Always consider the debugger when exiting contexts

When in an uncertain teardown state and in debug mode a context can be
popped from actor runtime before a child finished debugging (the case
when the parent is tearing down but the child hasn't closed/completed
its tty lock IPC exit phase) and the child sends the "stop" message to
unlock the debugger but it's ignored bc the parent has already dropped
the ctx. Instead we call `._debug.maybe_wait_for_deugger()` before these
context removals to avoid the root getting stuck thinking the lock was
never released.

Further, add special `Actor._cancel_task()` handling code inside
`_invoke()` which continues to execute the method despite the IPC
channel to the caller being broken and thus avoiding potential hangs due
to a target (child) actor task remaining alive.

tractor/_actor.py

@@ -87,9 +87,10 @@ async def _invoke(
 
     '''
     __tracebackhide__ = True
-    treat_as_gen = False
+    treat_as_gen: bool = False
+    failed_resp: bool = False
 
-    # possible a traceback (not sure what typing is for this..)
+    # possibly a traceback (not sure what typing is for this..)
     tb = None
 
     cancel_scope = trio.CancelScope()
@@ -190,7 +191,8 @@ async def _invoke(
                     ctx._scope_nursery = scope_nursery
                     cs = scope_nursery.cancel_scope
                     task_status.started(cs)
-                    await chan.send({'return': await coro, 'cid': cid})
+                    res = await coro
+                    await chan.send({'return': res, 'cid': cid})
 
             except trio.MultiError:
                 # if a context error was set then likely
@@ -204,7 +206,12 @@ async def _invoke(
                 # XXX: only pop the context tracking if
                 # a ``@tractor.context`` entrypoint was called
                 assert chan.uid
+
+                # don't pop the local context until we know the
+                # associated child isn't in debug any more
+                await _debug.maybe_wait_for_debugger()
                 ctx = actor._contexts.pop((chan.uid, cid))
+
                 if ctx:
                     log.runtime(
                         f'Context entrypoint {func} was terminated:\n{ctx}'
@@ -235,10 +242,24 @@ async def _invoke(
 
         else:
             # regular async function
+            try:
                 await chan.send({'functype': 'asyncfunc', 'cid': cid})
+            except trio.BrokenResourceError:
+                failed_resp = True
+                if is_rpc:
+                    raise
+                else:
+                    log.warning(
+                        f'Failed to respond to non-rpc request: {func}'
+                    )
+
             with cancel_scope as cs:
                 task_status.started(cs)
-                await chan.send({'return': await coro, 'cid': cid})
+                result = await coro
+                log.cancel(f'result: {result}')
+                if not failed_resp:
+                    # only send result if we know IPC isn't down
+                    await chan.send({'return': result, 'cid': cid})
 
     except (
         Exception,
@@ -283,6 +304,7 @@ async def _invoke(
         except (
             trio.ClosedResourceError,
             trio.BrokenResourceError,
+            BrokenPipeError,
         ):
             # if we can't propagate the error that's a big boo boo
             log.error(
@@ -933,11 +955,13 @@ class Actor:
                         chan._exc = exc
                         raise exc
 
-                    log.runtime(
+                    log.info(
                         f"Processing request from {actorid}\n"
                         f"{ns}.{funcname}({kwargs})")
+
                     if ns == 'self':
                         func = getattr(self, funcname)
+
                         if funcname == 'cancel':
 
                             # don't start entire actor runtime
@@ -974,12 +998,17 @@ class Actor:
                                 # ``_async_main()``
                                 kwargs['chan'] = chan
                                 log.cancel(
-                                    f'{self.uid} was remotely cancelled by\n'
+                                    f'Remote request to cancel task\n'
-                                    f'{chan.uid}!'
+                                    f'remote actor: {chan.uid}\n'
+                                    f'task: {cid}'
                                 )
+                                try:
                                     await _invoke(
                                         self, cid, chan, func, kwargs, is_rpc=False
                                     )
+                                except BaseException:
+                                    log.exception("failed to cancel task?")
+
                                 continue
                     else:
                         # complain to client about restricted modules
@@ -1417,12 +1446,14 @@ class Actor:
     #             n.cancel_scope.cancel()
 
     async def _cancel_task(self, cid, chan):
-        """Cancel a local task by call-id / channel.
+        '''
+        Cancel a local task by call-id / channel.
 
         Note this method will be treated as a streaming function
         by remote actor-callers due to the declaration of ``ctx``
         in the signature (for now).
-        """
+
+        '''
         # right now this is only implicitly called by
         # streaming IPC but it should be called
         # to cancel any remotely spawned task

tractor/_portal.py

@@ -542,6 +542,17 @@ class Portal:
                     f'value from callee `{result}`'
                 )
 
+            # XXX: (MEGA IMPORTANT) if this is a root opened process we
+            # wait for any immediate child in debug before popping the
+            # context from the runtime msg loop otherwise inside
+            # ``Actor._push_result()`` the msg will be discarded and in
+            # the case where that msg is global debugger unlock (via
+            # a "stop" msg for a stream), this can result in a deadlock
+            # where the root is waiting on the lock to clear but the
+            # child has already cleared it and clobbered IPC.
+            from ._debug import maybe_wait_for_debugger
+            await maybe_wait_for_debugger()
+
             # remove the context from runtime tracking
             self.actor._contexts.pop((self.channel.uid, ctx.cid))