From: Brent Roman <brent@...>
Date: 2009-01-14T15:23:16+09:00
Subject: [ruby-core:21332] Re: [PATCH] drastically improve rb_waitpid for short-lived children


Evan,

Here's a quick Ruby-only hack demonstrating a drastically improved waitpid
for short-lived
children without resorting to any sort of polling.  Here's the output on my
1.6Ghz
mac mini running Ubuntu 7.10:

## ...  ###6.393058
## ...  ###0.42344

That's a 15x speedup.  Doing this right probably requires a 'C' patch to the
core
along these lines.  We'd need a handler for SIGCHLD and probably a hash that
maps pids to waiting threads.  Looks promising...

---------------

# quick demo of the speed up possible by trapping SIGCHLD 
# instead of waiting for Ruby's internal rbthreadpoll()
# A proof up concept for a possible patch

n = 100

def nullShell
  pid = fastShell
  Process.waitall
end

def fastShell
  fork {
    exec "echo", "-n", "#"
  }
end

def time
  start = Time.now
  yield
  Time.now - start
end

Thread.new {
  t=Thread.current
  puts time{n.times{nullShell}}

  Signal.trap("CHLD") {
    t.wakeup  #Ruby traps run on the Thread.main
  }

  puts time{n.times{nullShell}}
}.join

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