I'm not trying to mutually exclude anything.
You actually need to mutually exclude access to the condition variable. I don't use Perl threads much, but it looks like threads::shared has the necessary ingredients, and you can do something like this: 
my $cond : shared;
$thread1 = async {
    { lock($cond); cond_wait($cond) until $cond }
    # do stuff.
};

$thread2 = async {
    # do stuff.
    { lock($cond); $cond = "proceed"; cond_signal($cond) }
};

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In reply to Re^5: OT: Locking and syncing mechanisms available on *nix. by educated_foo
in thread OT: Locking and syncing mechanisms available on *nix. by BrowserUk

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