Re: [MacPerl] file-locking algorithm

["Paul J. Schinder" <schinder@pjstoaster.pg.md.us>]

pr1@club-internet.fr (Philippe de Rochambeau) writes:
}I am currently designing a Perl program that lets people search through a
}text-file database using an HTML form. Can anyone suggest a simple
}file-locking algorithm to prevent several users on the Web from opening the
}file at the same time?

If, as it sounds here, the file is open read-only, why does it matter if
several users are opening the file at the same time?

}
}Question: does the Perl command "open" die whenever a file is being used by
}another acgi on the server machine?

I haven't verified this by looking in Inside Macintosh, but the way my Mac
programs behave leads me to believe that only one Macintosh program at a
time can hold any file open for writing.  However, others can hold the same
file open for reading at the same time, and I haven't tested to see what
happens in MacPerl with open.  Time to do some testing, I think.  The open
certainly wouldn't fail if you ask for read permission only.

}
}Although I am designing and testing this Perl program on a Macintosh, I
}plan to eventually put it on an Unix server. As a result, the file-locking
}should also work on Unix, if possible.

This is a topic that's discussed too often on comp.lang.perl.misc, with the
tones of exasperation that leads me to think that the answer is in the Perl
FAQ.  The command is called "flock" (time for Shuck again), but using it
properly is apparently a little tricky.  If I were you, I'd track down the
latest Perl FAQ (try <http://www.perl.com/> or maybe
<http://www.perl.org/>).

}
}Many thanks.
}
}Philippe de Rochambeau
}
}______________________________________________________________________________
}Philippe de Rochambeau
}pr1@club-internet.fr
}
}
}
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--------
Paul J. Schinder
NASA Goddard Space Flight Center
Code 693
Greenbelt, MD 20770
schinder@pjstoaster.pg.md.us


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