fix: asyncio.PidfdChildWatcher may exist even in unsupported builds

src/aiotools/server.py

@@ -53,7 +53,7 @@ async def myserver(loop, pidx, args):
 
 from .compat import all_tasks, current_task, get_running_loop
 from .context import AbstractAsyncContextManager
-from .fork import AbstractChildProcess, afork
+from .fork import AbstractChildProcess, afork, _has_pidfd
 
 try:
  from typing import Literal
@@ -251,11 +251,14 @@ def helper(*args, **kwargs):
 
 def setup_child_watcher(loop: asyncio.AbstractEventLoop) -> None:
  try:
- asyncio.get_child_watcher()
  watcher_cls = getattr(asyncio, 'PidfdChildWatcher', None)
- if watcher_cls is not None:
+ if _has_pidfd and watcher_cls:
  watcher = watcher_cls()
  asyncio.set_child_watcher(watcher)
+ else:
+ # Just get the default child watcher.
+ watcher = asyncio.get_child_watcher()
+ if not watcher.is_active():
  watcher.attach_loop(loop)
  except NotImplementedError:
  pass # for uvloop