Merge pull request adafruit#34 from jepler/improve-await-never

Rework how the never singleton is invoked

Author: dhalbert

asyncio/core.py

@@ -94,11 +94,11 @@ def sleep(t):
 
 ################################################################################
 # "Never schedule" object"
-# Don't re-schedule the object that awaits the _never singleton.
+# Don't re-schedule the object that awaits _never().
 # For internal use only. Some constructs, like `await event.wait()`,
 # work by NOT re-scheduling the task which calls wait(), but by
 # having some other task schedule it later.
-class _Never:
+class _NeverSingletonGenerator:
  def __init__(self):
  self.state = None
  self.exc = StopIteration()
@@ -117,7 +117,10 @@ def __next__(self):
  self.exc.__traceback__ = None
  raise self.exc
 
-_never = _Never()
+def _never(sgen=_NeverSingletonGenerator()):
+ # assert sgen.state is None, "Check for a missing `await` in your code"
+ sgen.state = False
+ return sgen
 
 
 ################################################################################
@@ -150,13 +153,11 @@ def _dequeue(self, s):
 
  async def queue_read(self, s):
  self._enqueue(s, 0)
- _never.state = False
- await _never
+ await _never()
 
  async def queue_write(self, s):
  self._enqueue(s, 1)
- _never.state = False
- await _never
+ await _never()
 
  def remove(self, task):
  while True:

asyncio/event.py

@@ -62,8 +62,7 @@ async def wait(self):
  self.waiting.push_head(core.cur_task)
  # Set calling task's data to the event's queue so it can be removed if needed
  core.cur_task.data = self.waiting
- core._never.state = False
- await core._never
+ await core._never()
  return True
 
 

asyncio/lock.py

@@ -69,8 +69,7 @@ async def acquire(self):
  # Set calling task's data to the lock's queue so it can be removed if needed
  core.cur_task.data = self.waiting
  try:
- core._never.state = False
- await core._never
+ await core._never()
  except core.CancelledError as er:
  if self.state == core.cur_task:
  # Cancelled while pending on resume, schedule next waiting Task