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Monitor.Enter Método

Definição

Adquire um bloqueio exclusivo em um objeto especificado.

Sobrecargas

Enter(Object)

Adquire um bloqueio exclusivo no objeto especificado.

Enter(Object, Boolean)

Obtém um bloqueio exclusivo no objeto especificado e define automaticamente um valor que indica se o bloqueio foi realizado.

Enter(Object)

Origem:
Monitor.cs
Origem:
Monitor.cs
Origem:
Monitor.cs

Adquire um bloqueio exclusivo no objeto especificado.

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)

Parâmetros

obj
Object

O objeto no qual adquirir o bloqueio do monitor.

Exceções

O parâmetro obj é null.

Exemplos

O exemplo a seguir demonstra como usar o Enter método .

#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

Comentários

Use Enter para adquirir o Monitor no objeto passado como o parâmetro . Se outro thread tiver executado um Enter no objeto, mas ainda não tiver executado o correspondente Exit, o thread atual será bloqueado até que o outro thread libere o objeto. É legal que o mesmo thread invoque Enter mais de uma vez sem que ele bloqueie; no entanto, um número igual de Exit chamadas deve ser invocado antes que outros threads que aguardam o objeto sejam desbloqueados.

Use Monitor para bloquear objetos (ou seja, tipos de referência), não tipos de valor. Quando você passa uma variável de tipo de valor para Enter, ela é boxada como um objeto . Se você passar a mesma variável para Enter novamente, ela será boxada como um objeto separado e o thread não será bloqueado. Nesse caso, o código que Monitor supostamente está protegendo não está protegido. Além disso, quando você passa a variável para Exit, ainda é criado outro objeto separado. Como o objeto passado para Exit é diferente do objeto passado para Enter, Monitor lança SynchronizationLockException. Para obter mais informações, consulte o tópico conceitual Monitores.

Interrupt pode interromper threads que estão aguardando para inserir um Monitor em um objeto . Um ThreadInterruptedException será lançado.

Use um C# try... finally block (Try...Finally no Visual Basic) para garantir que você libere o monitor ou use a instrução C# lock (SyncLock no Visual Basic), que encapsula os Enter métodos e Exit em um try... finally Bloco.

Confira também

Aplica-se a

Enter(Object, Boolean)

Origem:
Monitor.CoreCLR.cs
Origem:
Monitor.CoreCLR.cs
Origem:
Monitor.CoreCLR.cs

Obtém um bloqueio exclusivo no objeto especificado e define automaticamente um valor que indica se o bloqueio foi realizado.

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)

Parâmetros

obj
Object

O objeto no qual aguardar.

lockTaken
Boolean

O resultado da tentativa de adquirir o bloqueio, passado por referência. A entrada deve ser false. A saída será true se o bloqueio for adquirido; caso contrário, a saída será false. A saída é definida mesmo se ocorrer uma exceção durante a tentativa de adquirir o bloqueio.

Observação Se nenhuma exceção ocorrer, a saída desse método será sempre true.

Exceções

A entrada para lockTaken é true.

O parâmetro obj é null.

Exemplos

O código a seguir mostra o padrão básico para usar a sobrecarga do Enter(Object, Boolean) método. Essa sobrecarga sempre define o valor da variável que é passada para o ref parâmetro (ByRef no Visual Basic), lockTakenmesmo que o método gere uma exceção, portanto, o valor da variável é uma maneira confiável de testar se o bloqueio deve ser liberado.

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

Comentários

Use Enter para adquirir o Monitor no objeto passado como o obj parâmetro . Se outro thread tiver executado um Enter no objeto, mas ainda não tiver executado o correspondente Exit, o thread atual será bloqueado até que o outro thread libere o objeto. É legal que o mesmo thread invoque Enter mais de uma vez sem que ele bloqueie; no entanto, um número igual de Exit chamadas deve ser invocado antes que outros threads que aguardam o objeto sejam desbloqueados.

Se o bloqueio não tiver sido feito porque uma exceção foi gerada, a variável especificada para o parâmetro será false após o lockTaken término desse método. Isso permite que o programa determine, em todos os casos, se é necessário liberar o bloqueio. Se esse método retornar sem gerar uma exceção, a variável especificada para o lockTaken parâmetro será sempre truee não será necessário testá-la.

Use Monitor para bloquear objetos (ou seja, tipos de referência), não tipos de valor. Quando você passa uma variável de tipo de valor para Enter, ela é boxada como um objeto . Se você passar a mesma variável para Enter novamente, ela será boxada como um objeto separado e o thread não será bloqueado. Nesse caso, o código que Monitor supostamente está protegendo não está protegido. Além disso, quando você passa a variável para Exit, outro objeto separado é criado. Como o objeto passado para Exit é diferente do objeto passado para Enter, Monitor lança SynchronizationLockException. Para obter mais informações, consulte o tópico conceitual Monitores.

Interrupt pode interromper threads que estão aguardando para inserir um Monitor em um objeto . Um ThreadInterruptedException será lançado.

Aplica-se a