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Copy pathtaskgroup.py
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315 lines (258 loc) · 10.7 KB
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#
# This source file is part of the EdgeDB open source project.
#
# Copyright 2016-present MagicStack Inc. and the EdgeDB authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
from __future__ import annotations
import asyncio
import itertools
import sys
import textwrap
import traceback
import types
import weakref
class TaskGroup:
def __init__(self, *, name=None):
if name is None:
self._name = f'tg-{_name_counter()}'
else:
self._name = str(name)
self._entered = False
self._exiting = False
self._aborting = False
self._loop = None
self._parent_task = None
self._parent_cancel_requested = False
self._tasks = weakref.WeakSet()
self._unfinished_tasks = 0
self._errors = []
self._base_error = None
self._on_completed_fut = None
def get_name(self):
return self._name
def __repr__(self):
msg = f'<TaskGroup {self._name!r}'
if self._tasks:
msg += f' tasks:{len(self._tasks)}'
if self._unfinished_tasks:
msg += f' unfinished:{self._unfinished_tasks}'
if self._errors:
msg += f' errors:{len(self._errors)}'
if self._aborting:
msg += ' cancelling'
elif self._entered:
msg += ' entered'
msg += '>'
return msg
async def __aenter__(self):
if self._entered:
raise RuntimeError(
f"TaskGroup {self!r} has been already entered")
self._entered = True
if self._loop is None:
self._loop = asyncio.get_running_loop()
self._parent_task = asyncio.current_task(self._loop)
if self._parent_task is None:
raise RuntimeError(
f'TaskGroup {self!r} cannot determine the parent task')
self._patch_task(self._parent_task)
return self
async def __aexit__(self, et, exc, tb):
self._exiting = True
propagate_cancellation_error = None
if (exc is not None and
self._is_base_error(exc) and
self._base_error is None):
self._base_error = exc
if et is asyncio.CancelledError:
if self._parent_cancel_requested:
# Only if we did request task to cancel ourselves
# we mark it as no longer cancelled.
self._parent_task.__cancel_requested__ = False
else:
propagate_cancellation_error = et
if et is not None and not self._aborting:
# Our parent task is being cancelled:
#
# async with TaskGroup() as g:
# g.create_task(...)
# await ... # <- CancelledError
#
if et is asyncio.CancelledError:
propagate_cancellation_error = et
# or there's an exception in "async with":
#
# async with TaskGroup() as g:
# g.create_task(...)
# 1 / 0
#
self._abort()
# We use while-loop here because "self._on_completed_fut"
# can be cancelled multiple times if our parent task
# is being cancelled repeatedly (or even once, when
# our own cancellation is already in progress)
while self._unfinished_tasks:
if self._on_completed_fut is None:
self._on_completed_fut = self._loop.create_future()
try:
await self._on_completed_fut
except asyncio.CancelledError as ex:
if not self._aborting:
# Our parent task is being cancelled:
#
# async def wrapper():
# async with TaskGroup() as g:
# g.create_task(foo)
#
# "wrapper" is being cancelled while "foo" is
# still running.
propagate_cancellation_error = ex
self._abort()
self._on_completed_fut = None
assert self._unfinished_tasks == 0
self._on_completed_fut = None # no longer needed
if self._base_error is not None:
raise self._base_error
if propagate_cancellation_error is not None:
# The wrapping task was cancelled; since we're done with
# closing all child tasks, just propagate the cancellation
# request now.
raise propagate_cancellation_error
if et is not None and et is not asyncio.CancelledError:
self._errors.append(exc)
if self._errors:
# Exceptions are heavy objects that can have object
# cycles (bad for GC); let's not keep a reference to
# a bunch of them.
errors = self._errors
self._errors = None
me = TaskGroupError('unhandled errors in a TaskGroup',
errors=errors)
raise me from None
def create_task(self, coro):
if not self._entered:
raise RuntimeError(f"TaskGroup {self!r} has not been entered")
if self._exiting:
raise RuntimeError(f"TaskGroup {self!r} is awaiting in exit")
task = self._loop.create_task(coro)
task.add_done_callback(self._on_task_done)
self._unfinished_tasks += 1
self._tasks.add(task)
return task
if sys.version_info >= (3, 8):
# In Python 3.8 Tasks propagate all exceptions correctly,
# except for KeybaordInterrupt and SystemExit which are
# still considered special.
def _is_base_error(self, exc: BaseException) -> bool:
assert isinstance(exc, BaseException)
return isinstance(exc, (SystemExit, KeyboardInterrupt))
else:
# In Python prior to 3.8 all BaseExceptions are special and
# are bypassing the proper propagation through async/await
# code, essentially aborting the execution.
def _is_base_error(self, exc: BaseException) -> bool:
assert isinstance(exc, BaseException)
return not isinstance(exc, Exception)
def _patch_task(self, task):
# In Python 3.8 we'll need proper API on asyncio.Task to
# make TaskGroups possible. We need to be able to access
# information about task cancellation, more specifically,
# we need a flag to say if a task was cancelled or not.
# We also need to be able to flip that flag.
if sys.version_info >= (3, 9):
def _task_cancel(self, msg=None):
self.__cancel_requested__ = True
return asyncio.Task.cancel(self, msg)
else:
def _task_cancel(self):
self.__cancel_requested__ = True
return asyncio.Task.cancel(self)
if hasattr(task, '__cancel_requested__'):
return
task.__cancel_requested__ = False
# confirm that we were successful at adding the new attribute:
assert not task.__cancel_requested__
task.cancel = types.MethodType(_task_cancel, task)
def _abort(self):
self._aborting = True
for t in self._tasks:
if not t.done():
t.cancel()
def _on_task_done(self, task):
self._unfinished_tasks -= 1
assert self._unfinished_tasks >= 0
if self._exiting and not self._unfinished_tasks:
if not self._on_completed_fut.done():
self._on_completed_fut.set_result(True)
if task.cancelled():
return
exc = task.exception()
if exc is None:
return
self._errors.append(exc)
if self._is_base_error(exc) and self._base_error is None:
self._base_error = exc
if self._parent_task.done():
# Not sure if this case is possible, but we want to handle
# it anyways.
self._loop.call_exception_handler({
'message': f'Task {task!r} has errored out but its parent '
f'task {self._parent_task} is already completed',
'exception': exc,
'task': task,
})
return
self._abort()
if not self._parent_task.__cancel_requested__:
# If parent task *is not* being cancelled, it means that we want
# to manually cancel it to abort whatever is being run right now
# in the TaskGroup. But we want to mark parent task as
# "not cancelled" later in __aexit__. Example situation that
# we need to handle:
#
# async def foo():
# try:
# async with TaskGroup() as g:
# g.create_task(crash_soon())
# await something # <- this needs to be canceled
# # by the TaskGroup, e.g.
# # foo() needs to be cancelled
# except Exception:
# # Ignore any exceptions raised in the TaskGroup
# pass
# await something_else # this line has to be called
# # after TaskGroup is finished.
self._parent_cancel_requested = True
self._parent_task.cancel()
class MultiError(Exception):
def __init__(self, msg, *args, errors=()):
if errors:
types = set(type(e).__name__ for e in errors)
msg = f'{msg}; {len(errors)} sub errors: ({", ".join(types)})'
for er in errors:
msg += f'\n + {type(er).__name__}: {er}'
if er.__traceback__:
er_tb = ''.join(traceback.format_tb(er.__traceback__))
er_tb = textwrap.indent(er_tb, ' | ')
msg += f'\n{er_tb}\n'
super().__init__(msg, *args)
self.__errors__ = tuple(errors)
def get_error_types(self):
return {type(e) for e in self.__errors__}
def __reduce__(self):
return (type(self), (self.args,), {'__errors__': self.__errors__})
class TaskGroupError(MultiError):
pass
_name_counter = itertools.count(1).__next__