- a new mutex that was added in 0.3.9 causes the pool_timeout

feature to fail during a race condition; threads would
raise TimeoutError immediately with no delay if many threads
push the pool into overflow at the same time.  this issue has been
fixed.

1 files changed, 9 insertions, 2 deletions

diff --git a/lib/sqlalchemy/pool.py b/lib/sqlalchemy/pool.py
index c3a317c3f..cf442c928 100644
--- a/lib/sqlalchemy/pool.py
+++ b/lib/sqlalchemy/pool.py
@@ -493,11 +493,18 @@ class QueuePool(Pool):
         try:
             return self._pool.get(self._max_overflow > -1 and self._overflow >= self._max_overflow, self._timeout)
         except Queue.Empty:
+            if self._max_overflow > -1 and self._overflow >= self._max_overflow:
+                raise exceptions.TimeoutError("QueuePool limit of size %d overflow %d reached, connection timed out, timeout %d" % (self.size(), self.overflow(), self._timeout))
+
             if self._overflow_lock is not None:
                 self._overflow_lock.acquire()
+
+            if self._max_overflow > -1 and self._overflow >= self._max_overflow:
+                if self._overflow_lock is not None:
+                    self._overflow_lock.release()
+                return self.do_get()
+
             try:
-                if self._max_overflow > -1 and self._overflow >= self._max_overflow:
-                    raise exceptions.TimeoutError("QueuePool limit of size %d overflow %d reached, connection timed out" % (self.size(), self.overflow()))
                 con = self.create_connection()
                 self._overflow += 1
             finally: