LockCookie Struct

Definition

Namespace:

System.Threading

Assembly:

System.Threading.dll

Source:

LockCookie.cs

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

public value class LockCookie : IEquatable<System::Threading::LockCookie>

public struct LockCookie : IEquatable<System.Threading.LockCookie>

type LockCookie = struct

Public Structure LockCookie
Implements IEquatable(Of LockCookie)

Inheritance

Object

ValueType

LockCookie

Implements

IEquatable<LockCookie>

Examples

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.
using namespace System;
using namespace System::Threading;
public ref class Test
{
public:

   // Declaring the ReaderWriterLock at the class level
   // makes it visible to all threads.
   static ReaderWriterLock^ rwl = gcnew ReaderWriterLock;

   // For this example, the shared resource protected by the
   // ReaderWriterLock is just an integer.
   static int resource = 0;

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

public class Example
{
   static ReaderWriterLock rwl = new ReaderWriterLock();
   // Define the shared resource protected by the ReaderWriterLock.
   static int resource = 0;

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

Public Module Example
   Private rwl As New ReaderWriterLock()
   ' Define the shared resource protected by the ReaderWriterLock.
   Private 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.
static void UpgradeDowngrade( Random^ rnd, int timeOut )
{
   try
   {
      rwl->AcquireReaderLock( timeOut );
      try
      {

         // It is safe for this thread to read from
         // the shared resource.
         Display( String::Format( "reads resource value {0}", 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( String::Format( "writes resource value {0}", resource ) );
               Interlocked::Increment( writes );
            }
            finally
            {

               // Ensure that the lock is released.
               rwl->DowngradeFromWriterLock( lc );
            }

         }
         catch ( ApplicationException^ )
         {

            // The upgrade request timed out.
            Interlocked::Increment( writerTimeouts );
         }


         // When the lock has been downgraded, it is
         // still safe to read from the resource.
         Display( String::Format( "reads resource value {0}", resource ) );
         Interlocked::Increment( reads );
      }
      finally
      {

         // Ensure that the lock is released.
         rwl->ReleaseReaderLock();
      }

   }
   catch ( ApplicationException^ )
   {

      // The reader lock request timed out.
      Interlocked::Increment( readerTimeouts );
   }

}

// Requests a reader lock, upgrades the reader lock to the writer
// lock, and downgrades it to a reader lock again.
static void UpgradeDowngrade(Random rnd, int timeOut)
{
   try {
      rwl.AcquireReaderLock(timeOut);
      try {
         // It's safe for this thread to read from the shared resource.
         Display("reads resource value " + resource);
         Interlocked.Increment(ref reads);

         // To write to the resource, either release the reader lock and
         // request the writer lock, or upgrade the reader lock. 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's safe for this thread to read or write from the shared resource.
               resource = rnd.Next(500);
               Display("writes resource value " + resource);
               Interlocked.Increment(ref writes);
            }
            finally {
               // Ensure that the lock is released.
               rwl.DowngradeFromWriterLock(ref lc);
            }
         }
         catch (ApplicationException) {
            // The upgrade request timed out.
            Interlocked.Increment(ref writerTimeouts);
         }

         // If the lock was downgraded, it's still safe to read from the resource.
         Display("reads resource value " + resource);
         Interlocked.Increment(ref reads);
      }
      finally {
         // Ensure that the lock is released.
         rwl.ReleaseReaderLock();
      }
   }
   catch (ApplicationException) {
      // The reader lock request timed out.
      Interlocked.Increment(ref readerTimeouts);
   }
}

' Requests a reader lock, upgrades the reader lock to the writer
' lock, and downgrades it to a reader lock again.
Sub UpgradeDowngrade(rnd As Random, timeOut As Integer)
   Try
      rwl.AcquireReaderLock(timeOut)
      Try
         ' It's safe for this thread to read from the shared resource.
         Display("reads resource value " & resource)
         Interlocked.Increment(reads)
         
         ' To write to the resource, either release the reader lock and
         ' request the writer lock, or upgrade the reader lock. 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's 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
         
         ' If the lock was downgraded, it's 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

};

}

End Module

Methods

Equals(LockCookie)	Indicates whether the current instance is equal to the specified LockCookie.
Equals(Object)	Indicates whether a specified object is a LockCookie and is equal to the current instance.
GetHashCode()	Returns the hash code for this instance.

Operators

Equality(LockCookie, LockCookie)	Indicates whether two LockCookie structures are equal.
Inequality(LockCookie, LockCookie)	Indicates whether two LockCookie structures are not equal.

Thread Safety

This type is thread safe.

See also

• ReaderWriterLock
• Managed Threading
• Reader-Writer Locks