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    <p>Why do you want to store these in a set. Unless you doing something out of the ordinary, there will be a small number of threads. The overhead of maintaining a set is probably higher than just putting them in a vector and doing a linear search. </p> <p>If searching will happen more frequently than adding and deleting, you can just use a sorted vector. There is a &lt; operator defined for boost::thread::id, so you can sort the vector (or insert into the correct place) after each addition or deletion, and use <code>lower_bound()</code> to do a binary search. This is the same complexity as searching a set, and should have lower overhead for small amounts of data. </p> <p>If you still need to do this, how about just treating it as a sizeof(boost::thread:id) bytes, and operating on those.</p> <p>This example assumes that the size of boost::thread::id is a multiple of the size of an int, and that there is no packing, and no virtual functions. If that is not true, it will have to be modified, or will not work at all.</p> <p>EDIT: I took a look at the <code>boost::thread::id</code> class, and it has a <code>boost::shared_pointer&lt;&gt;</code> as a member, so the code below is horribly broken. I think the only solution is to have the authors of <code>boost::thread</code> add a hash function. I'm leaving the example just in case its useful in some other context.</p> <pre><code>boost::thread::id id; unsigned* data; // The next line doesn't do anything useful in this case. data = reinterpret_cast&lt;unsigned *&gt;(&amp;id); unsigned hash = 0; for (unsigned int i = 0; i &lt; sizeof(boost::thread::id)/4; i++) hash ^= data[i]; </code></pre>
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    1. USBenjamin
    1. USKeithB
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    1. COKeith, thank you for your insights. However, we are using this code in a library that may end being used from an indeterminate number of threads (hundreds), so I don't want to make the thread indexing a bottleneck. Finally, how can you determine that for two different boost::thread::id objects, their sizeof would be different? In other words, using the sizeof you propose doesn't help in identifying the thread itself. Regards, diego.
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      1. USDiego Sevilla
    2. COI'll add an example to make it clear. It may be that with hundreds of threads a map makes more sense, but I would still benchmark it. I'll added another alternative to my answer.
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