calls the TryEnterUpgradeableReadLock method blocks until those threads have either timed out or entered write mode and then exited from it, or until the calling thread's own time-out interval expires.


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

Universal Windows Platform
Available since 8
.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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