Unregister file descriptors when streams close.

[hathawsh]

When I run MongoDB under Supervisor 4.0-dev, MongoDB closes its stdout stream and Supervisor reacts by spinning the CPU at 100%. This patch fixes the problem by unregistering file descriptors that are no longer readable or writable.

(Both MongoDB and Supervisor remained responsive; this bug was really just a pure CPU drain.)

[msabramo]

Cool! Thanks!

[drewp]

I'm on 3.3.1 so I have this patch, but my supervisord is also at 100%. strace shows this repeating many times per second:

wait4(-1, 0x7ffd1fad6b4c, WNOHANG, NULL) = 0
poll([{fd=4, events=POLLIN|POLLPRI|POLLHUP}, {fd=7, events=POLLIN|POLLPRI|POLLHUP}, {fd=9, events=POLLIN|POLLPRI|POLLHUP}, {fd=10, events=POLLIN|POLLPRI|POLLHUP}, {fd=15, events=POLLIN|POLLPRI|POLLHUP}, {fd=22, events=POLLIN|POLLPRI|POLLHUP}, {fd=23, events=POLLIN|POLLPRI|POLLHUP}, {fd=26, events=POLLIN|POLLPRI|POLLHUP}, ...], 277, 1000) = 2 ([...])

(return from poll is always 2)

I am running mongodb, among 135+ other processes. According to /proc, the supervisord process has 718 open fds: 275 to log files, 411 are pipe:[...]. No process's log files are growing continuously.

Incidentally, mongodb (3.2.7) has written 30MB to its stdout and nothing to its stderr.

ubuntu 16.04.1, kernel 4.4.0-62-generic.

[drewp]

Sorry, #807 is the more recent discussion of this symptom.