Monitor.Enter 方法
定义
重要
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获取指定对象上的排他锁。
重载
| Enter(Object) |
在指定对象上获取排他锁。 |
| Enter(Object, Boolean) |
获取指定对象上的排他锁，并自动设置一个值，指示是否获取了该锁。 |
Enter(Object)
在指定对象上获取排他锁。
public:
static void Enter(System::Object ^ obj);public static void Enter (object obj);static member Enter : obj -> unitPublic Shared Sub Enter (obj As Object)参数
- obj
- Object
在其上获取监视器锁的对象。
例外
obj 参数为 null。
示例
下面的示例演示如何使用 Enter 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
注解
用于 Enter 获取 Monitor 作为参数传递的对象。 如果另一个线程已对对象执行某个 Enter 对象，但尚未执行相应的 Exit操作，则当前线程将阻止，直到其他线程释放该对象。 同一线程在未阻止的情况下多次调用 Enter 是合法的;但是，在等待对象的其他线程解除阻止之前，必须调用相等数量的 Exit 调用。
用于 Monitor 锁定 (的对象，即引用类型) ，而不是值类型。 将值类型变量 Enter传递给时，它将作为对象装箱。 如果将同一变量再次传递给 Enter ，则会将其装箱为单独的对象，并且线程不会阻止。 在这种情况下，应该保护的代码 Monitor 不受保护。 此外，将变量传递给 Exit该变量时，还会创建另一个单独的对象。 由于传递给 Exit 的对象不同于传递给 Enter的对象， Monitor 因此引发 SynchronizationLockException。 有关详细信息，请参阅概念主题 监视器。
Interrupt 可以中断等待输入 Monitor 对象上的线程。 将引发 A ThreadInterruptedException 。
使用 C# try...finally 块 (Try...Finally 在 Visual Basic) 以确保释放监视器或使用 Visual Basic) 中的 C# lock 语句 (SyncLock语句，这将包装 Enter ...中的try和Exit方法finally 块。
另请参阅
适用于
Enter(Object, Boolean)
获取指定对象上的排他锁，并自动设置一个值，指示是否获取了该锁。
public:
static void Enter(System::Object ^ obj, bool % lockTaken);public static void Enter (object obj, ref bool lockTaken);static member Enter : obj * bool -> unitPublic Shared Sub Enter (obj As Object, ByRef lockTaken As Boolean)参数
- obj
- Object
要在其上等待的对象。
- lockTaken
- Boolean
尝试获取锁的结果，通过引用传递。 输入必须为 false。 如果已获取锁，则输出为 true；否则输出为 false。 即使在尝试获取锁的过程中发生异常，也会设置输出。
注意 如果没有发生异常，则此方法的输出始终为 true。
例外
lockTaken 的输入为 true。
obj 参数为 null。
示例
以下代码显示了使用 Enter(Object, Boolean) 方法重载的基本模式。 此重载始终设置在 Visual Basic lockTaken) 中传递给ref参数 (ByRef的变量的值，即使该方法引发异常，因此变量的值是测试是否必须释放锁的可靠方法。
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
注解
用于 Enter 获取 Monitor 作为 obj 参数传递的对象。 如果另一个线程已对对象执行某个 Enter 对象，但尚未执行相应的 Exit操作，则当前线程将阻止，直到其他线程释放该对象。 同一线程在未阻止的情况下多次调用 Enter 是合法的;但是，在等待对象的其他线程解除阻止之前，必须调用相等数量的 Exit 调用。
如果未由于引发异常而引发锁，则 lockTaken 为参数指定的变量在 false 此方法结束时。 这允许程序在所有情况下确定是否有必要释放锁。 如果此方法返回时不引发异常，则为 lockTaken 参数指定的变量始终 true为该变量，并且无需对其进行测试。
用于 Monitor 锁定 (的对象，即引用类型) ，而不是值类型。 将值类型变量 Enter传递给时，它将作为对象装箱。 如果将同一变量再次传递给 Enter ，则会将其装箱为单独的对象，并且线程不会阻止。 在这种情况下，应该保护的代码 Monitor 不受保护。 此外，将变量传递给该变量 Exit时，会创建另一个单独的对象。 由于传递给 Exit 的对象不同于传递给 Enter的对象， Monitor 因此引发 SynchronizationLockException。 有关详细信息，请参阅概念主题 监视器。
Interrupt 可以中断等待输入 Monitor 对象上的线程。 将引发 A ThreadInterruptedException 。