Always restore the `trio` SIGINT handler

Pretty sure this is the final touch to alleviate all our debug lock
headaches! Instead of trying to revert to the "last" handler (as `pdb`
does internally in the stdlib) we always just revert to the handler
`trio` registers during startup. Further this seems to allow cancelling
the root-side locking task if it's detected as stale IFF we only do this
when the root actor is in a "no more IPC peers" state.

Deatz:
- always `._debug.Lock._trio_handler` as the `trio` version, not some
  last used handler to make sure we're getting the ctrl-c handling we
  want when not in debug mode.
- assign the trio handler in `open_root_actor()`
  `._runtime._async_main()` to be sure it's applied in subactors as well
  as the root.
- only do debug lock blocking and root-side-locking-task cancels when
  a "no peers" condition is detected in the root actor: i.e. no IPC
  channels are detected by the root meaning it's impossible any actor
  has a sane lock-state ongoing for debug mode.

tractor/_debug.py

@@ -107,16 +107,16 @@ class Lock:
     @classmethod
     def shield_sigint(cls):
         cls._orig_sigint_handler = signal.signal(
-                signal.SIGINT,
-                shield_sigint,
-            )
+            signal.SIGINT,
+            shield_sigint,
+        )
 
     @classmethod
     def unshield_sigint(cls):
-        # always restore (some) sigint handler, either
-        # the prior or at least ``trio``'s.
-        orig = cls._orig_sigint_handler or cls._trio_handler
-        signal.signal(signal.SIGINT, orig)
+        # always restore ``trio``'s sigint handler. see notes below in
+        # the pdb factory about the nightmare that is that code swapping
+        # out the handler when the repl activates...
+        signal.signal(signal.SIGINT, cls._trio_handler)
         cls._orig_sigint_handler = None
 
     @classmethod

tractor/_root.py

@@ -34,7 +34,11 @@ import warnings
 from exceptiongroup import BaseExceptionGroup
 import trio
 
-from ._runtime import Actor, Arbiter, async_main
+from ._runtime import (
+    Actor,
+    Arbiter,
+    async_main,
+)
 from . import _debug
 from . import _spawn
 from . import _state
@@ -88,7 +92,7 @@ async def open_root_actor(
 
     # attempt to retreive ``trio``'s sigint handler and stash it
     # on our debugger lock state.
-    _debug.Lock._trio_handler = signal.getsignal(signal.SIGINT)
+    _debug.Lock._trio_handler =  signal.getsignal(signal.SIGINT)
 
     # mark top most level process as root actor
     _state._runtime_vars['_is_root'] = True

tractor/_runtime.py

@@ -25,14 +25,15 @@ from itertools import chain
 import importlib
 import importlib.util
 import inspect
-import uuid
+import signal
+import sys
 from typing import (
     Any, Optional,
     Union, TYPE_CHECKING,
     Callable,
 )
+import uuid
 from types import ModuleType
-import sys
 import os
 from contextlib import ExitStack
 import warnings
@@ -709,6 +710,14 @@ class Actor:
                 log.runtime(f"No more channels for {chan.uid}")
                 self._peers.pop(uid, None)
 
+            log.runtime(f"Peers is {self._peers}")
+
+            # No more channels to other actors (at all) registered
+            # as connected.
+            if not self._peers:
+                log.runtime("Signalling no more peer channel connections")
+                self._no_more_peers.set()
+
                 # NOTE: block this actor from acquiring the
                 # debugger-TTY-lock since we have no way to know if we
                 # cancelled it and further there is no way to ensure the
@@ -722,23 +731,16 @@ class Actor:
                     # if a now stale local task has the TTY lock still
                     # we cancel it to allow servicing other requests for
                     # the lock.
+                    db_cs = pdb_lock._root_local_task_cs_in_debug
                     if (
-                        pdb_lock._root_local_task_cs_in_debug
-                        and not pdb_lock._root_local_task_cs_in_debug.cancel_called
+                        db_cs
+                        and not db_cs.cancel_called
                     ):
                         log.warning(
                             f'STALE DEBUG LOCK DETECTED FOR {uid}'
                         )
                         # TODO: figure out why this breaks tests..
-                        # pdb_lock._root_local_task_cs_in_debug.cancel()
-
-            log.runtime(f"Peers is {self._peers}")
-
-            # No more channels to other actors (at all) registered
-            # as connected.
-            if not self._peers:
-                log.runtime("Signalling no more peer channel connections")
-                self._no_more_peers.set()
+                        pdb_lock._root_local_task_cs_in_debug.cancel()
 
             # XXX: is this necessary (GC should do it)?
             if chan.connected():
@@ -1229,6 +1231,10 @@ async def async_main(
     and when cancelled effectively cancels the actor.
 
     '''
+    # attempt to retreive ``trio``'s sigint handler and stash it
+    # on our debugger lock state.
+    _debug.Lock._trio_handler = signal.getsignal(signal.SIGINT)
+
     registered_with_arbiter = False
     try: