LinuxQuestions.org - lock file between two process

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lock file between two process

I need to lock a file, which will be accessed by a Java program (multi-thread). The content of the file is written by a C programme. I try the file lock (similar to the book - Advanced Linux Programming). It doesn't work because when reading the file and paring it, it returned with a error, saying no content inside the file (but `cat file_name` I can see the content exactly there). How can I lock a file that can prevent other processes (the Java programme) access the file before the writing process (the C programme) finishes its jobs? Or what to do to prevent such problem occurs?

The code snippet of locking file in C I write is as follow:

Code:

...

        memset(&lock, 0, sizeof(lock));

        lock.l_type = F_WRLCK;

        fcntl(fd, F_SETLK, &lock);



        //prepare content

...

        /* unlocking file */

        lock.l_type = F_UNLCK;

        fcntl(fd, F_SETLK, &lock);

...

Thanks in advice,

Most file locking is "advisory locking", in which processes must cooperate with each other in order for the locking to take effect. If you're trying to lock out from a file any arbitrary unknown code, advisory locking won't work.

No, you want "mandatory locking". See:

http://linux-security.cn/ebooks/ulk3...12-SECT-7.html

For words from the Linux horse's mouth, see:

http://www.in-ulm.de/~mascheck/vario.../mandatory.txt

Hope this helps.