You may find this File Locking tutorial useful. This is a typical basic method. We use a suck it and see approach. If we can't get a lock on the file we die.

open(MYFILE, ">>$myfile") || die "Can't append to $myfile, Perl says $
+!";
flock(MYFILE, 2) || die "Can't lock $myfile, Perl says $!";
print MYFILE "Hello World!\n";
close MYFILE;
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Do you realise that you have written an infinite loop? Your outer loop:

for ($i=0; defined($i); $i++){
    print "Help! I'm trapped in an infinite loop\n";
}
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will never end as the exit condition defined($i) will always be true. If you really want an infinite loop you could just write:

while (1) {
   print "foo";
}

# or you can write

for (;;) {
   print "foo"
}
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In either case you will need break out of the loop using a last, unless you are in one of those moods and want to hang the system :-)

Cheers

tachyon

Let's look at: unless (-e "./tempads/$i.dat" || <file is locked> )

What is this guard supposed to do? "-e" tests whether the file exists, and if not, you check whether the file is locked. But for a file to be locked, it should exists first. I am not sure what you want to do, do you want to write to the file unless it is locked, or only if it exists and it's not locked?

To check whether a file is locked, open it, and try to acquire a lock. But you have to that non-blocking, or else the command will block till you have a lock. And don't open the file ">", or else you wipe out the content before checking for a lock. Use "+<", and truncate after done writing.

-- Abigail