Question

my C# application reads data from special USB device. The data are read as so-called “messages”, each of them having 24 bytes. The amount of messages that must be read per second may differ (maximal frequency is quite high, about 700 messages per second), but the application must read them all.

The only way to read the messages is by calling function “ReadMessage”, that returns one message read from the device. The function is from external DLL and I cannot modify it.

My solution: I’ve got a seperate thread, that is running all the time during the program run and it’s only job is to read the messages in cycle. The received messages are then processed in main application thread.

The function executed in the “reading thread” is the following:

private void ReadingThreadFunction() {
    int cycleCount;
    try {
        while (this.keepReceivingMessages) {
            cycleCount++;
            TRxMsg receivedMessage;
            ReadMessage(devHandle, out receivedMessage);

            //...do something with the message...
        }
    }
    catch {
        //... catch exception if reading failed...
    }
}

This solution works fine and all messages are correctly received. However, the application consumes too much resources, the CPU of my computer runs at more than 80%. Therefore I’d like to reduce it.

Thanks to the “cycleCount” variable I know that the “cycling speed” of the thread is about 40 000 cycles per second. This is unnecessarily too much, since I need to receive maximum 700 messagges/sec. (and the device has buffer for about 100 messages, so the cycle speed can be even a little lower)

I tried to reduce the cycle speed by suspending the thread for 1 ms by Thread.Sleep(1); command. Of course, this didn’t work and the cycle speed became about 70 cycles/second which was not enough to read all messages. I know that this attempt was silly, that putting the thread to sleep and then waking him up takes much longer than 1 ms.

However, I don’t know what else to do: Is there some other way how to slow the thread execution down (to reduce CPU consumption) other than Thread.Sleep? Or am I completely wrong and should I use something different for this task instead of Thread, maybe Threading.Timer or ThreadPool?

Thanks a lot in advance for all suggestions. This is my first question here and I’m a beginner at using threads, so please excuse me if it’s not clear enough.

Answer 1

I would do:

//...do something with the message... 

// If the message is null, it indicates that we've read everything there is to be read.
// So lets sleep for 1ms to give the buffer chance to receive a few extra messages.
If (theMessage == null) // Buffer is empty as we failed to read a new message
{
    Thread.Sleep(1);
}

This way probably gives you maximum performance, other than hammering your CPU.