In the trivial example below, we use the SIGUSR1 signal to inform the child that the parent has died. I know printf() should not be used in a signal handler, it just makes the example simpler.
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/prctl.h>
#include <err.h>
void sigusr1_handler(int dummy)
{
printf("Parent died, child now exiting\n");
exit(0);
}
int main()
{
pid_t pid;
pid = fork();
if (pid < 0)
err(1, "fork failed");
if (pid == 0) {
/* Child */
if (signal(SIGUSR1, sigusr1_handler) == SIG_ERR)
err(1, "signal failed");
if (prctl(PR_SET_PDEATHSIG, SIGUSR1) < 0)
err(1, "prctl failed");
for (;;)
sleep(60);
}
if (pid > 0) {
/* Parent */
sleep(5);
printf("Parent exiting...\n");
}
return 0;
}
..the child process sits in an infinite loop, performing 60 second sleeps. The parent sleeps for 5 seconds and then exits. The child is then sent a SIGUSR1 signal and the handler exits. In practice the signal handler would be used to trigger a more sophisticated clean up of resources if required.
Anyhow, this is a useful Linux feature that seems to be overlooked.
