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Refs #36315 -- Replaced calls to asyncio.gather with TaskGroup. #19370

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Refs #36315 -- Replaced calls to asyncio.gather with TaskGroup. #19370

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42 changes: 32 additions & 10 deletions django/dispatch/dispatcher.py
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,28 @@ def _make_id(target):
NO_RECEIVERS = object()


async def _gather(*coros):
if len(coros) == 0:
return []

if len(coros) == 1:
return [await coros[0]]

async def run(i, coro):
results[i] = await coro

try:
async with asyncio.TaskGroup() as tg:
results = [None] * len(coros)
for i, coro in enumerate(coros):
tg.create_task(run(i, coro))
return results
except BaseExceptionGroup as exception_group:
if len(exception_group.exceptions) == 1:
raise exception_group.exceptions[0]
raise
Comment on lines +25 to +44
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Can this be simplified to:

Suggested change
async def _gather(*coros):
if len(coros) == 0:
return []
if len(coros) == 1:
return [await coros[0]]
async def run(i, coro):
results[i] = await coro
try:
async with asyncio.TaskGroup() as tg:
results = [None] * len(coros)
for i, coro in enumerate(coros):
tg.create_task(run(i, coro))
return results
except BaseExceptionGroup as exception_group:
if len(exception_group.exceptions) == 1:
raise exception_group.exceptions[0]
raise
async def gather_tasks(*coros):
async with asyncio.TaskGroup() as tg:
tasks = [tg.create_task(coro) for coro in coros]
return [task.result() for task in tasks]

unless there's reason for the error handling? (BaseExceptionGroup).

Also, it might be worth moving the function to a utils.py file, so that it can easily be reused by other places.

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Yes the error handling is important to maintain backwards compatibility with the old use of gather

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@graingert graingert Apr 26, 2025 •
edited
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Keeping an extra reference to tasks here will result in reference cycles in the traceback of any errors that will delay garbage collection if there's any errors in signals

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To maintain backward compatibility, shouldn't the first exception be raised even when the exception group contains multiple exceptions?



class Signal:
"""
Base class for all signals
Expand Down Expand Up @@ -166,7 +188,7 @@ def send(self, sender, **named):

If any receivers are asynchronous, they are called after all the
synchronous receivers via a single call to async_to_sync(). They are
also executed concurrently with asyncio.gather().
also executed concurrently with asyncio.TaskGroup().

Arguments:

Expand All @@ -191,7 +213,7 @@ def send(self, sender, **named):
if async_receivers:

async def asend():
async_responses = await asyncio.gather(
async_responses = await _gather(
*(
receiver(signal=self, sender=sender, **named)
for receiver in async_receivers
Expand All @@ -215,7 +237,7 @@ async def asend(self, sender, **named):
sync_to_async() adaption before executing any asynchronous receivers.

If any receivers are asynchronous, they are grouped and executed
concurrently with asyncio.gather().
concurrently with asyncio.TaskGroup().

Arguments:

Expand Down Expand Up @@ -248,9 +270,9 @@ def sync_send():
async def sync_send():
return []

responses, async_responses = await asyncio.gather(
responses, async_responses = await _gather(
sync_send(),
asyncio.gather(
_gather(
*(
receiver(signal=self, sender=sender, **named)
for receiver in async_receivers
Expand All @@ -274,7 +296,7 @@ def send_robust(self, sender, **named):

If any receivers are asynchronous, they are called after all the
synchronous receivers via a single call to async_to_sync(). They are
also executed concurrently with asyncio.gather().
also executed concurrently with asyncio.TaskGroup().

Arguments:

Expand Down Expand Up @@ -320,7 +342,7 @@ async def asend_and_wrap_exception(receiver):
return response

async def asend():
async_responses = await asyncio.gather(
async_responses = await _gather(
*(
asend_and_wrap_exception(receiver)
for receiver in async_receivers
Expand All @@ -339,7 +361,7 @@ async def asend_robust(self, sender, **named):
sync_to_async() adaption before executing any asynchronous receivers.

If any receivers are asynchronous, they are grouped and executed
concurrently with asyncio.gather.
concurrently with asyncio.TaskGroup.

Arguments:

Expand Down Expand Up @@ -394,9 +416,9 @@ async def asend_and_wrap_exception(receiver):
return err
return response

responses, async_responses = await asyncio.gather(
responses, async_responses = await _gather(
sync_send(),
asyncio.gather(
_gather(
*(asend_and_wrap_exception(receiver) for receiver in async_receivers),
),
)
Expand Down
2 changes: 1 addition & 1 deletion docs/topics/signals.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -321,7 +321,7 @@ in order to reduce the number of sync/async calling-style switches within a
they are async before being called. This means that an asynchronous receiver
registered before a synchronous receiver may be executed after the synchronous
receiver. In addition, async receivers are executed concurrently using
``asyncio.gather()``.
``asyncio.TaskGroup()``.

All built-in signals, except those in the async request-response cycle, are
dispatched using :meth:`Signal.send`.
Expand Down
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