Augie Fackler <augie@google.com> [Wed, 16 Nov 2016 23:29:28 -0500] rev 30427
merge with stable
Jun Wu <quark@fb.com> [Sat, 12 Nov 2016 03:06:07 +0000] rev 30426
worker: stop using a separate thread waiting for children
Now that we have a SIGCHLD hander, and it could get executed when waiting
for I/O. It's no longer necessary to have a separated waitpid thread. So
just remove it.
Jun Wu <quark@fb.com> [Sat, 12 Nov 2016 03:07:22 +0000] rev 30425
worker: add a SIGCHLD handler to collect worker immediately
As planned by previous patches, add a SIGCHLD handler to get notifications
about worker exits, and deals with worker failure immediately.
Note that the SIGCHLD handler gets unregistered before killworkers(), so
SIGCHLD won't interrupt "killworkers" - making it harder to send kill
signals to waited processes.
Jun Wu <quark@fb.com> [Tue, 15 Nov 2016 02:12:16 +0000] rev 30424
worker: make waitforworkers reentrant
We are going to use it in the SIGCHLD handler. The handler will be executed
in the main thread with the non-blocking version of waitpid, while the
waitforworkers thread runs the blocking version. It's possible that one of
them collects a worker and makes the other error out (no child to wait).
This patch handles these errors: ECHILD is ignored. EINTR needs a retry.
The "pids" set is designed to be only modifiable by "waitforworkers". And we
only remove items after a successful waitpid. Since a child process can only
be "waitpid"-ed once. It's guaranteed that "pids.remove(p)" won't be called
with duplicated "p"s. And once a "p" is removed from "pids", that "p" does
not need to be killed or waited any more.