[PATCH 3 of 4 V2] chgcache: implement the background preloading thread

Jun Wu quark at fb.com
Thu Mar 2 16:32:23 EST 2017

Excerpts from Yuya Nishihara's message of 2017-03-03 00:51:12 +0900:
> I hope so, but googling "fork thread" or "fork thread python" made me feel
> bad. I haven't read them carefully, but they seemed to say "don't do it."

Good catch!

I had a look at CPython source code. The most related function is
PyOS_AfterFork(void), which will be executed by the child. It does not
handle all lock issues (like malloc() in libc).

I think we can use os.fork() in master and avoid threading to solve the

  worker              master        forked master
    | send(repopath) -> |
                        | fork() -----> |
                                        | preload() 
                                        | replace master's socket
    | connect() ----------------------> |

This solves other problems - like parsers.c has some slow functions that may
block accept().

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