多进程编程

源代码：
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

int main(int arg, char **argc)
{
    pid_t childPID = 0;
    int ret = 0;
    int x = 0;
    x++;
    printf("PID=%d, PPID=%d x=%d\n", getpid(), getppid(), x);
    ret = fork();
    if (ret == -1) {
        printf("failed to create child process\n");
        exit(0);
    } else if (ret == 0) {      /* 这是在子进程里 */
        printf("PID=%d, PPID=%d child-created OK, ret=%d\n", getpid(),
               getppid(), ret);
        x = x + 5;
        printf("child-x=%d\n", x);
        sleep(5);
        printf("child-x=%d\n", x);
        sleep(5);
    } else {                    /* 这是在父进程里 */
        childPID = ret;
        printf("PID=%d, PPID=%d parent-created OK, child PID=%d\n",
               getpid(), getppid(), childPID);
        printf("parent-x=%d\n", x);
        sleep(15);
        x = x + 10;
        printf("parent-x=%d\n", x);
    }
    printf("PID=%d, PPID=%d Last:x=%d\n", getpid(), getppid(), x);
    return 0;
}

编译：gcc fork.c  -Wall
运行：. /a.out
结果：
PID=14858, PPID=6194 x=1
PID=14859, PPID=14858 child-created OK, ret=0
child-x=6
PID=14858, PPID=6194 parent-created OK, child PID=14859
parent-x=1
child-x=6
PID=14859, PPID=14858 Last:x=6
parent-x=11
PID=14858, PPID=6194 Last:x=11


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