fork出子进程后父进程并不想关心子进程了，也不想费心wait，自顾自的继续执行自己的代码，之后子进程退出时会变成僵尸进程。要避免产生僵尸进程，使用sigaction函数设置SIGCHLD信号处理，并设置sa_flags 为 SA_NOCLDWAIT，man sigaction可见SA_NOCLDWAIT描述：
SA_NOCLDWAIT (Since Linux 2.6) If signum is SIGCHLD, do not transform children into zombies when they terminate. See also waitpid(2). This flag is only mean- ingful when establishing a handler for SIGCHLD, or when setting that signal’s disposition to SIG_DFL. If the SA_NOCLDWAIT flag is set when establishing a handler for SIGCHLD, POSIX.1 leaves it unspecified whether a SIGCHLD signal is generated when a child process terminates. On Linux, a SIGCHLD signal is generated in this case; on some other implementations, it is not. 代码测试如下： 1 #include <unistd.h> 2 #include <signal.h> 3 #include <stdio.h> 4 #include <stdlib.h> 5 6 int main(int argc, char *argv[]) { 7 struct sigaction act; 8 act.sa_handler = SIG_DFL; 9 act.sa_flags = SA_NOCLDWAIT; 10 if (sigaction(SIGCHLD, &act, NULL) < 0) { 11 perror("sigaction"); 12 return -1; 13 } 14 pid_t pid; 15 if ((pid = fork()) == 0) { 16 printf("I'am child process\n"); 17 // do something 18 sleep(5); 19 exit(0); 20 } else if (pid > 0) { 21 // wake up until child exit 22 sleep(10); 23 printf("parent process exit\n"); 24 } else { 25 perror("fork"); 26 return -1; 27 } 28 return 0; 29 }
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