[libcxx-commits] [PATCH] D67086: Implement syncstream (p0053)

[Marshall Clow via Phabricator via libcxx-commits]

mclow.lists added inline comments.


================
Comment at: libcxx/include/syncstream:208
+template <class _CharT, class _Traits, class _Allocator>
+_VSTD::unordered_map<
+    typename basic_syncbuf<_CharT, _Traits, _Allocator>::streambuf_type*,
----------------
zoecarver wrote:
> mclow.lists wrote:
> > Why `unordered_map` as opposed to `map`? Does `std::hash< streambuf_type*>` have some behavior that you want?  [ Note: `unordered_map` might be the right choice. But you should say //why// it is the right choice somewhere. ]
> The pointer specialization of `std::hash` should help with memory usage. Unordered map has a find complexity of O(1) which is the real reason I think it should be used. This stream should be CPU performant above all else, with hundreds of threads trying to access an element, I think the benefit of find speed outweighs the slight increase in memory consumption. Do you agree?
> The pointer specialization of std::hash should help with memory usage. 

How?

>Unordered map has a find complexity of O(1) which is the real reason I think it should be used.
Unordered map has a find complexity of O(1) in the best case. O(N) in the worst case. Which one this?


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  https://reviews.llvm.org/D67086/new/

https://reviews.llvm.org/D67086