Brethren-

I've been scratching my head at this for a couple days, perhaps your collective wisdom can shed some light on my problem.

I am trying to use cond_wait for synchronisation, but am either failing or hitting race conditions (depending on how I attempt to do it). Here is some example code: 
use strict; use warnings;         # hallelujah
use threads; use threads::shared; # threads, oh how I hate

my $lockvar : shared = 0;
my $thrHandle = threads->create( &exampleSub );

{lock $lockvar;
cond_wait ($lockvar);}
# code that should be executed at the same time as the
# block below
$thrHandle->join();
sub exampleSub {
    # some initialisation which may, or may not, take a lot
    # of time
    {lock $lockvar;
    cond_signal( $lockvar );}
    # code that should be executed at the same time as the 
    # block above
}

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This is a grossly simplified example, but it should show the problem. If the cond_signal is reached before the other thread reaches the cond_wait, the signal is discarded and the cond_wait will block forever.

The threading POD states that careful locking will prevent this from happening, but no example is provided and I can't figure it out myself.

Thanks for your help!

updated: Added the lock on $lockvar

In reply to Blocking cond_signal until someone cond_waits by bucky0

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