Export (0) Print
Expand All
0 out of 1 rated this helpful - Rate this topic

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

/** @attribute ComVisibleAttribute(true) */ 
public final class LockCookie extends ValueType
JScript suports the use of structures, but not the declaration of new ones.

' 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 

// The complete code is located in the ReaderWriterLock
// class topic.
import System.*;
import System.Threading.*;
import System.Threading.Thread;    

public class Test
{
    // Declaring the ReaderWriterLock at the class level
    // makes it visible to all threads.
    private static ReaderWriterLock rwl = new ReaderWriterLock();

    // For this example, the shared resource protected by the
    // ReaderWriterLock is just an integer.
    private static int resource = 0;
...    // Shows how to request a reader lock, upgrade the
    // reader lock to the writer lock, and downgrade to a
    // reader lock again.
    static void UpgradeDowngrade(int timeOut)
    {
        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 {
                    LockCookie lc = 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);
                    }
                }
                catch (ApplicationException exp) {
                    // The upgrade request timed out.
                    Interlocked.Increment(writerTimeouts);
                }

                // 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();
            }
        }
        catch (ApplicationException exp) {
            // The reader lock request timed out.
            Interlocked.Increment(readerTimeouts);
        }
    } //UpgradeDowngrade
...}

This type is safe for multithreaded operations.

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

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

.NET Framework

Supported in: 2.0, 1.1, 1.0
Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback

Community Additions

ADD
Show:
© 2014 Microsoft. All rights reserved.