using signal in c and resuming from specific point in program

Question

I'm writing a program where I need to catch SIGINT signal so that I can kill child processes without the parent process exiting. I can kill child processes by sending them SIGKILL.

But after a signal is handled the main program resumes from where it left off. I want it to resume from somewhere else. For example say I have a loop and a signal is caught somewhere within loop; after handling the signal I want the program to resume from the beginning of the loop, rather than the middle.

I your example when you resume from handling the signal you can use "continue" and initialize your loop condition. i.e. for while (i — Gaston, Feb 15 '15 at 15:28

score 2 · Answer 1 · answered Feb 15 '15 at 15:49

It lies in the nature of asynchronous signals that they can interupt the code at any time.

If there are sections in the code where such an interuption is unwanted then disable signals for those parts.

In all other sections do relevant checks to determine whether an interuption occured and make the code react accordingly.

user590028 · Answer 2 · 2015-02-15T15:49:38.307

-1

It's really bad form to catch SIGINT and that do anything other than terminate. If you want to intercept the signal so you can kill children, then you should do an and exit -- do NOT continuing your program normally.

In your signal handler, set a global flag that indicates SIGINT was received, then from within your loop, test this variable, and execute conditional branch logic.

edited Feb 15 '15 at 15:49

answered Feb 15 '15 at 15:41

user590028

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How would a `setjmp()` help? – alk Feb 15 '15 at 15:42
Instead of returning from handler, he could execute `longjmp()` to just above his loop. This is *REALLY* a bad idea -- but sometimes bad ideas are the only way to get something done. – user590028 Feb 15 '15 at 15:44
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Also I know quite a few common programs which on receiving a `SIGINT` do something else but terminate. – alk Feb 15 '15 at 15:44
What would happend after the next call to `return`? – alk Feb 15 '15 at 15:45
Sure -- doing clean shutdown is OK, but continuing a loop is not likely the right course of action. – user590028 Feb 15 '15 at 15:45
"...*What would happend after the next call to return?...* -- BAD THINGS. It would then return from the signal handler. – user590028 Feb 15 '15 at 15:46
... and would continue from where left off when receiving the signal. So you gained nothing by the `longjmp()`. – alk Feb 15 '15 at 15:47
You're assuming he would return. It's possible he just calls exit(-1) – user590028 Feb 15 '15 at 15:48
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But leaving the program is what the OP does not seem to want. – alk Feb 15 '15 at 15:48
Tell you what -- I've removed the reference to `setjmp`. It's an advanced use and requires too much special explanation. – user590028 Feb 15 '15 at 15:50
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if i jump from signal_handler then it not take/catch signal next time becoz the first handler has not returned yet.... – Nischimtz Floater Feb 15 '15 at 17:13

using signal in c and resuming from specific point in program

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