Question

I am trying to port some code from C++ to C#.

I came across this in the C++ code:

watchdogTimer = SetTimer(1,1000,NULL);
...
KillTimer(watchdogTimer);

What is this code doing, and how can this be ported to C#?

Thanks.

Answer 1

The CWnd::SetTimer function you’re looking at creates a timer that sends WM_TIMER events to the window. This is analogous to the System.Windows.Forms.Timer component in .NET. It behaves somewhat differently than the System.Timers.Timer. There are two differences that are particularly relevant:

Windows.Forms.Timer calls the event handler on the UI thread. By default, System.Timers.Timer calls the event handler on a threadpool thread. You can use SynchronizingObject property to have the System.Timers.Timer call on the UI thread.

Another difference is that it’s not possible to encounter reentrancy problems with the Windows Forms timer because Windows won’t allow multiple WM_TIMER messages from the same timer in the queue, nor will it place a WM_TIMER message in the queue if one is already being processed. This is generally a good thing.

System.Timers.Timer, on the other hand, will allow reentrancy. So if your timer event handler takes longer than the timer period, you can be processing multiple events for the same timer concurrently. If your timer period is 100 ms and processing takes 150 ms, you’re going to get another notification while you’re processing the first one. If you use the SynchronizingObject to force the callback on the UI thread, this can lead to a whole bunch of pending callbacks being queued.

The implementation of the two timers is quite different. The Windows Forms timer uses old style Windows timers that have been around for 20 years. This type of timer requires a window handle and a message loop, and is therefore used only in GUI programs. System.Timers.Timer is a thin wrapper around System.Threading.Timer, which uses the Windows Thread Pool Timers.