Monitor.Exit(Object) Monitor.Exit(Object) Monitor.Exit(Object) Monitor.Exit(Object) Method

Definition

Releases an exclusive lock on the specified object.

public:
 static void Exit(System::Object ^ obj);
public static void Exit (object obj);
static member Exit : obj -> unit
Public Shared Sub Exit (obj As Object)

Parameters

obj
Object Object Object Object

The object on which to release the lock.

Exceptions

Examples

The following example demonstrates how to use the Exit method.

#using <System.dll>

using namespace System;
using namespace System::Threading;
using namespace System::Collections::Generic;
using namespace System::Text;

generic <typename T> public ref class SafeQueue
{
private:
   // A queue that is protected by Monitor.
   Queue<T>^ m_inputQueue;

public:
   SafeQueue()
   {
      m_inputQueue = gcnew Queue<T>();
   };

   // Lock the queue and add an element.
   void Enqueue(T qValue)
   {
      // Request the lock, and block until it is obtained.
      Monitor::Enter(m_inputQueue);
      try
      {
         // When the lock is obtained, add an element.
         m_inputQueue->Enqueue(qValue);
      }
      finally
      {
         // Ensure that the lock is released.
         Monitor::Exit(m_inputQueue);
      }
   };

   // Try to add an element to the queue: Add the element to the queue 
   // only if the lock is immediately available.
   bool TryEnqueue(T qValue)
   {
      // Request the lock.
      if (Monitor::TryEnter(m_inputQueue))
      {
         try
         {
            m_inputQueue->Enqueue(qValue);
         }
         finally
         {
            // Ensure that the lock is released.
            Monitor::Exit(m_inputQueue);
         }
         return true;
      }
      else
      {
         return false;
      }
   };

   // Try to add an element to the queue: Add the element to the queue 
   // only if the lock becomes available during the specified time
   // interval.
   bool TryEnqueue(T qValue, int waitTime)
   {
      // Request the lock.
      if (Monitor::TryEnter(m_inputQueue, waitTime))
      {
         try
         {
            m_inputQueue->Enqueue(qValue);
         }
         finally
         {
            // Ensure that the lock is released.
            Monitor::Exit(m_inputQueue);
         }
         return true;
      }
      else
      {
         return false;
      }
   };

   // Lock the queue and dequeue an element.
   T Dequeue()
   {
      T retval;

      // Request the lock, and block until it is obtained.
      Monitor::Enter(m_inputQueue);
      try
      {
         // When the lock is obtained, dequeue an element.
         retval = m_inputQueue->Dequeue();
      }
      finally
      {
         // Ensure that the lock is released.
         Monitor::Exit(m_inputQueue);
      }

      return retval;
   };

   // Delete all elements that equal the given object.
   int Remove(T qValue)
   {
      int removedCt = 0;

      // Wait until the lock is available and lock the queue.
      Monitor::Enter(m_inputQueue);
      try
      {
         int counter = m_inputQueue->Count;
         while (counter > 0)
            // Check each element.
         {
            T elem = m_inputQueue->Dequeue();
            if (!elem->Equals(qValue))
            {
               m_inputQueue->Enqueue(elem);
            }
            else
            {
               // Keep a count of items removed.
               removedCt += 1;
            }
            counter = counter - 1;
         }
      }
      finally
      {
         // Ensure that the lock is released.
         Monitor::Exit(m_inputQueue);
      }

      return removedCt;
   };

   // Print all queue elements.
   String^ PrintAllElements()
   {
      StringBuilder^ output = gcnew StringBuilder();

      // Lock the queue.
      Monitor::Enter(m_inputQueue);
      try
      {
         for each ( T elem in m_inputQueue )
         {
            // Print the next element.
            output->AppendLine(elem->ToString());
         }
      }
      finally
      {
         // Ensure that the lock is released.
         Monitor::Exit(m_inputQueue);
      }

      return output->ToString();
   };
};

public ref class Example
{
private:
   static SafeQueue<int>^ q = gcnew SafeQueue<int>();
   static int threadsRunning = 0;
   static array<array<int>^>^ results = gcnew array<array<int>^>(3);

   static void ThreadProc(Object^ state)
   {
      DateTime finish = DateTime::Now.AddSeconds(10);
      Random^ rand = gcnew Random();
      array<int>^ result = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
      int threadNum = (int) state;

      while (DateTime::Now < finish)

      {
         int what = rand->Next(250);
         int how = rand->Next(100);

         if (how < 16)
         {
            q->Enqueue(what);
            result[(int)ThreadResultIndex::EnqueueCt] += 1;
         }
         else if (how < 32)
         {
            if (q->TryEnqueue(what))
            {
               result[(int)ThreadResultIndex::TryEnqueueSucceedCt] += 1;
            }
            else
            {
               result[(int)ThreadResultIndex::TryEnqueueFailCt] += 1;
            }
         }
         else if (how < 48)
         {
            // Even a very small wait significantly increases the success 
            // rate of the conditional enqueue operation.
            if (q->TryEnqueue(what, 10))
            {
               result[(int)ThreadResultIndex::TryEnqueueWaitSucceedCt] += 1;
            }
            else
            {
               result[(int)ThreadResultIndex::TryEnqueueWaitFailCt] += 1;
            }
         }
         else if (how < 96)
         {
            result[(int)ThreadResultIndex::DequeueCt] += 1;
            try
            {
               q->Dequeue();
            }
            catch (Exception^ ex)
            {
               result[(int)ThreadResultIndex::DequeueExCt] += 1;
            }
         }
         else
         {
            result[(int)ThreadResultIndex::RemoveCt] += 1;
            result[(int)ThreadResultIndex::RemovedCt] += q->Remove(what);
         }         
      }

      results[threadNum] = result;

      if (0 == Interlocked::Decrement(threadsRunning))      
      {
         StringBuilder^ sb = gcnew StringBuilder(
            "                               Thread 1 Thread 2 Thread 3    Total\n");

         for (int row = 0; row < 9; row++)
         {
            int total = 0;
            sb->Append(titles[row]);

            for(int col = 0; col < 3; col++)
            {
               sb->Append(String::Format("{0,9}", results[col][row]));
               total += results[col][row];
            }

            sb->AppendLine(String::Format("{0,9}", total));
         }

         Console::WriteLine(sb->ToString());
      }
   };

   static array<String^>^ titles = {
      "Enqueue                       ", 
      "TryEnqueue succeeded          ", 
      "TryEnqueue failed             ", 
      "TryEnqueue(T, wait) succeeded ", 
      "TryEnqueue(T, wait) failed    ", 
      "Dequeue attempts              ", 
      "Dequeue exceptions            ", 
      "Remove operations             ", 
      "Queue elements removed        "};

   enum class ThreadResultIndex
   {
      EnqueueCt, 
      TryEnqueueSucceedCt, 
      TryEnqueueFailCt, 
      TryEnqueueWaitSucceedCt, 
      TryEnqueueWaitFailCt, 
      DequeueCt, 
      DequeueExCt, 
      RemoveCt, 
      RemovedCt
   };

public:
   static void Demo()
   {
      Console::WriteLine("Working...");

      for(int i = 0; i < 3; i++)
      {
         Thread^ t = gcnew Thread(gcnew ParameterizedThreadStart(Example::ThreadProc));
         t->Start(i);
         Interlocked::Increment(threadsRunning);
      }
   };
};

void main()
{
   Example::Demo();
}


/* This example produces output similar to the following:

Working...
                               Thread 1 Thread 2 Thread 3    Total
Enqueue                          274718   513514   337895  1126127
TryEnqueue succeeded             274502   513516   337480  1125498
TryEnqueue failed                   119      235      141      495
TryEnqueue(T, wait) succeeded    274552   513116   338532  1126200
TryEnqueue(T, wait) failed            0        1        0        1
Dequeue attempts                 824038  1541866  1015006  3380910
Dequeue exceptions                12828    23416    14799    51043
Remove operations                 68746   128218    84306   281270
Queue elements removed            11464    22024    14470    47958
Queue elements removed            2921     4690     2982    10593
 */
using System;
using System.Threading;
using System.Collections.Generic;
using System.Text;

class SafeQueue<T>
{
   // A queue that is protected by Monitor.
   private Queue<T> m_inputQueue = new Queue<T>();

   // Lock the queue and add an element.
   public void Enqueue(T qValue)
   {
      // Request the lock, and block until it is obtained.
      Monitor.Enter(m_inputQueue);
      try
      {
         // When the lock is obtained, add an element.
         m_inputQueue.Enqueue(qValue);
      }
      finally
      {
         // Ensure that the lock is released.
         Monitor.Exit(m_inputQueue);
      }
   }

   // Try to add an element to the queue: Add the element to the queue 
   // only if the lock is immediately available.
   public bool TryEnqueue(T qValue)
   {
      // Request the lock.
      if (Monitor.TryEnter(m_inputQueue))
      {
         try
         {
            m_inputQueue.Enqueue(qValue);
         }
         finally
         {
            // Ensure that the lock is released.
            Monitor.Exit(m_inputQueue);
         }
         return true;
      }
      else
      {
         return false;
      }
   }

   // Try to add an element to the queue: Add the element to the queue 
   // only if the lock becomes available during the specified time
   // interval.
   public bool TryEnqueue(T qValue, int waitTime)
   {
      // Request the lock.
      if (Monitor.TryEnter(m_inputQueue, waitTime))
      {
         try
         {
            m_inputQueue.Enqueue(qValue);
         }
         finally
         {
            // Ensure that the lock is released.
            Monitor.Exit(m_inputQueue);
         }
         return true;
      }
      else
      {
         return false;
      }
   }

   // Lock the queue and dequeue an element.
   public T Dequeue()
   {
      T retval;

      // Request the lock, and block until it is obtained.
      Monitor.Enter(m_inputQueue);
      try
      {
         // When the lock is obtained, dequeue an element.
         retval = m_inputQueue.Dequeue();
      }
      finally
      {
         // Ensure that the lock is released.
         Monitor.Exit(m_inputQueue);
      }

      return retval;
   }

   // Delete all elements that equal the given object.
   public int Remove(T qValue)
   {
      int removedCt = 0;

      // Wait until the lock is available and lock the queue.
      Monitor.Enter(m_inputQueue);
      try
      {
         int counter = m_inputQueue.Count;
         while (counter > 0)
            // Check each element.
         {
            T elem = m_inputQueue.Dequeue();
            if (!elem.Equals(qValue))
            {
               m_inputQueue.Enqueue(elem);
            }
            else
            {
               // Keep a count of items removed.
               removedCt += 1;
            }
            counter = counter - 1;
         }
      }
      finally
      {
         // Ensure that the lock is released.
         Monitor.Exit(m_inputQueue);
      }

      return removedCt;
   }

   // Print all queue elements.
   public string PrintAllElements()
   {
      StringBuilder output = new StringBuilder();

      // Lock the queue.
      Monitor.Enter(m_inputQueue);
      try
      {
         foreach( T elem in m_inputQueue )
         {
            // Print the next element.
            output.AppendLine(elem.ToString());
         }
      }
      finally
      {
         // Ensure that the lock is released.
         Monitor.Exit(m_inputQueue);
      }

      return output.ToString();
   }
}

public class Example
{
   private static SafeQueue<int> q = new SafeQueue<int>();
   private static int threadsRunning = 0;
   private static int[][] results = new int[3][];

   static void Main()
   {
      Console.WriteLine("Working...");

      for(int i = 0; i < 3; i++)
      {
         Thread t = new Thread(ThreadProc);
         t.Start(i);
         Interlocked.Increment(ref threadsRunning);
      }
   }

   private static void ThreadProc(object state)
   {
      DateTime finish = DateTime.Now.AddSeconds(10);
      Random rand = new Random();
      int[] result = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
      int threadNum = (int) state;

      while (DateTime.Now < finish)

      {
         int what = rand.Next(250);
         int how = rand.Next(100);

         if (how < 16)
         {
            q.Enqueue(what);
            result[(int)ThreadResultIndex.EnqueueCt] += 1;
         }
         else if (how < 32)
         {
            if (q.TryEnqueue(what))
            {
               result[(int)ThreadResultIndex.TryEnqueueSucceedCt] += 1;
            }
            else
            {
               result[(int)ThreadResultIndex.TryEnqueueFailCt] += 1;
            }
         }
         else if (how < 48)
         {
            // Even a very small wait significantly increases the success 
            // rate of the conditional enqueue operation.
            if (q.TryEnqueue(what, 10))
            {
               result[(int)ThreadResultIndex.TryEnqueueWaitSucceedCt] += 1;
            }
            else
            {
               result[(int)ThreadResultIndex.TryEnqueueWaitFailCt] += 1;
            }
         }
         else if (how < 96)
         {
            result[(int)ThreadResultIndex.DequeueCt] += 1;
            try
            {
               q.Dequeue();
            }
            catch
            {
               result[(int)ThreadResultIndex.DequeueExCt] += 1;
            }
         }
         else
         {
            result[(int)ThreadResultIndex.RemoveCt] += 1;
            result[(int)ThreadResultIndex.RemovedCt] += q.Remove(what);
         }         
      }

      results[threadNum] = result;

      if (0 == Interlocked.Decrement(ref threadsRunning))      
      {
         StringBuilder sb = new StringBuilder(
            "                               Thread 1 Thread 2 Thread 3    Total\n");

         for(int row = 0; row < 9; row++)
         {
            int total = 0;
            sb.Append(titles[row]);

            for(int col = 0; col < 3; col++)
            {
               sb.Append(String.Format("{0,9}", results[col][row]));
               total += results[col][row];
            }

            sb.AppendLine(String.Format("{0,9}", total));
         }

         Console.WriteLine(sb.ToString());
      }
   }

   private static string[] titles = {
      "Enqueue                       ", 
      "TryEnqueue succeeded          ", 
      "TryEnqueue failed             ", 
      "TryEnqueue(T, wait) succeeded ", 
      "TryEnqueue(T, wait) failed    ", 
      "Dequeue attempts              ", 
      "Dequeue exceptions            ", 
      "Remove operations             ", 
      "Queue elements removed        "};

   private enum ThreadResultIndex
   {
      EnqueueCt, 
      TryEnqueueSucceedCt, 
      TryEnqueueFailCt, 
      TryEnqueueWaitSucceedCt, 
      TryEnqueueWaitFailCt, 
      DequeueCt, 
      DequeueExCt, 
      RemoveCt, 
      RemovedCt
   };
}

/* This example produces output similar to the following:

Working...
                               Thread 1 Thread 2 Thread 3    Total
Enqueue                          277382   515209   308464  1101055
TryEnqueue succeeded             276873   514621   308099  1099593
TryEnqueue failed                   109      181      134      424
TryEnqueue(T, wait) succeeded    276913   514434   307607  1098954
TryEnqueue(T, wait) failed            2        0        0        2
Dequeue attempts                 830980  1544081   924164  3299225
Dequeue exceptions                12102    21589    13539    47230
Remove operations                 69550   129479    77351   276380
Queue elements removed            11957    22572    13043    47572
 */
Imports System.Threading
Imports System.Collections.Generic
Imports System.Text

Class SafeQueue(Of T)

   ' A queue that is protected by Monitor.
   Private m_inputQueue As New Queue(Of T)

   ' Lock the queue and add an element.
   Public Sub Enqueue(ByVal qValue As T)

      ' Request the lock, and block until it is obtained.
      Monitor.Enter(m_inputQueue)
      Try
         ' When the lock is obtained, add an element.
         m_inputQueue.Enqueue(qValue)

      Finally
         ' Ensure that the lock is released.
         Monitor.Exit(m_inputQueue)
      End Try
   End Sub

   ' Try to add an element to the queue: Add the element to the queue 
   ' only if the lock is immediately available.
   Public Function TryEnqueue(ByVal qValue As T) As Boolean

      ' Request the lock.
      If Monitor.TryEnter(m_inputQueue) Then
         Try
            m_inputQueue.Enqueue(qValue)

         Finally
            ' Ensure that the lock is released.
            Monitor.Exit(m_inputQueue)
         End Try
         Return True
      Else
         Return False
      End If
   End Function

   ' Try to add an element to the queue: Add the element to the queue 
   ' only if the lock becomes available during the specified time
   ' interval.
   Public Function TryEnqueue(ByVal qValue As T, ByVal waitTime As Integer) As Boolean

      ' Request the lock.
      If Monitor.TryEnter(m_inputQueue, waitTime) Then
         Try
            m_inputQueue.Enqueue(qValue)

         Finally
            ' Ensure that the lock is released.
            Monitor.Exit(m_inputQueue)
         End Try
         Return True
      Else
         Return False
      End If
   End Function

   ' Lock the queue and dequeue an element.
   Public Function Dequeue() As T

      Dim retval As T

      ' Request the lock, and block until it is obtained.
      Monitor.Enter(m_inputQueue)
      Try
         ' When the lock is obtained, dequeue an element.
         retval = m_inputQueue.Dequeue()

      Finally
         ' Ensure that the lock is released.
         Monitor.Exit(m_inputQueue)
      End Try

      Return retval
   End Function

   ' Delete all elements that equal the given object.
   Public Function Remove(ByVal qValue As T) As Integer

      Dim removedCt As Integer = 0

      ' Wait until the lock is available and lock the queue.
      Monitor.Enter(m_inputQueue)
      Try
         Dim counter As Integer = m_inputQueue.Count
         While (counter > 0)
            'Check each element.
            Dim elem As T = m_inputQueue.Dequeue()
            If Not elem.Equals(qValue) Then
               m_inputQueue.Enqueue(elem)
            Else
               ' Keep a count of items removed.
               removedCt += 1
            End If
            counter = counter - 1
         End While

      Finally
         ' Ensure that the lock is released.
         Monitor.Exit(m_inputQueue)
      End Try

      Return removedCt
   End Function

   ' Print all queue elements.
   Public Function PrintAllElements() As String

      Dim output As New StringBuilder()

      'Lock the queue.
      Monitor.Enter(m_inputQueue)
      Try
         For Each elem As T In m_inputQueue
            ' Print the next element.
            output.AppendLine(elem.ToString())
         Next

      Finally
         ' Ensure that the lock is released.
         Monitor.Exit(m_inputQueue)
      End Try

      Return output.ToString()
   End Function
End Class

Public Class Example

   Private Shared q As New SafeQueue(Of Integer)
   Private Shared threadsRunning As Integer = 0
   Private Shared results(2)() As Integer

   Friend Shared Sub Main()

      Console.WriteLine("Working...")

      For i As Integer = 0 To 2

         Dim t As New Thread(AddressOf ThreadProc)
         t.Start(i)
         Interlocked.Increment(threadsRunning)

      Next i

   End Sub

   Private Shared Sub ThreadProc(ByVal state As Object)

      Dim finish As DateTime = DateTime.Now.AddSeconds(10)
      Dim rand As New Random()
      Dim result() As Integer = { 0, 0, 0, 0, 0, 0, 0, 0, 0 }
      Dim threadNum As Integer = CInt(state)

      While (DateTime.Now < finish)

         Dim what As Integer = rand.Next(250)
         Dim how As Integer = rand.Next(100)

         If how < 16 Then
            q.Enqueue(what)
            result(ThreadResultIndex.EnqueueCt) += 1
         Else If how < 32 Then
            If q.TryEnqueue(what)
               result(ThreadResultIndex.TryEnqueueSucceedCt) += 1
            Else
               result(ThreadResultIndex.TryEnqueueFailCt) += 1
            End If
         Else If how < 48 Then
            ' Even a very small wait significantly increases the success 
            ' rate of the conditional enqueue operation.
            If q.TryEnqueue(what, 10)
               result(ThreadResultIndex.TryEnqueueWaitSucceedCt) += 1
            Else
               result(ThreadResultIndex.TryEnqueueWaitFailCt) += 1
            End If
         Else If how < 96 Then
            result(ThreadResultIndex.DequeueCt) += 1
            Try
               q.Dequeue()
            Catch
               result(ThreadResultIndex.DequeueExCt) += 1
            End Try
         Else
            result(ThreadResultIndex.RemoveCt) += 1
            result(ThreadResultIndex.RemovedCt) += q.Remove(what)
         End If
         
      End While

      results(threadNum) = result

      If 0 = Interlocked.Decrement(threadsRunning) Then
      
         Dim sb As New StringBuilder( _
            "                               Thread 1 Thread 2 Thread 3    Total" & vbLf)

         For row As Integer = 0 To 8

            Dim total As Integer = 0
            sb.Append(titles(row))

            For col As Integer = 0 To 2

               sb.Append(String.Format("{0,9}", results(col)(row)))
               total += results(col)(row)

            Next col

            sb.AppendLine(String.Format("{0,9}", total))

         Next row

         Console.WriteLine(sb.ToString())

      End If     
    
   End Sub

   Private Shared titles() As String = { _
      "Enqueue                       ", _
      "TryEnqueue succeeded          ", _
      "TryEnqueue failed             ", _
      "TryEnqueue(T, wait) succeeded ", _
      "TryEnqueue(T, wait) failed    ", _
      "Dequeue attempts              ", _
      "Dequeue exceptions            ", _
      "Remove operations             ", _
      "Queue elements removed        "  _
   }

   Private Enum ThreadResultIndex
      EnqueueCt
      TryEnqueueSucceedCt
      TryEnqueueFailCt
      TryEnqueueWaitSucceedCt
      TryEnqueueWaitFailCt
      DequeueCt
      DequeueExCt
      RemoveCt
      RemovedCt
   End Enum

End Class

' This example produces output similar to the following:
'
'Working...
'                               Thread 1 Thread 2 Thread 3    Total
'Enqueue                          294357   512164   302838  1109359
'TryEnqueue succeeded             294486   512403   303117  1110006
'TryEnqueue failed                   108      234      127      469
'TryEnqueue(T, wait) succeeded    294259   512796   302556  1109611
'TryEnqueue(T, wait) failed            1        1        1        3
'Dequeue attempts                 882266  1537993   907795  3328054
'Dequeue exceptions                12691    21474    13480    47645
'Remove operations                 74059   128715    76187   278961
'Queue elements removed            12667    22606    13219    48492

Remarks

The calling thread must own the lock on the obj parameter. If the calling thread owns the lock on the specified object, and has made an equal number of Exit and Enter calls for the object, then the lock is released. If the calling thread has not invoked Exit as many times as Enter, the lock is not released.

If the lock is released and other threads are in the ready queue for the object, one of the threads acquires the lock. If other threads are in the waiting queue waiting to acquire the lock, they are not automatically moved to the ready queue when the owner of the lock calls Exit. To move one or more waiting threads into the ready queue, call Pulse or PulseAll before invoking Exit.

Applies to

See also