JobQueue: minimize the amount of places changing self.__tick state

- start the jobqueue (by default) during __init__() instead of during
   put()
 - protect self._next_peek and self.__tick with a Lock
 - rename self._start() to self._main_loop()
 - stop() is now blocking until the event loop thread exits

telegram/ext/jobqueue.py

@@ -21,7 +21,7 @@
 import logging
 import time
 from threading import Thread, Lock, Event
-from queue import PriorityQueue
+from queue import PriorityQueue, Empty
 
 
 class JobQueue(object):
@@ -30,30 +30,38 @@ class JobQueue(object):
     Attributes:
         queue (PriorityQueue):
         bot (Bot):
+        prevent_autostart (Optional[bool]): If ``True``, the job queue will not be started
+                automatically. Defaults to ``False``
 
     Args:
         bot (Bot): The bot instance that should be passed to the jobs
 
     """
 
-    def __init__(self, bot):
+    def __init__(self, bot, prevent_autostart=False):
         self.queue = PriorityQueue()
         self.bot = bot
         self.logger = logging.getLogger(self.__class__.__name__)
-        self.__lock = Lock()
+        self.__start_lock = Lock()
+        self.__next_peek_lock = Lock()  # to protect self._next_peek & self.__tick
         self.__tick = Event()
+        self.__thread = None
+        """:type: Thread"""
         self._next_peek = None
+        """:type: float"""
         self._running = False
 
-    def put(self, job, next_t=None, prevent_autostart=False):
+        if not prevent_autostart:
+            self.logger.debug('Auto-starting %s', self.__class__.__name__)
+            self.start()
+
+    def put(self, job, next_t=None):
         """Queue a new job. If the JobQueue is not running, it will be started.
 
         Args:
             job (Job): The ``Job`` instance representing the new job
             next_t (Optional[float]): Time in seconds in which the job should be executed first.
                 Defaults to ``job.interval``
-            prevent_autostart (Optional[bool]): If ``True``, the job queue will not be started
-                automatically if it is not running. Defaults to ``False``
 
         """
         job.job_queue = self
@@ -68,13 +76,18 @@ class JobQueue(object):
         self.queue.put((next_t, job))
 
         # Wake up the loop if this job should be executed next
-        if not self._next_peek or self._next_peek > next_t:
+        self._set_next_peek(next_t)
-            self._next_peek = next_t
-            self.__tick.set()
 
-        if not self._running and not prevent_autostart:
+    def _set_next_peek(self, t):
-            self.logger.debug('Auto-starting JobQueue')
+        """
-            self.start()
+        Set next peek if not defined or `t` is before next peek.
+        In case the next peek was set, also trigger the `self.__tick` event.
+
+        """
+        with self.__next_peek_lock:
+            if not self._next_peek or self._next_peek > t:
+                self._next_peek = t
+                self.__tick.set()
 
     def tick(self):
         """
@@ -85,74 +98,80 @@ class JobQueue(object):
 
         self.logger.debug('Ticking jobs with t=%f', now)
 
-        while not self.queue.empty():
+        while True:
-            t, job = self.queue.queue[0]
+            try:
+                t, job = self.queue.get(False)
+            except Empty:
+                break
+
             self.logger.debug('Peeked at %s with t=%f', job.name, t)
 
-            if t <= now:
+            if t > now:
-                self.queue.get()
+                # we can get here in two conditions:
-
+                # 1. At the second or later pass of the while loop, after we've already processed
-                if job._remove.is_set():
+                #    the job(s) we were supposed to at this time.
-                    self.logger.debug('Removing job %s', job.name)
+                # 2. At the first iteration of the loop only if `self.put()` had triggered
-                    continue
+                #    `self.__tick` because `self._next_peek` wasn't set
-
+                self.logger.debug("Next task isn't due yet. Finished!")
-                elif job.enabled:
+                self.queue.put((t, job))
-                    self.logger.debug('Running job %s', job.name)
+                self._set_next_peek(t)
-
+                break
-                    try:
-                        job.run(self.bot)
-
-                    except:
-                        self.logger.exception(
-                            'An uncaught error was raised while executing job %s', job.name)
-
-                else:
-                    self.logger.debug('Skipping disabled job %s', job.name)
-
-                if job.repeat:
-                    self.put(job)
 
+            if job._remove.is_set():
+                self.logger.debug('Removing job %s', job.name)
                 continue
 
-            self.logger.debug('Next task isn\'t due yet. Finished!')
+            if job.enabled:
-            self._next_peek = t
+                self.logger.debug('Running job %s', job.name)
-            break
 
-        else:
+                try:
-            self._next_peek = None
+                    job.run(self.bot)
 
-        self.__tick.clear()
+                except:
+                    self.logger.exception(
+                        'An uncaught error was raised while executing job %s', job.name)
+
+            else:
+                self.logger.debug('Skipping disabled job %s', job.name)
+
+            if job.repeat:
+                self.put(job)
 
     def start(self):
         """
         Starts the job_queue thread.
 
         """
-        self.__lock.acquire()
+        self.__start_lock.acquire()
 
         if not self._running:
             self._running = True
-            self.__lock.release()
+            self.__start_lock.release()
-            job_queue_thread = Thread(target=self._start, name="job_queue")
+            self.__thread = Thread(target=self._main_loop, name="job_queue")
-            job_queue_thread.start()
+            self.__thread.start()
             self.logger.debug('%s thread started', self.__class__.__name__)
 
         else:
-            self.__lock.release()
+            self.__start_lock.release()
 
-    def _start(self):
+    def _main_loop(self):
         """
         Thread target of thread ``job_queue``. Runs in background and performs ticks on the job
         queue.
 
         """
         while self._running:
-            self.__tick.wait(self._next_peek and self._next_peek - time.time())
+            # self._next_peek may be (re)scheduled during self.tick() or self.put()
-
+            with self.__next_peek_lock:
-            # If we were woken up by set(), wait with the new timeout
+                tmout = self._next_peek and self._next_peek - time.time()
-            if self.__tick.is_set():
+                self._next_peek = None
                 self.__tick.clear()
-                continue
+
+            self.__tick.wait(tmout)
+
+            # If we were woken up by self.stop(), just bail out
+            if not self._running:
+                break
 
             self.tick()
 
@@ -162,10 +181,12 @@ class JobQueue(object):
         """
         Stops the thread
         """
-        with self.__lock:
+        with self.__start_lock:
             self._running = False
 
         self.__tick.set()
+        if self.__thread is not None:
+            self.__thread.join()
 
     def jobs(self):
         """Returns a tuple of all jobs that are currently in the ``JobQueue``"""