From 89ca5b412ba6eac59e40d445b82dc02a366ac308 Mon Sep 17 00:00:00 2001
From: Jarrod Johnon <jbjohnso@us.ibm.com>
Date: Fri, 19 Sep 2014 08:57:17 -0400
Subject: [PATCH] Fix race condition on configuration writeback

If the sync thread had moved beyond the point of checking _writepending, but had not quite managed to trigger
isAlive() to be false, the sync cfg to file would transition to never work.  Address this by adding one lock and one boolean.
Inside the lock, the two booleans are manipulated to atomically mark the end of thread sync activity linked with
check for pending data to write.
---
 .../confluent/config/configmanager.py         | 28 +++++++++++--------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/confluent_server/confluent/config/configmanager.py b/confluent_server/confluent/config/configmanager.py
index 8a08c64d..b98565dd 100644
--- a/confluent_server/confluent/config/configmanager.py
+++ b/confluent_server/confluent/config/configmanager.py
@@ -405,6 +405,8 @@ class ConfigManager(object):
     _cfgdir = "/etc/confluent/cfg/"
     _cfgwriter = None
     _writepending = False
+    _syncrunning = False
+    _syncstate = threading.RLock()
     _attribwatchers = {}
     _nodecollwatchers = {}
     _notifierids = {}
@@ -1123,15 +1125,13 @@ class ConfigManager(object):
 
     @classmethod
     def _bg_sync_to_file(cls):
-        if cls._writepending:
-            # already have a write scheduled
-            return
-        elif cls._cfgwriter is not None and cls._cfgwriter.isAlive():
-            #write in progress, request write when done
-            cls._writepending = True
-        else:
-            cls._cfgwriter = threading.Thread(target=cls._sync_to_file)
-            cls._cfgwriter.start()
+        with cls._syncstate:
+            if cls._syncrunning:
+                cls._writepending = True
+                return
+            cls._syncrunning = True
+        cls._cfgwriter = threading.Thread(target=cls._sync_to_file)
+        cls._cfgwriter.start()
 
     @classmethod
     def _sync_to_file(cls):
@@ -1170,8 +1170,14 @@ class ConfigManager(object):
                                 del dbf[ck]
                         else:
                             dbf[ck] = cPickle.dumps(currdict[category][ck])
-        if cls._writepending:
-            cls._writepending = False
+        willrun = False
+        with cls._syncstate:
+            if cls._writepending:
+                cls._writepending = False
+                willrun = True
+            else:
+                cls._syncrunning = False
+        if willrun:
             return cls._sync_to_file()
 
     def _recalculate_expressions(self, cfgobj, formatter, node, changeset):