Linux中的fcntl文件锁基础实验

/*lock_set.c*/ int lock_set(int fd,int type) { struct flock old_lock,lock; /*定义flock结构体*/ lock.l_whence=SEEK_SET; /*加锁整个文件*/ lock.l_start=0; lock.l_len=0; lock.l_type=type; lock.l_pid=-1; /*判断文件是否可以上锁 */ fcntl(fd,F_GETLK,&lock); if(lock.l_type!=F_UNLCK) { /*判断文件不能上锁的原因 */ if(lock.l_type==F_RDLCK) /*该文件已经有读取锁 */ { printf("Read lock already set by %d\n",lock.l_pid); } else if(lock.l_type==F_WRLCK) /*该文件已经有写入锁 */ { printf("Write lock already set by %d\n",lock.l_pid); } } /*l_type 可能在执行完上述判断后被修改了*/ lock.l_type=type; /*根据不同的type值进行阻塞式上锁或解锁*/ if((fcntl(fd,F_SETLKW,&lock))<0) { printf("Lock failed:type=%d\n",lock.l_type); return 1; } switch(lock.l_type) { case F_RDLCK: { printf("Read lock set by %d\n",getpid());/*getpid()用来得到当前的进程号*/ } break; case F_WRLCK: { printf("Write lock set by %d\n",getpid()); } break; case F_UNLCK: { printf("Release lock set by %d\n",getpid()); return 1; } break; default:break; } /*end of switch*/ return 0; }