"_write_to_self" Resource temporarily unavailable

[mdavidsaver]

With py3.11 using P4P with asyncio. Connecting to a large number of channels too longer than I expected. Turning on asyncio debugging shows many repetitions of:

DEBUG:asyncio:Fail to write a null byte into the self-pipe socket
Traceback (most recent call last):
  File "/usr/lib/python3.11/asyncio/selector_events.py", line 139, in _write_to_self
    csock.send(b'\0')
BlockingIOError: [Errno 11] Resource temporarily unavailable

@coretl Does this look familiar? I recall your mentioning seeing a scalability issue with asyncio call_soon_threadsafe().

[coretl]

I haven't seen this before, but I do recall performance issues when doing large numbers of call_soon_threadsafe(). My strategy was to copy the wakeup code from cothread and adapt for asyncio.

• Create a version of call_soon_threadsafe which only actually wakes up asyncio if it isn't already processing callbacks: https://github.com/dls-controls/aioca/blob/216bcc3e91d7215cd7ccbfa6bbe942abe196fd5b/aioca/_catools.py#L308-L312
• Then when it is actually awake then manage the flags that control this: https://github.com/dls-controls/aioca/blob/216bcc3e91d7215cd7ccbfa6bbe942abe196fd5b/aioca/_catools.py#L302-L306