"per-process limit on the number of open file descriptors has been reached"

[Moses Moore]

I usually leave Clementine running all the time in the background, playing music most of the time. After a week or so, clementine will still make animations with progress bars and changing playlist, but does not make any sound. I see these messages on stderr:

(clementine:27280): GStreamer-CRITICAL **: gst_poll_write_control: assertion 'set != NULL' failed
(clementine:27280): GStreamer-CRITICAL **: gst_poll_free: assertion 'set != NULL' failed
The per-process limit on the number of open file descriptors has been reached.
ERROR: cannot create wakeup pipe
The per-process limit on the number of open file descriptors has been reached.
ERROR: cannot create wakeup pipe
AL lib: (EE) ALCplaybackAlsa_open: Could not open playback device 'default': Too many open files

difficult to reproduce, since I must leave clementine running for many days to get this, but it's happened twice before; this was the first time I kept an xterm open to watch stderr.

Before you ask "why are you using ALSA instead of Pulseaudio?" I had to ditch pulseaudio because it would crash with clementine, and I would have to reboot both pulsed and clementine every three days, sometimes more often, and clementine wasn't the only program that would get pulsed wedged hard -- also happened with Chromium, VLC, totem, and even Audacity.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: clementine 1.3.1+git276-g3485bbe43+dfsg-1
ProcVersionSignature: Ubuntu 4.13.0-25.29-generic 4.13.13
Uname: Linux 4.13.0-25-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.7-0ubuntu3.7
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat Mar 3 22:21:09 2018
InstallationDate: Installed on 2016-06-05 (636 days ago)
InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: clementine
UpgradeStatus: Upgraded to artful on 2017-10-22 (133 days ago)