Monitor.TryEnter 方法

  • 參考

定義

命名空間:
System.Threading
組件:
System.Threading.dll
組件:
mscorlib.dll
組件:
netstandard.dll

嘗試取得指定物件的獨佔鎖定。

多載

TryEnter(Object, TimeSpan, Boolean)

嘗試在指定的時間內取得指定之物件的獨佔鎖定，並且完整設定值，指出是否採用鎖定。
TryEnter(Object, Int32, Boolean)

嘗試在指定的毫秒數內取得指定之物件的獨佔鎖定，並且完整設定值，指出是否採用鎖定。
TryEnter(Object, TimeSpan)

嘗試取得指定物件的獨佔鎖定 (在指定的時間內)。
TryEnter(Object, Boolean)

嘗試取得指定之物件的獨佔鎖定，並且完整設定值，指出是否採用鎖定。
TryEnter(Object)

嘗試取得指定物件的獨佔鎖定。
TryEnter(Object, Int32)

嘗試取得指定物件的獨佔鎖定 (在指定的毫秒數時間內)。

TryEnter(Object, TimeSpan, Boolean)

Source:
Monitor.cs
Source:
Monitor.cs
Source:
Monitor.cs

嘗試在指定的時間內取得指定之物件的獨佔鎖定，並且完整設定值，指出是否採用鎖定。

public:
 static void TryEnter(System::Object ^ obj, TimeSpan timeout, bool % lockTaken);
public static void TryEnter (object obj, TimeSpan timeout, ref bool lockTaken);
static member TryEnter : obj * TimeSpan * bool -> unit
Public Shared Sub TryEnter (obj As Object, timeout As TimeSpan, ByRef lockTaken As Boolean)

參數

obj
Object

要取得鎖定的物件。

timeout
TimeSpan

等候鎖定的時間長度。 -1 毫秒的值會指定無限期等候。

lockTaken
Boolean

嘗試取得鎖定的結果 (以傳址方式傳遞)。 輸入必須是 false。 如果已取得鎖定，輸出就是 true；否則輸出為 false。 嘗試取得鎖定期間，即使發生例外狀況，仍然會設定輸出。

例外狀況

ArgumentException

lockTaken 的輸入為 true。

ArgumentNullException

obj 參數為 null。

ArgumentOutOfRangeException

以毫秒為單位的 timeout 值為負值，且不等於 Infinite (-1 毫秒) ，或大於 Int32.MaxValue。

備註

如果轉換成毫秒的參數 timeout 值等於 -1，則這個方法相當於 Enter(Object) 。 如果 的值 timeout 等於 0，這個方法就 TryEnter(Object) 等於 。

如果因為擲回例外狀況而未取得鎖定，則為 lockTaken 參數指定的變數會在 false 此方法結束時。 這可讓程式在所有情況下判斷是否需要釋放鎖定。

注意

用來 Monitor 鎖定物件 (也就是參考型別) ，而不是實值型別。 如需詳細資訊，請參閱 Monitor 類別主題。

若要確保執行緒未進入關鍵區段，您應該檢查 的值，並只在關鍵區段中的值 lockTaken 是 true 時執行程式碼。 下列程式碼片段顯示用來呼叫這個方法的模式。 請注意，您應該在 區塊中 finally 呼叫 Exit ，以確保當發生例外狀況時，呼叫執行緒會在重大區段上釋放其鎖定。

var lockObj = new Object();
var timeout = TimeSpan.FromMilliseconds(500);
bool lockTaken = false;

try {
   Monitor.TryEnter(lockObj, timeout, ref lockTaken);
   if (lockTaken) {
      // The critical section.
   }
   else {
      // The lock was not acquired.
   }
}
finally {
   // Ensure that the lock is released.
   if (lockTaken) {
      Monitor.Exit(lockObj);
   }
}

Dim lockObj As New Object()
Dim timeout = TimeSpan.FromMilliseconds(500)
Dim lockTaken As Boolean = False

Try
   Monitor.TryEnter(lockObj, timeout, lockTaken)
   If lockTaken Then
      ' The critical section.
   Else
      ' The lock was not acquired.
   End If
Finally
   ' Ensure that the lock is released.
   If lockTaken Then Monitor.Exit(lockObj)
End Try

另請參閱

適用於

TryEnter(Object, Int32, Boolean)

Source:
Monitor.CoreCLR.cs
Source:
Monitor.CoreCLR.cs
Source:
Monitor.CoreCLR.cs

嘗試在指定的毫秒數內取得指定之物件的獨佔鎖定，並且完整設定值，指出是否採用鎖定。

public:
 static void TryEnter(System::Object ^ obj, int millisecondsTimeout, bool % lockTaken);
public static void TryEnter (object obj, int millisecondsTimeout, ref bool lockTaken);
static member TryEnter : obj * int * bool -> unit
Public Shared Sub TryEnter (obj As Object, millisecondsTimeout As Integer, ByRef lockTaken As Boolean)

參數

obj
Object

要取得鎖定的物件。

millisecondsTimeout
Int32

等候鎖定的毫秒數。

lockTaken
Boolean

嘗試取得鎖定的結果 (以傳址方式傳遞)。 輸入必須是 false。 如果已取得鎖定，輸出就是 true；否則輸出為 false。 嘗試取得鎖定期間，即使發生例外狀況，仍然會設定輸出。

例外狀況

ArgumentException

lockTaken 的輸入為 true。

ArgumentNullException

obj 參數為 null。

ArgumentOutOfRangeException

millisecondsTimeout 是負數，且不等於 Infinite。

範例

下列程式碼顯示使用 TryEnter(Object, Boolean) 方法多載的基本模式。 即使方法擲回例外狀況，這個多載一律會設定傳遞至 ref Visual Basic lockTaken) 中參數 (ByRef 變數的值，因此變數的值是測試是否必須釋放鎖定的可靠方法。

bool acquiredLock = false;

try
{
    Monitor.TryEnter(lockObject, 500, ref acquiredLock);
    if (acquiredLock)
    {

        // Code that accesses resources that are protected by the lock.
    }
    else
    {
    
        // Code to deal with the fact that the lock was not acquired.
    }
}
finally
{
    if (acquiredLock)
    {
        Monitor.Exit(lockObject);
    }
}

Dim acquiredLock As Boolean = False

Try
    Monitor.TryEnter(lockObject, 500, acquiredLock)
    If acquiredLock Then

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

    Else

        ' Code to deal with the fact that the lock was not acquired.

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

備註

millisecondsTimeout如果 參數等於 Infinite ，則這個方法相當於 Enter(Object) 。 如果 millisecondsTimeout 等於 0，則這個方法相當於 TryEnter(Object) 。

如果因為擲回例外狀況而未取得鎖定，則為 lockTaken 參數指定的變數會在 false 此方法結束時。 這可讓程式在所有情況下判斷是否需要釋放鎖定。

注意

用來 Monitor 鎖定物件 (也就是參考型別) ，而不是實值型別。 如需詳細資訊，請參閱 Monitor 類別主題。

若要確保執行緒未進入關鍵區段，您應該檢查 的值，並只在關鍵區段中的值 lockTaken 是 true 時執行程式碼。 下列程式碼片段顯示用來呼叫這個方法的模式。 請注意，您應該在 區塊中 finally 呼叫 Exit ，以確保當發生例外狀況時，呼叫執行緒會在重大區段上釋放其鎖定。

var lockObj = new Object();
int timeout = 500;
bool lockTaken = false;

try {
   Monitor.TryEnter(lockObj, timeout, ref lockTaken);
   if (lockTaken) {
      // The critical section.
   }
   else {
      // The lock was not acquired.
   }
}
finally {
   // Ensure that the lock is released.
   if (lockTaken) {
      Monitor.Exit(lockObj);
   }   
}

Dim lockObj As New Object()
Dim timeout As Integer = 500
Dim lockTaken As Boolean = False

Try
   Monitor.TryEnter(lockObj, timeout, lockTaken)
   If lockTaken Then
      ' The critical section.
   Else
      ' The lock was not acquired.
   End If
Finally
   ' Ensure that the lock is released.
   If lockTaken Then Monitor.Exit(lockObj)
End Try

適用於

TryEnter(Object, TimeSpan)

Source:
Monitor.cs
Source:
Monitor.cs
Source:
Monitor.cs

嘗試取得指定物件的獨佔鎖定 (在指定的時間內)。

public:
 static bool TryEnter(System::Object ^ obj, TimeSpan timeout);
public static bool TryEnter (object obj, TimeSpan timeout);
static member TryEnter : obj * TimeSpan -> bool
Public Shared Function TryEnter (obj As Object, timeout As TimeSpan) As Boolean

參數

obj
Object

要取得鎖定的物件。

timeout
TimeSpan

TimeSpan，代表等候鎖定的時間量。 -1 毫秒的值會指定無限期等候。

傳回

Boolean

如果目前執行緒取得鎖定，則為 true；否則為 false。

例外狀況

ArgumentNullException

obj 參數為 null。

ArgumentOutOfRangeException

以毫秒為單位的 timeout 值為負值，且不等於 Infinite (-1 毫秒) ，或大於 Int32.MaxValue。

備註

如果轉換成毫秒的參數 timeout 值等於 -1，則這個方法相當於 Enter 。 如果 的值 timeout 等於 0，這個方法就 TryEnter 等於 。

注意

用來 Monitor 鎖定物件 (也就是參考型別) ，而不是實值型別。 如需詳細資訊，請參閱 Monitor 類別主題。

若要確保執行緒未進入關鍵區段，您應該檢查方法的傳回值，並在關鍵區段中執行程式碼，只有當其傳回值為 true 時，才在關鍵區段中執行程式碼。 下列程式碼片段顯示用來呼叫這個方法的模式。 請注意，您應該在 區塊中 finally 呼叫 Exit ，以確保當發生例外狀況時，呼叫執行緒會在重大區段上釋放其鎖定。

var lockObj = new Object();
var timeout = TimeSpan.FromMilliseconds(500);

if (Monitor.TryEnter(lockObj, timeout)) {
   try {
      // The critical section.
   }
   finally {
      // Ensure that the lock is released.
      Monitor.Exit(lockObj);
   }
}
else {
   // The lock was not acquired.
}

Dim lockObj As New Object()
Dim timeout = TimeSpan.FromMilliseconds(500)

If Monitor.TryEnter(lockObj, timeout) Then
   Try
      ' The critical section.
   Finally
      ' Ensure that the lock is released.
      Monitor.Exit(lockObj)
   End Try
Else
   ' The lock was not acquired.
End If

另請參閱

適用於

TryEnter(Object, Boolean)

Source:
Monitor.CoreCLR.cs
Source:
Monitor.CoreCLR.cs
Source:
Monitor.CoreCLR.cs

嘗試取得指定之物件的獨佔鎖定，並且完整設定值，指出是否採用鎖定。

public:
 static void TryEnter(System::Object ^ obj, bool % lockTaken);
public static void TryEnter (object obj, ref bool lockTaken);
static member TryEnter : obj * bool -> unit
Public Shared Sub TryEnter (obj As Object, ByRef lockTaken As Boolean)

參數

obj
Object

要取得鎖定的物件。

lockTaken
Boolean

嘗試取得鎖定的結果 (以傳址方式傳遞)。 輸入必須是 false。 如果已取得鎖定，輸出就是 true；否則輸出為 false。 嘗試取得鎖定期間，即使發生例外狀況，仍然會設定輸出。

例外狀況

ArgumentException

lockTaken 的輸入為 true。

ArgumentNullException

obj 參數為 null。

範例

下列程式碼顯示使用 TryEnter(Object, Boolean) 方法多載的基本模式。 即使方法擲回例外狀況，這個多載一律會設定傳遞至 ref Visual Basic lockTaken) 中參數 (ByRef 變數的值，因此變數的值是測試是否必須釋放鎖定的可靠方法。

bool acquiredLock = false;

try
{
    Monitor.TryEnter(lockObject, ref acquiredLock);
    if (acquiredLock)
    {

        // Code that accesses resources that are protected by the lock.
    }
    else
    {
    
        // Code to deal with the fact that the lock was not acquired.
    }
}
finally
{
    if (acquiredLock)
    {
        Monitor.Exit(lockObject);
    }
}

Dim acquiredLock As Boolean = False

Try
    Monitor.TryEnter(lockObject, acquiredLock)
    If acquiredLock Then

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

    Else

        ' Code to deal with the fact that the lock was not acquired.

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

備註

如果成功，此方法會取得 參數的 obj 獨佔鎖定。 不論鎖定是否可用，這個方法都會立即傳回 。

如果因為擲回例外狀況而未取得鎖定，則為 lockTaken 參數指定的變數會在 false 此方法結束時。 這可讓程式在所有情況下判斷是否需要釋放鎖定。

這個方法類似于 Enter(Object, Boolean) ，但永遠不會封鎖目前的執行緒。 如果執行緒在未封鎖的情況下無法輸入，當方法傳回時， lockTaken 引數會設定為 false 。

注意

用來 Monitor 鎖定物件 (也就是參考型別) ，而不是實值型別。 如需詳細資訊，請參閱 Monitor 文章。

若要確保執行緒未進入關鍵區段，您應該檢查 的值，並只在關鍵區段中的值 lockTaken 是 true 時執行程式碼。 下列程式碼片段顯示用來呼叫這個方法的模式。 請注意，您應該在 區塊中 finally 呼叫 Exit ，以確保當發生例外狀況時，呼叫執行緒會在重大區段上釋放其鎖定。

var lockObj = new Object();
bool lockTaken = false;

try {
   Monitor.TryEnter(lockObj, ref lockTaken); 
   if (lockTaken) {
      // The critical section.
   }
   else {
      // The lock was not acquired.
   }
}
finally {
   // Ensure that the lock is released.
   if (lockTaken) {
      Monitor.Exit(lockObj);
   }
}

Dim lockObj As New Object()
Dim lockTaken As Boolean = False

Try 
   Monitor.TryEnter(lockObj, lockTaken) 
   If lockTaken Then
      ' The critical section.
   Else 
      ' The lock was not acquired.
   End If
Finally 
   ' Ensure that the lock is released.
   If lockTaken Then Monitor.Exit(lockObj)
End Try

適用於

TryEnter(Object)

Source:
Monitor.CoreCLR.cs
Source:
Monitor.CoreCLR.cs
Source:
Monitor.CoreCLR.cs

嘗試取得指定物件的獨佔鎖定。

public:
 static bool TryEnter(System::Object ^ obj);
public static bool TryEnter (object obj);
static member TryEnter : obj -> bool
Public Shared Function TryEnter (obj As Object) As Boolean

參數

obj
Object

要取得鎖定的物件。

傳回

Boolean

如果目前執行緒取得鎖定，則為 true；否則為 false。

例外狀況

ArgumentNullException

obj 參數為 null。

範例

下列程式碼範例會示範如何使用 TryEnter 方法。

#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

備註

如果成功，此方法會取得 參數的 obj 獨佔鎖定。 這個方法會立即傳回，無論鎖定是否可用。

這個方法類似于 Enter ，但它永遠不會封鎖目前的執行緒。 如果執行緒在未封鎖的情況下無法輸入，則方法會傳 false, 回 。

注意

使用 Monitor (鎖定物件，也就是參考型別) ，而非實值型別。 如需詳細資訊，請參閱 Monitor 文章。

若要確保執行緒未進入關鍵區段，您應該檢查方法的傳回值，並在關鍵區段中執行程式碼，只有當其傳回值為 true 時， 才會執行。 下列程式碼片段顯示用來呼叫此方法的模式。 請注意，您應該在 區塊中 finally 呼叫 Exit ，以確保呼叫執行緒會在發生例外狀況時，釋放其重大區段上的鎖定。

var lockObj = new Object();

if (Monitor.TryEnter(lockObj)) {
   try {
      // The critical section.
   }
   finally {
      // Ensure that the lock is released.
      Monitor.Exit(lockObj);
   }
}
else {
   // The lock was not axquired.
}

Dim lockObj As New Object()

If Monitor.TryEnter(lockObj) Then
   Try
      ' The critical section.
   Finally
      ' Ensure that the lock is released.
      Monitor.Exit(lockObj)
   End Try
Else
   ' The lock was not acquired.
End If

另請參閱

適用於

TryEnter(Object, Int32)

Source:
Monitor.CoreCLR.cs
Source:
Monitor.CoreCLR.cs
Source:
Monitor.CoreCLR.cs

嘗試取得指定物件的獨佔鎖定 (在指定的毫秒數時間內)。

public:
 static bool TryEnter(System::Object ^ obj, int millisecondsTimeout);
public static bool TryEnter (object obj, int millisecondsTimeout);
static member TryEnter : obj * int -> bool
Public Shared Function TryEnter (obj As Object, millisecondsTimeout As Integer) As Boolean

參數

obj
Object

要取得鎖定的物件。

millisecondsTimeout
Int32

等候鎖定的毫秒數。

傳回

Boolean

如果目前執行緒取得鎖定，則為 true；否則為 false。

例外狀況

ArgumentNullException

obj 參數為 null。

ArgumentOutOfRangeException

millisecondsTimeout 是負數，且不等於 Infinite。

備註

millisecondsTimeout如果 參數等於 Infinite ，則這個方法相當於 Enter 。 如果 millisecondsTimeout 等於 0，則這個方法相當於 TryEnter 。

注意

使用 Monitor (鎖定物件，也就是參考型別) ，而非實值型別。 如需詳細資訊，請參閱 Monitor 文章。

若要確保執行緒未進入關鍵區段，您應該檢查方法的傳回值，並在關鍵區段中執行程式碼，只有當其傳回值為 true 時， 才會執行。 下列程式碼片段顯示用來呼叫此方法的模式。 請注意，您應該在 區塊中 finally 呼叫 Exit ，以確保呼叫執行緒會在發生例外狀況時，釋放其重大區段上的鎖定。

var lockObj = new Object();
int timeout = 500;

if (Monitor.TryEnter(lockObj, timeout)) {
   try {
      // The critical section.
   }
   finally {
      // Ensure that the lock is released.
      Monitor.Exit(lockObj);
   }
}
else {
   // The lock was not acquired.
}

Dim lockObj As New Object()
Dim timeout As Integer = 500

If Monitor.TryEnter(lockObj, timeout) Then
   Try
      ' The critical section.
   Finally
      ' Ensure that the lock is released.
      Monitor.Exit(lockObj)
   End Try
Else
   ' The lock was not acquired.
End If

另請參閱

適用於