[PATCH 3 of 8 V4] worker: allow waitforworkers to be non-blocking

[Jun Wu]

Excerpts from Sean Farley's message of 2016-11-14 13:42:35 -0800:
> Jun Wu <quark at fb.com> writes:
> 
> > # HG changeset patch
> > # User Jun Wu <quark at fb.com>
> > # Date 1469735827 -3600
> > #      Thu Jul 28 20:57:07 2016 +0100
> > # Node ID 15594c001edb494e4ee4faff6fc6730772271768
> > # Parent  05485a528446de24eb8b81819f66ad36f0730802
> > # Available At https://bitbucket.org/quark-zju/hg-draft 
> > #              hg pull https://bitbucket.org/quark-zju/hg-draft  -r 15594c001edb
> > worker: allow waitforworkers to be non-blocking
> >
> > This patch adds a boolean flag to waitforworkers and makes it non-blocking
> > if set to True.
> >
> > This is to make it possible that we can reap our workers while keep other
> > unrelated children untouched, after receiving SIGCHLD.
> >
> > diff --git a/mercurial/worker.py b/mercurial/worker.py
> > --- a/mercurial/worker.py
> > +++ b/mercurial/worker.py
> > @@ -95,7 +95,9 @@ def _posixworker(ui, func, staticargs, a
> >                  if err.errno != errno.ESRCH:
> >                      raise
> > -    def waitforworkers():
> > +    def waitforworkers(blocking=True):
> >          for pid in pids:
> > -            st = _exitstatus(os.waitpid(pid, 0)[1])
> > +            p, st = os.waitpid(pid, 0 if blocking else os.WNOHANG)
> 
> Minor nit: is if/else pattern this allowed?

Searching the codebase, I could find other places using the pattern.
I guess a pair of parentheses would make it look better.