i am programming a simple program and want to deal with signals.
i want to understand and work with the old signal-concept under unix,
but i have a problem, hope you can help or knoew where i can get help.
i use just one sig-handler, if a signal is recognized, then the sig-handler should handle this.
after i do a sig-longjmp() and finally i got back to the point where sigsetjmp() was saving it.
my idea is to put an alarm() everytime, if there's no answer.
if a signal is beeing processed and finished, after sigsetjmp() i do an alarm() again, but there's the problem, it's just working one time.
if i do nothing on keyboard, then the alarm() does SIGARLM one time.
After it's setted again, it's doing nothing.
i also looked for the mask, but it's NULL everytime, so the signal SIGARLM can not be ignored, or?
Hopefully, 1 month delay is not too long for an answer:
The main thing is this: just before a signal handler is called, subsequent signals on that same signal are blocked. The return function from a signal handler is "special" in that it unblocks that mask. I'm not sure where this is documented, but you can demonstrated it by adding a couple of printf("%x\n",siggetmask()); calls, in the signal handler, and right after the alarm() call. But because your signal handler does a longjmp instead of a return, the signal mask never gets reset.
Or, to do it "by hand", you can do this in your signal handler (or on return from it):
All you need to do is set savemask=1 when you declare it. Then things will work the way you intended. This tells the setlongjmp() call to restore the original signal mask when it does the jump -- in effect, emulating the normal return-from-signal code.
There is also a problem mixing SIGALRM and wait(). From the wait(3) man page:
Last edited by otheus; 02-03-2009 at 12:03 PM..
Reason: added sigprocmask()
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