c - SIGTSTP signal handler to ignore/act on SIGTSTP based on condition -

c - SIGTSTP signal handler to ignore/act on SIGTSTP based on condition -

like question says, want handle sigtstp signal differently based on conditions. final code won't simple i'm trying work first:

class="snippet-code-js lang-js prettyprint-override">static void stphandler(int signo) { sigset_t mask; //unblock sigtstp sigemptyset( & mask); sigaddset( & mask, sigtstp); sigprocmask(sig_unblock, & mask, null); if (getpid() != ultimateparent) { printf("not parent process\n"); exit(0); } else { printf("this parent process"); } }

code on parent process initialization:

ultimateparent=getpid(); sa_stp.sa_handler = stphandler; sigemptyset(&sa_stp.sa_mask); sa_stp.sa_flags = sa_restart; sigaction(sigtstp, &sa_stp, null);

code create child:

//leave args blank. maintain wc waiting input execerr=execvp("wc",args); if(errno==eacces) { fprintf(stderr,"%s: permission denied.\n",command); } else { fprintf(stderr,"%s: command not found.\n",command); } exit(0);

here did , output got:

in parent:

when parent running , nail ctrl+z output is: ^z

when nail homecoming key, printf command executes on next line:

"this parent process"

question: why wait me nail homecoming key proceed?

in child

it prints ^z many times generate signal, goes next line homecoming key- ignores ctrl+d (which cause wc read eof , finish execution) or other signal matter, besides sigquit.

question: why ignore farther signals after ctrl+z? there way create kid exit instead?

i sense i'm missing important signals , signal handlers in general. help, articles or other references appreciated.

c unix signals