是否可以使用 Monitor.Enter 获得排队线程的计数？

Question

我正在运行一些非线程安全的单例代码，并且需要一些时间才能运行。 它偶尔会被多个用户同时调用，所以我使用 Monitor 来处理处理请求排队，如下所示；

bool lockWasTaken = false;
try
{
    Monitor.TryEnter(lockObject, ref lockWasTaken); // returns lockWasTaken = true if it can get a lock
    if (!lockWasTaken)
    {
        log.Warn("Locked by existing request. Request is queued.");
        Monitor.Enter(lockObject, ref lockWasTaken); // Goes into the queue to access the object
    }

    // Do the Singleton processing

}
catch(Exception ex)
{
    log.Fatal(ex);
}
finally
{
    if (lockWasTaken)
    {
        Monitor.Exit(lockObject);
    }
}

这一切都很好。但我想做的是能够记录有多少排队的请求。 这可能吗？

Answer 1

感谢@Theodor Zoulias 使用 Interlocked 类为以下解决方案指明了正确的方向；

private static readonly Object lockObject = new Object(); // just a random object used to decide whether the thread has locked the Singleton functions
private static int queueCount = 0; // tracked across multiple threads

bool lockWasTaken = false;
try
{
    // Increments the queueCount variable across multiple threads
    // https://docs.microsoft.com/en-us/dotnet/api/system.threading.interlocked.increment?view=netframework-4.8
    int currentQueueCount = Interlocked.Increment(ref queueCount);

    Monitor.TryEnter(lockObject, ref lockWasTaken); // returns lockWasTaken = true if it can get a lock
    if (!lockWasTaken)
    {
        log.Warn("Locked by existing request. Request is queued. Queue length is " + (currentQueueCount - 1).ToString()); // subtract since the first request is already processing
        Monitor.Enter(lockObject, ref lockWasTaken); // Goes into the queue to access the object
    }

    // Do the Singleton processing

}
catch(Exception ex)
{
    log.Fatal(ex);
}
finally
{
    if (lockWasTaken)
    {
        Monitor.Exit(lockObject);
    }
    // Reduce the queue count
    Interlocked.Decrement(ref queueCount);
}