PYTHON-2699 Emit PoolReadyEvent before resuming the background thread (mongodb#683)

Author: ShaneHarvey

pymongo/pool.py

@@ -1199,10 +1199,12 @@ def __init__(self, address, options, handshake=True):
  self.ntxns = 0
 
  def ready(self):
- old_state, self.state = self.state, PoolState.READY
- if old_state != PoolState.READY:
- if self.enabled_for_cmap:
- self.opts.event_listeners.publish_pool_ready(self.address)
+ # Take the lock to avoid the race condition described in PYTHON-2699.
+ with self.lock:
+ if self.state != PoolState.READY:
+ self.state = PoolState.READY
+ if self.enabled_for_cmap:
+ self.opts.event_listeners.publish_pool_ready(self.address)
 
  @property
  def closed(self):
@@ -1284,8 +1286,10 @@ def remove_stale_sockets(self, reference_generation, all_credentials):
  `generation` at the point in time this operation was requested on the
  pool.
  """
- if self.state != PoolState.READY:
- return
+ # Take the lock to avoid the race condition described in PYTHON-2699.
+ with self.lock:
+ if self.state != PoolState.READY:
+ return
 
  if self.opts.max_idle_time_seconds is not None:
  with self.lock: