Monitor.Enter Méthode

Source:

Monitor.CoreCLR.cs

Source:

Monitor.CoreCLR.cs

Source:

Monitor.cs

Source:

Monitor.cs

Source:

Monitor.cs

public:
 static void Enter(System::Object ^ obj);

public static void Enter(object obj);

static member Enter : obj -> unit

Public Shared Sub Enter (obj As Object)

Paramètres

Exceptions

Exemples

L’exemple suivant montre comment utiliser la Enter méthode.

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

Remarques

Permet Enter d’acquérir l’objet Monitor passé en tant que paramètre. Si un autre thread a exécuté un Enter thread sur l’objet mais n’a pas encore exécuté le thread correspondant Exit, le thread actuel se bloque jusqu’à ce que l’autre thread libère l’objet. Il est légal que le même thread s’appelle Enter plusieurs fois sans qu’il ne bloque. Toutefois, un nombre égal d’appels Exit doit être appelé avant que d’autres threads en attente sur l’objet se débloquent.

Permet Monitor de verrouiller des objets (c’est-à-dire des types référence), et non des types valeur. Lorsque vous passez une variable de type valeur à Enter, elle est boxée en tant qu’objet. Si vous passez la même variable à Enter nouveau, elle est boxée en tant qu’objet distinct et le thread ne bloque pas. Dans ce cas, le code censé Monitor protéger n’est pas protégé. En outre, lorsque vous passez la variable à Exit, un autre objet distinct est créé. Étant donné que l’objet passé à Exit est différent de l’objet passé à Enter, Monitor lève SynchronizationLockException. Pour plus d’informations, consultez les moniteurs de rubriques conceptuelles.

Interrupt peut interrompre les threads qui attendent d’entrer un Monitor objet. A ThreadInterruptedException sera levée.

Utiliser un C# try...bloc finally (Try... Finally dans Visual Basic) pour vous assurer que vous relâchez le moniteur, ou utilisez l’instruction C# lock (instruction SyncLock dans Visual Basic), qui encapsule les méthodes Enter et Exit dans un try... finally Bloc.

Voir aussi

• Thread
• Monitor
• Threading managé

Source:

Monitor.CoreCLR.cs

Source:

Monitor.cs

Source:

Monitor.CoreCLR.cs

Source:

Monitor.CoreCLR.cs

Source:

Monitor.CoreCLR.cs

public:
 static void Enter(System::Object ^ obj, bool % lockTaken);

public static void Enter(object obj, ref bool lockTaken);

static member Enter : obj * bool -> unit

Public Shared Sub Enter (obj As Object, ByRef lockTaken As Boolean)

Paramètres

Exceptions

Exemples

Le code suivant montre le modèle de base pour l’utilisation de la Enter(Object, Boolean) surcharge de méthode. Cette surcharge définit toujours la valeur de la variable transmise au paramètre ref (ByRef dans Visual Basic) lockTaken, même si la méthode lève une exception, de sorte que la valeur de la variable est un moyen fiable de tester si le verrou doit être libéré.

bool acquiredLock = false;

try
{
    Monitor.Enter(lockObject, ref acquiredLock);

    // Code that accesses resources that are protected by the lock.
}
finally
{
    if (acquiredLock)
    {
        Monitor.Exit(lockObject);
    }
}

Dim acquiredLock As Boolean = False

Try
    Monitor.Enter(lockObject, acquiredLock)

    ' Code that accesses resources that are protected by the lock.

Finally
    If acquiredLock Then
        Monitor.Exit(lockObject)
    End If
End Try

Remarques

Permet Enter d’acquérir l’objet Monitor passé en tant que obj paramètre. Si un autre thread a exécuté un Enter thread sur l’objet mais n’a pas encore exécuté le thread correspondant Exit, le thread actuel se bloque jusqu’à ce que l’autre thread libère l’objet. Il est légal que le même thread s’appelle Enter plusieurs fois sans qu’il ne bloque. Toutefois, un nombre égal d’appels Exit doit être appelé avant que d’autres threads en attente sur l’objet se débloquent.

Si le verrou n’a pas été pris parce qu’une exception a été levée, la variable spécifiée pour le lockTaken paramètre se termine false après la fin de cette méthode. Cela permet au programme de déterminer, dans tous les cas, s’il est nécessaire de libérer le verrou. Si cette méthode retourne sans lever d’exception, la variable spécifiée pour le lockTaken paramètre est toujours true, et il n’est pas nécessaire de la tester.

Permet Monitor de verrouiller des objets (c’est-à-dire des types référence), et non des types valeur. Lorsque vous passez une variable de type valeur à Enter, elle est boxée en tant qu’objet. Si vous passez la même variable à Enter nouveau, elle est boxée en tant qu’objet distinct et le thread ne bloque pas. Dans ce cas, le code censé Monitor protéger n’est pas protégé. En outre, lorsque vous passez la variable à Exit, un autre objet distinct est créé. Étant donné que l’objet passé à Exit est différent de l’objet passé à Enter, Monitor lève SynchronizationLockException. Pour plus d’informations, consultez les moniteurs de rubriques conceptuelles.

Interrupt peut interrompre les threads qui attendent d’entrer un Monitor objet. A ThreadInterruptedException sera levée.