[tor-commits] [ooni-probe/master] Generators do not work well in a concurrent environment.

[art at torproject.org]

commit 007685b2fbf8ec5e51ed8004af832d0299f4429e
Author: Arturo Filastò <arturo at filasto.net>
Date:   Wed Jun 15 12:43:23 2016 +0300

    Generators do not work well in a concurrent environment.
    
    Use a mutex lock on the tasks generator to avoid concurrency issues.
---
 ooni/managers.py | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/ooni/managers.py b/ooni/managers.py
index 65e4ce1..f139f20 100644
--- a/ooni/managers.py
+++ b/ooni/managers.py
@@ -1,4 +1,5 @@
 import itertools
+from twisted.internet import defer
 
 from ooni.utils import log
 from ooni.settings import config
@@ -24,6 +25,7 @@ class TaskManager(object):
         self._tasks = iter(())
         self._active_tasks = []
         self.failures = 0
+        self.task_lock = defer.DeferredLock()
 
     def _failed(self, failure, task):
         """
@@ -55,17 +57,17 @@ class TaskManager(object):
         Called on test completion and schedules measurements to be run for the
         available slots.
         """
+        d = self.task_lock.acquire()
+        d.addCallback(lambda _: self._scheduleNextTask())
+
+    def _scheduleNextTask(self):
         for _ in range(self.availableSlots):
             try:
-                task = self._tasks.next()
+                task = next(self._tasks)
                 self._run(task)
             except StopIteration:
                 break
-            except ValueError:
-                # XXX this is a workaround the race condition that leads the
-                # _tasks generator to throw the exception
-                # ValueError: generator already called.
-                continue
+        self.task_lock.release()
 
     def _run(self, task):
         """