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  • Rodrigo Damazio Bovendorp's avatar
    procutil: always waiting on child processes to prevent zombies with 'hg serve' · ed684a82e29b
    Rodrigo Damazio Bovendorp authored
    When runbgcommand is invoked by an extension with ensurestart=False, we never
    called waitpid - which is fine in most cases, except if that's happening on a
    command server (e.g. chg), in which case the child defunct process will just
    sit there for as long as the server is running.
    
    The actual semantics of SIGCHLD signal handling is a lot more complex than
    it seems, and the POSIX standard *seems* to read that it's ignored by default
    and everything would just work without the waitpid if we're not listening for
    it, but the truth is that it's only ignored if we *explicitly* set it to
    SIG_IGN. We further cannot set it to SIG_IGN or to a catch-all handler across
    all of 'hg serve', because Python's suprocess.Popen relies on that signal,
    and a few specific parts of hg also set custom handlers, so instead we wait
    for specific PIDs in dedicated threads.
    
    I did a poor-man's benchmark of the thread creation and it seems to take
    about 1ms, which is way better than the 20+ms from ensurestart=True.
    
    Differential Revision: https://phab.mercurial-scm.org/D8497
    
    --HG--
    branch : stable
    ed684a82e29b
procutil.py 19.8 KB