Optimize auto-commit thread

The previous commit optimized the commit thread such that the timer
started only when there were messages to be consumed. This commit
goes a step further and ensures the following:
* Only one timer thread is created
* The main app does not block on exit (waiting for timer thread to finish)

This is ensured by having a single thread blocking on an event and
keeps calling a function. We use events instead of time.sleep() so
as to prevent the python interpreter from running every 50ms checking
if the timer has expired (logic copied from threading.Timer)

Author: mahendra

kafka/consumer.py

@@ -58,7 +58,8 @@ def __init__(self, client, group, topic, auto_commit=True,
         # Set up the auto-commit timer
         if auto_commit is True and auto_commit_every_t is not None:
             self.commit_timer = ReentrantTimer(auto_commit_every_t,
-                                               self._timed_commit)
+                                               self.commit)
+            self.commit_timer.start()
 
         def get_or_init_offset_callback(resp):
             if resp.error == ErrorMapping.NO_ERROR:
@@ -149,15 +150,6 @@ def pending(self, partitions=[]):
 
         return total
 
-    def _timed_commit(self):
-        """
-        Commit offsets as part of timer
-        """
-        self.commit()
-
-        # Once the commit is done, start the timer again
-        # self.commit_timer.start()
-
     def commit(self, partitions=[]):
         """
         Commit offsets for this consumer
@@ -166,11 +158,17 @@ def commit(self, partitions=[]):
                     all of them
         """
 
-        # short circuit if nothing happened
+        # short circuit if nothing happened. This check is kept outside
+        # to prevent un-necessarily acquiring a lock for checking the state
         if self.count_since_commit == 0:
             return
 
         with self.commit_lock:
+            # Do this check again, just in case the state has changed
+            # during the lock acquiring timeout
+            if self.count_since_commit == 0:
+                return
+
             reqs = []
             if len(partitions) == 0:  # commit all partitions
                 partitions = self.offsets.keys()
@@ -200,12 +198,7 @@ def _auto_commit(self):
             return
 
         if self.count_since_commit > self.auto_commit_every_n:
-            if self.commit_timer is not None:
-                self.commit_timer.stop()
-                self.commit()
-                self.commit_timer.start()
-            else:
-                self.commit()
+            self.commit()
 
     def __iter__(self):
         """
@@ -223,10 +216,6 @@ def __iter__(self):
             if len(iters) == 0:
                 break
 
-            # Now that we are consuming data, start the commit thread
-            if self.commit_timer and not self.commit_timer.is_active:
-                self.commit_timer.start()
-
             for partition, it in iters.items():
                 try:
                     yield it.next()

kafka/util.py

@@ -1,7 +1,7 @@
 from collections import defaultdict
 from itertools import groupby
 import struct
-from threading import Timer
+from threading import Thread, Event
 
 
 def write_int_string(s):
@@ -81,22 +81,41 @@ class ReentrantTimer(object):
 
     t: timer interval in milliseconds
     fn: a callable to invoke
+    args: tuple of args to be passed to function
+    kwargs: keyword arguments to be passed to function
     """
-    def __init__(self, t, fn):
-        self.timer = None
-        self.t = t
+    def __init__(self, t, fn, *args, **kwargs):
+
+        if t <= 0:
+            raise ValueError('Invalid timeout value')
+
+        if not callable(fn):
+            raise ValueError('fn must be callable')
+
+        self.thread = None
+        self.t = t / 1000.0
         self.fn = fn
-        self.is_active = False
+        self.args = args
+        self.kwargs = kwargs
+        self.active = None
+
+    def _timer(self, active):
+        while not active.wait(self.t):
+            self.fn(*self.args, **self.kwargs)
 
     def start(self):
-        if self.timer is not None:
-            self.timer.cancel()
+        if self.thread is not None:
+            self.stop()
 
-        self.timer = Timer(self.t / 1000., self.fn)
-        self.is_active = True
-        self.timer.start()
+        self.active = Event()
+        self.thread = Thread(target=self._timer, args=(self.active))
+        self.thread.daemon = True  # So the app exits when main thread exits
+        self.thread.start()
 
     def stop(self):
-        self.timer.cancel()
+        if self.thread is None:
+            return
+
+        self.active.set()
+        self.thread.join(self.t + 1)
         self.timer = None
-        self.is_active = False