Question

I want to implement the following functionality in C# console application:

1. spawn several worker threads in main thread;
2. each worker thread processes data and send string message to main thread periodically;
3. main thread processes messages and wait for all worker threads to finish;
4. main thread exit.

Now I’m using TPL, but I don’t know how to send messages from worker threads to main thread. Thank you for help!

Answer 1

You could use a Producer / Consumer pattern with the TPL as demonstrated in this example on an MSDN blog.

Or, you could kick it old-school and use signaling, see AutoResetEvent.

Or if you care to work at a very low level, use Monitor.Pulse with Monitor.WaitOne (as demonstrated here).

Either way, you are looking for Synchronization, which you can read up on here.

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Other option, if you don’t actually care what thread the update is running on, would be to take a delegate as an argument and print the update there, à la:

static Task<string> ReadFile(string filename, Action<string> updateStatus)
{

    //do stuf synchronously
    return Task<string>.Factory.StartNew(() => {
        System.Threading.Thread.Sleep(1000);
        //do async stuff
        updateStatus("update message");
        //do other stuff
        return "The result";
    });
}

public static void Main(string[] args) 
{
    var getStringTask = ReadFile("File.txt", (update) => {
        Console.WriteLine(update)
    });
    Console.Writeline("Reading file...");
    //do other stuff here
    //getStringTask.Result will wait if not complete
    Console.WriteLine("File contents: {0}", getStringTask.Result);
}

would print:

Reading file...
update message
File contents: The result

The "update message" call to Console.WriteLine would still occur on the ThreadPool thread, but it may still fill your need.