int main(int argc, char const *argv[])
{
int status;
pid_t child_pid;
switch(fork())
{
case -1:
printf("创建子进程失败\n");
exit(EXIT_FAILURE);
case 0: // 子进程
printf("子进程开始运行， PID：%ld\n", (long)getpid());
if(argc > 1)
exit(atoi(argv[1]));
else
{
for(;;)
pause();
}
exit(EXIT_FAILURE);
default:
/**
* 检测子进程的状态
* 如果子进程的状态没有发生改变，立即返回
* 子进程收到信号停止也会返回
*/
for(;;)
{
child_pid = waitpid(-1, &status, WUNTRACED
#ifdef WCONTINUED
| WCONTINUED
#endif
);
if(child_pid == -1)
{
printf("waitpid调用失败\n");
exit(EXIT_FAILURE);
}
printf("waitpid() 返回： PID=%ld； status=0x%04x (%d, %d)\n", (long)child_pid, (unsigned int)status, status>>8, status&0xff);
print_wait_status(NULL, status);
if(WIFEXITED(status) || WIFSIGNALED(status))
{
exit(EXIT_SUCCESS);
}
}
}
return 0;
}
int
main (void)
{
struct sigaction sa;
sigset_t sigMask;
pid_t chldPid;
int status;
// establish handler for SIGCHLD
sigemptyset (&sa.sa_mask);
sa.sa_flags = 0;
sa.sa_handler = signal_handler;
sigaction (SIGCHLD, &sa, NULL);
// block SIGCHLD
sigemptyset (&sigMask);
sigaddset (&sigMask, SIGCHLD);
sigprocmask (SIG_BLOCK, &sigMask, NULL);
switch (chldPid = fork ()) {
case -1:
perror ("fork()");
return 1;
case 0: // child
_exit (0);
default:
// wait for child to exit
sleep (2);
// unblock SIGCHLD
sigprocmask (SIG_UNBLOCK, &sigMask, NULL);
waitpid (chldPid, &status, 0);
print_wait_status (status);
break;
}
return 0;
}
static void sig_child_handler(int sig)
{
int status, saved_errno;
pid_t child_pid;
/* UNSAFE: This handler uses non-async-signal-safe functions
* (printf(), print_wait_status(), curr_time())
*/
saved_errno = errno; /* In case we modify 'errno' */
printf("%s handler: Caught SIGCHLD\n", curr_time("%T"));
while((child_pid = waitpid(-1, &status, WNOHANG)) > 0)
{
printf("%s handler: Reaped child %ld - ", curr_time("%T"), (long)child_pid);
print_wait_status(NULL, status);
num_live_children--;
}
if (child_pid == -1 && errno != ECHILD)
err_msg("waitpid");
printf("%s handler: return\n", curr_time("%T"));
}
int
main (void)
{
int ret;
#if (DONT_HANDLE_SIGCHLD == 0)
struct sigaction sa;
// don't care about zombies
sigemptyset (&sa.sa_mask);
sa.sa_flags = 0;
sa.sa_handler = SIG_IGN;
sigaction (SIGCHLD, &sa, NULL);
#endif
ret = system ("sleep 3");
if (ret == -1) {
perror ("system()");
return 1;
}
print_wait_status (ret);
return 0;
}
