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