Sort of SyncLock

Question

我正在检查这段代码，它正在执行类似于SyncLock的操作，但其他线程没有等待，而是跳过了代码。

代码是用变量来实现的；我想知道是否有一个内置的.net函数可以做到这一点？

Private _previousValueCount As Integer = 0
Private Sub F()
   If _previousValueCount = 0 Then
       _previousValueCount = 1
       ' ...
       _previousValueCount = 0
   End If
End Sub

Answer 1

有很多方法；一种方法是做一些类似的事情：

int lockTaken = 0;
...
bool haveLock = false;
try {
    haveLock = Interlocked.CompareExchange(ref lockTaken, 1, 0) == 0;
    if(haveLock) {
       // it was zero, it is now one; you won the lock: do something
    }
} finally {
    if(haveLock) Interlocked.Exchange(ref lockTaken, 0);
}

另一种方法是使用超时为零的Monitor.TryEnter：

readonly object syncLock = new object();
...
bool haveLock = false;
try {
    Monitor.TryEnter(syncLock, 0, ref haveLock);
    if(haveLock) {
      // you won it; do something
    }
} finally {
    if(haveLock) Monitor.Exit(syncLock);
}

Answer 2

您可以使用Monitor类，该类试图获取任何类型的全局对象的锁。如果在某个时间跨度/毫秒内未获得锁定，则可以根据需要执行操作。

bool acquiredLock = false;
try
{
  Monitor.TryEnter(lockObject, 1000, ref acquiredLock);
  if (acquiredLock)
  {
    // got lock, do something
  }
  else
  {
    // no lock - warning/error/...
  }
}
finally
{
  if (acquiredLock)
     Monitor.Exit(lockObject);  // release lock!
}