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# Ensure that an asyncio task can wait on an Event when the
# _task_queue is empty, in the context of an async iterator
# https://github.com/micropython/micropython/issues/16318
try:
import asyncio
except ImportError:
print("SKIP")
raise SystemExit
# This test requires checking that the asyncio scheduler
# remains active "indefinitely" when the task queue is empty.
#
# To check this, we need another independent scheduler that
# can wait for a certain amount of time. So we have to
# create one using micropython.schedule() and time.ticks_ms()
#
# Technically, this code breaks the rules, as it is clearly
# documented that Event.set() should _NOT_ be called from a
# schedule (soft IRQ) because in some cases, a race condition
# can occur, resulting in a crash. However:
# - since the risk of a race condition in that specific
# case has been analysed and excluded
# - given that there is no other simple alternative to
# write this test case,
# an exception to the rule was deemed acceptable. See
# https://github.com/micropython/micropython/pull/16772
import micropython, time
try:
micropython.schedule
except AttributeError:
print("SKIP")
raise SystemExit
ai = None
def schedule_watchdog(end_ticks):
if time.ticks_diff(end_ticks, time.ticks_ms()) <= 0:
print("good: asyncio iterator is still pending, exiting")
# Caution: ai.fetch_data() will invoke Event.set()
# (see the note in the comment above)
ai.fetch_data(None)
return
micropython.schedule(schedule_watchdog, end_ticks)
async def test(ai):
for x in range(3):
await asyncio.sleep(0.1)
ai.fetch_data("bar {}".format(x))
class AsyncIterable:
def __init__(self):
self.message = None
self.evt = asyncio.Event()
def __aiter__(self):
return self
async def __anext__(self):
await self.evt.wait()
self.evt.clear()
if self.message is None:
raise StopAsyncIteration
return self.message
def fetch_data(self, message):
self.message = message
self.evt.set()
async def main():
global ai
ai = AsyncIterable()
asyncio.create_task(test(ai))
schedule_watchdog(time.ticks_add(time.ticks_ms(), 500))
async for message in ai:
print(message)
print("end main")
asyncio.run(main())
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