[puddly]

This is an alternative approach to ASH auto-ACKing.

Our current approach of using a second thread for the event loop is unfortunately flawed: when the main thread has GC stutters, so does the gateway thread. This can get bad enough to still trigger ASH resets. We can use a subinterpreter (3.14+) or subprocess as a parallelism mechanism that is more isolated than a thread.

It's comparable to threading for all of the happy paths.

---

Measurement	Thread	Subprocess	Subinterpreter	In-process
20 ms timer p99 under main-interpreter GC storm (3.14)	170 ms	2.5 ms	4.2 ms	n/a
20 ms timer max under GC storm (3.14)	185 ms	18 ms	8.4 ms	n/a
20 ms timer p99 under GC storm (3.15.0b1)	–	–	2.7 ms	n/a
Bridge round trip, trivial call, p50	66 µs	–	73 µs	0.1 µs
Bridge round trip, trivial call, p99	102 µs	–	162 µs	0.2 µs
send_data with NCP ACK over TCP, p50	226 µs	–	260 µs	138 µs
send_data with NCP ACK over TCP, p99	399 µs	–	382 µs	253 µs
Startup cost	~0	~0.3 s	~0.13 s	0
Memory cost	~0	~50 MB	~20 MB	0

GC storm: 3 million object heap in the main interpreter, gc.collect() every 0.5 s, each collection ~180 ms.

Related: #753
Related: #766
Related: #735

[codecov]

Codecov Report

❌ Patch coverage is 92.22222% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.00%. Comparing base (aea9248) to head (18b2c23).

Files with missing lines	Patch %	Lines
bellows/uart.py	91.53%	27 Missing ⚠️
bellows/ezsp/__init__.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #770      +/-   ##
==========================================
- Coverage   99.58%   99.00%   -0.58%     
==========================================
  Files          64       63       -1     
  Lines        4331     4540     +209     
==========================================
+ Hits         4313     4495     +182     
- Misses         18       45      +27     

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[puddly]

Ah, there's a fatal problem with this approach... esphome-hass:// does not and cannot work 😅

[puddly]

That being said, we will need to come up with a solution to esphome-hass:// when ZHA moves into its own app either way. By that point, something like this will not be needed.