Question

I have the scenario where a command comes in over a socket which requires a fair amount of work. Only one thread can process the data at a time. The commands will come in faster than can process it. Over time there will be quiet a back log.

The good part is that I can discard waiting threads and really only have to process the last one that is waiting – (or process the first one in and discard all the other once). I was thinking about using a semaphore to control the critical section of code and to use a boolean to see if there are any threads blocking. If there are blocking thread I would just discard the thread.

My mind is drawing a blank on how to implement it nicely I would like to implement it with out using an integer or boolean to see if there is a thread waiting already.

I am coding this in c#

Answer 1

You can use Monitor.TryEnter to see whether a lock is already taken on an object:

void ProcessConnection(TcpClient client)
{
    bool lockTaken = false;

    Monitor.TryEnter(lockObject, out lockTaken);

    if (!lockTaken)
    {
        client.Close();
        return;
    }

    try
    {
        // long-running process here
    }
    finally
    {
        Monitor.Exit(lockObject);
        client.Close();
    }
}

Note that for this to work you’ll still have to invoke the method in a thread, for example:

client = listener.AcceptTcpClient();
ThreadPool.QueueUserWorkItem(notused => ProcessConnection(client));

FYI, the lock statement is just sugar for:

Monitor.Enter(lockObject);

try
{
    // code within lock { }
}
finally
{
    Monitor.Exit(lockObject);
}