You have a race condition due to your flock being cancelled when you
close the file.
A open IN
A flock IN
A open OUT (truncates $tmp_db)
A while loop
B blocks
A close IN
B open IN
A close OUT
B open OUT (truncates $tmp_db)
A unlinks main_db
A tries to move $tmp_db to $main_bd, but $tmp_db is empty.
If you're married to using flock, you can flock a semaphore file for the
whole operation:
sub Update_db {
$main_db = $_[0];
$tmp_db = $_[1];
$update = $_[2];
$lock_file = 'somefile';
open LOCK, ">$lock_file";
flock( LOCK, LOCK_EX ) or print "Unable to acquire lock: $!.
Aborting"; #ps, this is a blocking call, it shouldnt fail
open IN, "<$main_db" or print "Can't open $main_db: $!\n";
open OUT, ">$tmp_db" or print "Can't open temporary file $tmp_db:
$!\n";
while ( <IN> ) {
($name, $team, $location)= split(/\|/, $_);
next unless $name eq $update;
$new_location = "palm_bay";
$_ = join( "|", $name, $team, $new_location);
}
continue {
print OUT $_ or print "Error writing $tmp_db: $!\n";
}
close IN;
close OUT;
unlink $main_db;
rename $tmp_db, $main_db or print "Can't rename '$tmp_db' to
'$main_db':$!\n";
flock(LOCK, LOCK_UN);
close(LOCK);
}
Otherwise you consider using a semaphore (perldoc IPC::Semaphore).
On Wednesday, July 17, 2002, at 08:31 PM, Jeff wrote:
> John,
>
> unix,
>
> sub Update_db {
> $main_db = $_[0];
> $tmp_db = $_[1];
> $update = $_[2];
> open IN, "<$main_db" or print "Can't open $main_db: $!\n";
> flock( IN, LOCK_EX ) or print "Unable to acquire lock: $!. Aborting";
> open OUT, ">$tmp_db" or print "Can't open temporary file $tmp_db:
> $!\n";
> flock( OUT, LOCK_EX ) or print "Unable to acquire lock: $!. Aborting";
> while ( <IN> ) {
> ($name, $team, $location)= split(/\|/, $_);
> next unless $name eq $update;
> $new_location = "palm_bay";
> $_ = join( "|", $name, $team, $new_location);
> }
> continue {
> print OUT $_ or print "Error writing $tmp_db: $!\n";
> }
> close IN;
> close OUT;
> unlink $main_db;
> rename $tmp_db, $main_db or print "Can't rename '$tmp_db' to
> '$main_db':
> $!\n";
> }
>
>
> -----Original Message-----
> From: John W. Krahn [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, July 17, 2002 8:11 PM
> To: [EMAIL PROTECTED]
> Subject: Re: Flat File Db
>
>
> Jeff wrote:
>>
>> I'm use flat files to manage a list containing approx 25,000 records.
>> For
>> updates, I write to a temp file then unlink main and rename temp file
>> to
>> main. I use flock for both temp and main files during update. My main
> file
>> gets blown away on occasions. What gives? I can't figure out why this
>> happens. Thanks for any help!
>
> OS? code?
>
>
> John
> --
> use Perl;
> program
> fulfillment
>
> --
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// George Schlossnagle
// Principal Consultant
// OmniTI, Inc http://www.omniti.com
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