Tuesday, November 4, 2014

The internals H2O (or how to write a fast server)

Yesterday, I had the opportunity to speak at the HTTP2Conference held in Tokyo.

Until now, I have rather been silent about H2O since I think it is still premature for wild use. But you do not need to worry about such thing in a technology conference, so I happily talked about the motives behind H2O, and its implementation.

IMO the talk should be interesting not only to people working with HTTP server implementations but also to those interested in programming in general, since it covers the common performance pitfalls (or misconceptions as I see) in many server implementations.

Below are the slides and the recorded video of my presentation.


PS. Please forgive me for the provocative attitude in the questions raised in the last part of the slides. They were intentionally written as such in order to spark discussion at the hall.

my talk starts a 3h15m (in Japanese)

Related links:


  1. You mentioned speed without using SIMD instructions. I see that you are doing a subtraction for every char, would it be faster to use SIMD to do 4 substractions at once?

    1. Recently a PR that uses pcmpestri (a SSE4.2 instruction) has been merged. The PR is https://github.com/h2o/picohttpparser/pull/5 and the benchmark numbers are https://github.com/h2o/picohttpparser/#benchmark

  2. I was looking at the src/main.c and found that each thread is creating it's own listeners queue using the server listeners. Isn't this a mistake ?
    What will happen when there is more than one thread ?
    All of then will wakeup and try to manage the accepted socket ?
    Why not accepting the listeners only in main process and distribute the accepted sockets to threads after ?

    Am I missing something here ?

    Cheers !

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