[Signal] The examples of using alarm() and sigaction()

In the following URL, it provides a good explanation about signal and signal handling.
https://www.sharcnet.ca/help/index.php/Signal_Handling_and_Checkpointing

Handling signal is a important job when we want to write a great code.
There are several signal functions that we could use often in programming. I will give some examples of how to use alarm() and sigaction() functions as below.
P.S: the URL link is the orginal source code which is from.


The follwing two examples are about how to use alarm() and ualarm().
http://jyhshin.pixnet.net/blog/post/27749178-linux-%E8%A8%88%E6%99%82%E5%99%A8-alarm-signal-%281%29

/* Example of using alarm() */ #include <unistd.h> #include <stdio.h> #include <signal.h> int main(int argc, char *argv[]) { sigset_t block; sigemptyset(&block); sigaddset(&block, SIGALRM); sigprocmask(SIG_BLOCK, &block, NULL); while (1) { alarm(2); printf("%d\n", time(NULL)); sigwaitinfo(&block, NULL); } return 0; }


/* Example of using ualarm() */ #define _XOPEN_SOURCE 500 #include <unistd.h> #include <stdio.h> #include <signal.h> int main(int argc, char *argv[]) { sigset_t block; sigemptyset(&block); sigaddset(&block, SIGALRM); sigprocmask(SIG_BLOCK, &block, NULL); ualarm(500000, 500000); while (1) { printf("%d\n", time(NULL)); sigwaitinfo(&block, NULL); } return 0; }


Actually, sigaction() is widely used in handling signal, for instance, SIGINT (interrupt), SIGCHLD, and so on. Here are the examples to show the usage of sigaction with SIGINT.
http://www.linuxprogrammingblog.com/code-examples/sigaction

/* Example of using sigaction() to setup a signal handler with 3 arguments * including siginfo_t. */ #include <stdio.h> #include <unistd.h> #include <signal.h> #include <string.h> static void hdl (int sig, siginfo_t *siginfo, void *context) { printf ("Sending PID: %ld, UID: %ld\n", (long)siginfo->si_pid, (long)siginfo->si_uid); } int main (int argc, char *argv[]) { struct sigaction act; memset (&act, '\0', sizeof(act)); /* Use the sa_sigaction field because the handles has two additional parameters */ act.sa_sigaction = &hdl; /* The SA_SIGINFO flag tells sigaction() to use the sa_sigaction field, not sa_handler. */ act.sa_flags = SA_SIGINFO; if (sigaction(SIGINT, &act, NULL) < 0) { perror ("sigaction error"); return 1; } while (1) sleep (10); return 0; }

http://fanqiang.chinaunix.net/a4/b2/20010508/113528_b.html

/* Example of using sigaction() to setup a signal handler * with setting sa_handler */ #include <stdio.h> #include <unistd.h> #include <signal.h> #include <string.h> #include <errno.h> #define PROMPT "Do you want to terminate the process?" char *prompt=PROMPT; void ctrl_c_oper(int signo) { write(STDERR_FILENO,prompt,strlen(prompt)); } int main() { struct sigaction act; act.sa_handler=ctrl_c_oper; sigemptyset(&act.sa_mask); act.sa_flags=0; if(sigaction(SIGINT,&act,NULL)<0) { fprintf(stderr,"Install Signal Action Error:%s\n\a",strerror(errno)); exit(1); } while(1); }

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