Export (0) Print
Expand All

ReaderWriterLock.ReleaseLock Method

Releases the lock, regardless of the number of times the thread acquired the lock.

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

'Declaration
Public Function ReleaseLock As LockCookie

Return Value

Type: System.Threading.LockCookie
A LockCookie value representing the released lock.

ReleaseLock releases the reader lock or writer lock, regardless of the recursive lock count. To restore the state of the lock, including the lock count, pass the LockCookie to RestoreLock.

The following code example shows how to use the ReleaseLock method to release the lock, regardless of how many times it has been acquired by the thread, and how to restore the state of the lock later.

This code is part of a larger example provided for the ReaderWriterLock class.


' The complete code is located in the ReaderWriterLock 
' class topic. 
Imports System
Imports System.Threading
Imports Microsoft.VisualBasic

Public Class Test
    ' Declaring the ReaderWriterLock at the class level 
    ' makes it visible to all threads. 
    Private Shared rwl As New ReaderWriterLock()
    ' For this example, the shared resource protected by the 
    ' ReaderWriterLock is just an integer. 
    Private Shared resource As Integer = 0


...


' Shows how to release all locks and later restore 
' the lock state. Shows how to use sequence numbers 
' to determine whether another thread has obtained 
' a writer lock since this thread last accessed the 
' resource. 
Shared Sub ReleaseRestore(timeOut As Integer)
    Dim lastWriter As Integer 

    Try
        rwl.AcquireReaderLock(timeOut)
        Try 
            ' It is safe for this thread to read from 
            ' the shared resource. Cache the value. (You 
            ' might do this if reading the resource is 
            ' an expensive operation.) 
            Dim resourceValue As Integer = resource
            Display("reads resource value " & resourceValue)
            Interlocked.Increment(reads)

            ' Save the current writer sequence number.
            lastWriter = rwl.WriterSeqNum

            ' Release the lock, and save a cookie so the 
            ' lock can be restored later. 
            Dim lc As LockCookie = rwl.ReleaseLock()

            ' Wait for a random interval (up to a  
            ' quarter of a second), and then restore 
            ' the previous state of the lock. Note that 
            ' there is no time-out on the Restore method.
            Thread.Sleep(rnd.Next(250))
            rwl.RestoreLock(lc)

            ' Check whether other threads obtained the 
            ' writer lock in the interval. If not, then 
            ' the cached value of the resource is still 
            ' valid. 
            If rwl.AnyWritersSince(lastWriter) Then
                resourceValue = resource
                Interlocked.Increment(reads)
                Display("resource has changed " & resourceValue)
            Else
                Display("resource has not changed " & resourceValue)
            End If 
        Finally 
            ' Ensure that the lock is released.
            rwl.ReleaseReaderLock()
        End Try 
    Catch ex As ApplicationException
        ' The reader lock request timed out.
        Interlocked.Increment(readerTimeouts)
    End Try 
End Sub 'ReleaseRestore


...


End Class 'Test 

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Show:
© 2014 Microsoft