把源代码运行一遍就知道了
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <pthread.h>
pthread_mutex_t* g_mutex;
//创建共享的mutex
void init_mutex(void)
{
int ret;
//g_mutex一定要是进程间可以共享的，否则无法达到进程间互斥
g_mutex=(pthread_mutex_t*)mmap(NULL, sizeof(pthread_mutex_t), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
if( MAP_FAILED==g_mutex )
{
perror("mmap");
exit(1);
}
//设置attr的属性
pthread_mutexattr_t attr;
pthread_mutexattr_init(&attr);
//一定要设置为PTHREAD_PROCESS_SHARED
//具体可以参考http://blog.chinaunix.net/u/22935/showart_340408.html
ret=pthread_mutexattr_setpshared(&attr,PTHREAD_PROCESS_SHARED);
if( ret!=0 )
{
perror("init_mutex pthread_mutexattr_setpshared");
exit(1);
}
pthread_mutex_init(g_mutex, &attr);
}
int main(int argc, char *argv[])
{
init_mutex();
int ret;
char str1[]="this is child process\r\n";
char str2[]="this is father process\r\n";
int fd=open("tmp", O_RDWR|O_CREAT|O_TRUNC, 0666);
if( -1==fd )
{
perror("open");
exit(1);
}
pid_t pid;
pid=fork();
if( pid<0 )
{
perror("fork");
exit(1);
}
else if( 0==pid )
{
ret=pthread_mutex_lock(g_mutex);
if( ret!=0 )
{
perror("child pthread_mutex_lock");
}
sleep(10);//测试是否能够阻止父进程的写入
write(fd, str1, sizeof(str1));
ret=pthread_mutex_unlock(g_mutex);
if( ret!=0 )
{
perror("child pthread_mutex_unlock");
}
}
else
{
sleep(2);//保证子进程先执行
ret=pthread_mutex_lock(g_mutex);
if( ret!=0 )
{
perror("father pthread_mutex_lock");
}
write(fd, str2, sizeof(str2));
ret=pthread_mutex_unlock(g_mutex);
if( ret!=0 )
{
perror("father pthread_mutex_unlock");
}
}
