The ops never return junk; they will return values consistent with whatever thread did the most recent update. For example, this will never die: 
use threads;
use threads::shared;
my $x : shared;

for (0..9) {
    threads->new(sub { 
            while (1) {
            $x = $_[0];
            die unless $x =~ /^\d$/;
            }
        },
        $_
    );
}
sleep;

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There is one iterator per shared object, which is why I mentioned earlier that if other threads do each/keys/value too, it will affect the result

Dave.

In reply to Re^4: threads::shared - when to lock a hash ? by dave_the_m
in thread threads::shared - when to lock a hash ? by Anonymous Monk

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