2026-05-01T16:16:53.769827000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (main c0e0640*?) % cat task_within_a_thread.py
import asyncio
import threading
import time


# Start a new async task in a new thread.
def sleeper():
    asyncio.run(asyncio.sleep(99))


threading.Thread(target=sleeper, daemon=True).start()
time.sleep(99)
2026-05-01T16:16:55.131980000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (main c0e0640*?) % cat repro_min.py           
import os
import subprocess
import sys
import time
import _remote_debugging

SCRIPT = os.path.join(
    os.path.dirname(os.path.abspath(__file__)), "task_within_a_thread.py"
)

p = subprocess.Popen([sys.executable, SCRIPT])
try:
    time.sleep(0.5)

    u = _remote_debugging.RemoteUnwinder(p.pid, all_threads=True, debug=True)

    # Returns stack traces for all interpreters and threads in process.
    sync = {t.thread_id for i in u.get_stack_trace() for t in i.threads}
    # Get all tasks and their awaited_by relationships from the remote process.
    aio = {a.thread_id for a in u.get_all_awaited_by()}

    delta = sync - aio

    print(
        f"pid {p.pid} | sync {sorted(sync)} | asyncio iter {sorted(aio)} | misssed {sorted(delta)}"
    )
finally:
    p.terminate()
    p.wait()
2026-05-01T16:16:56.529442000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (main c0e0640*?) % sudo ./python.exe repro_min.py 
pid 12620 | sync [12624866, 12624867] | asyncio iter [0, 12624866] | misssed [12624867]
2026-05-01T16:17:01.050645000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (main c0e0640*?) % ./python.exe task_within_a_thread.py & PID=$!
[1] 12649
2026-05-01T16:17:06.852587000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (main c0e0640*?) % sudo ./python.exe -m profiling.sampling attach --async-aware --async-mode all -d 2 --collapsed -o async.txt $PID
Captured 2,000 samples in 2.00 seconds
Sample rate: 999.94 samples/sec
Error rate: 0.00
Collapsed stack output written to async.txt
2026-05-01T16:17:51.811493000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (main c0e0640*?) % cat async.txt 
2026-05-01T16:17:54.585041000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (main c0e0640*?) % ls -l async.txt 
-rw-r--r--@ 1 root  staff  0 May  1 16:17 async.txt
2026-05-01T16:17:56.808086000+0200 maurycy@gimel /Users/maurycy/src/github.com/maurycy/cpython (main c0e0640*?) %