daverave has asked for the wisdom of the Perl Monks concerning the following question:

My Perl script nstore-ed a, hash but the resulting "binary" files only contains:

    pst0^E^G^L^D^Q^Tthreads::shared::tie
            440097248

[download]

My program indeed uses multi-threading and the hash I am trying to store is shared (created by shared_clone, then some keys added to it) -- see a previous discussion Multi-threads newbie questions.

Thanks!

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Re: Bad nstore of a shared hash
by BrowserUk (Patriarch) on Sep 21, 2010 at 15:25 UTC

    threads::shared::tie does not play nice with Storable. The solution is to make a copy of the hash before writing it to disk: 

    #! perl -slw
use strict;
use threads;
use threads::shared;
use Storable qw[ nstore retrieve ];
use Data::Dump qw[ pp ];

my %hash :shared = (
    a=>1,
    b=>1,
);

async {
    nstore { %hash }, 'fred.bin';
}->join;

my $hash2 = retrieve 'fred.bin';

pp $hash2;

__END__
C:\test>junk42
{ a => 1, b => 1 }

    [download]

    That does mean you'll have to share_clone() it if you need it shared once you retrieve() it.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
      Let me see if I got it right. You use async just to get a copy of the hash? You don't really need that fork, right?

      Also, how is that the copy created is not shared also?

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[d/l]
        You use async just to get a copy of the hash?

        No. I used the async to demonstrate Storable work fine within threads; that the problem you encountered is with threads::shared::tie.

        So yes, the threading was unnecessary to demonstrate that Storable works, but we know that already ;)

        Also, how is that the copy created is not shared also?

        Because nothing is shared unless you explicitly share it.

        The reference to the shared hash %hash, simply results in a list of values. Placing them inside an anonymous hash constructor, constructs a thread-local (ie.non-shared), anonymous hash. Which Storable can nstore() in the usual way.

        It is effectively the same as just: nstore { 1, 'a', 2, 'b }, 'fred.bin';. Except that the values come from a shared hash rather than constants.

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
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