title: uWSGI "SIGNAL QUEUE IS FULL" errors
body: <p>I have a Django application running with uWSGI. </p>
  
  <p>Sometimes, when restarting the uWSGI service, I get a bunch of <code>*** SIGNAL QUEUE IS FULL: buffer size 212992 bytes (you can tune it with --signal-bufsize) ***</code> errors.</p>
  
  <p>When that happens, I'm unable to access the Django app. Restarting uWSGI again usually works.</p>
  
  <p>Any ideas what happening here?</p>
  
  <p>On startup of my application, I have a bunch of crons and timers that are initialized, like:</p>
  
  <pre><code>@uwsgidecorators.timer(30)
  def send_queued_mail(*args, **kwargs):
  
    ...
  </code></pre>
  
  <p>The full output of the wsgi process is below:</p>
  
  <pre><code>chdir() to /etc/uwsgi/vassals
  closing all non-uwsgi socket fds &gt; 2 (max_fd = 1024)...
  found fd 3 mapped to socket 0 (/var/run/uwsgi/MY_APP.sock)
  running /usr/local/bin/uwsgi
  *** has_emperor mode detected (fd: 7) ***
  [uWSGI] getting INI configuration from MY_APP.ini
  *** Starting uWSGI 2.0.17.1 (64bit) on [Thu Feb  6 22:22:18 2020] ***
  compiled with version: 4.8.4 on 07 August 2018 17:29:43
  os: Linux-4.2.0-42-generic #49~14.04.1-Ubuntu SMP Wed Jun 29 20:22:11 UTC 2016
  nodename: spuzzum
  machine: x86_64
  clock source: unix
  pcre jit disabled
  detected number of CPU cores: 4
  current working directory: /etc/uwsgi/vassals
  detected binary path: /usr/local/bin/uwsgi
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  chdir() to /opt/MY_APP
  your processes number limit is 128614
  your memory page size is 4096 bytes
  detected max file descriptor number: 1024
  lock engine: pthread robust mutexes
  thunder lock: disabled (you can enable it with --thunder-lock)
  uwsgi socket 0 inherited UNIX address /var/run/uwsgi/MY_APP.sock fd 3
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  Python version: 3.6.7 (default, Oct 21 2018, 00:00:00)  [GCC 4.8.4]
  Set PythonHome to /opt/MY_APP/venv/MY_APP-3.6
  Python main interpreter initialized at 0x24b1a00
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  python threads support enabled
  your server socket listen backlog is limited to 100 connections
  your mercy for graceful operations on workers is 60 seconds
  mapped 609552 bytes (595 KB) for 5 cores
  *** Operational MODE: preforking ***
  *** Starting uWSGI 2.0.17.1 (64bit) on [Thu Feb  6 22:22:21 2020] ***
  compiled with version: 4.8.4 on 07 August 2018 17:29:43
  os: Linux-4.2.0-42-generic #49~14.04.1-Ubuntu SMP Wed Jun 29 20:22:11 UTC 2016
  nodename: spuzzum
  machine: x86_64
  clock source: unix
  pcre jit disabled
  detected number of CPU cores: 4
  current working directory: /etc/uwsgi/vassals
  detected binary path: /usr/local/bin/uwsgi
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  chdir() to /opt/MY_APP
  your processes number limit is 128614
  your memory page size is 4096 bytes
  detected max file descriptor number: 1024
  lock engine: pthread robust mutexes
  thunder lock: disabled (you can enable it with --thunder-lock)
  uwsgi socket 0 inherited UNIX address /var/run/uwsgi/MY_APP.sock fd 3
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  Python version: 3.6.7 (default, Oct 21 2018, 00:00:00)  [GCC 4.8.4]
  Set PythonHome to /opt/MY_APP/venv/MY_APP-3.6
  Python main interpreter initialized at 0x24b1a00
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  python threads support enabled
  your server socket listen backlog is limited to 100 connections
  your mercy for graceful operations on workers is 60 seconds
  mapped 609552 bytes (595 KB) for 5 cores
  *** Operational MODE: preforking ***
  *** Starting uWSGI 2.0.17.1 (64bit) on [Thu Feb  6 22:22:21 2020] ***
  compiled with version: 4.8.4 on 07 August 2018 17:29:43
  os: Linux-4.2.0-42-generic #49~14.04.1-Ubuntu SMP Wed Jun 29 20:22:11 UTC 2016
  nodename: spuzzum
  machine: x86_64
  clock source: unix
  pcre jit disabled
  detected number of CPU cores: 4
  current working directory: /etc/uwsgi/vassals
  detected binary path: /usr/local/bin/uwsgi
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  chdir() to /opt/MY_APP
  your processes number limit is 128614
  your memory page size is 4096 bytes
  detected max file descriptor number: 1024
  lock engine: pthread robust mutexes
  thunder lock: disabled (you can enable it with --thunder-lock)
  uwsgi socket 0 bound to UNIX address /var/run/uwsgi/MY_APP.sock fd 3
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  Python version: 3.6.7 (default, Oct 21 2018, 00:00:00)  [GCC 4.8.4]
  Set PythonHome to /opt/MY_APP/venv/MY_APP-3.6
  Python main interpreter initialized at 0x10899e0
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  python threads support enabled
  your server socket listen backlog is limited to 100 connections
  your mercy for graceful operations on workers is 60 seconds
  mapped 609552 bytes (595 KB) for 5 cores
  *** Operational MODE: preforking ***
  *** has_emperor mode detected (fd: 7) ***
  unable to load configuration from from multiprocessing.semaphore_tracker import main;main(17)
  [uwsgi-signal] signum 0 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 1 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 2 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 3 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 4 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 5 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 6 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 7 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 8 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 9 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 10 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 11 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 12 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 13 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 14 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 15 registered (wid: 0 modifier1: 0 target: default, any worker)
  [uwsgi-signal] signum 16 registered (wid: 0 modifier1: 0 target: default, any worker)
  WSGI app 0 (mountpoint='') ready in 11 seconds on interpreter 0x10899e0 pid: 8515 (default app)
  uWSGI running as root, you can use --uid/--gid/--chroot options
  *** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
  *** uWSGI is running in multiple interpreter mode ***
  spawned uWSGI master process (pid: 8515)
  spawned uWSGI worker 1 (pid: 8548, cores: 1)
  spawned uWSGI worker 2 (pid: 8549, cores: 1)
  spawned uWSGI worker 3 (pid: 8550, cores: 1)
  spawned uWSGI worker 4 (pid: 8551, cores: 1)
  spawned uWSGI worker 5 (pid: 8552, cores: 1)
  *** Stats server enabled on /tmp/MY_APP-stats.socket fd: 23 ***
  subprocess 8540 exited with code 1
  *** SIGNAL QUEUE IS FULL: buffer size 212992 bytes (you can tune it with --signal-bufsize) ***
  could not deliver signal 14 to workers pool
  *** SIGNAL QUEUE IS FULL: buffer size 212992 bytes (you can tune it with --signal-bufsize) ***
  could not deliver signal 0 to workers pool
  *** SIGNAL QUEUE IS FULL: buffer size 212992 bytes (you can tune it with --signal-bufsize) ***
  could not deliver signal 0 to workers pool
  *** SIGNAL QUEUE IS FULL: buffer size 212992 bytes (you can tune it with --signal-bufsize) ***
  could not deliver signal 13 to workers pool
  *** SIGNAL QUEUE IS FULL: buffer size 212992 bytes (you can tune it with --signal-bufsize) ***
  could not deliver signal 14 to workers pool
  *** SIGNAL QUEUE IS FULL: buffer size 212992 bytes (you can tune it with --signal-bufsize) ***
  </code></pre>