Monitor.TryEnter Method (Object, TimeSpan, Boolean)

 

Attempts, for the specified amount of time, to acquire an exclusive lock on the specified object, and atomically sets a value that indicates whether the lock was taken.

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

Public Shared Sub TryEnter (
	obj As Object,
	timeout As TimeSpan,
	ByRef lockTaken As Boolean
)

Parameters

obj
Type: System.Object

The object on which to acquire the lock.

timeout
Type: System.TimeSpan

The amount of time to wait for the lock. A value of –1 millisecond specifies an infinite wait.

lockTaken
Type: System.Boolean

The result of the attempt to acquire the lock, passed by reference. The input must be false. The output is true if the lock is acquired; otherwise, the output is false. The output is set even if an exception occurs during the attempt to acquire the lock.

Exception Condition
ArgumentException

The input to lockTaken is true.

ArgumentNullException

The obj parameter is null.

ArgumentOutOfRangeException

The value of timeout in milliseconds is negative and is not equal to Infinite (–1 millisecond), or is greater than MaxValue.

If the value of the timeout parameter converted to milliseconds equals –1, this method is equivalent to Enter(Object). If the value of timeout equals 0, this method is equivalent to TryEnter(Object).

If the lock was not taken because an exception was thrown, the variable specified for the lockTaken parameter is false after this method ends. This allows the program to determine, in all cases, whether it is necessary to release the lock.

System_CAPS_noteNote

Use Monitor to lock objects (that is, reference types), not value types. For more information, see the Monitor class topic.

To ensure that the thread does not enter the critical section, you should examine the value of lockTaken and execute code in the critical section only if its value is true. The following code fragment shows the pattern used to call this method. Note that you should call Exit in a finally block to ensure that the calling thread releases its lock on the critical section if an exception occurs.

Dim lockObj As New Object()
Dim timeout = TimeSpan.FromMilliseconds(500)
Dim lockTaken As Boolean = False

Try
   Monitor.TryEnter(lockObj, timeout, lockTaken)
   If lockTaken Then
      ' The critical section.
   Else
      ' The lock was not acquired.
   End If
Finally
   ' Ensure that the lock is released.
   If lockTaken Then Monitor.Exit(lockObj)
End Try

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
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