Getting Started with QNX Neutrino - QNX Software Systems

Advanced topics
© 2009, QNX Software Systems GmbH & Co. KG.
struct sigevent event;
int
rval;
...
// set up the event -- this can be done once
// This or event.sigev_notify = SIGEV_UNBLOCK:
SIGEV_UNBLOCK_INIT (&event);
// set up for 10 second timeout
timeout = 10LL * SEC_NSEC;
TimerTimeout (CLOCK_REALTIME, _NTO_TIMEOUT_JOIN,
&event, &timeout, NULL);
rval = pthread_join (thread_id, NULL);
if (rval == ETIMEDOUT) {
printf ("Thread %d still running after 10 seconds!\n",
thread_id);
}
...
(You’ll find the complete version of tt1.c in the Sample Programs appendix.)
We used the SIGEV_UNBLOCK_INIT() macro to initialize the event structure, but we
could have set the sigev_notify member to SIGEV_UNBLOCK ourselves. Even more
elegantly, we could pass NULL as the struct sigevent — TimerTimeout()
understands this to mean that it should use a SIGEV_UNBLOCK.
If the thread (specified in thread_id) is still running after 10 seconds, then the kernel
call will be timed out — pthread_join() will return with an errno of ETIMEDOUT.
You can use another shortcut — by specifying a NULL for the timeout value (ntime in
the formal declaration above), this tells the kernel not to block in the given state. This
can be used for polling. (While polling is generally discouraged, you could use it quite
effectively in the case of the pthread_join() — you’d periodically poll to see if the
thread you’re interested in was finished yet. If not, you could perform other work.)
Here’s a code sample showing a non-blocking pthread_join():
int
pthread_join_nb (int tid, void **rval)
{
TimerTimeout (CLOCK_REALTIME, _NTO_TIMEOUT_JOIN,
NULL, NULL, NULL);
return (pthread_join (tid, rval));
}
Kernel timeouts with message passing
Things get a little trickier when you’re using kernel timeouts with message passing.
Recall from the Message Passing chapter (in the “Message passing and client/server”
part) that the server may or may not be waiting for a message when the client sends it.
This means that the client could be blocked in either the SEND-blocked state (if the
server hasn’t received the message yet), or the REPLY-blocked state (if the server has
received the message, and hasn’t yet replied). The implication here is that you should
164 Chapter 3 • Clocks, Timers, and Getting a Kick Every So Often April 30, 2009