The restart_pool remote control command now requires the CELERYD_POOL_RESTARTS setting to be enabled. Disabling the sentinel event by default reduces the number of sempahores required to run the pool.

celery/app/defaults.py

@@ -177,6 +177,7 @@ NAMESPACES = {
         'MAX_TASKS_PER_CHILD': Option(type='int'),
         'POOL': Option(DEFAULT_POOL),
         'POOL_PUTLOCKS': Option(True, type='bool'),
+        'POOL_RESTARTS': Option(False, type='bool'),
         'PREFETCH_MULTIPLIER': Option(4, type='int'),
         'STATE_DB': Option(),
         'TASK_LOG_FORMAT': Option(DEFAULT_TASK_LOG_FMT),

celery/worker/__init__.py

@@ -84,7 +84,8 @@ class Pool(bootsteps.StartStopComponent):
     name = 'worker.pool'
     requires = ('queues', 'beat', )
 
-    def __init__(self, w, autoscale=None, no_execv=False, **kwargs):
+    def __init__(self, w, autoscale=None, autoreload=False,
+            no_execv=False, **kwargs):
         w.autoscale = autoscale
         w.pool = None
         w.max_concurrency = None
@@ -92,6 +93,7 @@ class Pool(bootsteps.StartStopComponent):
         w.no_execv = no_execv
         if w.autoscale:
             w.max_concurrency, w.min_concurrency = w.autoscale
+        self.autoreload_enabled = autoreload
 
     def on_poll_init(self, pool, hub):
         apply_after = hub.timer.apply_after
@@ -148,6 +150,7 @@ class Pool(bootsteps.StartStopComponent):
         if not threaded:
             semaphore = w.semaphore = BoundedSemaphore(procs)
             max_restarts = 100
+        allow_restart = self.autoreload_enabled or w.pool_restarts
         pool = w.pool = self.instantiate(w.pool_cls, w.min_concurrency,
                             initargs=(w.app, w.hostname),
                             maxtasksperchild=w.max_tasks_per_child,
@@ -157,6 +160,7 @@ class Pool(bootsteps.StartStopComponent):
                             lost_worker_timeout=w.worker_lost_wait,
                             threads=threaded,
                             max_restarts=max_restarts,
+                            allow_restart=allow_restart,
                             semaphore=semaphore)
         if w.hub:
             w.hub.on_init.append(partial(self.on_poll_init, pool))
@@ -287,6 +291,7 @@ class WorkController(configurated):
     task_soft_time_limit = from_config()
     max_tasks_per_child = from_config()
     pool_putlocks = from_config()
+    pool_restarts = from_config()
     force_execv = from_config()
     prefetch_multiplier = from_config()
     state_db = from_config()

docs/configuration.rst

@@ -1429,6 +1429,16 @@ the built-in aliases: ``processes``, ``eventlet``, ``gevent``.
 
 Default is ``processes``.
 
+.. setting:: CELERYD_POOL_RESTARTS
+
+CELERYD_POOL_RESTARTS
+~~~~~~~~~~~~~~~~~~~~~
+
+If enabled the worker pool can be restarted using the
+:control:`pool_restart` remote control command.
+
+Disabled by default.
+
 .. setting:: CELERYD_AUTOSCALER
 
 CELERYD_AUTOSCALER

docs/userguide/workers.rst

@@ -575,6 +575,8 @@ Pool Restart Command
 
 .. versionadded:: 2.5
 
+Requires the :setting:`CELERYD_POOL_RESTARTS` setting to be enabled.
+
 The remote control command :control:`pool_restart` sends restart requests to
 the workers child processes.  It is particularly useful for forcing
 the worker to import new modules, or for reloading already imported