Monitor.TryEnter Method (Object, Int32, Boolean)
Attempts, for the specified number of milliseconds, to acquire an exclusive lock on the specified object, and atomically sets a value that indicates whether the lock was taken.
Assembly: mscorlib (in mscorlib.dll)
Public Shared Sub TryEnter ( obj As Object, millisecondsTimeout As Integer, ByRef lockTaken As Boolean )
The object on which to acquire the lock.
The number of milliseconds to wait for the lock.
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.
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.
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 As Integer = 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
The following code shows the basic pattern for using the TryEnter(Object, Boolean) method overload. This overload always sets the value of the variable that is passed to the ref parameter (ByRef in Visual Basic) lockTaken, even if the method throws an exception, so the value of the variable is a reliable way to test whether the lock has to be released.
Dim acquiredLock As Boolean = False Try Monitor.TryEnter(lockObject, 500, acquiredLock) If acquiredLock Then ' Code that accesses resources that are protected by the lock. Else ' Code to deal with the fact that the lock was not acquired. End If Finally If acquiredLock Then Monitor.Exit(lockObject) End If End Try
Available since 8
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Available since 4.0
Windows Phone Silverlight
Available since 7.1
Available since 8.1