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    <p>The overhead of stringifying <code>thread::id</code> (only to compute the string hash afterward) is, as you almost said yourself, astronomical compared to any performance benefits a <code>tr1::unordered_map</code> might confer vis-a-vis <code>std::map</code>. So the short answer would be: <strong>stick with std::map&lt; thread::id, ... ></strong></p> <p>If you <em>absolutely</em> must use unordered containers, <strong>try to use<code>native_handle_type</code></strong> instead of <code>thread::id</code> if possible, i.e. prefer <code>tr1::unordered_map&lt; thread::native_handle_type, ... &gt;</code>, invoking <code>thread::native_handle()</code> instead of <code>thread::get_id()</code> when <code>insert</code>ing and <code>find</code>ing.</p> <p><strong>DO NOT attempt anything like the following</strong>:</p> <pre><code>struct boost_thread_id_hash { // one and only member of boost::thread::id is boost::thread::id::thread_data // of type boost::detail::thread_data_ptr; // boost::thread::id::operator==(const id&amp;) compares boost::thread::id::thread_data's size_t operator()(boost::thread::id const&amp; id) const { const boost::detail::thread_data_ptr* pptdp = \ reinterpret_cast&lt; boost::detail::thread_data_ptr* &gt;(&amp;id); return h(pptdp-&gt;get()); } }; </code></pre> <p>It could work, but is extremely brittle and an almost guaranteed timebomb. It assumes intimate knowledge of the inner workings of the <code>thread::id</code> implementation. It will get you cursed at by other developers. Don't do it if maintainability is of any concern! Even patching <code>boost/thread/detail/thread.hpp</code> to add <code>size_t hash_value(const id&amp; tid)</code> as a friend of <code>thread::id</code> is "better". :)</p>
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    1. CO+1, and thanks for your answer. Actually, I think it is the best of them all, so I'm going to accept it. I'm not sure how "standard" `native_handle` and the related `native_handle_type` would be in the long term. Chances seem to be that `thread::id` hashing could be included in a reasonable time in boost, as there was some report against TR1 for not having it either if I remember well... In summary: thanks, I didn't think of `native_handle_type`.
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      1. USDiego Sevilla
 

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