Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Clocks and timers
This notification type is a little scary! You could have a whole slew of threads created
if the timer fires often enough and, if there are higher priority threads waiting to run,
this could chew up all available resources on the system! Use with caution!
General tricks for notification
There are some convenience macros in to make filling in the
notification structures easier (see the entry for sigevent in the Neutrino Library
Reference):
Pulse notification
SIGEV_SIGNAL_INIT (eventp, signo)
Fill eventp with SIGEV_SIGNAL, and the appropriate signal number signo.
SIGEV_SIGNAL_CODE_INIT (eventp, signo, value, code)
Fill eventp with SIGEV_SIGNAL_CODE, the signal number signo, as well as the
value and code.
SIGEV_SIGNAL_THREAD_INIT (eventp, signo, value, code)
Fill eventp with SIGEV_SIGNAL_THREAD, the signal number signo, as well as
the value and code.
SIGEV_PULSE_INIT (eventp, coid, priority, code, value)
Fill eventp with SIGEV_SIGNAL_PULSE, the connection to the channel in coid
and a priority, code, and value. Note that there is a special value for priority of
SIGEV_PULSE_PRIO_INHERIT that causes the receiving thread to run at the
process’s initial priority.
SIGEV_UNBLOCK_INIT (eventp)
Fill eventp with SIGEV_UNBLOCK.
SIGEV_INTR_INIT (eventp)
Fill eventp with SIGEV_INTR.
SIGEV_THREAD_INIT (eventp, func, val, attributes)
Fill eventp with the thread function (func) and the attributes structure
(attributes). The value in val is passed to the function in func when the thread is
executed.
Suppose you’re designing a server that spent most of its life RECEIVE blocked,
waiting for a message. Wouldn’t it be ideal to receive a special message, one that told
you that the time you had been waiting for finally arrived?
This scenario is exactly where you should use pulses as the notification scheme. In the
“Using timers” section below, I’ll show you some sample code that can be used to get
periodic pulse messages.
April 30, 2009 Chapter 3 • Clocks, Timers, and Getting a Kick Every So Often 145