1

我找不到有关如何锁定文件以进行读写的答案。

lock.l_type = F_WRLCK //for write.
lock.l_type = F_RDLCK //for read
lock.l_type = F_RDLCK|F_WRLCK //maybe for read/write????

下面的代码是否正确？

fd=MyOpenWrite(name,O_RDWR);  //for read/write
//(open file for read/write, but lock for write)
...
fd=MyOpenRead(name,O_RDONLY);  //open and lock for read
...
fd=MyOpenWrite(name,O_CREAT|O_WRONLY|O_TRUNC); //for write
...
fd=MyOpenWrite(name,O_WRONLY|O_APPEND);  //for append

int MyOpenRead(char *name,int flags) {
    int fd;
    struct flock    lock;
    fd = open(name,flags);
    if (fd<0) return -1;
    lock.l_type = F_RDLCK;
    lock.l_start = 0;
    lock.l_whence = SEEK_SET;
    lock.l_len = 0;
    fcntl(fd,F_SETLKW,&lock);
    return fd;
}

int MyOpenWrite(char *name,int flags) {
    int fd;
    struct stat st;
    fd = open(name,flags,S_IREAD|S_IWRITE|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH);
    if (fd<0) return -1;

    lock.l_type = F_WRLCK;
    lock.l_start = 0;
    lock.l_whence = SEEK_SET;
    lock.l_len = 0;
    fcntl(fd,F_SETLKW,&lock);
    return fd;
}
4

1 回答 1

3

写锁也会阻塞读者。它是一个排他锁，因此只有所有者*可以访问锁定的字节，其他人无法访问这些字节，无论是通过读取还是写入。

* fcntl() 锁是咨询锁。因此，如果其他人不合作，打开文件的任何人都可以自由地读/写它，并且还使用 fcntl() 来获取锁。如果您需要强制锁定，请参见此处

于 2013-03-19T09:47:24.610 回答