SIGCHLD函数

SIGCHLD的产生条件

子进程终止时

子进程接收到SIGSTOP信号停止时

子进程处在停止态，接受到SIGCONT后唤醒时

借助SIGCHLD信号回收子进程

子进程结束运行，其父进程会收到SIGCHLD信号。该信号的默认处理动作是忽略。可以捕捉该信号，在捕捉函数中完成子进程状态的回收。

/***
sigchild.c
***/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <signal.h>void sys_err(char *str)
{perror(str);exit(1);
}
void do_sig_child(int signo)
{int status;    pid_t pid;while ((pid = waitpid(0, &status, WNOHANG)) > 0) {if (WIFEXITED(status))printf("child %d exit %d\n", pid, WEXITSTATUS(status));else if (WIFSIGNALED(status))printf("child %d cancel signal %d\n", pid, WTERMSIG(status));}
}
int main(void)
{pid_t pid;    int i;for (i = 0; i < 10; i++) {if ((pid = fork()) == 0)break;else if (pid < 0)sys_err("fork");}if (pid == 0) {    int n = 1;while (n--) {printf("child ID %d\n", getpid());sleep(1);}return i+1;} else if (pid > 0) {struct sigaction act;act.sa_handler = do_sig_child;sigemptyset(&act.sa_mask);act.sa_flags = 0;sigaction(SIGCHLD, &act, NULL);while (1) {printf("Parent ID %d\n", getpid());sleep(1);}}return 0;
}

/***
my_sigchild.c
***/
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<signal.h>void sys_err(char *str)
{perror(str);exit(1);
}void do_sig_child(int signo)
{int status;pid_t pid;while( (pid = waitpid(0,&status,WNOHANG)) > 0){if(WIFEXITED(status))printf("----------child %d exit %d\n",pid,WEXITSTATUS(status));else if(WIFSIGNALED(status)){printf("child %d cancel signal %d\n",pid,WTERMSIG(status));}}
}int main()
{pid_t pid;int i;for(i = 0; i < 10; i++){if((pid = fork()) == 0){break;}else if(pid < 0){    sys_err("fork");}    }if(0 == pid){int n = 1;while(n--){printf("child ID %d\n",getpid());sleep(1);}return i+1;}else if(pid > 0){struct sigaction act;act.sa_handler = do_sig_child;sigemptyset(&act.sa_mask);while(1){printf("Parent ID %d\n",getpid());sleep(1);    }}return 0;
}