Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Using timers
Timers delivering signals
Timers creating threads
So far, we’ve seen just about all there is to see with timers, except for one small thing.
We’ve been delivering messages (via a pulse), but you can also deliver POSIX signals.
Let’s see how this is done:
timer_create (CLOCK_REALTIME, NULL, &timerid);
This is the simplest way to create a timer that sends you a signal. This method raises
SIGALRM when the timer fires. If we had actually supplied a struct sigevent,we
could specify which signal we actually want to get:
struct sigevent event;
SIGEV_SIGNAL_INIT (&event, SIGUSR1);
timer_create (CLOCK_REALTIME, &event, &timerid);
This hits us with SIGUSR1 instead of SIGALRM.
You catch timer signals with normal signal handlers, there’s nothing special about
them.
If you’d like to create a new thread every time a timer fires, then you can do so with
the struct sigevent and all the other timer stuff we just discussed:
struct sigevent event;
SIGEV_THREAD_INIT (&event, maintenance_func, NULL);
You’ll want to be particularly careful with this one, because if you specify too short an
interval, you’ll be flooded with new threads! This could eat up all your CPU and
memory resources!
Getting and setting the realtime clock and more
Apart from using timers, you can also get and set the current realtime clock, and adjust
it gradually. The following functions can be used for these purposes:
Function Type? Description
ClockAdjust() Neutrino Gradually adjust the time
ClockCycles() Neutrino High-resolution snapshot
clock_getres() POSIX Fetch the base timing resolution
clock_gettime() POSIX Get the current time of day
ClockPeriod() Neutrino Get or set the base timing resolution
clock_settime() POSIX Set the current time of day
ClockTime() Neutrino Get or set the current time of day
April 30, 2009 Chapter 3 • Clocks, Timers, and Getting a Kick Every So Often 157