Now, first of all, from this point on, I can quite willing to be corrected, however to my mind in order to prevent a race condition, the very next operation which should be carried out following the determination of the file name is the acquisition of an exclusive lock on the file. While your code iterates through the loop until a non-existent file name is determined, to my thinking, the next operation must be to open the file and acquire the lock rather than the test for existent (which should fail, thereby exiting the loop and allowing the file to subsequently opened) - The difference in code is minute and frankly I don't really know if its absolutely necessary, however, if I were requested to rewrite the code, the following is how I would rewrite it:

(Note that this philosophy with regard to order of actions to prevent race conditions with temporary files is based upon discussions within the comp.lang.perl.moderated newsgroup thread here and a BUGTRAQ post from Tom Christiansen here)

#!/usr/bin/perl

use Fcntl;
use strict;

my $fname = nextunique( 'aaa', [ map { m/tmp_(\D+).txt$/ } glob('./tmp
+_*.txt') ] );
do {
    $fname = nextunique( $fname, [ map { m/tmp_(\D+).txt$/ } glob('./t
+mp_*.txt') ] );
} until open (FH, $fname, O_RDWR|O_CREAT|O_EXCL, 0666);
#   code follows
close FH;


sub nextunique {
    my ($test_item, $item_list) = @_;
    exit 1 unless UNIVERSAL::isa( $item_list, 'ARRAY' );

    foreach ( @{ $item_list } ) {
        if ( $_ eq $test_item ) {
            ++$test_item;
            last;
        }
    }
    return $test_item;
}

[download]

You will also note that I have removed the while loop within the nextunique subroutine, thereby minimising the chance of an infinite loop should the element $new_item not exist within @{ $item_list }. A more defensive approach to programming? Maybe, maybe not ...

 

perl -e 's&&rob@cowsnet.com.au&&&split/[@.]/&&s&.com.&_&&&print'

In reply to Re: Re: get new item name by rob_au
in thread get new item name by mkmcconn

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