signal and wait

kill -9 （SIGKILL）是不可以被进程捕获的，因此是杀死进程的可靠方法
子进程：

#include <stdlib.h>
  2 #include <unistd.h>
  3 #include <sys/types.h>
  4
  5 int main(int argc,char* argv[])
  6 {
  7     pid_t pid;
  8
  9     pid = getpid();
 10     sleep(20);
 11
 12     if(atoi(argv[1]) % 2)
 13     {
 14         printf("child process %d kill itself.\n", pid);
 15         kill(pid, 9);
 16     }
 17     else
 18     {
 19         printf("child process %d exit.\n", pid);
 20         _exit(0);
 21     }
 22     return 0;
 23 }

父进程：

include <stdio.h>
  2 #include <unistd.h>
  3 #include <sys/types.h>
  4 #include <sys/wait.h>
  5
  6 int main(int argc, char * argv[])
  7 {
  8     pid_t pid,waitpid;
  9     int status;
 10     int i;
 11
 12     for(i=1;i<argc;i++)
 13         if(0 == (pid = fork()))
 14         {
 15             execlp("./childproc","childproc",argv[i],(char *)NULL);
 16         }
 17         else
 18         {
 19             printf("child process %d has been created.\n", pid);
 20         }
 21
 22     while((waitpid = wait(&status)) && (-1 != waitpid))
 23     {
 24         printf("child process %d exit with code:%d\n",waitpid,status);
 25     }
 26     return 0;
 27 }

其中，当父进程没有子进程可以wait时，wait()返回-1，此时退出while循环。

运行结果：
lisong@lisong:~/code/experiment/proc/wait$ gcc parentproc.c -o parentproc
lisong@lisong:~/code/experiment/proc/wait$ ./parentproc 1 1 2 2 &
[1] 2356
child process 2357 has been created.
lisong@lisong:~/code/experiment/proc/wait$ child process 2358 has been created.
child process 2359 has been created.
child process 2360 has been created.

lisong@lisong:~/code/experiment/proc/wait$ ps
  PID TTY          TIME CMD
 2181 pts/1    00:00:01 bash
 2356 pts/1    00:00:00 parentproc
 2357 pts/1    00:00:00 childproc
 2358 pts/1    00:00:00 childproc
 2359 pts/1    00:00:00 childproc
 2360 pts/1    00:00:00 childproc
 2361 pts/1    00:00:00 ps
lisong@lisong:~/code/experiment/proc/wait$ kill -9 2359
child process 2359 exit with code:9
lisong@lisong:~/code/experiment/proc/wait$ child process 2357 kill itself.
child process 2357 exit with code:9
child process 2358 kill itself.
child process 2358 exit with code:9
child process 2360 exit.
child process 2360 exit with code:0

[1]+  完成                  ./parentproc 1 1 2 2
lisong@lisong:~/code/experiment/proc/wait$ ps
  PID TTY          TIME CMD
 2181 pts/1    00:00:01 bash
 2363 pts/1    00:00:00 ps