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ReaderWriterLock.ReleaseLock Method

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

[Visual Basic]
Public Function ReleaseLock() As LockCookie
[C#]
public LockCookie ReleaseLock();
[C++]
public: LockCookie ReleaseLock();
[JScript]
public function ReleaseLock() : LockCookie;

Return Value

A LockCookie value representing the released lock.

Remarks

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.

Example

[Visual Basic] 

' 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 

[C#] 
// The complete code is located in the ReaderWriterLock
// class topic.
using System;
using System.Threading;

public class Test
{
    // Declaring the ReaderWriterLock at the class level
    // makes it visible to all threads.
    static ReaderWriterLock rwl = new ReaderWriterLock();
    // For this example, the shared resource protected by the
    // ReaderWriterLock is just an integer.
    static int resource = 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.
    static void ReleaseRestore(int timeOut)
    {
        int lastWriter;

        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.)
                int resourceValue = resource;
                Display("reads resource value " + resourceValue); 
                Interlocked.Increment(ref reads);

                // Save the current writer sequence number.
                lastWriter = rwl.WriterSeqNum;

                // Release the lock, and save a cookie so the
                // lock can be restored later.
                LockCookie lc = 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(ref 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))
                {
                    resourceValue = resource;
                    Interlocked.Increment(ref reads);
                    Display("resource has changed " + resourceValue);
                }
                else
                {
                    Display("resource has not changed " + resourceValue);
                }
            }        
            finally
            {
                // Ensure that the lock is released.
                rwl.ReleaseReaderLock();
            }
        }
        catch (ApplicationException)
        {
            // The reader lock request timed out.
            Interlocked.Increment(ref readerTimeouts);
        }
    }
    . . . 
}

[C++] 
// The complete code is located in the ReaderWriterLock
// class topic.
#using <mscorlib.dll>

using namespace System;
using namespace System::Threading;

public __gc class Test 
{
public:
    // Declaring the ReaderWriterLock at the class level
    // makes it visible to all threads.
    static ReaderWriterLock* rwl = new ReaderWriterLock();
    // For this example, the shared resource protected by the
    // ReaderWriterLock is just an integer.
    static int resource = 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.
    static void ReleaseRestore(int timeOut) 
    {
        int lastWriter;

        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.)
                int resourceValue = resource;
                Display(String::Format(S"reads resource value {0}", __box(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.
                LockCookie lc = 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-->Item[Out] on* the Restore method.
                Thread::Sleep(rnd->Next(250));
                rwl->RestoreLock(__box(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)) 
                {
                    resourceValue = resource;
                    Interlocked::Increment(&reads);

                    Display(String::Format(S"resource has changed {0}", __box(resourceValue)));
                }
                else 
                {
                    Display(String::Format(S"resource has not changed {0}", __box(resourceValue)));
                }
            }        
            __finally 
            {
                // Ensure that the lock is released.
                rwl->ReleaseReaderLock();
            }
        } 
        catch (ApplicationException*) 
        {
            // The reader lock request timed out.
            Interlocked::Increment(&readerTimeouts);
        }
    }
    . . . 
};

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

ReaderWriterLock Class | ReaderWriterLock Members | System.Threading Namespace | Threading | ReaderWriterLock

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