fix(spanner): return sessions from pool in LIFO order

spanner/google/cloud/spanner_v1/pool.py

@@ -156,7 +156,7 @@ def __init__(self, size=DEFAULT_SIZE, default_timeout=DEFAULT_TIMEOUT, labels=No
  super(FixedSizePool, self).__init__(labels=labels)
  self.size = size
  self.default_timeout = default_timeout
- self._sessions = queue.Queue(size)
+ self._sessions = queue.LifoQueue(size)
 
  def bind(self, database):
  """Associate the pool with a database.
@@ -242,7 +242,7 @@ def __init__(self, target_size=10, labels=None):
  super(BurstyPool, self).__init__(labels=labels)
  self.target_size = target_size
  self._database = None
- self._sessions = queue.Queue(target_size)
+ self._sessions = queue.LifoQueue(target_size)
 
  def bind(self, database):
  """Associate the pool with a database.

spanner/tests/unit/test_pool.py

@@ -162,15 +162,16 @@ def test_bind(self):
  def test_get_non_expired(self):
  pool = self._make_one(size=4)
  database = _Database("name")
- SESSIONS = [_Session(database)] * 4
+ SESSIONS = sorted([_Session(database) for i in range(0, 4)])
  database._sessions.extend(SESSIONS)
  pool.bind(database)
 
- session = pool.get()
-
- self.assertIs(session, SESSIONS[0])
- self.assertTrue(session._exists_checked)
- self.assertFalse(pool._sessions.full())
+ # check if sessions returned in LIFO order
+ for i in (3, 2, 1, 0):
+ session = pool.get()
+ self.assertIs(session, SESSIONS[i])
+ self.assertTrue(session._exists_checked)
+ self.assertFalse(pool._sessions.full())
 
  def test_get_expired(self):
  pool = self._make_one(size=4)
@@ -875,7 +876,10 @@ def __init__(self, name):
  self._sessions = []
 
  def session(self):
- return self._sessions.pop()
+ # always return first session in the list
+ # to avoid reversing the order of putting
+ # sessions into pool (important for order tests)
+ return self._sessions.pop(0)
 
 
 class _Queue(object):