Repeating BackgroundWorker task using DistpatcherTimer

Question

I'm trying to figure out the best way to approach this.

I have a BackgroundWorker which is being used to make a socket connection on a timer.

Public Shared AllUsersWorker As New BackgroundWorker
Public Shared AllUsersWorkerTimer As New DispatcherTimer

AllUsersWorkerTimer.Interval = TimeSpan.FromSeconds(2)
AllUsersWorkerTimer.Start()

AddHandler AllUsersWorkerTimer.Tick, AddressOf All_Users_Worker_Timer_Tick

Public Shared Sub All_Users_Worker_Timer_Tick()
    AllUsersWorker.RunWorkerAsync()
End Sub

Public Shared Sub AllUsersWorker_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)

    tcpClient = New TcpClient
    tcpClient.Connect("localhost", 9999)

    networkStream = tcpClient.GetStream

    If networkStream.CanWrite And networkStream.CanRead Then
        Read_All_Connections()
    End If
    tcpClient.Close()
End Sub

I want to start the BackgroundWorker thread which establishes a TCP connection, reads/write some data and then close the connection and repeat every 2 seconds.

I want to physically open/close the connection each time because from time to time the server I'm connecting to doesn't send data and the readByte call halts waiting for data and the process can't continue until I reset the program (hence wanting to use a different thread to my UI).

At the moment I'm trying to use a DispatcherTimer with an Interval of 2 seconds to call Worker.RunWorkerAsync. When RunWorkerAsync is called, the DoEvents method runs - this is working ok for the first time but on subsequent DispatcherTimer tick's I'm finding the previous thread isn't closing so when calling RunWorkerAsync I'm getting

"This BackgroundWorker is currently busy and cannot run multiple tasks concurrently"

What is the best way I can achieve this?

Is there a better way?

edit: thinking about it. It would be good if I could somehow build a watchdog into it, so if the BackgroundWorker thread is found to be running for more than 2 seconds, it's terminated as this would indicate the thread has been held up by the tcp connection.

Ben

It would help if you posted some code: how you configure the DispatcherTimer and what's in the DoEvents method. — Louis Kottmann, Oct 28 '11 at 11:18
Just stop the timer in the Tick event handler, start it back up in the RunWorkerCompleted event handler. Or create a new BGW if that makes sense (it rarely does). — Hans Passant, Oct 28 '11 at 11:57

score 1 · Accepted Answer · answered Oct 28 '11 at 12:14

The BackgroundWorker.CancelAsync doesnt really auto-cancels the worker but that is just a flag which comes into ther DoWork(object sender, DoWorkEventArgs e) call as e.Cancel = true and \ or BackgroundWorker.CancellationPending so that a code condition can check it and return from the DoWork() thereby manually cancelling the work itself.

This is what MSDN says...

The worker code should periodically check the CancellationPending property to see if it has been set to true.

For the auto-cancellation there is Thread.Abort() call, but it may throw a ThreadAbortException. So be ready to try \ catch AllUsersWorker.RunWorkerAsync() call.

score 0 · Answer 2 · answered Oct 28 '11 at 11:40

0

To know if the worker is not available you can check the property: IsBusy

So when the timer ticks for the second time, you could just check if the first one is busy (in which case you can cancel it by using CancelAsync) and run a new one.

answered Oct 28 '11 at 11:40

Louis Kottmann

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Just tried that. The IsBusy is True on the second time around, but even calling CancelAsync doesn't seem to kill it. – Ben Oct 28 '11 at 11:45
CancelAsync() just sets the property "CancellationPending" to true in your backgroundworker, it is your responsibility to check that property and end DoEvents when you encounter it. I don't do VB but I'm sure you can find plenty of example all over the web. – Louis Kottmann Oct 28 '11 at 11:53
Canceling and waiting for it to stop being busy doesn't work. That's called deadlock. – Hans Passant Oct 28 '11 at 11:56
That's not what i meant. I advised that if the worker is busy, then cancel it and make another one while the firt one stops gracefully. There's no deadlock if he uses 2 objets. – Louis Kottmann Oct 28 '11 at 11:57

Repeating BackgroundWorker task using DistpatcherTimer

2 Answers2