Question

Can anybody suggest any reasons why a C# timer (created in a code-behind class) would stop without being told to?

My timer starts on page load and then stops when I click a button. I don’t need to click the button for it to sometimes stop. IIS is not being restarted to my knowledge and no errors are being thrown either.

This is confusing me quite a bit…

Thanks.

    // This gets called on page_load
    private void checkTimer()
    {
        if (!parentTimer.Enabled) // If parent timer is not enabled then it is probably the start of a new day (after a night time server backup which kills timers)
        {
            parentTimer.Interval = 60000; // One minute
            parentTimer.Elapsed += new ElapsedEventHandler(parentTimer_Elapsed); // Define what happens when elapsed
            parentTimer.AutoReset = true; // Set timer to repeat
            parentTimer.Enabled = true; // Start the timer
        }
    }

    protected void btnCancel_Click(object sender, System.EventArgs e)
    {
        parentTimer.Stop();
        ...etc...
    }

Note: I do not change ParentTimer at all in its elapsed method.

Basically ParentTimer governs a list of ChildTimers. If ParentTimer elapses it checks if one or more of the ChildTimers have elapsed too, if so, there is an event, if not then it resets the ChildTimer and carries on.

Answer 1

A timer is tied to the thread that created it and in the case of ASP.net the thread that handles each page request issued by a given user will change frequently due to the use of worker threads and the thread pool.

Using a timer at page-level simply won’t work; you need to be tracking the state at Session-level (tied to the particular user) as your starting point.

In fact, I just wouldn’t use timers at all in a web application, because their execution is simply not guaranteed.

If you’re using this to run a background task – consider firing up your own worker thread in Application_Start or something like that. The thread will be terminated when the app pool recycles. You should also look at manually shutting the thread down the application is being shut down too.

Be careful with this, however, this thread can’t assume it’s always the only one running – due to IIS overlapped recycling, when a new one fires up the old one could still be running in the old AppDomain.