# Adapted with permission from the EdgeDB project;
# license: PSFL.
__all__ = ["TaskGroup"]
from . import events
from . import exceptions
from . import tasks
class TaskGroup:
"""Asynchronous context manager for managing groups of tasks.
Example use:
async with asyncio.TaskGroup() as group:
task1 = group.create_task(some_coroutine(...))
task2 = group.create_task(other_coroutine(...))
print("Both tasks have completed now.")
All tasks are awaited when the context manager exits.
Any exceptions other than `asyncio.CancelledError` raised within
a task will cancel all remaining tasks and wait for them to exit.
The exceptions are then combined and raised as an `ExceptionGroup`.
"""
def __init__(self):
self._entered = False
self._exiting = False
self._aborting = False
self._loop = None
self._parent_task = None
self._parent_cancel_requested = False
self._tasks = set()
self._errors = []
self._base_error = None
self._on_completed_fut = None
def __repr__(self):
info = ['']
if self._tasks:
info.append(f'tasks={len(self._tasks)}')
if self._errors:
info.append(f'errors={len(self._errors)}')
if self._aborting:
info.append('cancelling')
elif self._entered:
info.append('entered')
info_str = ' '.join(info)
return f'<TaskGroup{info_str}>'
async def __aenter__(self):
if self._entered:
raise RuntimeError(
f"TaskGroup {self!r} has already been entered")
if self._loop is None:
self._loop = events.get_running_loop()
self._parent_task = tasks.current_task(self._loop)
if self._parent_task is None:
raise RuntimeError(
f'TaskGroup {self!r} cannot determine the parent task')
self._entered = True
return self
async def __aexit__(self, et, exc, tb):
self._exiting = True
if (exc is not None and
self._is_base_error(exc) and
self._base_error is None):
self._base_error = exc
propagate_cancellation_error = \
exc if et is exceptions.CancelledError else None
if self._parent_cancel_requested:
# If this flag is set we *must* call uncancel().
if self._parent_task.uncancel() == 0:
# If there are no pending cancellations left,
# don't propagate CancelledError.
propagate_cancellation_error = None
if et is not None:
if not self._aborting:
# Our parent task is being cancelled:
#
# async with TaskGroup() as g:
# g.create_task(...)
# await ... # <- CancelledError
#
# 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._tasks:
if self._on_completed_fut is None:
self._on_completed_fut = self._loop.create_future()
try:
await self._on_completed_fut
except exceptions.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 not self._tasks
if self._base_error is not None:
raise self._base_error
# Propagate CancelledError if there is one, except if there
# are other errors -- those have priority.
if propagate_cancellation_error and not self._errors:
raise propagate_cancellation_error
if et is not None and et is not exceptions.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.
try:
me = BaseExceptionGroup('unhandled errors in a TaskGroup', self._errors)
raise me from None
finally:
self._errors = None
def create_task(self, coro, *, name=None, context=None):
"""Create a new task in this group and return it.
Similar to `asyncio.create_task`.
"""
if not self._entered:
raise RuntimeError(f"TaskGroup {self!r} has not been entered")
if self._exiting and not self._tasks:
raise RuntimeError(f"TaskGroup {self!r} is finished")
if self._aborting:
raise RuntimeError(f"TaskGroup {self!r} is shutting down")
if context is None:
task = self._loop.create_task(coro)
else:
task = self._loop.create_task(coro, context=context)
tasks._set_task_name(task, name)
task.add_done_callback(self._on_task_done)
self._tasks.add(task)
return task
# Since Python 3.8 Tasks propagate all exceptions correctly,
# except for KeyboardInterrupt and SystemExit which are
# still considered special.
def _is_base_error(self, exc: BaseException) -> bool:
assert isinstance(exc, BaseException)
return isinstance(exc, (SystemExit, KeyboardInterrupt))
def _abort(self):
self._aborting = True
for t in self._tasks:
if not t.done():
t.cancel()
def _on_task_done(self, task):
self._tasks.discard(task)
if self._on_completed_fut is not None and not self._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
if not self._aborting and not self._parent_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._abort()
self._parent_cancel_requested = True
self._parent_task.cancel()
| Name | Type | Size | Permission | Actions |
|---|---|---|---|---|
| __pycache__ | Folder | 0755 |
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| __init__.py | File | 1.16 KB | 0644 |
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| __main__.py | File | 3.26 KB | 0644 |
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| base_events.py | File | 73.62 KB | 0644 |
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| base_futures.py | File | 1.96 KB | 0644 |
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| base_subprocess.py | File | 8.66 KB | 0644 |
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| base_tasks.py | File | 2.58 KB | 0644 |
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| constants.py | File | 1.29 KB | 0644 |
|
| coroutines.py | File | 3.32 KB | 0644 |
|
| events.py | File | 27.97 KB | 0644 |
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| exceptions.py | File | 1.71 KB | 0644 |
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| format_helpers.py | File | 2.35 KB | 0644 |
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| futures.py | File | 13.88 KB | 0644 |
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| locks.py | File | 18.57 KB | 0644 |
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| log.py | File | 124 B | 0644 |
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| mixins.py | File | 481 B | 0644 |
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| proactor_events.py | File | 32.48 KB | 0644 |
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| protocols.py | File | 6.79 KB | 0644 |
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| queues.py | File | 7.79 KB | 0644 |
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| runners.py | File | 6.68 KB | 0644 |
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| selector_events.py | File | 44.34 KB | 0644 |
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| sslproto.py | File | 31 KB | 0644 |
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| staggered.py | File | 5.85 KB | 0644 |
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| streams.py | File | 26.86 KB | 0644 |
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| subprocess.py | File | 7.5 KB | 0644 |
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| taskgroups.py | File | 8.27 KB | 0644 |
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| tasks.py | File | 33.63 KB | 0644 |
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| threads.py | File | 790 B | 0644 |
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| timeouts.py | File | 5.2 KB | 0644 |
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| transports.py | File | 10.47 KB | 0644 |
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| trsock.py | File | 2.42 KB | 0644 |
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| unix_events.py | File | 50.7 KB | 0644 |
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| windows_events.py | File | 33.88 KB | 0644 |
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| windows_utils.py | File | 4.94 KB | 0644 |
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