Here is what I want to do. I want to create a timer and set it to expire after certain time. When It expires I want to send some data to the signal handler. The data is multiple bytes (may be as much as 24 bytes). Here is how you can help me out:

1. Point me to some tutorial which will explain the intricacies of timer functionality in Linux.
2. Provide pointers to help me solve the problem.

Thanks for all helpful suggestions.

Srini

Is this a programming question or are you
looking for the "at" command?


Cheers,
Tink

Thanks for taking time to read my request.

This is more of a programming question.

Kind regards

Srini

man setitimer
man getitimer

Or, if you're looking for a portable C++
solution, have a look at Qt's qtimer class.

The latter comes with programming examples,
too :)


Cheers,
Tink

P.S.: You should ask a mod to move the
thread to the programming-forum. It clearly
doesn't belong here.

Ya, look at the man page for setitimer. It'll allow you to set the timer, and it tells you what signal is fired when it runs out. You can then define what happens when you get that signal.

Thanks for all the good replies. "setitimer" may be too restrictive because from what I understand you can have no more than three interval timers per process. In my case I have several devices on which I will have to react based on the timers. My next questions are:

1. Is there a limitation to the number of timers per process/task I can create via timer_create() function?
2. If I can create a number of timers, I am still at a loss as to how I can associate the timer expiry to a particular device.

Thanks for all helpful suggestions.

Srini

Well the way a timer like that works is it typically triggers a software interupt which causes a signal to be sent to the processor. You have to create a function that is suppose to run based on that signal. Are you using this for doing operations on hardware? Perhaps you should write a kernel module.

I assume this is a simple user-space program, not a kernel module, so let's keep it simple here...

1) Have a linked list of "timer" objects that contain references back to the particular device.
2) Keep the list sorted by the expiration time, most recent first.
3) Use setitimer to send a signal when the earliest expiration time will occur.
4) In the signal handler, walk through the timer list, calling an "expire" method against the object if the timeout has occurred. Stop when you hit a timer that hasn't expired.
5) Calculate the next interval and set your itimer.

I haven't used the qtimer classes, but I'll bet they are just what you are looking for.

If you need it, I can whip up a simple set of timer classes for an example.

-Craig