文件锁的操作

#include<stdio.h>#include<unistd.h>#include<sys/types.h>#include<sys/file.h>#include<stdlib.h>#include<sys/stat.h>#include<fcntl.h>int lock_set(int fd,int type){struct flock old_lock,lock;lock.l_whence = SEEK_SET;lock.l_start = 0;lock.l_len = 0;lock.l_type = type;lock.l_pid = -1;fcntl(fd,F_GETLK,&lock);if(lock.l_type != F_UNLCK){if(lock.l_type == F_RDLCK)printf("read lock already set by %d\n",lock.l_pid);else if(lock.l_type == F_WRLCK)printf("write lock already set by %d\n",lock.l_pid);}lock.l_type = type;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());break;case F_WRLCK: printf("write lock set by %d\n",getpid());break;case F_UNLCK:       {printf("release lock by %d\n",getpid());return 1;      break;      }default:break;}return 0;}int main(void){int  fd;fd = open("hello",O_RDWR|O_CREAT,0644);if(fd <0){printf("open file failed \n");return -1;}lock_set(fd,F_RDLCK);getchar();lock_set(fd,F_UNLCK);getchar();close(fd);return 0;}