 unlock/lock when Boost.Python is invoking iterator
        changes via <code class="computeroutput"><span class="identifier">invoke</span><span class="special">.</span><span class="identifier">hpp</span></code>.
      </p>
<p>
        There is a patched <code class="computeroutput"><span class="identifier">invoke</span><span class="special">.</span><span class="identifier">hpp</span></code> posted
        on the C++-SIG mailing list archives and you can find a real implementation
        of all the machine