Monitor.Wait Method (Object)

Releases the lock on an object and blocks the current thread until it reacquires the lock.

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

public static bool Wait (
	Object obj
public static boolean Wait (
	Object obj
public static function Wait (
	obj : Object
) : boolean



The object on which to wait.

Return Value

true if the call returned because the caller reacquired the lock for the specified object. This method does not return if the lock is not reacquired.

Exception typeCondition


The obj parameter is a null reference (Nothing in Visual Basic).


The calling thread does not own the lock for the specified object.


The thread that invokes Wait is later interrupted from the waiting state. This happens when another thread calls this thread's Interrupt method.

The thread that currently owns the lock on the specified object invokes this method in order to release the object so that another thread can access it. The caller is blocked while waiting to reacquire the lock. This method is called when the caller needs to wait for a state change that will occur as a result of another thread's operations.

When a thread calls Wait, it releases the lock on the object and enters the object's waiting queue. The next thread in the object's ready queue (if there is one) acquires the lock and has exclusive use of the object. All threads that call Wait remain in the waiting queue until they receive a signal from Pulse or PulseAll, sent by the owner of the lock. If Pulse is sent, only the thread at the head of the waiting queue is affected. If PulseAll is sent, all threads that are waiting for the object are affected. When the signal is received, one or more threads leave the waiting queue and enter the ready queue. A thread in the ready queue is permitted to reacquire the lock.

This method returns when the calling thread reacquires the lock on the object. Note that this method blocks indefinitely if the holder of the lock does not call Pulse or PulseAll.

The caller executes Wait once, regardless of the number of times Enter has been invoked for the specified object. Conceptually, the Wait method stores the number of times the caller invoked Enter on the object and invokes Exit as many times as necessary to fully release the locked object. The caller then blocks while waiting to reacquire the object. When the caller reacquires the lock, the system calls Enter as many times as necessary to restore the saved Enter count for the caller. Calling Wait releases the lock for the specified object only; if the caller is the owner of locks on other objects, these locks are not released.

Note that a synchronized object holds several references, including a reference to the thread that currently holds the lock, a reference to the ready queue, which contains the threads that are ready to obtain the lock, and a reference to the waiting queue, which contains the threads that are waiting for notification of a change in the object's state.

The Pulse, PulseAll, and Wait methods must be invoked from within a synchronized block of code.

The remarks for the Pulse method explain what happens if Pulse is called when no threads are waiting.

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

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