fix: Improve checks for pidfd availability

changes/51.fix.md

@@ -0,0 +1 @@
+Improve checks for pidfd availability to avoid corner cases that may fail on Linux kernel 5.1 and 5.2 where `signal.pidfd_send_signal()` is available but `os.pidfd_open()` is not

src/aiotools/fork.py

@@ -28,11 +28,14 @@
 logger = logging.getLogger(__name__)
 
 _has_pidfd = False
-if hasattr(signal, 'pidfd_send_signal'):
+if hasattr(os, 'pidfd_open'):
+ # signal.pidfd_send_signal() is available in Linux kernel 5.1+
+ # and os.pidfd_open() is available in Linux kernel 5.3+.
+ # So let's check with os.pidfd_open() which requires higher version.
  try:
- signal.pidfd_send_signal(0, 0) # type: ignore
+ os.pidfd_open(0, 0) # type: ignore
  except OSError as e:
- if e.errno == errno.EBADF:
+ if e.errno in (errno.EBADF, errno.EINVAL):
  _has_pidfd = True
  # if the kernel does not support this,
  # it will say errno.ENOSYS or errno.EPERM

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