Question

I have a desktop app (.net 3.5) which communicates with the server using classic web services.
I need to make numerous calls to web service functions, wait for them all to finish, and then proceed.

I’d like to do these calls in parallel; so obviously I’m looking to utilize the MyFunctionAsync method.
The thing is- i’m not sure how to verify that all calls have returned. I’m probably missing some simple synchronization mechanism here.

here’s what i’d like to be able to do:

public void DoWork()
{
   service.MyFuncCompleted+= MyFunc_Completed;
   foreach (var i in items)
   {
      service.MyFuncAsync(i);
      syncMechanism.WaitForAnother(1);  //signal that we have to wait for 1 more task to finish
   }
   syncMechanism.WaitForAllTasksToFinsih();  //wait until specified number of tasks have finished

   //continue
}

public void MyFunc_Completed(EventArgs e)
{
   //process result...
   syncMechanism.Signal(1);  //signal that 1 task has finished
}

anybody know anything like this is c#?

Answer 1

This ( fork / join ) is a lot easier in .NET 4, but you’re on 3.5 so you’ll have to do it the old-fashioned way.

Basically, increment a counter for each operation and then decrement it in your Completed handler. Then check if it’s got down to zero and if so signal a wait handle to indicate all operations have completed.

Here’s an example of the idea:

static ManualResetEvent mre = new ManualResetEvent( false );
static int inFlight = 1; // start with 1 to fix race condition

static void DoWork()
{
    for ( int i = 0 ; i < 10 ; i++ )
    {
        var bw = new BackgroundWorker();

        bw.DoWork += bw_DoWork;
        bw.RunWorkerCompleted += bw_RunWorkerCompleted;

        Interlocked.Increment( ref inFlight );

        bw.RunWorkerAsync();
    }

    if ( Interlocked.Decrement( ref inFlight ) == 0 ) mre.Set();

    mre.WaitOne(); // this blocks until all workers have completed
}

static void bw_DoWork( object sender, DoWorkEventArgs e )
{
    Thread.Sleep( 1000 );
}

static void bw_RunWorkerCompleted( object sender, RunWorkerCompletedEventArgs e )
{
    if ( Interlocked.Decrement( ref inFlight ) == 0 ) mre.Set();
}