bucky0 has asked for the wisdom of the Perl Monks concerning the following question:

Brothers-

I have (what seems to be) a trivial problem with threads. I have an object, and I'd like for it to be able to cond_signal to alert any interested threads of interesting events. My idea was to have different hash values store the signals.

However, all my attempts to lock the values of a hash fail with the error: "lock can only be used on shared values". Here is an example:
use strict; use warnings;
use threads;
use threads::shared;

# make the shared value
my %hash : shared;

# create the key I want
$hash{testElem} = 0;

# attempt to lock it
lock $hash{testElem};
# which fails.

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Any suggestions? As far as I know, this should be a valid operation.

Replies are listed 'Best First'.
Re: Locking hash values
by jettero (Monsignor) on Dec 18, 2006 at 18:06 UTC
    You can sorta get this to work like so: 
    my $scalar : shared = 0;
my %hash;

$hash{key} = \$scalar;

lock $hash{key};

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    I'm not sure how reliable that is when you start new threads though. You're probably better off just sticking with a few shared scalars in my opinion. Perl's threading isn't one of it's strongest features. At least you're not stuck with IPC.

    -Paul

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      Perhaps I'm doing something wrong, but that code fails out as well...perl's threading hurts me, this should be a simple thing to do. Not only that, it's mentioned in the POD as working.
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        I think that should be 

        lock ${$hash{key}};

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        The idea is that $scalar is shared, and therefore lockable.

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