- Made a slight adjustment to the logic which waits for a pooled

connection to be available, such that for a connection pool
with no timeout specified, it will every half a second break out of
the wait to check for the so-called "abort" flag, which allows the
waiter to break out in case the whole connection pool was dumped;
normally the waiter should break out due to a notify_all() but it's
possible this notify_all() is missed in very slim cases.
This is an extension of logic first introduced in 0.8.0, and the
issue has only been observed occasionally in stress tests.

1 files changed, 8 insertions, 2 deletions

diff --git a/lib/sqlalchemy/util/queue.py b/lib/sqlalchemy/util/queue.py
index b66738aff..639b23a93 100644
--- a/lib/sqlalchemy/util/queue.py
+++ b/lib/sqlalchemy/util/queue.py
@@ -151,7 +151,6 @@ class Queue:
         return an item if one is immediately available, else raise the
         ``Empty`` exception (`timeout` is ignored in that case).
         """
-
         self.not_empty.acquire()
         try:
             if not block:
@@ -159,7 +158,11 @@ class Queue:
                     raise Empty
             elif timeout is None:
                 while self._empty():
-                    self.not_empty.wait()
+                    # wait for only half a second, then
+                    # loop around, so that we can see a change in
+                    # _sqla_abort_context in case we missed the notify_all()
+                    # called by abort()
+                    self.not_empty.wait(.5)
                     if self._sqla_abort_context:
                         raise SAAbort(self._sqla_abort_context)
             else:
@@ -188,6 +191,9 @@ class Queue:
         if not self.not_full.acquire(False):
             return
         try:
+            # note that this is now optional
+            # as the waiters in get() both loop around
+            # to check the _sqla_abort_context flag periodically
             self.not_empty.notify_all()
         finally:
             self.not_full.release()