fork系统调用

/* * simple fork usage */#include <unistd.h>#include <stdio.h>#include <stdlib.h>int main(){pid_t child;if ((child = fork()) == -1){perror("fork");exit(EXIT_FAILURE);}else if(child == 0){puts("in child");printf ("\tchild pid = %d\n", getpid());printf ("\tchild ppid = %d\n", getppid());exit(EXIT_SUCCESS);}else{puts("in parent");printf ("\tparent pid = %d\n", getpid());printf ("\tparent ppid = %d\n", getppid());}return (EXIT_SUCCESS);}

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第一次运行结果如下：

in parent

in child
parent pid = 4836
parent ppid = 4835
child pid = 4837

child ppid = 4836

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第二次运行结果变这样了：

in parent
parent pid = 4855
in child
parent ppid = 4854
child pid = 4856
child ppid = 4855

使用fork时， 夫进程和子进程的运行顺序是随机的，也就是说他的执行是异步的。