Threads and event handlers

[TMattC]

I´m writing a communication library and have a threaded method listening for incoming data:

///// Inside my library /////
public partial class MCSerialPort
{
(SerialPort)port.DataReceived += DataReceivedHandler;

// The event handler method
private async void DataReceivedHandler(object sender, SerialDataReceivedEventArgs args)
{
await ReadData();
}

private async Task ReadData()
{
await Task.Run(() =>
{
... // Reading incoming
// Triggering an event
PackageReceived(this, new PackageReceivedEventArgs(package));
});
}
}

///// Inside the "client" using the library /////
(MCSerialPort)port.PackageReceived += PackageReceivedHandler;

private void PackageReceivedHandler(object sender, PackageReceivedEventArgs args)
{
Package p = args.Package;
receivedRtb.Invoke((Action)delegate{receivedRtb.Text += p.ToString();} );
}

The thing is that when using this library in a "client" project the PackageReceived event handler method in the client (here the PackageReceivedHandler()) seems to be running on the same thread as the librarys ReadData() method, because I have to call Invoke() in this example in order to get the info into the receivedRtb RichTextBox. This complicates things slightly for the average library user, who might not think of having to write threadsafe code in the handler method. Is there any convenient way to make PackageReceivedHandler() run on the "main" thread?

[PIEBALDconsult]

TMattC wrote:

the PackageReceivedHandler()) seems to be running on the same thread as the librarys ReadData() method

Correct. I think it's fine the way it is; the library should neither know nor care about the concerns of the calling application.

[Richard Deeming]

TMattC wrote:

... the PackageReceived event handler method in the client (here the PackageReceivedHandler()) seems to be running on the same thread as the librarys ReadData() method, because I have to call Invoke() ...

No, you have to call Invoke() because the PackageReceivedHandler isn't running on the UI thread. There are various ways to raise the event on the UI thread - for example, using the SynchronizationContext class[^]. (It's All About the SynchronizationContext - MSDN Magazine[^]) However, since most libraries don't both doing this, most UI developers should be used to having to marshal the event handler code to the UI thread.

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