Jun Wu <quark@fb.com> [Tue, 15 Nov 2016 02:12:16 +0000] rev 30414
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.
Jun Wu <quark@fb.com> [Tue, 15 Nov 2016 02:10:40 +0000] rev 30413
worker: change "pids" to a set
There is no need to keep any order of the "pids" array. A set is more
efficient for the "remove" operation. And the following patch will use that.