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$mutex->enter( $shared->set( $_ => $fetch->($_) ) );

...
3. then stores the result into a shared hash
4. finally, leaves the mutex

    mce_loop {
        MCE->yield;
...
        # ...
    }

    mce_loop {
        MCE->yield;
...

    }

    tie my %hash, 'MCE::Shared';
    my $shared = MCE::Shared->hash();
...
    # 1 trip via the OO interface
    $shared->incrby( number => 2 );