Terminating the program gracefully in C

Question

I have sort of a homework and it asks me to end the program gracefully without explicit termination such as calling exit() or killing the threads. However I cannot think of any other methods than return 0, so what are the methods to end a program gracefully?

`main` will by default return *0* in the lack of a `return 0;` statement. — obataku, Sep 09 '12 at 15:31
@Cnicutar, I don't think so as it does not allow us to use exit() — Sarp Kaya, Sep 09 '12 at 15:32
Can you post the text of the homework ? Maybe you're not reading it completely right :-) — cnicutar, Sep 09 '12 at 15:33
@cnicutar "The input 'q' indicates that the simulation has terminated. Note that the simulation must end gracefully without explicit termination such as calling exit() or killing the threads." — Sarp Kaya, Sep 09 '12 at 15:35
I believe what your homework says is that you should not have more than 1 exit point. Be it a `return 0`, or an `exit(0)`, it should not make any difference. — jweyrich, Sep 09 '12 at 15:36

score 5 · Accepted Answer · edited May 23 '17 at 11:55

5

Killing the threads is absolutely not a graceful way to terminate a program. I think what your instructor means is that all your parent threads should wait on their child threads before terminating themselves.

Ideally, an explicit call pthread_exit from the main thread would ensure that all it's children continue running even after it exits. Refer to this link. But, the safest way to wait on your child threads before exiting is to use pthread_join.

Nevertheless, exit(0) is the graceful return for a process as such.

edited May 23 '17 at 11:55

Community

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answered Sep 09 '12 at 16:00

Deepanjan Mazumdar

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This is correct answer, when I asked to my teacher, what needs to be done was actually `pthread_join` waits the thread to return NULL with `pthread(threadname, NULL);` so in my threads there were loops inside of them, so the solution was to finish these loops with a variable so that all threads could return NULL – Sarp Kaya Sep 14 '12 at 09:23

score 1 · Answer 2 · answered Sep 09 '12 at 15:48

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I think you are missing to tell us that you have a multi-threaded program. I suppose that the the idea of gracefully terminating the program is meant to terminate all your threads by setting a flag or something like that. And then only to terminate your main after all your threads have provably ended. The way you actually then terminate your main is of lesser importance.

answered Sep 09 '12 at 15:48

Jens Gustedt

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+1. It's not about language syntax nor methods of terminating a process. It's about properly ending threads, closing and deallocating resources, etc. That's what I understand from *gracefully*. – jweyrich Sep 09 '12 at 15:51

score 0 · Answer 3 · answered Sep 09 '12 at 15:32

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exit(0) generally indicates that process (your program) terminated gracefully. In case of error it would exit(-1) or some other error code.

answered Sep 09 '12 at 15:32

Rohan

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AirUp · Answer 4 · 2012-09-09T16:01:53.573

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No idea what they could mean with gracefully but my first idea was just a return 0.

Or exit(0)

edited Sep 09 '12 at 16:01

answered Sep 09 '12 at 15:33

AirUp

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score 0 · Answer 5 · edited May 23 '17 at 12:03

See my comment.

main will by default return 0 in the lack of a return 0; statement.

See §5.1.2.2.3¶1 of the C99 standard.

If the return type of the main function is a type compatible with int, a return from the initial call to the main function is equivalent to calling the exit function with the value returned by the main function as its argument; reaching the } that terminates the main function returns a value of 0. If the return type is not compatible with int, the termination status returned to the host environment is unspecified.

So, the following terminates gracefully although implicitly, distinguished from an explicit exit or return in main.

main() { }

score 0 · Answer 6 · answered Sep 09 '12 at 15:58

They may be referring to how you handle errors in lower-level routines. Rather than doing something like

printf("ERROR: couldn't initialize the claveman\n");
exit(1);

You would return from that routine (possibly printing the error message at that level or waiting to do it at a higher level like main()).

return CLAVEMAN_INITIALIZE_ERROR;

All your routines would return zero for success or non-zero error codes, up until the code in main was able to return either EXIT_SUCCESS or an error code indicating the failure.

Terminating the program gracefully in C

6 Answers6