Page 1 of 1
uasyncio task freezing
Posted: Sat Oct 02, 2021 7:54 pm
by coayer
Hi everyone,
I have a uasyncio task running on an ESP8266 which sends DNS lookups (UDP). I'm using uasyncio.StreamReader (and writer) on the socket object to do this asynchronously. Most requests are successful, but sometimes the task indefinitely hangs on "await reader.read(128)", which is reading the response from the server. There's a timeout set on the socket.
I have a main() task with its own infinite loop, and I can see that when the DNS read gets stuck the main loop keeps running just fine.
If I press CTRL-C, I get:
Code: Select all
Traceback (most recent call last):
File "main.py", line 290, in <module>
File "uasyncio/core.py", line 1, in run
File "uasyncio/core.py", line 1, in run_until_complete
File "uasyncio/core.py", line 1, in wait_io_event
KeyboardInterrupt:
Am I missing something or is this a bug I should report?
Re: uasyncio task freezing
Posted: Sun Oct 03, 2021 8:29 am
by pythoncoder
If you are using socket.getaddrinfo() this is a blocking call. This is a known issue which hasn't yet been fixed.
Re: uasyncio task freezing
Posted: Sun Oct 03, 2021 9:42 am
by coayer
I am using getaddrinfo, but directly on an IP address (1.1.1.1) so that I can create a socket to the DNS server — I'm doing the DNS lookup manually. That's not the line that is freezing though, it's the "await reader.read(8)" after a "writer.write" and "await writer.drain".
Re: uasyncio task freezing
Posted: Mon Oct 04, 2021 9:18 am
by pythoncoder
My MicroPython work has been with nonblocking sockets so I'm not entirely sure about the behaviour of blocking sockets. I would imagine that, in the absence of the requested number of characters,
read(n) would terminate on timeout with as much data as was available. It would seem this isn't the case.
One option would be to investigate this and find out how
read(n) behaves on CPython. Another way would be to impose a timeout on the read() using
a uasyncio timeout. I think this is probably the orthodox uasyncio approach, rather than having a socket timeout.
Re: uasyncio task freezing
Posted: Wed Oct 13, 2021 6:46 pm
by coayer
Thanks for the advice — I've swapped over to using
Code: Select all
await asyncio.wait_for(reader.read(X), Y)
but it isn't raising a TimeoutError even if the socket is connected to an unreachable IP (the program hangs on that line). Is this the appropriate way to use timeouts on nonblocking sockets with asyncio?
On the Python docs, it says
Changed in version 3.7: When aw is cancelled due to a timeout, wait_for waits for aw to be cancelled. Previously, it raised asyncio.TimeoutError immediately.
which sounds like the problem.
Re: uasyncio task freezing
Posted: Thu Oct 14, 2021 8:38 am
by pythoncoder
coayer wrote: ↑Wed Oct 13, 2021 6:46 pm
Is this the appropriate way to use timeouts on nonblocking sockets with asyncio?...
I thought you were using blocking sockets. You can't use timeouts with nonblocking sockets as read(n) always returns immediately. With nonblocking sockets you need to explicitly code timeouts. The code
here is an example.
On the Python docs, it says
Changed in version 3.7: When aw is cancelled due to a timeout, wait_for waits for aw to be cancelled. Previously, it raised asyncio.TimeoutError immediately.
which sounds like the problem.
MicroPython behaves as described
here.
Re: uasyncio task freezing
Posted: Thu Oct 14, 2021 11:41 am
by coayer
pythoncoder wrote: ↑Thu Oct 14, 2021 8:38 am
coayer wrote: ↑Wed Oct 13, 2021 6:46 pm
Is this the appropriate way to use timeouts on nonblocking sockets with asyncio?...
I thought you were using blocking sockets. You can't use timeouts with nonblocking sockets as read(n) always returns immediately. With nonblocking sockets you need to explicitly code timeouts. The code
here is an example.
On the Python docs, it says
Changed in version 3.7: When aw is cancelled due to a timeout, wait_for waits for aw to be cancelled. Previously, it raised asyncio.TimeoutError immediately.
which sounds like the problem.
MicroPython behaves as described
here.
Ah, I see. Thanks for your help — this is my first time working with async programming so it's still a bit confusing!
Re: uasyncio task freezing
Posted: Fri Oct 15, 2021 10:02 am
by ozzkuma
coayer wrote: ↑Sat Oct 02, 2021 7:54 pm
Hi everyone,
I have a uasyncio task running on an ESP8266 which sends DNS lookups (UDP). I'm using uasyncio.StreamReader (and writer) on the socket object to do this asynchronously. Most requests are successful, but sometimes the task indefinitely hangs on "await reader.read(128)", which is reading the response from the server
VPower 777 APK. There's a timeout set on the socket.
I have a main() task with its own infinite loop, and I can see that when the DNS read gets stuck the main loop keeps running just fine.
If I press CTRL-C, I get:
Code: Select all
Traceback (most recent call last):
File "main.py", line 290, in <module>
File "uasyncio/core.py", line 1, in run
File "uasyncio/core.py", line 1, in run_until_complete
File "uasyncio/core.py", line 1, in wait_io_event
KeyboardInterrupt:
Am I missing something or is this a bug I should report?
I am using getaddrinfo and doing DNS lookup manually.
Re: uasyncio task freezing
Posted: Fri Aug 19, 2022 4:30 am
by AntoniaUnderwood
Do you know any way to DNS automatically?
Re: uasyncio task freezing
Posted: Fri Aug 19, 2022 4:45 am
by jimmo
AntoniaUnderwood wrote: ↑Fri Aug 19, 2022 4:30 am
Do you know any way to DNS automatically?
Not sure what you mean by automatically, but it's straightforward to use "getaddrinfo"
Code: Select all
addr_info = socket.getaddrinfo("micropython.org", 80)
If you're using a higher-level library like urequests, then it happens automatically
Code: Select all
response = urequests.get("http://micropython.org/")