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我的程序是父,子2个进程尝试对一个打开的文件的同一区域加写锁。先让子进程获得锁,然后再让父进程去锁。按正常的运行,应该是父进程测试锁时会发现已有一个排斥它的锁存在,但是实际程序运行却发现父进程会发现可以加锁。代码如下:- void pflock(struct flock *fl)
- {
- printf("fl.l_type:%d,fl.l_whence::%d,fl.l_start:%d,fl.l_len:%d,fl.l_pid:%lu\n",fl->l_type,fl->l_whence,fl->l_start,fl->l_len,(long)fl->l_pid);
- }
- int main(void)
- {
- int fd, ret;
- pid_t pid;
- struct flock fl;
-
- fd = open("./d", O_RDWR);
- if ( fd < 0 )
- {
- perror("open");
- return -1;
- }
- pid = fork();
- if ( pid < 0 )
- {
- perror("fork");
- close(fd);
- return -1;
- }
- else if ( pid == 0 )
- {
- printf("child pid:%lu\n",(long)getpid());
- fl.l_type = F_WRLCK;
- fl.l_whence = SEEK_SET;
- fl.l_start = 1;
- fl.l_len = 2;
- fl.l_pid = getpid();
-
- ret = fcntl(fd, F_GETLK, &fl);
- if ( fl.l_type != F_UNLCK )
- {
- printf("already have a file lock\n");
- pflock(&fl);
- close(fd);
- exit(0);
- }
- printf("child set flock\n");
- ret = fcntl(fd, F_SETLK, &fl);
- if ( ret < 0 )
- {
- perror("fcntl");
- close(fd);
- exit(0);
- }
- while(1);
- }
- else
- {
- printf("parent pid:%lu\n",(long)getpid());
- sleep(1); //let child process get a flock before parents
-
- fl.l_type = F_WRLCK;
- fl.l_whence = SEEK_SET;
- fl.l_start = 1;
- fl.l_len = 2;
- fl.l_pid = getpid();
-
- ret = fcntl(fd, F_GETLK, &fl);
- if ( fl.l_type != F_UNLCK )
- {
- printf("already have a file lock\n");
- pflock(&fl);
- close(fd);
- exit(0);
- }
-
- printf("parent set flock\n");
- ret = fcntl(fd, F_SETLK, &fl);
- if ( ret < 0 )
- {
- perror("fcntl");
- close(fd);
- exit(0);
- }
- while(1);
- }
- close(fd);
- exit(0);
- }
复制代码 按我的预期是,父进程在 if ( fl.l_type != F_UNLCK ) 这个判断中会退出。而实际运行却发现程序继续运行了下去,并加了写锁。 |
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