I have a script that needs to update a flat text file by deleting some records from it. To avoid race conditions I need to generate a lockfile to guarantee that the text file is not changed while this update is being performed.

Here is the code 

#!/usr/bin/perl -Tw 
 
use strict;
use Fcntl (':flock');

....

sub DeleteRecords {

    no strict 'subs'; # strict does not like O_EXCL and O_CREAT??
    my($file, @delete_these) = @_;
    # avoid race conditions, where subscriber.txt is changed between
    # reading contents with &GetRecords and writing new subscriber 
    # list with &SetRecords. We create a lockfile only if it does
    # not already exist ie no other process performing &DeleteRecords
    my $count = 0;
    until (sysopen (LOCK, "$path_to_files/lockfile.txt", O_EXCL | O_CR
+EAT | O_WRONLY)) {
        sleep 1;
        DieNice("Can't create lockfile '$path_to_files/lockfile.txt': 
+$!\n") if ++$count >= $timeout;
    }
    my @records = &GetRecords($file);
    for my $record (@delete_these) {
        @records = grep{ $_ ne $record }@records;
    }
    &SetRecords($file, @records);
    close LOCK;
    unlink "$path_to_files/lockfile.txt" or DieNice("Can't unlink lock
+file: $!\n");
  return;
}

[download]

The code times out. The DieNice function reports the error as: Error Message: Can't create lockfile '/vs/mydomain.com/work/lockfile.txt': No such file or directory

Well I know the damn file does not exist (that's what I check for!) but it is not being created either.

So far I have confirmed that it is not a permissions problem as substituting a simple open for the sysopen works fine. 

open (LOCK, ">$path_to_files/lockfile.txt")

In the camel book I note that this function is dependent on the open(2) and fdopen(3) C lib and that some MODE flags may not be available. These would seem pretty standard but I am waiting to hear back from my sysadmin :-)

Question: Is this syntax related or system related?

cheers

tachyon

In reply to sysopen failing to work by tachyon

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