File locking

[c4n]

Could anyone please give me a short tutorial on "file locking" in CGI?

Thanks in advance!

 

[tsdragon]

It only works on *nix systems, not windows.

(Short enough?)
Tracy Dryden
tracy@bydisn.com

http://www.bydisn.com

Meddle not in the affairs of dragons,
For you are crunchy, and good with mustard.

 

[goBoating]

From a prompt,
prompt>perldoc -f flock -return-

gives...

use Fcntl ':flock'; # import LOCK_* constants

sub lock {
    flock(MBOX,LOCK_EX);
    # and, in case someone appended
    # while we were waiting...
    seek(MBOX, 0, 2);
}

sub unlock {
    flock(MBOX,LOCK_UN);
}

open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
        or die "Can't open mailbox: $!";

lock();
print MBOX $msg,"\n\n";
unlock();

Essentially, all programs that are using flock will cooperate with each other. Once a program has a file (f)locked, all other programs that are also using flock, will wait their turns. This will not prevent a program that is not trying to lock the file before use from using it without hesitation. 'hope this helps

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