linux进程互斥锁

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进程间同步

互斥量mutex

进程间也可以使用互斥锁，来达到同步的目的。但应在pthread_mutex_init初始化之前，修改其属性为进程间共享。mutex的属性修改函数主要有以下几个。

主要应用函数：

pthread_mutexattr_t mattr 类型：用于定义mutex锁的【属性】

pthread_mutexattr_init函数：初始化一个mutex属性对象

int pthread_mutexattr_init(pthread_mutexattr_t *attr);

pthread_mutexattr_destroy函数：销毁mutex属性对象 (而非销毁锁)

int pthread_mutexattr_destroy(pthread_mutexattr_t *attr);

pthread_mutexattr_setpshared函数：修改mutex属性。

int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared);

参2：pshared取值：

线程锁：PTHREAD_PROCESS_PRIVATE (mutex的默认属性即为线程锁，进程间私有)

进程锁：PTHREAD_PROCESS_SHARED

进程间mutex示例

进程间使用mutex来实现同步：

#include <stdio.h>#include <unistd.h>#include <fcntl.h>#include <stdlib.h>#include <string.h>#include <pthread.h>#include <sys/mman.h>#include <sys/wait.h>struct mt {    int num;    pthread_mutex_t mutex;    pthread_mutexattr_t mutexattr;};int main(void){    int i;    struct mt *mm;    pid_t pid;/*    int 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)++;            pthread_mutex_unlock(&mm->mutex);            printf("-child----------num++   %d\n", mm->num);        }    } else if (pid > 0) {        for ( i = 0; i < 10; i++) {        //    sleep(1);            pthread_mutex_lock(&mm->mutex);            mm->num += 2;            pthread_mutex_unlock(&mm->mutex);            printf("-------parent---num+=2  %d\n", mm->num);        }        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;}

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