Question

I have written this code for a Message Receiving class that uses a backgroundworker to check for new files in a directory (the files are SMS messages received from users that are updating continuously). If the directory is not empty, I send an acknowledgement message to every new SMS and start the worker again.

 public MessageReceiving()
    {
        bw.DoWork += new DoWorkEventHandler(bw_DoWork);
        bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);           
    }
void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {   
        if(e.Result == true)
        { 
        SendAcknowledgement();
        if(!bw.IsBusy)
            bw.RunWorkerAsync();
        }
    }

void bw_DoWork(object sender, DoWorkEventArgs e)
    {
       bool flag = false;
        while (flag.Equals(false))
        {
            string path = @"C:\SMS";
            if (Directory.GetFiles(path).Length > 0)
            {
                e.Result = true;
                flag = true;
            }
            else
            {
                e.Result = false;
            }
        }

    }

I initialize the worker from the main thread once –

MessageReceiving mr = new MessageReceiving();
mr.bw.RunWorkerAsync();

I did all this to allow me to send messages synchronously to users – As soon as a user send an SMS, I send him an ACK. The problem is that the user is getting multiple ACKs even on sending one SMS – why is this happening? I have thought of every possibility, but to no avail!

Answer 1

Consider what happens when this starts:

• You start running bw_DoWork
• That then tight-loops (not a good idea to start with) until it finds a file
• The background worker completes, and you send an acknowledgement
• You then immediately run the background worker again… which will find the file again unless you’ve deleted the file during SendAcknowledgement. Have you?

I suspect what you really want instead of any of this is a FileSystemWatcher by the way. Also note that just because a file is present doesn’t mean that it’s finished being written to yet, or that you can read it.

Additionally, your tight loop can be made a lot simpler:

void bw_DoWork(object sender, DoWorkEventArgs e)
{
    string path = @"C:\SMS";
    while (!e.Result)
    {
        e.Result = Directory.GetFiles(path).Any();
    }
}

and I would likewise change

if (e.Result == true)

to

if (e.Result)

(Assuming e.Result is typed as a bool; if it’s not, your current code has other problems.)