extmod/asyncio/stream.py: Fix cancellation handling of start_server.

The following code:

  server = await asyncio.start_server(...)
  async with server:
    ... code that raises ...

would lose the original exception because the server's task would not have
had a chance to be scheduled yet, and so awaiting the task in wait_closed
would raise the cancellation instead of the original exception.

Additionally, ensures that explicitly cancelling the parent task delivers
the cancellation correctly (previously was masked by the server loop), now
this only happens if the server was closed, not when the task was
cancelled.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
This commit is contained in:
Jim Mussared 2022-07-11 15:23:20 +10:00 committed by Damien George
parent a93ebd0e03
commit 977dc9a369
3 changed files with 79 additions and 3 deletions

View File

@ -127,20 +127,30 @@ class Server:
await self.wait_closed()
def close(self):
# Note: the _serve task must have already started by now due to the sleep
# in start_server, so `state` won't be clobbered at the start of _serve.
self.state = True
self.task.cancel()
async def wait_closed(self):
await self.task
async def _serve(self, s, cb):
self.state = False
# Accept incoming connections
while True:
try:
yield core._io_queue.queue_read(s)
except core.CancelledError:
# Shutdown server
except core.CancelledError as er:
# The server task was cancelled, shutdown server and close socket.
s.close()
return
if self.state:
# If the server was explicitly closed, ignore the cancellation.
return
else:
# Otherwise e.g. the parent task was cancelled, propagate
# cancellation.
raise er
try:
s2, addr = s.accept()
except:
@ -167,6 +177,16 @@ async def start_server(cb, host, port, backlog=5):
# Create and return server object and task.
srv = Server()
srv.task = core.create_task(srv._serve(s, cb))
try:
# Ensure that the _serve task has been scheduled so that it gets to
# handle cancellation.
await core.sleep_ms(0)
except core.CancelledError as er:
# If the parent task is cancelled during this first sleep, then
# we will leak the task and it will sit waiting for the socket, so
# cancel it.
srv.task.cancel()
raise er
return srv

View File

@ -22,6 +22,44 @@ async def test():
print("sleep")
await asyncio.sleep(0)
# Test that cancellation works before the server starts if
# the subsequent code raises.
print("create server3")
server3 = await asyncio.start_server(None, "0.0.0.0", 8000)
try:
async with server3:
raise OSError
except OSError as er:
print("OSError")
# Test that closing doesn't raise CancelledError.
print("create server4")
server4 = await asyncio.start_server(None, "0.0.0.0", 8000)
server4.close()
await server4.wait_closed()
print("server4 closed")
# Test that cancelling the task will still raise CancelledError, checking
# edge cases around how many times the tasks have been re-scheduled by
# sleep.
async def task(n):
print("create task server", n)
srv = await asyncio.start_server(None, "0.0.0.0", 8000)
await srv.wait_closed()
# This should be unreachable.
print("task finished")
for num_sleep in range(0, 5):
print("sleep", num_sleep)
t = asyncio.create_task(task(num_sleep))
for _ in range(num_sleep):
await asyncio.sleep(0)
t.cancel()
try:
await t
except asyncio.CancelledError:
print("CancelledError")
print("done")

View File

@ -2,4 +2,22 @@ create server1
create server2
OSError
sleep
create server3
OSError
create server4
server4 closed
sleep 0
CancelledError
sleep 1
create task server 1
CancelledError
sleep 2
create task server 2
CancelledError
sleep 3
create task server 3
CancelledError
sleep 4
create task server 4
CancelledError
done