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LockCookie Structure

Defines the lock that implements single-writer/multiple-reader semantics. This is a value type.

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

'Declaration
<ComVisibleAttribute(True)> _
Public Structure LockCookie
'Usage
Dim instance As LockCookie

The following example shows how to request a reader lock, upgrade the reader lock to a writer lock, and save the LockCookie. It then uses the LockCookie to downgrade to a reader lock again.

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 request a reader lock, upgrade the
' reader lock to the writer lock, and downgrade to a
' reader lock again.
Shared Sub UpgradeDowngrade(timeOut As Integer)
    Try
        rwl.AcquireReaderLock(timeOut)
        Try
            ' It is safe for this thread to read from
            ' the shared resource.
            Display("reads resource value " & resource)
            Interlocked.Increment(reads)

            ' If it is necessary to write to the resource,
            ' you must either release the reader lock and 
            ' then request the writer lock, or upgrade the
            ' reader lock. Note that upgrading the reader lock
            ' puts the thread in the write queue, behind any
            ' other threads that might be waiting for the 
            ' writer lock.
            Try
                Dim lc As LockCookie = rwl.UpgradeToWriterLock(timeOut)
                Try
                    ' It is safe for this thread to read or write
                    ' from the shared resource.
                    resource = rnd.Next(500)
                    Display("writes resource value " & resource)
                    Interlocked.Increment(writes)
                Finally
                    ' Ensure that the lock is released.
                    rwl.DowngradeFromWriterLock(lc)
                End Try
            Catch ex As ApplicationException
                ' The upgrade request timed out.
                Interlocked.Increment(writerTimeouts)
            End Try

            ' When the lock has been downgraded, it is 
            ' still safe to read from the resource.
            Display("reads resource value " & resource)
            Interlocked.Increment(reads)
        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 'UpgradeDowngrade


...


End Class 'Test 

This type is thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

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