uselect: poll instance produces unexpected results under fault conditions
Context: uasyncio StreamReader and StreamWriter objects hang indefinitely under fault conditions.
Under fault conditions uasyncio expects to receive POLLERR or POLLHUP conditions from the poll instance. In my testing this never occurs.
Testing was of client connections. Socket type was SOCK_STREAM. Two fault conditions were tested:
- Server outage.
- Socket closed by another coroutine.
Testing was performed with a server running under the Unix build. Clients were tested on:
- Unix build (on same machine as server).
- ESP8266.
- ESP32.
Results were as follows. Numbers represent the event no. received from the poll instance. "No trigger" means that the poll instance produced no response after the fault. On all platforms where the client was reading, a server outage produced a POLLIN (1) response. On all but ESP32 this repeated indefinitely causing the client endlessly to read empty bytes objects.
Numbers are base 10. Mode refers to the client mode. Expected refers to uasyncio.
| Mode | Platform | Outage | Closure | Expected |
|---|---|---|---|---|
| Read | Unix | 1 | 32 | 9 or 17 |
| Read | ESP8266 | 1 | No trigger | 9 or 17 |
| Read | ESP32 | 1 (once) | No trigger | 9 or 17 |
| Write | Unix | OSError | 32 | 12 or 20 |
| Write | ESP8266 | OSError | No trigger | 12 or 20 |
| Write | ESP832 | OSError | No trigger | 12 or 20 |
1 == POLLIN
4 == POLLOUT
9 == (POLLIN & POLLERR)
17 == (POLLIN & POLLHUP)
12 == (POLLOUT & POLLERR)
20 == (POLLOUT & POLLHUP)
32 == Search me.
Test scripts may be found here:
Server - can run in read or write mode
Read client
Write client
uasyncio stream reader/writer: unexpected behaviour with UART
Testing done on Pyboard V1.1. The sender coroutine iterates every 2 seconds but no output appears on pin X1:
import uasyncio as asyncio
from pyb import UART
uart = UART(4, 9600)
async def sender():
swriter = asyncio.StreamWriter(uart, {})
while True:
swriter.awrite('Hello uart\n')
await asyncio.sleep(2)
print('wrote')
loop = asyncio.get_event_loop()
loop.create_task(sender())
loop.run_forever()
The next script produces output on X1 as expected until a loopback is applied (link X1 and X2). At this point the UART sends data continuously. The data is read correctly, but the call to
await asyncio.sleep(2) no longer behaves as expected.
import uasyncio as asyncio
from pyb import UART
uart = UART(4, 9600)
async def sender():
while True:
uart.write('Hello uart\n')
await asyncio.sleep(2)
print('Wrote')
async def receiver():
sreader = asyncio.StreamReader(uart)
while True:
res = await sreader.readline()
print('Recieved', res)
loop = asyncio.get_event_loop()
loop.create_task(sender())
loop.create_task(receiver())
loop.run_forever()