The Linux Programming Interface

462 Chapter 22

We continue by using the shell kill command to send a signal to the catch_rtsigs pro-

gram. As before, we see that the siginfo_t structure received by the handler includes

the process ID and user ID of the sending process, but in this case, the si_code value

is SI_USER:

Press Enter to see next shell prompt

$ echo $$ Display PID of shell

12780

$ kill -40 12842 Uses kill(2) to send a signal

$ caught signal 40

si_signo=40, si_code=0 (SI_USER), si_value=0

si_pid=12780, si_uid=1000 PID is that of the shell

Press Enter to see next shell prompt

$ kill 12842 Kill catch_rtsigs by sending SIGTERM

Caught 6 signals

Press Enter to see notification from shell about terminated background job

[1]+ Done ./catch_rtsigs 60

Listing 22-3: Handling realtime signals

––––––––––––––––––––––––––––––––––––––––––––––––––––– signals/catch_rtsigs.c

#define _GNU_SOURCE

#include <string.h>

#include <signal.h>

#include "tlpi_hdr.h"

static volatile int handlerSleepTime;

static volatile int sigCnt = 0; /* Number of signals received */

static volatile int allDone = 0;

static void /* Handler for signals established using SA_SIGINFO */

siginfoHandler(int sig, siginfo_t *si, void *ucontext)

{

/* UNSAFE: This handler uses non-async-signal-safe functions

(printf()); see Section 21.1.2) */

/* SIGINT or SIGTERM can be used to terminate program */

if (sig == SIGINT || sig == SIGTERM) {

allDone = 1;

return;

}

sigCnt++;

printf("caught signal %d\n", sig);

printf(" si_signo=%d, si_code=%d (%s), ", si->si_signo, si->si_code,

(si->si_code == SI_USER)? "SI_USER" :

(si->si_code == SI_QUEUE)? "SI_QUEUE" : "other");

printf("si_value=%d\n", si->si_value.sival_int);

printf(" si_pid=%ld, si_uid=%ld\n", (long) si->si_pid, (long) si->si_uid);

sleep(handlerSleepTime);

}