arthur-tacca

"""This demonstrates Trio can have a class-based wait API.

The first part implements a Waiter class on top of Trio's existing
wait_task_rescheduled() and reschedule().

The second shows that those functions could be implemented in terms of Waiter,
so the two APIs are equivalent.

This is LLM generated code. The design and code is fine but the docstrings
will be usual LLM quality level.

arthur-tacca

Trio event loop notes

Event loop steps

These are the steps of the Trio event loop:

1. Compute timeout (0 if still tasks in runq i.e. the list of tasks ready to resume, else clock.deadline_to_sleep_time(deadlines.next_deadline()))
2. Wait for IO events or timeout (events = io_manager.get_events(timeout)) – this is the actual select()-like call.
3. Events are "processed" i.e. scheduled into the relevant task (io_manager.process_events(events) which calls _core.reschedule(self._registered[key], outcome.Value(event)) i.e. added to runq)
4. Deadlines are expired (deadlines.expire(clock.current_time()), which effectively calls task.reschedule(Cancelled) (via the task's abort function) i.e. adds the task to the runq)

arthur-tacca

"""Implementation of Trio event and chnanel types where cancellation always succeeds.

See: https://github.com/python-trio/trio/issues/2973
"""

import attr
from collections import deque
import trio
from typing import Generic, Optional, TypeVar

arthur-tacca

// Moved to:
// https://github.com/arthur-tacca/dart-cancel-examples/blob/main/lib/abort.dart

arthur-tacca

Proposal to Add Cancellation Tokens to Dart

This is now superceded by the proof of concept code:

https://github.com/arthur-tacca/dart-cancel-examples

arthur-tacca

# Adapted with permission from the EdgeDB project;
# license: PSFL.


__all__ = ("TaskGroup",)

from . import events
from . import exceptions
from . import tasks

arthur-tacca

# Question: if we cancel a scope, and another task is active in that scope, is it *guaranteed* that
# it will raise CancelledError when it next wakes? (Even if it is already queued to wake for some
# other reason.)
#
# The answer, at least in practice, is no: in this example, send_and_cancel() sends some data to
# a memory channel then cancels a scope, and then receive() (which is running in that scope) wakes
# with the first value that was sent.
#
# On my computer, this code produces the following output:
#

arthur-tacca

# Illustration of missed cleanup in an asyncio task group due to the way it
# cancels a task that has not started by never running it at all. See issue:
# https://github.com/python/cpython/issues/116048
#
# When run on my computer, I usually get the output:
#
#     Total connections created: 3300
#     Connections left unclosed: 0
#
# i.e., all connections that were created were cleaned up. But sometimes I get:

arthur-tacca

# aioresult variant of StreamResultsNursery
# Original idea by smurfix: https://gist.github.com/smurfix/0130817fa5ba6d3bb4a0f00e4d93cf86
# Fixed non-aioresult version: https://gist.github.com/arthur-tacca/6c676a21d0dcc0582edb50c9c2aa3e3c


from collections import deque
import math

from aioresult import ResultCapture
import trio

arthur-tacca

# Original idea by smurfix: https://gist.github.com/smurfix/0130817fa5ba6d3bb4a0f00e4d93cf86
# aioresult variant: https://gist.github.com/arthur-tacca/5c717ae68ac037e72ae45fd1e9ca1345

from collections import deque
import math
import trio


class StreamResultsNursery:
    def __init__(self, max_running_tasks=math.inf):