进程间同步

进程间使用mutex来实现同步：

#include <pthread.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include<stdio.h>
#include<stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include<string.h>

struct mt {
    int num;
    pthread_mutex_t mutex;
    pthread_mutexattr_t mutexattr;
};

int main(void)
{
    int fd, i;
    struct mt *mm;
    pid_t pid;

/*
    fd = open("mt_test", O_CREAT | O_RDWR, 0777);
    ftruncate(fd, sizeof(*mm));
    mm = mmap(NULL, sizeof(*mm), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
    close(fd);
    unlink("mt_test");*/
	
    mm = mmap(NULL, sizeof(*mm), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANON, -1, 0);
    memset(mm, 0, sizeof(*mm));

    pthread_mutexattr_init(&mm->mutexattr);                                  //初始化mutex属性对象
    pthread_mutexattr_setpshared(&mm->mutexattr, PTHREAD_PROCESS_SHARED);    //修改属性为进程间共享
    pthread_mutex_init(&mm->mutex, &mm->mutexattr);                          //初始化一把mutex琐

    pid = fork();
    if (pid == 0) {
        for (i = 0; i < 10; i++) {
            pthread_mutex_lock(&mm->mutex);
            (mm->num)++;
            printf("-child----num++   %d\n", mm->num);
            pthread_mutex_unlock(&mm->mutex);
            sleep(rand()%2+1);
        }
    } else if (pid > 0) {
        for ( i = 0; i < 10; i++) {
            sleep(rand()%2);
            pthread_mutex_lock(&mm->mutex);
            mm->num += 2;
            printf("-parent---num+=2  %d\n", mm->num);
            pthread_mutex_unlock(&mm->mutex);
        }
        wait(NULL);
    }

    pthread_mutexattr_destroy(&mm->mutexattr);          //销毁mutex属性对象
    pthread_mutex_destroy(&mm->mutex);                //销毁mutex
    munmap(mm,sizeof(*mm));                          //释放映射区
    return 0;
}

-child----num++ 1
-parent—num+=2 3
-parent—num+=2 5
-parent—num+=2 7
-child----num++ 8
-parent—num+=2 10
-child----num++ 11
-parent—num+=2 13
-parent—num+=2 15
-child----num++ 16
-parent—num+=2 18
-parent—num+=2 20
-parent—num+=2 22
-child----num++ 23
-parent—num+=2 25
-child----num++ 26
-child----num++ 27
-child----num++ 28
-child----num++ 29
-child----num++ 30