LockCookie Structure
Defines the lock that implements single-writer/multiple-reader semantics. This is a value type.
Assembly: mscorlib (in mscorlib.dll)
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
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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.