workerpool: Don't keep reference to task arguments

The workerpool should not keep any reference to task arguments after
they were processed by RunTask. Doing so led to jobs being cached
by the job queue's WeakValueDictionary for longer than they should've
been.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Manuel Franceschini <livewire@google.com>

lib/workerpool.py

@@ -78,9 +78,8 @@ class BaseWorker(threading.Thread, object):
     """
     pool = self.pool
 
-    assert self._current_task is None
-
     while True:
+      assert self._current_task is None
       try:
         # Wait on lock to be told either to terminate or to do a task
         pool._lock.acquire()
@@ -97,7 +96,11 @@ class BaseWorker(threading.Thread, object):
 
           self._current_task = task
 
+          # No longer needed, dispose of reference
+          del task
+
           assert self._HasRunningTaskUnlocked()
+
         finally:
           pool._lock.release()