WaitHandle.WaitOne Method (Int32, Boolean)


Blocks the current thread until the current WaitHandle receives a signal, using a 32-bit signed integer to specify the time interval and specifying whether to exit the synchronization domain before the wait.

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

Public Overridable Function WaitOne (
	millisecondsTimeout As Integer,
	exitContext As Boolean
) As Boolean


Type: System.Int32

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

Type: System.Boolean

true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it afterward; otherwise, false.

Return Value

Type: System.Boolean

true if the current instance receives a signal; otherwise, false.

Exception Condition

The current instance has already been disposed.


millisecondsTimeout is a negative number other than -1, which represents an infinite time-out.


The wait completed because a thread exited without releasing a mutex. This exception is not thrown on Windows 98 or Windows Millennium Edition.


The current instance is a transparent proxy for a WaitHandle in another application domain.

If millisecondsTimeout is zero, the method does not block. It tests the state of the wait handle and returns immediately.

AbandonedMutexException is new in the .NET Framework version 2.0. In previous versions, the WaitOne method returns true when a mutex is abandoned. An abandoned mutex often indicates a serious coding error. In the case of a system-wide mutex, it might indicate that an application has been terminated abruptly (for example, by using Windows Task Manager). The exception contains information useful for debugging.

The caller of this method blocks until the current instance receives a signal or a time-out occurs. Use this method to block until a WaitHandle receives a signal from another thread, such as is generated when an asynchronous operation completes. For more information, see the IAsyncResult interface.

Override this method to customize the behavior of derived classes.

The exitContext parameter has no effect unless the WaitOne method is called from inside a nondefault managed context. This can happen if your thread is inside a call to an instance of a class derived from ContextBoundObject. Even if you are currently executing a method on a class that does not derive from ContextBoundObject, like String, you can be in a nondefault context if a ContextBoundObject is on your stack in the current application domain.

When your code is executing in a nondefault context, specifying true for exitContext causes the thread to exit the nondefault managed context (that is, to transition to the default context) before executing the WaitOne method. The thread returns to the original nondefault context after the call to the WaitOne method completes.

This can be useful when the context-bound class has SynchronizationAttribute. In that case, all calls to members of the class are automatically synchronized, and the synchronization domain is the entire body of code for the class. If code in the call stack of a member calls the WaitOne method and specifies true for exitContext, the thread exits the synchronization domain, allowing a thread that is blocked on a call to any member of the object to proceed. When the WaitOne method returns, the thread that made the call must wait to reenter the synchronization domain.

The following example shows how the WaitOne(Int32, Boolean) method overload behaves when it is called within a synchronization domain. First, a thread waits with exitContext set to false and blocks until the wait timeout expires. A second thread executes after the first thread terminates and waits with exitContext set to true. The call to signal the wait handle for this second thread is not blocked, and the thread completes before the wait timeout.

Imports System
Imports System.Threading
Imports System.Runtime.Remoting.Contexts

Public Class SyncingClass
    Inherits ContextBoundObject

    Private waitHandle As EventWaitHandle

    Public Sub New()
         waitHandle = New EventWaitHandle(false, EventResetMode.ManualReset)
    End Sub

    Public Sub Signal()
        Console.WriteLine("Thread[{0:d4}]: Signalling...", Thread.CurrentThread.GetHashCode())
    End Sub

    Public Sub DoWait(leaveContext As Boolean)
        Dim signalled As Boolean

        Console.WriteLine("Thread[{0:d4}]: Waiting...", Thread.CurrentThread.GetHashCode())
        signalled = waitHandle.WaitOne(3000, leaveContext)
        If signalled Then
            Console.WriteLine("Thread[{0:d4}]: Wait released!!!", Thread.CurrentThread.GetHashCode())
            Console.WriteLine("Thread[{0:d4}]: Wait timeout!!!", Thread.CurrentThread.GetHashCode())
        End If
    End Sub
End Class

Public Class TestSyncDomainWait
    Public Shared Sub Main()
        Dim syncClass As New SyncingClass()

        Dim runWaiter As Thread

        Console.WriteLine(vbNewLine + "Wait and signal INSIDE synchronization domain:" + vbNewLine)
        runWaiter = New Thread(AddressOf RunWaitKeepContext)
        Console.WriteLine("Thread[{0:d4}]: Signal...", Thread.CurrentThread.GetHashCode())
        ' This call to Signal will block until the timeout in DoWait expires.

        Console.WriteLine(vbNewLine + "Wait and signal OUTSIDE synchronization domain:" + vbNewLine)
        runWaiter = New Thread(AddressOf RunWaitLeaveContext)
        Console.WriteLine("Thread[{0:d4}]: Signal...", Thread.CurrentThread.GetHashCode())
        ' This call to Signal is unblocked and will set the wait handle to
        ' release the waiting thread.
    End Sub

    Public Shared Sub RunWaitKeepContext(parm As Object)
        Dim syncClass As SyncingClass = CType(parm, SyncingClass)
    End Sub

    Public Shared Sub RunWaitLeaveContext(parm As Object)
        Dim syncClass As SyncingClass = CType(parm, SyncingClass)
    End Sub
End Class

' The output for the example program will be similar to the following:
' Wait and signal INSIDE synchronization domain:
' Thread[0004]: Waiting...
' Thread[0001]: Signal...
' Thread[0004]: Wait timeout!!!
' Thread[0001]: Signalling...
' Wait and signal OUTSIDE synchronization domain:
' Thread[0006]: Waiting...
' Thread[0001]: Signal...
' Thread[0001]: Signalling...
' Thread[0006]: Wait released!!!

.NET Framework
Available since 1.1
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