“kill -15” triggers the sigaction code but does not terminate my C program

问题

I have a program developed in C. I added to this program a sigaction handler inorder to execute some C code before quit the program:

void signal_term_handler(int sig)
{
    printf("EXIT :TERM signal Received!\n");
    int rc = flock(pid_file, LOCK_UN | LOCK_NB);
    if(rc) {
        char *piderr = "PID file unlock failed!";
        fprintf(stderr, "%s\n", piderr);
        printf(piderr);
    }
    exit(EXIT_SUCCESS);
}

int main(int argc, char **argv)
{
    struct sigaction sigint_action;

    sigint_action.sa_handler = &signal_term_handler;
    sigemptyset(&sigint_action.sa_mask);

    sigint_action.sa_flags = SA_RESETHAND;
    sigaction(SIGTERM, &sigint_action, NULL);
        ...........
}

Note: My program contains 2 subthreads running

When I execute myprogram and then I call kill -15 <pidnumber> to kill my program. I get the message "EXIT :TERM signal Received!\n" printed in the stdout but the program is not exited.

Am I missing someting in my sigaction code?

回答1:

exit() is not necessarily async-signal safe.

To end a process directly from a signal handler call either _exit() or abort().

flock() and all members of the printf family of functions aren't async-signal-save either.

For full list of async-signal-safe functions you might like to click here.

回答2:

I still suspect you have an XY-problem, that is trying to un-flock() a file on receiving SIGTERM.

To achieve this (and with this get around the limitation to only be able to use async-signal-safe functions on signal reception use the following approach:

Mask out all signals to be handled by the app in the main thread.
Create a thread.
Make this thread receive all signals to be handled, by modifing the thread's signal mask.
In this thread loop around sigwaitinfo() to receive and dispatch signals.
Then depending on the signal received by this thread do what needs to be done without any limitation due to missing async-signal-saftyness of any function.

回答3:

Most likely this is because you aren't really allowed to do much of anything in a signal handler (and calling library functions is certainly sketchy).

The normal way to handle something like this is for the signal handler to set a variable or queue up an event that the normal main loop will handle and then exit.

来源：https://stackoverflow.com/questions/16966353/kill-15-triggers-the-sigaction-code-but-does-not-terminate-my-c-program

标签

Linux

signals

kill