進程間同步

互斥量mutex

進程間也可以使用互斥鎖，來達到同步的目的。但應在pthread_mutex_init初始化之前，修改其屬性為進程間共享。mutex的屬性修改函數主要有以下幾個。

主要應用函數：

?????? pthread_mutexattr_t mattr 類型：??? ?????? 用于定義mutex鎖的【屬性】

?????? pthread_mutexattr_init函數：??????? ?????? 初始化一個mutex屬性對象

????????????? int pthread_mutexattr_init(pthread_mutexattr_t *attr);

?????? pthread_mutexattr_destroy函數： ?????? 銷毀mutex屬性對象 (而非銷毀鎖)

????????????? int pthread_mutexattr_destroy(pthread_mutexattr_t *attr);

?????? pthread_mutexattr_setpshared函數：? 修改mutex屬性。

????????????? int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared);

????????????? 參2：pshared取值：

???????????????????? 線程鎖：PTHREAD_PROCESS_PRIVATE (mutex的默認屬性即為線程鎖，進程間私有)

???????????????????? 進程鎖：PTHREAD_PROCESS_SHARED

進程間mutex示例

進程間使用mutex來實現同步：

#include <fcntl.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 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屬性對象pthread_mutexattr_setpshared(&mm->mutexattr, PTHREAD_PROCESS_SHARED);    //修改屬性為進程間共享pthread_mutex_init(&mm->mutex, &mm->mutexattr);                          //初始化一把mutex瑣
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(1);}} else if (pid > 0) {for ( i = 0; i < 10; i++) {sleep(1);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);          //銷毀mutex屬性對象pthread_mutex_destroy(&mm->mutex);                //銷毀mutexmunmap(mm,sizeof(*mm));                          //釋放映射區return 0;
}        

運行結果：

ubuntu1604@ubuntu:~/wangqinghe/linux/20190821$ ./process_mutex

---------parent-------num+=2?? 2

-child-----------------num++?? 3

---------parent-------num+=2?? 5

-child-----------------num++?? 6

---------parent-------num+=2?? 8

-child-----------------num++?? 9

---------parent-------num+=2?? 11

-child-----------------num++?? 12

---------parent-------num+=2?? 14

-child-----------------num++?? 15

---------parent-------num+=2?? 17

-child-----------------num++?? 18

---------parent-------num+=2?? 20

-child-----------------num++?? 21

---------parent-------num+=2?? 23

-child-----------------num++?? 24

---------parent-------num+=2?? 26

-child-----------------num++?? 27

---------parent-------num+=2?? 29

-child-----------------num++?? 30

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