避免生成僵尸进程

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
");
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
");
24     } else {
25         perror("fork");
26         return -1;
27     }
28     return 0;
29 }