• Article

Monitor.Wait Method (Object)

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

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

Syntax

'Declaration
Public Shared Function Wait ( _
    obj As Object _
) As Boolean

public static bool Wait(
    Object obj
)

Parameters

Return Value

Type: System.Boolean
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.

Exceptions

Exception Condition
ArgumentNullException

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

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

Remarks

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.

Version Notes

Silverlight for Windows Phone Silverlight for Windows Phone

When a user navigates away from a Windows Phone application, the application is typically put into a dormant state. When the user returns to a dormant application, the application automatically resumes. If the application is put into a dormant state while this API is being used, the API will not complete as expected. Applications should be designed to handle this possibility. For more information about the Windows Phone execution model, see Execution Model for Windows Phone.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.