in reply to Re: Storable and passed filehandles
in thread Storable and passed filehandles

I am working on a unix system (FreeBSD), and thanks for the semaphore pointer (further explained here).
I guess I'm just surprised that the above doesn't work. As I test and test and re-test I am completely duped that even this simple code doesn't work...

#!/usr/bin/perl -w
# start with no existing giant.db file
use strict;
use Fcntl qw(:DEFAULT :flock);
use Storable qw(store_fd fd_retrieve retrieve);
use Data::Dumper;
$Data::Dumper::Deepcopy=1;
$Data::Dumper::Purity=1;
$Data::Dumper::Sortkeys=1;

my %data = ( 1 => 'FEE', 2 => 'FYE',
             3 => 'FOH', 4 => 'FUM', );

sysopen(*DB, "giant.db", O_RDWR|O_CREAT, 0666) or die("sysopen: $!\n")
+;
flock(*DB, LOCK_EX) or die("flock: $!\n");
my $hashref = fd_retrieve(*DB);

# modify the data, do work, etc..
$hashref->{$_} = $data{$_} for sort keys %data;

store_fd($hashref, *DB) or die("store_fd: $!\n");
truncate(*DB, tell(*DB));
close(*DB);

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I'm totally spent and frustrated. Does anyone have any idea why this doesn't work? I must be missing something. I'm just trying to block access to a file while I change it. The above SHOULD work, shouldn't it?....shouldn't it?....please?

Thanks

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Re^3: Storable and passed filehandles
by Roger (Parson) on Aug 15, 2005 at 23:26 UTC
    Try the flock implemented by Storable first... 
    #!/opt/kalm/bin/perl -w
use strict;
use Storable qw(lock_store lock_retrieve);
use Data::Dumper;
$Data::Dumper::Deepcopy=1;
$Data::Dumper::Purity=1;
$Data::Dumper::Sortkeys=1;

my %data = ( 1 => 'FEE', 2 => 'FYE',
             3 => 'FOH', 4 => 'FUM', );

my $file = 'test.dat';
lock_store \%data, $file;
my $hashref = lock_retrieve $file;

print Dumper($hashref);

    [download]
[reply]
[d/l]
      I had tried that, but it doesn't do what I need. It only locks the file during the actual read and write. It doesn't hold the lock to prevent other processes from changing the data while I do my thing.

      When we commit our changes we blast over each others changes.

[reply]
Re^3: Storable and passed filehandles (ref to glob)
by tye (Sage) on Aug 15, 2005 at 23:27 UTC

    In general, passing in \*DB is better than just *DB.

    Looking at the docs for Storable I see both ways documented.

    However, when reading the source, it looks like using just *DB would get you a fatal "not a ref" thrown, though I don't see you describe the failure beyong "doesn't work" (the universal useless problem description) in your node.

    - tye        

[reply]
      Doh. Sorry 'bout that. The error I'm getting is:

      Magic number checking on storable file failed at ../../lib/Storable.pm (autosplit into ../../lib/auto/Storable/fd_retrieve.al) line 341, at ./483993.pl line 16

      using the second, much smaller code snippet I posted.
[reply]

        Quoting the Storable docs:

        At the cost of a slight header overhead, you may store to an already opened file descriptor using the store_fd routine, and retrieve from a file via fd_retrieve.

        So you probably wrote that file with something other than store_fd and so it doesn't contain the "slight header overhead" that fd_retrieve is expecting.

        - tye        

[reply]

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