micropython/extmod/asyncio/core.py

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# MicroPython asyncio module
# MIT license; Copyright (c) 2019 Damien P. George
from time import ticks_ms as ticks, ticks_diff, ticks_add
import sys, select
# Import TaskQueue and Task, preferring built-in C code over Python code
try:
from _asyncio import TaskQueue, Task
except:
from .task import TaskQueue, Task
################################################################################
# Exceptions
class CancelledError(BaseException):
pass
class TimeoutError(Exception):
pass
# Used when calling Loop.call_exception_handler
_exc_context = {"message": "Task exception wasn't retrieved", "exception": None, "future": None}
################################################################################
# Sleep functions
# "Yield" once, then raise StopIteration
class SingletonGenerator:
def __init__(self):
self.state = None
self.exc = StopIteration()
def __iter__(self):
return self
def __next__(self):
if self.state is not None:
_task_queue.push(cur_task, self.state)
self.state = None
return None
else:
self.exc.__traceback__ = None
raise self.exc
# Pause task execution for the given time (integer in milliseconds, uPy extension)
# Use a SingletonGenerator to do it without allocating on the heap
def sleep_ms(t, sgen=SingletonGenerator()):
assert sgen.state is None
sgen.state = ticks_add(ticks(), max(0, t))
return sgen
# Pause task execution for the given time (in seconds)
def sleep(t):
return sleep_ms(int(t * 1000))
################################################################################
# Queue and poller for stream IO
class IOQueue:
def __init__(self):
self.poller = select.poll()
self.map = {} # maps id(stream) to [task_waiting_read, task_waiting_write, stream]
def _enqueue(self, s, idx):
if id(s) not in self.map:
entry = [None, None, s]
entry[idx] = cur_task
self.map[id(s)] = entry
self.poller.register(s, select.POLLIN if idx == 0 else select.POLLOUT)
else:
sm = self.map[id(s)]
assert sm[idx] is None
assert sm[1 - idx] is not None
sm[idx] = cur_task
self.poller.modify(s, select.POLLIN | select.POLLOUT)
# Link task to this IOQueue so it can be removed if needed
cur_task.data = self
def _dequeue(self, s):
del self.map[id(s)]
self.poller.unregister(s)
def queue_read(self, s):
self._enqueue(s, 0)
def queue_write(self, s):
self._enqueue(s, 1)
def remove(self, task):
while True:
del_s = None
for k in self.map: # Iterate without allocating on the heap
q0, q1, s = self.map[k]
if q0 is task or q1 is task:
del_s = s
break
if del_s is not None:
self._dequeue(s)
else:
break
def wait_io_event(self, dt):
for s, ev in self.poller.ipoll(dt):
sm = self.map[id(s)]
# print('poll', s, sm, ev)
if ev & ~select.POLLOUT and sm[0] is not None:
# POLLIN or error
_task_queue.push(sm[0])
sm[0] = None
if ev & ~select.POLLIN and sm[1] is not None:
# POLLOUT or error
_task_queue.push(sm[1])
sm[1] = None
if sm[0] is None and sm[1] is None:
self._dequeue(s)
elif sm[0] is None:
self.poller.modify(s, select.POLLOUT)
else:
self.poller.modify(s, select.POLLIN)
################################################################################
# Main run loop
# Ensure the awaitable is a task
def _promote_to_task(aw):
return aw if isinstance(aw, Task) else create_task(aw)
# Create and schedule a new task from a coroutine
def create_task(coro):
if not hasattr(coro, "send"):
raise TypeError("coroutine expected")
t = Task(coro, globals())
_task_queue.push(t)
return t
# Keep scheduling tasks until there are none left to schedule
def run_until_complete(main_task=None):
global cur_task
excs_all = (CancelledError, Exception) # To prevent heap allocation in loop
excs_stop = (CancelledError, StopIteration) # To prevent heap allocation in loop
while True:
# Wait until the head of _task_queue is ready to run
dt = 1
while dt > 0:
dt = -1
t = _task_queue.peek()
if t:
# A task waiting on _task_queue; "ph_key" is time to schedule task at
dt = max(0, ticks_diff(t.ph_key, ticks()))
elif not _io_queue.map:
# No tasks can be woken so finished running
return
# print('(poll {})'.format(dt), len(_io_queue.map))
_io_queue.wait_io_event(dt)
# Get next task to run and continue it
t = _task_queue.pop()
cur_task = t
try:
# Continue running the coroutine, it's responsible for rescheduling itself
exc = t.data
if not exc:
t.coro.send(None)
else:
extmod/uasyncio: Fix race with cancelled task waiting on finished task. This commit fixes a problem with a race between cancellation of task A and completion of task B, when A waits on B. If task B completes just before task A is cancelled then the cancellation of A does not work. Instead, the CancelledError meant to cancel A gets passed through to B (that's expected behaviour) but B handles it as a "Task exception wasn't retrieved" scenario, printing out such a message (this is because finished tasks point their "coro" attribute to themselves to indicate they are done, and implement the throw() method, but that method inadvertently catches the CancelledError). The correct behaviour is for B to bounce that CancelledError back out. This bug is mainly seen when wait_for() is used, and in that context the symptoms are: - occurs when using wait_for(T, S), if the task T being waited on finishes at exactly the same time as the wait-for timeout S expires - task T will have run to completion - the "Task exception wasn't retrieved message" is printed with "<class 'CancelledError'>" as the error (ie no traceback) - the wait_for(T, S) call never returns (it's never put back on the uasyncio run queue) and all tasks waiting on this are blocked forever from running - uasyncio otherwise continues to function and other tasks continue to be scheduled as normal The fix here reworks the "waiting" attribute of Task to be called "state" and uses it to indicate whether a task is: running and not awaited on, running and awaited on, finished and not awaited on, or finished and awaited on. This means the task does not need to point "coro" to itself to indicate finished, and also allows removal of the throw() method. A benefit of this is that "Task exception wasn't retrieved" messages can go back to being able to print the name of the coroutine function. Fixes issue #7386. Signed-off-by: Damien George <damien@micropython.org>
2021-06-14 13:32:51 +01:00
# If the task is finished and on the run queue and gets here, then it
# had an exception and was not await'ed on. Throwing into it now will
# raise StopIteration and the code below will catch this and run the
# call_exception_handler function.
t.data = None
t.coro.throw(exc)
except excs_all as er:
# Check the task is not on any event queue
assert t.data is None
# This task is done, check if it's the main task and then loop should stop
if t is main_task:
if isinstance(er, StopIteration):
return er.value
raise er
extmod/uasyncio: Fix race with cancelled task waiting on finished task. This commit fixes a problem with a race between cancellation of task A and completion of task B, when A waits on B. If task B completes just before task A is cancelled then the cancellation of A does not work. Instead, the CancelledError meant to cancel A gets passed through to B (that's expected behaviour) but B handles it as a "Task exception wasn't retrieved" scenario, printing out such a message (this is because finished tasks point their "coro" attribute to themselves to indicate they are done, and implement the throw() method, but that method inadvertently catches the CancelledError). The correct behaviour is for B to bounce that CancelledError back out. This bug is mainly seen when wait_for() is used, and in that context the symptoms are: - occurs when using wait_for(T, S), if the task T being waited on finishes at exactly the same time as the wait-for timeout S expires - task T will have run to completion - the "Task exception wasn't retrieved message" is printed with "<class 'CancelledError'>" as the error (ie no traceback) - the wait_for(T, S) call never returns (it's never put back on the uasyncio run queue) and all tasks waiting on this are blocked forever from running - uasyncio otherwise continues to function and other tasks continue to be scheduled as normal The fix here reworks the "waiting" attribute of Task to be called "state" and uses it to indicate whether a task is: running and not awaited on, running and awaited on, finished and not awaited on, or finished and awaited on. This means the task does not need to point "coro" to itself to indicate finished, and also allows removal of the throw() method. A benefit of this is that "Task exception wasn't retrieved" messages can go back to being able to print the name of the coroutine function. Fixes issue #7386. Signed-off-by: Damien George <damien@micropython.org>
2021-06-14 13:32:51 +01:00
if t.state:
# Task was running but is now finished.
waiting = False
if t.state is True:
# "None" indicates that the task is complete and not await'ed on (yet).
t.state = None
elif callable(t.state):
# The task has a callback registered to be called on completion.
t.state(t, er)
t.state = False
waiting = True
extmod/uasyncio: Fix race with cancelled task waiting on finished task. This commit fixes a problem with a race between cancellation of task A and completion of task B, when A waits on B. If task B completes just before task A is cancelled then the cancellation of A does not work. Instead, the CancelledError meant to cancel A gets passed through to B (that's expected behaviour) but B handles it as a "Task exception wasn't retrieved" scenario, printing out such a message (this is because finished tasks point their "coro" attribute to themselves to indicate they are done, and implement the throw() method, but that method inadvertently catches the CancelledError). The correct behaviour is for B to bounce that CancelledError back out. This bug is mainly seen when wait_for() is used, and in that context the symptoms are: - occurs when using wait_for(T, S), if the task T being waited on finishes at exactly the same time as the wait-for timeout S expires - task T will have run to completion - the "Task exception wasn't retrieved message" is printed with "<class 'CancelledError'>" as the error (ie no traceback) - the wait_for(T, S) call never returns (it's never put back on the uasyncio run queue) and all tasks waiting on this are blocked forever from running - uasyncio otherwise continues to function and other tasks continue to be scheduled as normal The fix here reworks the "waiting" attribute of Task to be called "state" and uses it to indicate whether a task is: running and not awaited on, running and awaited on, finished and not awaited on, or finished and awaited on. This means the task does not need to point "coro" to itself to indicate finished, and also allows removal of the throw() method. A benefit of this is that "Task exception wasn't retrieved" messages can go back to being able to print the name of the coroutine function. Fixes issue #7386. Signed-off-by: Damien George <damien@micropython.org>
2021-06-14 13:32:51 +01:00
else:
# Schedule any other tasks waiting on the completion of this task.
while t.state.peek():
_task_queue.push(t.state.pop())
extmod/uasyncio: Fix race with cancelled task waiting on finished task. This commit fixes a problem with a race between cancellation of task A and completion of task B, when A waits on B. If task B completes just before task A is cancelled then the cancellation of A does not work. Instead, the CancelledError meant to cancel A gets passed through to B (that's expected behaviour) but B handles it as a "Task exception wasn't retrieved" scenario, printing out such a message (this is because finished tasks point their "coro" attribute to themselves to indicate they are done, and implement the throw() method, but that method inadvertently catches the CancelledError). The correct behaviour is for B to bounce that CancelledError back out. This bug is mainly seen when wait_for() is used, and in that context the symptoms are: - occurs when using wait_for(T, S), if the task T being waited on finishes at exactly the same time as the wait-for timeout S expires - task T will have run to completion - the "Task exception wasn't retrieved message" is printed with "<class 'CancelledError'>" as the error (ie no traceback) - the wait_for(T, S) call never returns (it's never put back on the uasyncio run queue) and all tasks waiting on this are blocked forever from running - uasyncio otherwise continues to function and other tasks continue to be scheduled as normal The fix here reworks the "waiting" attribute of Task to be called "state" and uses it to indicate whether a task is: running and not awaited on, running and awaited on, finished and not awaited on, or finished and awaited on. This means the task does not need to point "coro" to itself to indicate finished, and also allows removal of the throw() method. A benefit of this is that "Task exception wasn't retrieved" messages can go back to being able to print the name of the coroutine function. Fixes issue #7386. Signed-off-by: Damien George <damien@micropython.org>
2021-06-14 13:32:51 +01:00
waiting = True
# "False" indicates that the task is complete and has been await'ed on.
t.state = False
if not waiting and not isinstance(er, excs_stop):
# An exception ended this detached task, so queue it for later
# execution to handle the uncaught exception if no other task retrieves
# the exception in the meantime (this is handled by Task.throw).
_task_queue.push(t)
extmod/uasyncio: Fix race with cancelled task waiting on finished task. This commit fixes a problem with a race between cancellation of task A and completion of task B, when A waits on B. If task B completes just before task A is cancelled then the cancellation of A does not work. Instead, the CancelledError meant to cancel A gets passed through to B (that's expected behaviour) but B handles it as a "Task exception wasn't retrieved" scenario, printing out such a message (this is because finished tasks point their "coro" attribute to themselves to indicate they are done, and implement the throw() method, but that method inadvertently catches the CancelledError). The correct behaviour is for B to bounce that CancelledError back out. This bug is mainly seen when wait_for() is used, and in that context the symptoms are: - occurs when using wait_for(T, S), if the task T being waited on finishes at exactly the same time as the wait-for timeout S expires - task T will have run to completion - the "Task exception wasn't retrieved message" is printed with "<class 'CancelledError'>" as the error (ie no traceback) - the wait_for(T, S) call never returns (it's never put back on the uasyncio run queue) and all tasks waiting on this are blocked forever from running - uasyncio otherwise continues to function and other tasks continue to be scheduled as normal The fix here reworks the "waiting" attribute of Task to be called "state" and uses it to indicate whether a task is: running and not awaited on, running and awaited on, finished and not awaited on, or finished and awaited on. This means the task does not need to point "coro" to itself to indicate finished, and also allows removal of the throw() method. A benefit of this is that "Task exception wasn't retrieved" messages can go back to being able to print the name of the coroutine function. Fixes issue #7386. Signed-off-by: Damien George <damien@micropython.org>
2021-06-14 13:32:51 +01:00
# Save return value of coro to pass up to caller.
t.data = er
elif t.state is None:
# Task is already finished and nothing await'ed on the task,
# so call the exception handler.
_exc_context["exception"] = exc
_exc_context["future"] = t
Loop.call_exception_handler(_exc_context)
# Create a new task from a coroutine and run it until it finishes
def run(coro):
return run_until_complete(create_task(coro))
################################################################################
# Event loop wrapper
async def _stopper():
pass
_stop_task = None
class Loop:
_exc_handler = None
def create_task(coro):
return create_task(coro)
def run_forever():
global _stop_task
_stop_task = Task(_stopper(), globals())
run_until_complete(_stop_task)
# TODO should keep running until .stop() is called, even if there're no tasks left
def run_until_complete(aw):
return run_until_complete(_promote_to_task(aw))
def stop():
global _stop_task
if _stop_task is not None:
_task_queue.push(_stop_task)
# If stop() is called again, do nothing
_stop_task = None
def close():
pass
def set_exception_handler(handler):
Loop._exc_handler = handler
def get_exception_handler():
return Loop._exc_handler
def default_exception_handler(loop, context):
print(context["message"], file=sys.stderr)
print("future:", context["future"], "coro=", context["future"].coro, file=sys.stderr)
sys.print_exception(context["exception"], sys.stderr)
def call_exception_handler(context):
(Loop._exc_handler or Loop.default_exception_handler)(Loop, context)
# The runq_len and waitq_len arguments are for legacy uasyncio compatibility
def get_event_loop(runq_len=0, waitq_len=0):
return Loop
def current_task():
return cur_task
def new_event_loop():
global _task_queue, _io_queue
# TaskQueue of Task instances
_task_queue = TaskQueue()
# Task queue and poller for stream IO
_io_queue = IOQueue()
return Loop
# Initialise default event loop
new_event_loop()