186 lines
7.0 KiB
Python
186 lines
7.0 KiB
Python
from __future__ import annotations
|
|
|
|
import signal
|
|
from collections import OrderedDict
|
|
from contextlib import contextmanager
|
|
from typing import TYPE_CHECKING
|
|
|
|
import trio
|
|
|
|
from ._util import ConflictDetector, is_main_thread, signal_raise
|
|
|
|
if TYPE_CHECKING:
|
|
from collections.abc import AsyncIterator, Callable, Generator, Iterable
|
|
from types import FrameType
|
|
|
|
from typing_extensions import Self
|
|
|
|
# Discussion of signal handling strategies:
|
|
#
|
|
# - On Windows signals barely exist. There are no options; signal handlers are
|
|
# the only available API.
|
|
#
|
|
# - On Linux signalfd is arguably the natural way. Semantics: signalfd acts as
|
|
# an *alternative* signal delivery mechanism. The way you use it is to mask
|
|
# out the relevant signals process-wide (so that they don't get delivered
|
|
# the normal way), and then when you read from signalfd that actually counts
|
|
# as delivering it (despite the mask). The problem with this is that we
|
|
# don't have any reliable way to mask out signals process-wide -- the only
|
|
# way to do that in Python is to call pthread_sigmask from the main thread
|
|
# *before starting any other threads*, and as a library we can't really
|
|
# impose that, and the failure mode is annoying (signals get delivered via
|
|
# signal handlers whether we want them to or not).
|
|
#
|
|
# - on macOS/*BSD, kqueue is the natural way. Semantics: kqueue acts as an
|
|
# *extra* signal delivery mechanism. Signals are delivered the normal
|
|
# way, *and* are delivered to kqueue. So you want to set them to SIG_IGN so
|
|
# that they don't end up pending forever (I guess?). I can't find any actual
|
|
# docs on how masking and EVFILT_SIGNAL interact. I did see someone note
|
|
# that if a signal is pending when the kqueue filter is added then you
|
|
# *don't* get notified of that, which makes sense. But still, we have to
|
|
# manipulate signal state (e.g. setting SIG_IGN) which as far as Python is
|
|
# concerned means we have to do this from the main thread.
|
|
#
|
|
# So in summary, there don't seem to be any compelling advantages to using the
|
|
# platform-native signal notification systems; they're kinda nice, but it's
|
|
# simpler to implement the naive signal-handler-based system once and be
|
|
# done. (The big advantage would be if there were a reliable way to monitor
|
|
# for SIGCHLD from outside the main thread and without interfering with other
|
|
# libraries that also want to monitor for SIGCHLD. But there isn't. I guess
|
|
# kqueue might give us that, but in kqueue we don't need it, because kqueue
|
|
# can directly monitor for child process state changes.)
|
|
|
|
|
|
@contextmanager
|
|
def _signal_handler(
|
|
signals: Iterable[int],
|
|
handler: Callable[[int, FrameType | None], object] | int | signal.Handlers | None,
|
|
) -> Generator[None, None, None]:
|
|
original_handlers = {}
|
|
try:
|
|
for signum in set(signals):
|
|
original_handlers[signum] = signal.signal(signum, handler)
|
|
yield
|
|
finally:
|
|
for signum, original_handler in original_handlers.items():
|
|
signal.signal(signum, original_handler)
|
|
|
|
|
|
class SignalReceiver:
|
|
def __init__(self) -> None:
|
|
# {signal num: None}
|
|
self._pending: OrderedDict[int, None] = OrderedDict()
|
|
self._lot = trio.lowlevel.ParkingLot()
|
|
self._conflict_detector = ConflictDetector(
|
|
"only one task can iterate on a signal receiver at a time"
|
|
)
|
|
self._closed = False
|
|
|
|
def _add(self, signum: int) -> None:
|
|
if self._closed:
|
|
signal_raise(signum)
|
|
else:
|
|
self._pending[signum] = None
|
|
self._lot.unpark()
|
|
|
|
def _redeliver_remaining(self) -> None:
|
|
# First make sure that any signals still in the delivery pipeline will
|
|
# get redelivered
|
|
self._closed = True
|
|
|
|
# And then redeliver any that are sitting in pending. This is done
|
|
# using a weird recursive construct to make sure we process everything
|
|
# even if some of the handlers raise exceptions.
|
|
def deliver_next() -> None:
|
|
if self._pending:
|
|
signum, _ = self._pending.popitem(last=False)
|
|
try:
|
|
signal_raise(signum)
|
|
finally:
|
|
deliver_next()
|
|
|
|
deliver_next()
|
|
|
|
def __aiter__(self) -> Self:
|
|
return self
|
|
|
|
async def __anext__(self) -> int:
|
|
if self._closed:
|
|
raise RuntimeError("open_signal_receiver block already exited")
|
|
# In principle it would be possible to support multiple concurrent
|
|
# calls to __anext__, but doing it without race conditions is quite
|
|
# tricky, and there doesn't seem to be any point in trying.
|
|
with self._conflict_detector:
|
|
if not self._pending:
|
|
await self._lot.park()
|
|
else:
|
|
await trio.lowlevel.checkpoint()
|
|
signum, _ = self._pending.popitem(last=False)
|
|
return signum
|
|
|
|
|
|
def get_pending_signal_count(rec: AsyncIterator[int]) -> int:
|
|
"""Helper for tests, not public or otherwise used."""
|
|
# open_signal_receiver() always produces SignalReceiver, this should not fail.
|
|
assert isinstance(rec, SignalReceiver)
|
|
return len(rec._pending)
|
|
|
|
|
|
@contextmanager
|
|
def open_signal_receiver(
|
|
*signals: signal.Signals | int,
|
|
) -> Generator[AsyncIterator[int], None, None]:
|
|
"""A context manager for catching signals.
|
|
|
|
Entering this context manager starts listening for the given signals and
|
|
returns an async iterator; exiting the context manager stops listening.
|
|
|
|
The async iterator blocks until a signal arrives, and then yields it.
|
|
|
|
Note that if you leave the ``with`` block while the iterator has
|
|
unextracted signals still pending inside it, then they will be
|
|
re-delivered using Python's regular signal handling logic. This avoids a
|
|
race condition when signals arrives just before we exit the ``with``
|
|
block.
|
|
|
|
Args:
|
|
signals: the signals to listen for.
|
|
|
|
Raises:
|
|
TypeError: if no signals were provided.
|
|
|
|
RuntimeError: if you try to use this anywhere except Python's main
|
|
thread. (This is a Python limitation.)
|
|
|
|
Example:
|
|
|
|
A common convention for Unix daemons is that they should reload their
|
|
configuration when they receive a ``SIGHUP``. Here's a sketch of what
|
|
that might look like using :func:`open_signal_receiver`::
|
|
|
|
with trio.open_signal_receiver(signal.SIGHUP) as signal_aiter:
|
|
async for signum in signal_aiter:
|
|
assert signum == signal.SIGHUP
|
|
reload_configuration()
|
|
|
|
"""
|
|
if not signals:
|
|
raise TypeError("No signals were provided")
|
|
|
|
if not is_main_thread():
|
|
raise RuntimeError(
|
|
"Sorry, open_signal_receiver is only possible when running in "
|
|
"Python interpreter's main thread"
|
|
)
|
|
token = trio.lowlevel.current_trio_token()
|
|
queue = SignalReceiver()
|
|
|
|
def handler(signum: int, frame: FrameType | None) -> None:
|
|
token.run_sync_soon(queue._add, signum, idempotent=True)
|
|
|
|
try:
|
|
with _signal_handler(signals, handler):
|
|
yield queue
|
|
finally:
|
|
queue._redeliver_remaining()
|