Mail Archives: djgpp/1999/04/15/08:35:30
On 15 Apr 1999, Alberto Chessa wrote:
> I'm writing a simple multi-threading C++ library and I'm trying to use
> alarm/setitimer for preemptive rescheduing. It works only with "big"
> interval timer value (>1sec). Lower values works for the first 1/4 timeout
> expirations (depending on interval timer value - 10..90ms), then it simple
> stop to call the signal handler (but the program - the last thread - still
> running - the resched counter stop).
Which version of DJGPP are you using (please always mention that when you
report problems with library functions)? If you are using v2.02, then
you should know that `setitimer' from the stock v2.02 distribution is
buggy. I have a corrected version that I can send you.
> setsignal(SIGALRM, Handler); // It's really required ?
It is not required in DJGPP to reinstall the handler, but other systems
may reset the handler to SIG_IGN or SIG_DFL, so you might need it there.
(I understand you used `signal', not `setsignal'.)
> Setup()
> {
> setsignal(SIGALRM, Handler);
> seitime( 10ms ); // off course, I really feel both it_value and it_interval
10ms is way too small, since the basic timer tick happens every 55ms.
The code should still work, even with 10ms, but any value less than 55ms
means that your program will reschedule every 55ms.
> - I lock all the critical kernel code (cotext switching, rescheduling
> routine, signal handler)
> - I lock all kernel data used by rescheduling routine and signal handler
You don't really need this, since the DJGPP implementation of signals
defers the signal delivery until the program is in its usual foreground
task, out of the interrupt handler. But locking cannot hurt.
> - I'm using DJGPP 2.8.1
This is the version of GCC, not of DJGPP. The version of DJGPP is
encoded in the djdevNNN.zip name: djdev202.zip means version 2.02.
> - I try under Win95B, both dos-box and command prompt only
This might give you some problems in the DOS box, since Windows sometimes
forcibly reprograms the timer. But if you see the same problems in plain
DOS mode, this is not the cause of the problems.
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