Merge pull request #358 from goodboy/switch_to_pdbp

Switch to `pdbp` 🏄🏼

docs/README.rst

@@ -6,8 +6,14 @@
 ``tractor`` is a `structured concurrent`_, multi-processing_ runtime
 built on trio_.
 
-Fundamentally ``tractor`` gives you parallelism via ``trio``-"*actors*":
+Fundamentally, ``tractor`` gives you parallelism via
-our nurseries_ let you spawn new Python processes which each run a ``trio``
+``trio``-"*actors*": independent Python processes (aka
+non-shared-memory threads) which maintain structured
+concurrency (SC) *end-to-end* inside a *supervision tree*.
+
+Cross-process (and thus cross-host) SC is accomplished through the
+combined use of our "actor nurseries_" and an "SC-transitive IPC
+protocol" constructed on top of multiple Pythons each running a ``trio``
 scheduled runtime - a call to ``trio.run()``.
 
 We believe the system adheres to the `3 axioms`_ of an "`actor model`_"
@@ -23,7 +29,8 @@ Features
 - **It's just** a ``trio`` API
 - *Infinitely nesteable* process trees
 - Builtin IPC streaming APIs with task fan-out broadcasting
-- A (first ever?) "native" multi-core debugger UX for Python using `pdb++`_
+- A "native" multi-core debugger REPL using `pdbp`_ (a fork & fix of
+  `pdb++`_ thanks to @mdmintz!)
 - Support for a swappable, OS specific, process spawning layer
 - A modular transport stack, allowing for custom serialization (eg. with
   `msgspec`_), communications protocols, and environment specific IPC
@@ -149,7 +156,7 @@ it **is a bug**.
 
 "Native" multi-process debugging
 --------------------------------
-Using the magic of `pdb++`_ and our internal IPC, we've
+Using the magic of `pdbp`_ and our internal IPC, we've
 been able to create a native feeling debugging experience for
 any (sub-)process in your ``tractor`` tree.
 
@@ -597,6 +604,7 @@ channel`_!
 .. _adherance to: https://www.youtube.com/watch?v=7erJ1DV_Tlo&t=1821s
 .. _trio gitter channel: https://gitter.im/python-trio/general
 .. _matrix channel: https://matrix.to/#/!tractor:matrix.org
+.. _pdbp: https://github.com/mdmintz/pdbp
 .. _pdb++: https://github.com/pdbpp/pdbpp
 .. _guest mode: https://trio.readthedocs.io/en/stable/reference-lowlevel.html?highlight=guest%20mode#using-guest-mode-to-run-trio-on-top-of-other-event-loops
 .. _messages: https://en.wikipedia.org/wiki/Message_passing

examples/advanced_faults/ipc_failure_during_stream.py

@@ -0,0 +1,151 @@
+'''
+Complex edge case where during real-time streaming the IPC tranport
+channels are wiped out (purposely in this example though it could have
+been an outage) and we want to ensure that despite being in debug mode
+(or not) the user can sent SIGINT once they notice the hang and the
+actor tree will eventually be cancelled without leaving any zombies.
+
+'''
+import trio
+from tractor import (
+    open_nursery,
+    context,
+    Context,
+    MsgStream,
+)
+
+
+async def break_channel_silently_then_error(
+    stream: MsgStream,
+):
+    async for msg in stream:
+        await stream.send(msg)
+
+        # XXX: close the channel right after an error is raised
+        # purposely breaking the IPC transport to make sure the parent
+        # doesn't get stuck in debug or hang on the connection join.
+        # this more or less simulates an infinite msg-receive hang on
+        # the other end.
+        await stream._ctx.chan.send(None)
+        assert 0
+
+
+async def close_stream_and_error(
+    stream: MsgStream,
+):
+    async for msg in stream:
+        await stream.send(msg)
+
+        # wipe out channel right before raising
+        await stream._ctx.chan.send(None)
+        await stream.aclose()
+        assert 0
+
+
+@context
+async def recv_and_spawn_net_killers(
+
+    ctx: Context,
+    break_ipc_after: bool | int = False,
+
+) -> None:
+    '''
+    Receive stream msgs and spawn some IPC killers mid-stream.
+
+    '''
+    await ctx.started()
+    async with (
+        ctx.open_stream() as stream,
+        trio.open_nursery() as n,
+    ):
+        async for i in stream:
+            print(f'child echoing {i}')
+            await stream.send(i)
+            if (
+                break_ipc_after
+                and i > break_ipc_after
+            ):
+                '#################################\n'
+                'Simulating child-side IPC BREAK!\n'
+                '#################################'
+                n.start_soon(break_channel_silently_then_error, stream)
+                n.start_soon(close_stream_and_error, stream)
+
+
+async def main(
+    debug_mode: bool = False,
+    start_method: str = 'trio',
+
+    # by default we break the parent IPC first (if configured to break
+    # at all), but this can be changed so the child does first (even if
+    # both are set to break).
+    break_parent_ipc_after: int | bool = False,
+    break_child_ipc_after: int | bool = False,
+
+) -> None:
+
+    async with (
+        open_nursery(
+            start_method=start_method,
+
+            # NOTE: even debugger is used we shouldn't get
+            # a hang since it never engages due to broken IPC
+            debug_mode=debug_mode,
+            loglevel='warning',
+
+        ) as an,
+    ):
+        portal = await an.start_actor(
+            'chitty_hijo',
+            enable_modules=[__name__],
+        )
+
+        async with portal.open_context(
+            recv_and_spawn_net_killers,
+            break_ipc_after=break_child_ipc_after,
+
+        ) as (ctx, sent):
+            async with ctx.open_stream() as stream:
+                for i in range(1000):
+
+                    if (
+                        break_parent_ipc_after
+                        and i > break_parent_ipc_after
+                    ):
+                        print(
+                            '#################################\n'
+                            'Simulating parent-side IPC BREAK!\n'
+                            '#################################'
+                        )
+                        await stream._ctx.chan.send(None)
+
+                    # it actually breaks right here in the
+                    # mp_spawn/forkserver backends and thus the zombie
+                    # reaper never even kicks in?
+                    print(f'parent sending {i}')
+                    await stream.send(i)
+
+                    with trio.move_on_after(2) as cs:
+
+                        # NOTE: in the parent side IPC failure case this
+                        # will raise an ``EndOfChannel`` after the child
+                        # is killed and sends a stop msg back to it's
+                        # caller/this-parent.
+                        rx = await stream.receive()
+
+                        print(f"I'm a happy user and echoed to me is {rx}")
+
+                    if cs.cancelled_caught:
+                        # pretend to be a user seeing no streaming action
+                        # thinking it's a hang, and then hitting ctl-c..
+                        print("YOO i'm a user anddd thingz hangin..")
+
+                print(
+                    "YOO i'm mad send side dun but thingz hangin..\n"
+                    'MASHING CTlR-C Ctl-c..'
+                )
+                raise KeyboardInterrupt
+
+
+if __name__ == '__main__':
+    trio.run(main)

examples/debugging/restore_builtin_breakpoint.py

@@ -0,0 +1,24 @@
+import os
+import sys
+
+import trio
+import tractor
+
+
+async def main() -> None:
+    async with tractor.open_nursery(debug_mode=True) as an:
+
+        assert os.environ['PYTHONBREAKPOINT'] == 'tractor._debug._set_trace'
+
+        # TODO: an assert that verifies the hook has indeed been, hooked
+        # XD
+        assert sys.breakpointhook is not tractor._debug._set_trace
+
+        breakpoint()
+
+    # TODO: an assert that verifies the hook is unhooked..
+    assert sys.breakpointhook
+    breakpoint()
+
+if __name__ == '__main__':
+    trio.run(main)

nooz/343.trivial.rst

@@ -0,0 +1,19 @@
+Rework our ``.trionics.BroadcastReceiver`` internals to avoid method
+recursion and approach a design and interface closer to ``trio``'s
+``MemoryReceiveChannel``.
+
+The details of the internal changes include:
+
+- implementing a ``BroadcastReceiver.receive_nowait()`` and using it
+  within the async ``.receive()`` thus avoiding recursion from
+  ``.receive()``.
+- failing over to an internal ``._receive_from_underlying()`` when the
+  ``_nowait()`` call raises ``trio.WouldBlock``
+- adding ``BroadcastState.statistics()`` for debugging and testing both
+  internals and by users.
+- add an internal ``BroadcastReceiver._raise_on_lag: bool`` which can be
+  set to avoid ``Lagged`` raising for possible use cases where a user
+  wants to choose between a [cheap or nasty
+  pattern](https://zguide.zeromq.org/docs/chapter7/#The-Cheap-or-Nasty-Pattern)
+  the the particular stream (we use this in ``piker``'s dark clearing
+  engine to avoid fast feeds breaking during HFT periods).

nooz/346.bugfix.rst

@@ -0,0 +1,15 @@
+Fixes to ensure IPC (channel) breakage doesn't result in hung actor
+trees; the zombie reaping and general supervision machinery will always
+clean up and terminate.
+
+This includes not only the (mostly minor) fixes to solve these cases but
+also a new extensive test suite in `test_advanced_faults.py` with an
+accompanying highly configurable example module-script in
+`examples/advanced_faults/ipc_failure_during_stream.py`. Tests ensure we
+never get hang or zombies despite operating in debug mode and attempt to
+simulate all possible IPC transport failure cases for a local-host actor
+tree.
+
+Further we simplify `Context.open_stream.__aexit__()` to just call
+`MsgStream.aclose()` directly more or less avoiding a pure duplicate
+code path.

nooz/349.trivial.rst

@@ -0,0 +1,10 @@
+Always redraw the `pdbpp` prompt on `SIGINT` during REPL use.
+
+There was recent changes todo with Python 3.10 that required us to pin
+to a specific commit in `pdbpp` which have recently been fixed minus
+this last issue with `SIGINT` shielding: not clobbering or not
+showing the `(Pdb++)` prompt on ctlr-c by the user. This repairs all
+that by firstly removing the standard KBI intercepting of the std lib's
+`pdb.Pdb._cmdloop()` as well as ensuring that only the actor with REPL
+control ever reports `SIGINT` handler log msgs and prompt redraws. With
+this we move back to using pypi `pdbpp` release.

nooz/356.trivial.rst

@@ -0,0 +1,7 @@
+Drop `trio.Process.aclose()` usage, copy into our spawning code.
+
+The details are laid out in https://github.com/goodboy/tractor/issues/330.
+`trio` changed is process running quite some time ago, this just copies
+out the small bit we needed (from the old `.aclose()`) for hard kills
+where a soft runtime cancel request fails and our "zombie killer"
+implementation kicks in.

nooz/358.feature.rst

@@ -0,0 +1,15 @@
+Switch to using the fork & fix of `pdb++`, `pdbp`:
+https://github.com/mdmintz/pdbp
+
+Allows us to sidestep a variety of issues that aren't being maintained
+in the upstream project thanks to the hard work of @mdmintz!
+
+We also include some default settings adjustments as per recent
+development on the fork:
+
+- sticky mode is still turned on by default but now activates when
+  a using the `ll` repl command.
+- turn off line truncation by default to avoid inter-line gaps when
+  resizing the terimnal during use.
+- when using the backtrace cmd either by `w` or `bt`, the config
+  automatically switches to non-sticky mode.

requirements-test.txt

@@ -1,7 +1,7 @@
 pytest
 pytest-trio
 pytest-timeout
-pdbpp
+pdbp
 mypy
 trio_typing
 pexpect

setup.py

@@ -26,12 +26,12 @@ with open('docs/README.rst', encoding='utf-8') as f:
 setup(
     name="tractor",
     version='0.1.0a6dev0',  # alpha zone
-    description='structured concurrrent "actors"',
+    description='structured concurrrent `trio`-"actors"',
     long_description=readme,
     license='AGPLv3',
     author='Tyler Goodlet',
     maintainer='Tyler Goodlet',
-    maintainer_email='jgbt@protonmail.com',
+    maintainer_email='goodboy_foss@protonmail.com',
     url='https://github.com/goodboy/tractor',
     platforms=['linux', 'windows'],
     packages=[
@@ -52,14 +52,15 @@ setup(
         # tooling
         'tricycle',
         'trio_typing',
-
-        # tooling
         'colorlog',
         'wrapt',
 
-        # serialization
+        # IPC serialization
         'msgspec',
 
+        # debug mode REPL
+        'pdbp',
+
         # pip ref docs on these specs:
         # https://pip.pypa.io/en/stable/reference/requirement-specifiers/#examples
         # and pep:
@@ -70,14 +71,9 @@ setup(
         # https://github.com/pdbpp/fancycompleter/issues/37
         'pyreadline3 ; platform_system == "Windows"',
 
-        # 3.10 has an outstanding unreleased issue and `pdbpp` itself
-        #   pins to patched forks of its own dependencies as well..and
-        #   we need a specific patch on master atm.
-        'pdbpp @ git+https://github.com/pdbpp/pdbpp@76c4be5#egg=pdbpp ; python_version > "3.9"',  # noqa: E501
-
     ],
     tests_require=['pytest'],
-    python_requires=">=3.9",
+    python_requires=">=3.10",
     keywords=[
         'trio',
         'async',

tests/conftest.py

@@ -7,6 +7,7 @@ import os
 import random
 import signal
 import platform
+import pathlib
 import time
 import inspect
 from functools import partial, wraps
@@ -113,14 +114,21 @@ no_windows = pytest.mark.skipif(
 )
 
 
-def repodir():
+def repodir() -> pathlib.Path:
-    """Return the abspath to the repo directory.
+    '''
-    """
+    Return the abspath to the repo directory.
-    dirname = os.path.dirname
+
-    dirpath = os.path.abspath(
+    '''
-        dirname(dirname(os.path.realpath(__file__)))
+    # 2 parents up to step up through tests/<repo_dir>
-        )
+    return pathlib.Path(__file__).parent.parent.absolute()
-    return dirpath
+
+
+def examples_dir() -> pathlib.Path:
+    '''
+    Return the abspath to the examples directory as `pathlib.Path`.
+
+    '''
+    return repodir() / 'examples'
 
 
 def pytest_addoption(parser):
@@ -151,7 +159,7 @@ def loglevel(request):
 
 
 @pytest.fixture(scope='session')
-def spawn_backend(request):
+def spawn_backend(request) -> str:
     return request.config.option.spawn_backend
 
 
@@ -205,16 +213,22 @@ def sig_prog(proc, sig):
 
 
 @pytest.fixture
-def daemon(loglevel, testdir, arb_addr):
+def daemon(
-    """Run a daemon actor as a "remote arbiter".
+    loglevel: str,
-    """
+    testdir,
+    arb_addr: tuple[str, int],
+):
+    '''
+    Run a daemon actor as a "remote arbiter".
+
+    '''
     if loglevel in ('trace', 'debug'):
         # too much logging will lock up the subproc (smh)
         loglevel = 'info'
 
     cmdargs = [
         sys.executable, '-c',
-        "import tractor; tractor.run_daemon([], arbiter_addr={}, loglevel={})"
+        "import tractor; tractor.run_daemon([], registry_addr={}, loglevel={})"
         .format(
             arb_addr,
             "'{}'".format(loglevel) if loglevel else None)

tests/test_advanced_faults.py

@@ -0,0 +1,193 @@
+'''
+Sketchy network blackoutz, ugly byzantine gens, puedes eschuchar la
+cancelacion?..
+
+'''
+from functools import partial
+
+import pytest
+from _pytest.pathlib import import_path
+import trio
+import tractor
+
+from conftest import (
+    examples_dir,
+)
+
+
+@pytest.mark.parametrize(
+    'debug_mode',
+    [False, True],
+    ids=['no_debug_mode', 'debug_mode'],
+)
+@pytest.mark.parametrize(
+    'ipc_break',
+    [
+        # no breaks
+        {
+            'break_parent_ipc_after': False,
+            'break_child_ipc_after': False,
+        },
+
+        # only parent breaks
+        {
+            'break_parent_ipc_after': 500,
+            'break_child_ipc_after': False,
+        },
+
+        # only child breaks
+        {
+            'break_parent_ipc_after': False,
+            'break_child_ipc_after': 500,
+        },
+
+        # both: break parent first
+        {
+            'break_parent_ipc_after': 500,
+            'break_child_ipc_after': 800,
+        },
+        # both: break child first
+        {
+            'break_parent_ipc_after': 800,
+            'break_child_ipc_after': 500,
+        },
+
+    ],
+    ids=[
+        'no_break',
+        'break_parent',
+        'break_child',
+        'break_both_parent_first',
+        'break_both_child_first',
+    ],
+)
+def test_ipc_channel_break_during_stream(
+    debug_mode: bool,
+    spawn_backend: str,
+    ipc_break: dict | None,
+):
+    '''
+    Ensure we can have an IPC channel break its connection during
+    streaming and it's still possible for the (simulated) user to kill
+    the actor tree using SIGINT.
+
+    We also verify the type of connection error expected in the parent
+    depending on which side if the IPC breaks first.
+
+    '''
+    if spawn_backend != 'trio':
+        if debug_mode:
+            pytest.skip('`debug_mode` only supported on `trio` spawner')
+
+        # non-`trio` spawners should never hit the hang condition that
+        # requires the user to do ctl-c to cancel the actor tree.
+        expect_final_exc = trio.ClosedResourceError
+
+    mod = import_path(
+        examples_dir() / 'advanced_faults' / 'ipc_failure_during_stream.py',
+        root=examples_dir(),
+    )
+
+    expect_final_exc = KeyboardInterrupt
+
+    # when ONLY the child breaks we expect the parent to get a closed
+    # resource error on the next `MsgStream.receive()` and then fail out
+    # and cancel the child from there.
+    if (
+
+        # only child breaks
+        (
+            ipc_break['break_child_ipc_after']
+            and ipc_break['break_parent_ipc_after'] is False
+        )
+
+        # both break but, parent breaks first
+        or (
+            ipc_break['break_child_ipc_after'] is not False
+            and (
+                ipc_break['break_parent_ipc_after']
+                > ipc_break['break_child_ipc_after']
+            )
+        )
+
+    ):
+        expect_final_exc = trio.ClosedResourceError
+
+    # when the parent IPC side dies (even if the child's does as well
+    # but the child fails BEFORE the parent) we expect the channel to be
+    # sent a stop msg from the child at some point which will signal the
+    # parent that the stream has been terminated.
+    # NOTE: when the parent breaks "after" the child you get this same
+    # case as well, the child breaks the IPC channel with a stop msg
+    # before any closure takes place.
+    elif (
+        # only parent breaks
+        (
+            ipc_break['break_parent_ipc_after']
+            and ipc_break['break_child_ipc_after'] is False
+        )
+
+        # both break but, child breaks first
+        or (
+            ipc_break['break_parent_ipc_after'] is not False
+            and (
+                ipc_break['break_child_ipc_after']
+                > ipc_break['break_parent_ipc_after']
+            )
+        )
+    ):
+        expect_final_exc = trio.EndOfChannel
+
+    with pytest.raises(expect_final_exc):
+        trio.run(
+            partial(
+                mod.main,
+                debug_mode=debug_mode,
+                start_method=spawn_backend,
+                **ipc_break,
+            )
+        )
+
+
+@tractor.context
+async def break_ipc_after_started(
+    ctx: tractor.Context,
+) -> None:
+    await ctx.started()
+    async with ctx.open_stream() as stream:
+        await stream.aclose()
+        await trio.sleep(0.2)
+        await ctx.chan.send(None)
+        print('child broke IPC and terminating')
+
+
+def test_stream_closed_right_after_ipc_break_and_zombie_lord_engages():
+    '''
+    Verify that is a subactor's IPC goes down just after bringing up a stream
+    the parent can trigger a SIGINT and the child will be reaped out-of-IPC by
+    the localhost process supervision machinery: aka "zombie lord".
+
+    '''
+    async def main():
+        async with tractor.open_nursery() as n:
+            portal = await n.start_actor(
+                'ipc_breaker',
+                enable_modules=[__name__],
+            )
+
+            with trio.move_on_after(1):
+                async with (
+                    portal.open_context(
+                        break_ipc_after_started
+                    ) as (ctx, sent),
+                ):
+                    async with ctx.open_stream():
+                        await trio.sleep(0.5)
+
+                    print('parent waiting on context')
+
+            print('parent exited context')
+            raise KeyboardInterrupt
+
+    with pytest.raises(KeyboardInterrupt):
+        trio.run(main)

tests/test_advanced_streaming.py

@@ -14,7 +14,7 @@ def is_win():
     return platform.system() == 'Windows'
 
 
-_registry: dict[str, set[tractor.ReceiveMsgStream]] = {
+_registry: dict[str, set[tractor.MsgStream]] = {
     'even': set(),
     'odd': set(),
 }

tests/test_debugger.py

@@ -14,6 +14,7 @@ import itertools
 from os import path
 from typing import Optional
 import platform
+import pathlib
 import sys
 import time
 
@@ -24,7 +25,10 @@ from pexpect.exceptions import (
     EOF,
 )
 
-from conftest import repodir, _ci_env
+from conftest import (
+    examples_dir,
+    _ci_env,
+)
 
 # TODO: The next great debugger audit could be done by you!
 # - recurrent entry to breakpoint() from single actor *after* and an
@@ -43,19 +47,13 @@ if platform.system() == 'Windows':
     )
 
 
-def examples_dir():
-    """Return the abspath to the examples directory.
-    """
-    return path.join(repodir(), 'examples', 'debugging/')
-
-
 def mk_cmd(ex_name: str) -> str:
-    """Generate a command suitable to pass to ``pexpect.spawn()``.
+    '''
-    """
+    Generate a command suitable to pass to ``pexpect.spawn()``.
-    return ' '.join(
+
-        ['python',
+    '''
-         path.join(examples_dir(), f'{ex_name}.py')]
+    script_path: pathlib.Path = examples_dir() / 'debugging' / f'{ex_name}.py'
-    )
+    return ' '.join(['python', str(script_path)])
 
 
 # TODO: was trying to this xfail style but some weird bug i see in CI
@@ -97,7 +95,7 @@ def spawn(
     return _spawn
 
 
-PROMPT = r"\(Pdb\+\+\)"
+PROMPT = r"\(Pdb\+\)"
 
 
 def expect(
@@ -153,27 +151,14 @@ def ctlc(
 
     use_ctlc = request.param
 
-    if (
-        sys.version_info <= (3, 10)
-        and use_ctlc
-    ):
-        # on 3.9 it seems the REPL UX
-        # is highly unreliable and frankly annoying
-        # to test for. It does work from manual testing
-        # but i just don't think it's wroth it to try
-        # and get this working especially since we want to
-        # be 3.10+ mega-asap.
-        pytest.skip('Py3.9 and `pdbpp` son no bueno..')
-
-    if ci_env:
     node = request.node
     markers = node.own_markers
     for mark in markers:
         if mark.name == 'has_nested_actors':
             pytest.skip(
-                    f'Test for {node} uses nested actors and fails in CI\n'
+                f'Test {node} has nested actors and fails with Ctrl-C.\n'
-                    f'The test seems to run fine locally but until we solve'
+                f'The test can sometimes run fine locally but until'
-                    'this issue this CI test will be xfail:\n'
+                ' we solve' 'this issue this CI test will be xfail:\n'
                 'https://github.com/goodboy/tractor/issues/320'
             )
 
@@ -196,13 +181,15 @@ def ctlc(
     ids=lambda item: f'{item[0]} -> {item[1]}',
 )
 def test_root_actor_error(spawn, user_in_out):
-    """Demonstrate crash handler entering pdbpp from basic error in root actor.
+    '''
-    """
+    Demonstrate crash handler entering pdb from basic error in root actor.
+
+    '''
     user_input, expect_err_str = user_in_out
 
     child = spawn('root_actor_error')
 
-    # scan for the pdbpp prompt
+    # scan for the prompt
     expect(child, PROMPT)
 
     before = str(child.before.decode())
@@ -233,8 +220,8 @@ def test_root_actor_bp(spawn, user_in_out):
     user_input, expect_err_str = user_in_out
     child = spawn('root_actor_breakpoint')
 
-    # scan for the pdbpp prompt
+    # scan for the prompt
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     assert 'Error' not in str(child.before)
 
@@ -275,7 +262,7 @@ def do_ctlc(
         if expect_prompt:
             before = str(child.before.decode())
             time.sleep(delay)
-            child.expect(r"\(Pdb\+\+\)")
+            child.expect(PROMPT)
             time.sleep(delay)
 
             if patt:
@@ -294,7 +281,7 @@ def test_root_actor_bp_forever(
     # entries
     for _ in range(10):
 
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
 
         if ctlc:
             do_ctlc(child)
@@ -304,7 +291,7 @@ def test_root_actor_bp_forever(
     # do one continue which should trigger a
     # new task to lock the tty
     child.sendline('continue')
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     # seems that if we hit ctrl-c too fast the
     # sigint guard machinery might not kick in..
@@ -315,10 +302,10 @@ def test_root_actor_bp_forever(
 
     # XXX: this previously caused a bug!
     child.sendline('n')
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     child.sendline('n')
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     # quit out of the loop
     child.sendline('q')
@@ -341,8 +328,8 @@ def test_subactor_error(
     '''
     child = spawn('subactor_error')
 
-    # scan for the pdbpp prompt
+    # scan for the prompt
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     before = str(child.before.decode())
     assert "Attaching to pdb in crashed actor: ('name_error'" in before
@@ -362,7 +349,7 @@ def test_subactor_error(
         # creating actor
         child.sendline('continue')
 
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
     before = str(child.before.decode())
 
     # root actor gets debugger engaged
@@ -389,8 +376,8 @@ def test_subactor_breakpoint(
 
     child = spawn('subactor_breakpoint')
 
-    # scan for the pdbpp prompt
+    # scan for the prompt
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     before = str(child.before.decode())
     assert "Attaching pdb to actor: ('breakpoint_forever'" in before
@@ -399,7 +386,7 @@ def test_subactor_breakpoint(
     # entries
     for _ in range(10):
         child.sendline('next')
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
 
         if ctlc:
             do_ctlc(child)
@@ -407,7 +394,7 @@ def test_subactor_breakpoint(
     # now run some "continues" to show re-entries
     for _ in range(5):
         child.sendline('continue')
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
         before = str(child.before.decode())
         assert "Attaching pdb to actor: ('breakpoint_forever'" in before
 
@@ -418,7 +405,7 @@ def test_subactor_breakpoint(
     child.sendline('q')
 
     # child process should exit but parent will capture pdb.BdbQuit
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     before = str(child.before.decode())
     assert "RemoteActorError: ('breakpoint_forever'" in before
@@ -450,8 +437,8 @@ def test_multi_subactors(
     '''
     child = spawn(r'multi_subactors')
 
-    # scan for the pdbpp prompt
+    # scan for the prompt
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     before = str(child.before.decode())
     assert "Attaching pdb to actor: ('breakpoint_forever'" in before
@@ -463,7 +450,7 @@ def test_multi_subactors(
     # entries
     for _ in range(10):
         child.sendline('next')
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
 
         if ctlc:
             do_ctlc(child)
@@ -472,7 +459,7 @@ def test_multi_subactors(
     child.sendline('c')
 
     # first name_error failure
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
     before = str(child.before.decode())
     assert "Attaching to pdb in crashed actor: ('name_error'" in before
     assert "NameError" in before
@@ -484,7 +471,7 @@ def test_multi_subactors(
     child.sendline('c')
 
     # 2nd name_error failure
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     # TODO: will we ever get the race where this crash will show up?
     # blocklist strat now prevents this crash
@@ -498,7 +485,7 @@ def test_multi_subactors(
 
     # breakpoint loop should re-engage
     child.sendline('c')
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
     before = str(child.before.decode())
     assert "Attaching pdb to actor: ('breakpoint_forever'" in before
 
@@ -514,7 +501,7 @@ def test_multi_subactors(
     ):
         child.sendline('c')
         time.sleep(0.1)
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
         before = str(child.before.decode())
 
         if ctlc:
@@ -533,11 +520,11 @@ def test_multi_subactors(
     # now run some "continues" to show re-entries
     for _ in range(5):
         child.sendline('c')
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
 
     # quit the loop and expect parent to attach
     child.sendline('q')
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
     before = str(child.before.decode())
 
     assert_before(child, [
@@ -581,7 +568,7 @@ def test_multi_daemon_subactors(
     '''
     child = spawn('multi_daemon_subactors')
 
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     # there can be a race for which subactor will acquire
     # the root's tty lock first so anticipate either crash
@@ -611,7 +598,7 @@ def test_multi_daemon_subactors(
     # second entry by `bp_forever`.
 
     child.sendline('c')
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
     assert_before(child, [next_msg])
 
     # XXX: hooray the root clobbering the child here was fixed!
@@ -633,7 +620,7 @@ def test_multi_daemon_subactors(
 
     # expect another breakpoint actor entry
     child.sendline('c')
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     try:
         assert_before(child, [bp_forever_msg])
@@ -649,7 +636,7 @@ def test_multi_daemon_subactors(
         # after 1 or more further bp actor entries.
 
         child.sendline('c')
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
         assert_before(child, [name_error_msg])
 
     # wait for final error in root
@@ -657,7 +644,7 @@ def test_multi_daemon_subactors(
     while True:
         try:
             child.sendline('c')
-            child.expect(r"\(Pdb\+\+\)")
+            child.expect(PROMPT)
             assert_before(
                 child,
                 [bp_forever_msg]
@@ -690,8 +677,8 @@ def test_multi_subactors_root_errors(
     '''
     child = spawn('multi_subactor_root_errors')
 
-    # scan for the pdbpp prompt
+    # scan for the prompt
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     # at most one subactor should attach before the root is cancelled
     before = str(child.before.decode())
@@ -706,7 +693,7 @@ def test_multi_subactors_root_errors(
 
     # due to block list strat from #337, this will no longer
     # propagate before the root errors and cancels the spawner sub-tree.
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     # only if the blocking condition doesn't kick in fast enough
     before = str(child.before.decode())
@@ -721,7 +708,7 @@ def test_multi_subactors_root_errors(
             do_ctlc(child)
 
         child.sendline('c')
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
 
     # check if the spawner crashed or was blocked from debug
     # and if this intermediary attached check the boxed error
@@ -738,7 +725,7 @@ def test_multi_subactors_root_errors(
             do_ctlc(child)
 
         child.sendline('c')
-        child.expect(r"\(Pdb\+\+\)")
+        child.expect(PROMPT)
 
     # expect a root actor crash
     assert_before(child, [
@@ -787,7 +774,7 @@ def test_multi_nested_subactors_error_through_nurseries(
 
     for send_char in itertools.cycle(['c', 'q']):
         try:
-            child.expect(r"\(Pdb\+\+\)")
+            child.expect(PROMPT)
             child.sendline(send_char)
             time.sleep(0.01)
 
@@ -829,7 +816,7 @@ def test_root_nursery_cancels_before_child_releases_tty_lock(
 
     child = spawn('root_cancelled_but_child_is_in_tty_lock')
 
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     before = str(child.before.decode())
     assert "NameError: name 'doggypants' is not defined" in before
@@ -844,7 +831,7 @@ def test_root_nursery_cancels_before_child_releases_tty_lock(
     for i in range(4):
         time.sleep(0.5)
         try:
-            child.expect(r"\(Pdb\+\+\)")
+            child.expect(PROMPT)
 
         except (
             EOF,
@@ -901,7 +888,7 @@ def test_root_cancels_child_context_during_startup(
     '''
     child = spawn('fast_error_in_root_after_spawn')
 
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     before = str(child.before.decode())
     assert "AssertionError" in before
@@ -918,7 +905,7 @@ def test_different_debug_mode_per_actor(
     ctlc: bool,
 ):
     child = spawn('per_actor_debug')
-    child.expect(r"\(Pdb\+\+\)")
+    child.expect(PROMPT)
 
     # only one actor should enter the debugger
     before = str(child.before.decode())

tests/test_docs_examples.py

@@ -12,17 +12,17 @@ import shutil
 
 import pytest
 
-from conftest import repodir
+from conftest import (
-
+    examples_dir,
-
+)
-def examples_dir():
-    """Return the abspath to the examples directory.
-    """
-    return os.path.join(repodir(), 'examples')
 
 
 @pytest.fixture
-def run_example_in_subproc(loglevel, testdir, arb_addr):
+def run_example_in_subproc(
+    loglevel: str,
+    testdir,
+    arb_addr: tuple[str, int],
+):
 
     @contextmanager
     def run(script_code):
@@ -32,8 +32,8 @@ def run_example_in_subproc(loglevel, testdir, arb_addr):
             # on windows we need to create a special __main__.py which will
             # be executed with ``python -m <modulename>`` on windows..
             shutil.copyfile(
-                os.path.join(examples_dir(), '__main__.py'),
+                examples_dir() / '__main__.py',
-                os.path.join(str(testdir), '__main__.py')
+                str(testdir / '__main__.py'),
             )
 
             # drop the ``if __name__ == '__main__'`` guard onwards from
@@ -88,6 +88,7 @@ def run_example_in_subproc(loglevel, testdir, arb_addr):
         and f[0] != '_'
         and 'debugging' not in p[0]
         and 'integration' not in p[0]
+        and 'advanced_faults' not in p[0]
     ],
 
     ids=lambda t: t[1],

tests/test_legacy_one_way_streaming.py

@@ -251,7 +251,7 @@ def test_a_quadruple_example(time_quad_ex, ci_env, spawn_backend):
 
     results, diff = time_quad_ex
     assert results
-    this_fast = 6 if platform.system() in ('Windows', 'Darwin') else 2.666
+    this_fast = 6 if platform.system() in ('Windows', 'Darwin') else 3
     assert diff < this_fast
 
 

tests/test_task_broadcasting.py

@@ -12,7 +12,10 @@ import pytest
 import trio
 from trio.lowlevel import current_task
 import tractor
-from tractor.trionics import broadcast_receiver, Lagged
+from tractor.trionics import (
+    broadcast_receiver,
+    Lagged,
+)
 
 
 @tractor.context
@@ -37,7 +40,7 @@ async def echo_sequences(
 
 async def ensure_sequence(
 
-    stream: tractor.ReceiveMsgStream,
+    stream: tractor.MsgStream,
     sequence: list,
     delay: Optional[float] = None,
 
@@ -211,7 +214,8 @@ def test_faster_task_to_recv_is_cancelled_by_slower(
     arb_addr,
     start_method,
 ):
-    '''Ensure that if a faster task consuming from a stream is cancelled
+    '''
+    Ensure that if a faster task consuming from a stream is cancelled
     the slower task can continue to receive all expected values.
 
     '''
@@ -460,3 +464,51 @@ def test_first_recver_is_cancelled():
                     assert value == 1
 
     trio.run(main)
+
+
+def test_no_raise_on_lag():
+    '''
+    Run a simple 2-task broadcast where one task is slow but configured
+    so that it does not raise `Lagged` on overruns using
+    `raise_on_lasg=False` and verify that the task does not raise.
+
+    '''
+    size = 100
+    tx, rx = trio.open_memory_channel(size)
+    brx = broadcast_receiver(rx, size)
+
+    async def slow():
+        async with brx.subscribe(
+            raise_on_lag=False,
+        ) as br:
+            async for msg in br:
+                print(f'slow task got: {msg}')
+                await trio.sleep(0.1)
+
+    async def fast():
+        async with brx.subscribe() as br:
+            async for msg in br:
+                print(f'fast task got: {msg}')
+
+    async def main():
+        async with (
+            tractor.open_root_actor(
+                # NOTE: so we see the warning msg emitted by the bcaster
+                # internals when the no raise flag is set.
+                loglevel='warning',
+            ),
+            trio.open_nursery() as n,
+        ):
+            n.start_soon(slow)
+            n.start_soon(fast)
+
+            for i in range(1000):
+                await tx.send(i)
+
+            # simulate user nailing ctl-c after realizing
+            # there's a lag in the slow task.
+            await trio.sleep(1)
+            raise KeyboardInterrupt
+
+    with pytest.raises(KeyboardInterrupt):
+        trio.run(main)

tractor/__init__.py

@@ -24,7 +24,6 @@ from ._clustering import open_actor_cluster
 from ._ipc import Channel
 from ._streaming import (
     Context,
-    ReceiveMsgStream,
     MsgStream,
     stream,
     context,
@@ -45,7 +44,10 @@ from ._exceptions import (
     ModuleNotExposed,
     ContextCancelled,
 )
-from ._debug import breakpoint, post_mortem
+from ._debug import (
+    breakpoint,
+    post_mortem,
+)
 from . import msg
 from ._root import (
     run_daemon,
@@ -64,7 +66,6 @@ __all__ = [
     'MsgStream',
     'BaseExceptionGroup',
     'Portal',
-    'ReceiveMsgStream',
     'RemoteActorError',
     'breakpoint',
     'context',

tractor/_debug.py

@@ -20,9 +20,13 @@ Multi-core debugging for da peeps!
 """
 from __future__ import annotations
 import bdb
+import os
 import sys
 import signal
-from functools import partial
+from functools import (
+    partial,
+    cached_property,
+)
 from contextlib import asynccontextmanager as acm
 from typing import (
     Any,
@@ -33,6 +37,7 @@ from typing import (
 )
 from types import FrameType
 
+import pdbp
 import tractor
 import trio
 from trio_typing import TaskStatus
@@ -49,17 +54,6 @@ from ._exceptions import (
 )
 from ._ipc import Channel
 
-
-try:
-    # wtf: only exported when installed in dev mode?
-    import pdbpp
-except ImportError:
-    # pdbpp is installed in regular mode...it monkey patches stuff
-    import pdb
-    xpm = getattr(pdb, 'xpm', None)
-    assert xpm, "pdbpp is not installed?"  # type: ignore
-    pdbpp = pdb
-
 log = get_logger(__name__)
 
 
@@ -73,6 +67,7 @@ class Lock:
     Mostly to avoid a lot of ``global`` declarations for now XD.
 
     '''
+    repl: MultiActorPdb | None = None
     # placeholder for function to set a ``trio.Event`` on debugger exit
     # pdb_release_hook: Optional[Callable] = None
 
@@ -111,7 +106,7 @@ class Lock:
     def shield_sigint(cls):
         cls._orig_sigint_handler = signal.signal(
             signal.SIGINT,
-            shield_sigint,
+            shield_sigint_handler,
         )
 
     @classmethod
@@ -146,24 +141,29 @@ class Lock:
         finally:
             # restore original sigint handler
             cls.unshield_sigint()
+            cls.repl = None
 
 
-class TractorConfig(pdbpp.DefaultConfig):
+class TractorConfig(pdbp.DefaultConfig):
     '''
-    Custom ``pdbpp`` goodness.
+    Custom ``pdbp`` goodness :surfer:
 
     '''
-    # use_pygments = True
+    use_pygments: bool = True
-    # sticky_by_default = True
+    sticky_by_default: bool = False
-    enable_hidden_frames = False
+    enable_hidden_frames: bool = False
+
+    # much thanks @mdmintz for the hot tip!
+    # fixes line spacing issue when resizing terminal B)
+    truncate_long_lines: bool = False
 
 
-class MultiActorPdb(pdbpp.Pdb):
+class MultiActorPdb(pdbp.Pdb):
     '''
-    Add teardown hooks to the regular ``pdbpp.Pdb``.
+    Add teardown hooks to the regular ``pdbp.Pdb``.
 
     '''
-    # override the pdbpp config with our coolio one
+    # override the pdbp config with our coolio one
     DefaultConfig = TractorConfig
 
     # def preloop(self):
@@ -184,6 +184,35 @@ class MultiActorPdb(pdbpp.Pdb):
         finally:
             Lock.release()
 
+    # XXX NOTE: we only override this because apparently the stdlib pdb
+    # bois likes to touch the SIGINT handler as much as i like to touch
+    # my d$%&.
+    def _cmdloop(self):
+        self.cmdloop()
+
+    @cached_property
+    def shname(self) -> str | None:
+        '''
+        Attempt to return the login shell name with a special check for
+        the infamous `xonsh` since it seems to have some issues much
+        different from std shells when it comes to flushing the prompt?
+
+        '''
+        # SUPER HACKY and only really works if `xonsh` is not used
+        # before spawning further sub-shells..
+        shpath = os.getenv('SHELL', None)
+
+        if shpath:
+            if (
+                os.getenv('XONSH_LOGIN', default=False)
+                or 'xonsh' in shpath
+            ):
+                return 'xonsh'
+
+            return os.path.basename(shpath)
+
+        return None
+
 
 @acm
 async def _acquire_debug_lock_from_root_task(
@@ -278,7 +307,7 @@ async def lock_tty_for_child(
 ) -> str:
     '''
     Lock the TTY in the root process of an actor tree in a new
-    inter-actor-context-task such that the ``pdbpp`` debugger console
+    inter-actor-context-task such that the ``pdbp`` debugger console
     can be mutex-allocated to the calling sub-actor for REPL control
     without interference by other processes / threads.
 
@@ -388,6 +417,7 @@ async def wait_for_parent_stdin_hijack(
 
         except ContextCancelled:
             log.warning('Root actor cancelled debug lock')
+            raise
 
         finally:
             Lock.local_task_in_debug = None
@@ -397,7 +427,7 @@ async def wait_for_parent_stdin_hijack(
 def mk_mpdb() -> tuple[MultiActorPdb, Callable]:
 
     pdb = MultiActorPdb()
-    # signal.signal = pdbpp.hideframe(signal.signal)
+    # signal.signal = pdbp.hideframe(signal.signal)
 
     Lock.shield_sigint()
 
@@ -435,7 +465,10 @@ async def _breakpoint(
     # with trio.CancelScope(shield=shield):
     #     await trio.lowlevel.checkpoint()
 
-    if not Lock.local_pdb_complete or Lock.local_pdb_complete.is_set():
+    if (
+        not Lock.local_pdb_complete
+        or Lock.local_pdb_complete.is_set()
+    ):
         Lock.local_pdb_complete = trio.Event()
 
     # TODO: need a more robust check for the "root" actor
@@ -484,6 +517,7 @@ async def _breakpoint(
                     wait_for_parent_stdin_hijack,
                     actor.uid,
                 )
+                Lock.repl = pdb
         except RuntimeError:
             Lock.release()
 
@@ -522,6 +556,7 @@ async def _breakpoint(
 
         Lock.global_actor_in_debug = actor.uid
         Lock.local_task_in_debug = task_name
+        Lock.repl = pdb
 
     try:
         # block here one (at the appropriate frame *up*) where
@@ -542,13 +577,13 @@ async def _breakpoint(
     #     # frame = sys._getframe()
     #     # last_f = frame.f_back
     #     # last_f.f_globals['__tracebackhide__'] = True
-    #     # signal.signal = pdbpp.hideframe(signal.signal)
+    #     # signal.signal = pdbp.hideframe(signal.signal)
 
 
-def shield_sigint(
+def shield_sigint_handler(
     signum: int,
     frame: 'frame',  # type: ignore # noqa
-    pdb_obj: Optional[MultiActorPdb] = None,
+    # pdb_obj: Optional[MultiActorPdb] = None,
     *args,
 
 ) -> None:
@@ -565,6 +600,7 @@ def shield_sigint(
     uid_in_debug = Lock.global_actor_in_debug
 
     actor = tractor.current_actor()
+    # print(f'{actor.uid} in HANDLER with ')
 
     def do_cancel():
         # If we haven't tried to cancel the runtime then do that instead
@@ -598,6 +634,9 @@ def shield_sigint(
                 )
                 return do_cancel()
 
+    # only set in the actor actually running the REPL
+    pdb_obj = Lock.repl
+
     # root actor branch that reports whether or not a child
     # has locked debugger.
     if (
@@ -612,10 +651,12 @@ def shield_sigint(
     ):
         # we are root and some actor is in debug mode
         # if uid_in_debug is not None:
+
+        if pdb_obj:
             name = uid_in_debug[0]
             if name != 'root':
                 log.pdb(
-                f"Ignoring SIGINT while child in debug mode: `{uid_in_debug}`"
+                    f"Ignoring SIGINT, child in debug mode: `{uid_in_debug}`"
                 )
 
             else:
@@ -625,19 +666,19 @@ def shield_sigint(
     elif (
         is_root_process()
     ):
+        if pdb_obj:
             log.pdb(
                 "Ignoring SIGINT since debug mode is enabled"
             )
 
-        # revert back to ``trio`` handler asap!
-        Lock.unshield_sigint()
         if (
             Lock._root_local_task_cs_in_debug
             and not Lock._root_local_task_cs_in_debug.cancel_called
         ):
             Lock._root_local_task_cs_in_debug.cancel()
 
-        # raise KeyboardInterrupt
+            # revert back to ``trio`` handler asap!
+            Lock.unshield_sigint()
 
     # child actor that has locked the debugger
     elif not is_root_process():
@@ -653,7 +694,10 @@ def shield_sigint(
             return do_cancel()
 
         task = Lock.local_task_in_debug
-        if task:
+        if (
+            task
+            and pdb_obj
+        ):
             log.pdb(
                 f"Ignoring SIGINT while task in debug mode: `{task}`"
             )
@@ -668,14 +712,21 @@ def shield_sigint(
         raise KeyboardInterrupt
 
     # NOTE: currently (at least on ``fancycompleter`` 0.9.2)
-    # it lookks to be that the last command that was run (eg. ll)
+    # it looks to be that the last command that was run (eg. ll)
     # will be repeated by default.
 
-    # TODO: maybe redraw/print last REPL output to console
+    # maybe redraw/print last REPL output to console since
+    # we want to alert the user that more input is expect since
+    # nothing has been done dur to ignoring sigint.
     if (
-        pdb_obj
+        pdb_obj  # only when this actor has a REPL engaged
-        and sys.version_info <= (3, 10)
     ):
+        # XXX: yah, mega hack, but how else do we catch this madness XD
+        if pdb_obj.shname == 'xonsh':
+            pdb_obj.stdout.write(pdb_obj.prompt)
+
+        pdb_obj.stdout.flush()
+
         # TODO: make this work like sticky mode where if there is output
         # detected as written to the tty we redraw this part underneath
         # and erase the past draw of this same bit above?
@@ -686,21 +737,13 @@ def shield_sigint(
         # https://github.com/goodboy/tractor/issues/130#issuecomment-663752040
         # https://github.com/prompt-toolkit/python-prompt-toolkit/blob/c2c6af8a0308f9e5d7c0e28cb8a02963fe0ce07a/prompt_toolkit/patch_stdout.py
 
-        # XXX: lol, see ``pdbpp`` issue:
+        # XXX LEGACY: lol, see ``pdbpp`` issue:
         # https://github.com/pdbpp/pdbpp/issues/496
 
-        # TODO: pretty sure this is what we should expect to have to run
-        # in total but for now we're just going to wait until `pdbpp`
-        # figures out it's own stuff on 3.10 (and maybe we'll help).
-        # pdb_obj.do_longlist(None)
-
-        # XXX: we were doing this but it shouldn't be required..
-        print(pdb_obj.prompt, end='', flush=True)
-
 
 def _set_trace(
-    actor: Optional[tractor.Actor] = None,
+    actor: tractor.Actor | None = None,
-    pdb: Optional[MultiActorPdb] = None,
+    pdb: MultiActorPdb | None = None,
 ):
     __tracebackhide__ = True
     actor = actor or tractor.current_actor()
@@ -710,7 +753,11 @@ def _set_trace(
     if frame:
         frame = frame.f_back  # type: ignore
 
-    if frame and pdb and actor is not None:
+    if (
+        frame
+        and pdb
+        and actor is not None
+    ):
         log.pdb(f"\nAttaching pdb to actor: {actor.uid}\n")
         # no f!#$&* idea, but when we're in async land
         # we need 2x frames up?
@@ -719,7 +766,8 @@ def _set_trace(
     else:
         pdb, undo_sigint = mk_mpdb()
 
-        # we entered the global ``breakpoint()`` built-in from sync code?
+        # we entered the global ``breakpoint()`` built-in from sync
+        # code?
         Lock.local_task_in_debug = 'sync'
 
     pdb.set_trace(frame=frame)
@@ -749,7 +797,7 @@ def _post_mortem(
     # https://github.com/pdbpp/pdbpp/issues/480
     # TODO: help with a 3.10+ major release if/when it arrives.
 
-    pdbpp.xpm(Pdb=lambda: pdb)
+    pdbp.xpm(Pdb=lambda: pdb)
 
 
 post_mortem = partial(
@@ -820,7 +868,10 @@ async def maybe_wait_for_debugger(
 
 ) -> None:
 
-    if not debug_mode() and not child_in_debug:
+    if (
+        not debug_mode()
+        and not child_in_debug
+    ):
         return
 
     if (

tractor/_portal.py

@@ -45,7 +45,10 @@ from ._exceptions import (
     NoResult,
     ContextCancelled,
 )
-from ._streaming import Context, ReceiveMsgStream
+from ._streaming import (
+    Context,
+    MsgStream,
+)
 
 
 log = get_logger(__name__)
@@ -101,7 +104,7 @@ class Portal:
         # it is expected that ``result()`` will be awaited at some
         # point.
         self._expect_result: Optional[Context] = None
-        self._streams: set[ReceiveMsgStream] = set()
+        self._streams: set[MsgStream] = set()
         self.actor = current_actor()
 
     async def _submit_for_result(
@@ -316,7 +319,7 @@ class Portal:
         async_gen_func: Callable,  # typing: ignore
         **kwargs,
 
-    ) -> AsyncGenerator[ReceiveMsgStream, None]:
+    ) -> AsyncGenerator[MsgStream, None]:
 
         if not inspect.isasyncgenfunction(async_gen_func):
             if not (
@@ -341,7 +344,7 @@ class Portal:
 
         try:
             # deliver receive only stream
-            async with ReceiveMsgStream(
+            async with MsgStream(
                 ctx, ctx._recv_chan,
             ) as rchan:
                 self._streams.add(rchan)
@@ -497,6 +500,10 @@ class Portal:
                     f'actor: {uid}'
                 )
                 result = await ctx.result()
+                log.runtime(
+                    f'Context {fn_name} returned '
+                    f'value from callee `{result}`'
+                )
 
             # though it should be impossible for any tasks
             # operating *in* this scope to have survived
@@ -518,12 +525,6 @@ class Portal:
                         f'task:{cid}\n'
                         f'actor:{uid}'
                     )
-            else:
-                log.runtime(
-                    f'Context {fn_name} returned '
-                    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

tractor/_root.py

@@ -22,11 +22,9 @@ from contextlib import asynccontextmanager
 from functools import partial
 import importlib
 import logging
-import os
 import signal
-from typing import (
+import sys
-    Optional,
+import os
-)
 import typing
 import warnings
 
@@ -58,27 +56,28 @@ logger = log.get_logger('tractor')
 @asynccontextmanager
 async def open_root_actor(
 
+    *,
     # defaults are above
-    arbiter_addr: Optional[tuple[str, int]] = (
+    arbiter_addr: tuple[str, int] | None = None,
-        _default_arbiter_host,
-        _default_arbiter_port,
-    ),
 
-    name: Optional[str] = 'root',
+    # defaults are above
+    registry_addr: tuple[str, int] | None = None,
+
+    name: str | None = 'root',
 
     # either the `multiprocessing` start method:
     # https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods
     # OR `trio` (the new default).
-    start_method: Optional[_spawn.SpawnMethodKey] = None,
+    start_method: _spawn.SpawnMethodKey | None = None,
 
     # enables the multi-process debugger support
     debug_mode: bool = False,
 
     # internal logging
-    loglevel: Optional[str] = None,
+    loglevel: str | None = None,
 
-    enable_modules: Optional[list] = None,
+    enable_modules: list | None = None,
-    rpc_module_paths: Optional[list] = None,
+    rpc_module_paths: list | None = None,
 
 ) -> typing.Any:
     '''
@@ -86,8 +85,10 @@ async def open_root_actor(
 
     '''
     # Override the global debugger hook to make it play nice with
-    # ``trio``, see:
+    # ``trio``, see much discussion in:
     # https://github.com/python-trio/trio/issues/1155#issuecomment-742964018
+    builtin_bp_handler = sys.breakpointhook
+    orig_bp_path: str | None = os.environ.get('PYTHONBREAKPOINT', None)
     os.environ['PYTHONBREAKPOINT'] = 'tractor._debug._set_trace'
 
     # attempt to retreive ``trio``'s sigint handler and stash it
@@ -112,10 +113,22 @@ async def open_root_actor(
     if start_method is not None:
         _spawn.try_set_start_method(start_method)
 
-    arbiter_addr = (host, port) = arbiter_addr or (
+    if arbiter_addr is not None:
+        warnings.warn(
+            '`arbiter_addr` is now deprecated and has been renamed to'
+            '`registry_addr`.\nUse that instead..',
+            DeprecationWarning,
+            stacklevel=2,
+        )
+
+    registry_addr = (host, port) = (
+        registry_addr
+        or arbiter_addr
+        or (
             _default_arbiter_host,
             _default_arbiter_port,
         )
+    )
 
     loglevel = (loglevel or log._default_loglevel).upper()
 
@@ -160,7 +173,7 @@ async def open_root_actor(
 
     except OSError:
         # TODO: make this a "discovery" log level?
-        logger.warning(f"No actor could be found @ {host}:{port}")
+        logger.warning(f"No actor registry found @ {host}:{port}")
 
     # create a local actor and start up its main routine/task
     if arbiter_found:
@@ -170,7 +183,7 @@ async def open_root_actor(
 
         actor = Actor(
             name or 'anonymous',
-            arbiter_addr=arbiter_addr,
+            arbiter_addr=registry_addr,
             loglevel=loglevel,
             enable_modules=enable_modules,
         )
@@ -186,7 +199,7 @@ async def open_root_actor(
 
         actor = Arbiter(
             name or 'arbiter',
-            arbiter_addr=arbiter_addr,
+            arbiter_addr=registry_addr,
             loglevel=loglevel,
             enable_modules=enable_modules,
         )
@@ -243,6 +256,16 @@ async def open_root_actor(
                 logger.cancel("Shutting down root actor")
                 await actor.cancel()
     finally:
+        _state._current_actor = None
+
+        # restore breakpoint hook state
+        sys.breakpointhook = builtin_bp_handler
+        if orig_bp_path is not None:
+            os.environ['PYTHONBREAKPOINT'] = orig_bp_path
+        else:
+            # clear env back to having no entry
+            os.environ.pop('PYTHONBREAKPOINT')
+
         logger.runtime("Root actor terminated")
 
 
@@ -250,13 +273,13 @@ def run_daemon(
     enable_modules: list[str],
 
     # runtime kwargs
-    name: Optional[str] = 'root',
+    name: str | None = 'root',
-    arbiter_addr: tuple[str, int] = (
+    registry_addr: tuple[str, int] = (
         _default_arbiter_host,
         _default_arbiter_port,
     ),
 
-    start_method: Optional[str] = None,
+    start_method: str | None = None,
     debug_mode: bool = False,
     **kwargs
 
@@ -278,7 +301,7 @@ def run_daemon(
     async def _main():
 
         async with open_root_actor(
-            arbiter_addr=arbiter_addr,
+            registry_addr=registry_addr,
             name=name,
             start_method=start_method,
             debug_mode=debug_mode,

tractor/_runtime.py

@@ -228,11 +228,11 @@ async def _invoke(
 
                 fname = func.__name__
                 if ctx._cancel_called:
-                    msg = f'{fname} cancelled itself'
+                    msg = f'`{fname}()` cancelled itself'
 
                 elif cs.cancel_called:
                     msg = (
-                        f'{fname} was remotely cancelled by its caller '
+                        f'`{fname}()` was remotely cancelled by its caller '
                         f'{ctx.chan.uid}'
                     )
 
@@ -319,7 +319,7 @@ async def _invoke(
             BrokenPipeError,
         ):
             # if we can't propagate the error that's a big boo boo
-            log.error(
+            log.exception(
                 f"Failed to ship error to caller @ {chan.uid} !?"
             )
 
@@ -455,7 +455,7 @@ class Actor:
         self._mods: dict[str, ModuleType] = {}
         self.loglevel = loglevel
 
-        self._arb_addr = (
+        self._arb_addr: tuple[str, int] | None = (
             str(arbiter_addr[0]),
             int(arbiter_addr[1])
         ) if arbiter_addr else None
@@ -488,7 +488,10 @@ class Actor:
         self._parent_chan: Optional[Channel] = None
         self._forkserver_info: Optional[
             tuple[Any, Any, Any, Any, Any]] = None
-        self._actoruid2nursery: dict[Optional[tuple[str, str]], 'ActorNursery'] = {}  # type: ignore  # noqa
+        self._actoruid2nursery: dict[
+            tuple[str, str],
+            ActorNursery | None,
+        ] = {}  # type: ignore  # noqa
 
     async def wait_for_peer(
         self, uid: tuple[str, str]
@@ -1381,6 +1384,7 @@ async def async_main(
             and not actor.is_arbiter
         ):
             failed = False
+            assert isinstance(actor._arb_addr, tuple)
             with trio.move_on_after(0.5) as cs:
                 cs.shield = True
                 try:
@@ -1605,7 +1609,10 @@ async def process_messages(
         # handshake for them (yet) and instead we simply bail out of
         # the message loop and expect the teardown sequence to clean
         # up.
-        log.runtime(f'channel from {chan.uid} closed abruptly:\n{chan}')
+        log.runtime(
+            f'channel from {chan.uid} closed abruptly:\n'
+            f'-> {chan.raddr}\n'
+        )
 
         # transport **was** disconnected
         return True

tractor/_spawn.py

@@ -23,13 +23,12 @@ import sys
 import platform
 from typing import (
     Any,
+    Awaitable,
     Literal,
-    Optional,
     Callable,
     TypeVar,
     TYPE_CHECKING,
 )
-from collections.abc import Awaitable
 
 from exceptiongroup import BaseExceptionGroup
 import trio
@@ -60,7 +59,7 @@ if TYPE_CHECKING:
 log = get_logger('tractor')
 
 # placeholder for an mp start context if so using that backend
-_ctx: Optional[mp.context.BaseContext] = None
+_ctx: mp.context.BaseContext | None = None
 SpawnMethodKey = Literal[
     'trio',  # supported on all platforms
     'mp_spawn',
@@ -86,7 +85,7 @@ else:
 def try_set_start_method(
     key: SpawnMethodKey
 
-) -> Optional[mp.context.BaseContext]:
+) -> mp.context.BaseContext | None:
     '''
     Attempt to set the method for process starting, aka the "actor
     spawning backend".
@@ -200,16 +199,37 @@ async def cancel_on_completion(
 async def do_hard_kill(
     proc: trio.Process,
     terminate_after: int = 3,
+
 ) -> None:
     # NOTE: this timeout used to do nothing since we were shielding
     # the ``.wait()`` inside ``new_proc()`` which will pretty much
     # never release until the process exits, now it acts as
     # a hard-kill time ultimatum.
+    log.debug(f"Terminating {proc}")
     with trio.move_on_after(terminate_after) as cs:
 
-        # NOTE: This ``__aexit__()`` shields internally.
+        # NOTE: code below was copied verbatim from the now deprecated
-        async with proc:  # calls ``trio.Process.aclose()``
+        # (in 0.20.0) ``trio._subrocess.Process.aclose()``, orig doc
-            log.debug(f"Terminating {proc}")
+        # string:
+        #
+        # Close any pipes we have to the process (both input and output)
+        # and wait for it to exit. If cancelled, kills the process and
+        # waits for it to finish exiting before propagating the
+        # cancellation.
+        with trio.CancelScope(shield=True):
+            if proc.stdin is not None:
+                await proc.stdin.aclose()
+            if proc.stdout is not None:
+                await proc.stdout.aclose()
+            if proc.stderr is not None:
+                await proc.stderr.aclose()
+        try:
+            await proc.wait()
+        finally:
+            if proc.returncode is None:
+                proc.kill()
+                with trio.CancelScope(shield=True):
+                    await proc.wait()
 
     if cs.cancelled_caught:
         # XXX: should pretty much never get here unless we have
@@ -260,7 +280,9 @@ async def soft_wait(
 
             if proc.poll() is None:  # type: ignore
                 log.warning(
-                    f'Process still alive after cancel request:\n{uid}')
+                    'Actor still alive after cancel request:\n'
+                    f'{uid}'
+                )
 
                 n.cancel_scope.cancel()
         raise
@@ -353,12 +375,11 @@ async def trio_proc(
         spawn_cmd.append("--asyncio")
 
     cancelled_during_spawn: bool = False
-    proc: Optional[trio.Process] = None
+    proc: trio.Process | None = None
     try:
         try:
             # TODO: needs ``trio_typing`` patch?
-            proc = await trio.lowlevel.open_process(    # type: ignore
+            proc = await trio.lowlevel.open_process(spawn_cmd)
-                spawn_cmd)
 
             log.runtime(f"Started {proc}")
 
@@ -442,8 +463,8 @@ async def trio_proc(
             nursery.cancel_scope.cancel()
 
     finally:
-        # The "hard" reap since no actor zombies are allowed!
+        # XXX NOTE XXX: The "hard" reap since no actor zombies are
-        # XXX: do this **after** cancellation/tearfown to avoid
+        # allowed! Do this **after** cancellation/teardown to avoid
         # killing the process too early.
         if proc:
             log.cancel(f'Hard reap sequence starting for {subactor.uid}')
@@ -457,6 +478,13 @@ async def trio_proc(
                             await proc.wait()
 
                 if is_root_process():
+                    # TODO: solve the following issue where we need
+                    # to do a similar wait like this but in an
+                    # "intermediary" parent actor that itself isn't
+                    # in debug but has a child that is, and we need
+                    # to hold off on relaying SIGINT until that child
+                    # is complete.
+                    # https://github.com/goodboy/tractor/issues/320
                     await maybe_wait_for_debugger(
                         child_in_debug=_runtime_vars.get(
                             '_debug_mode', False),

tractor/_streaming.py

@@ -50,12 +50,13 @@ log = get_logger(__name__)
 # - use __slots__ on ``Context``?
 
 
-class ReceiveMsgStream(trio.abc.ReceiveChannel):
+class MsgStream(trio.abc.Channel):
     '''
-    A IPC message stream for receiving logically sequenced values over
+    A bidirectional message stream for receiving logically sequenced
-    an inter-actor ``Channel``. This is the type returned to a local
+    values over an inter-actor IPC ``Channel``.
-    task which entered either ``Portal.open_stream_from()`` or
+
-    ``Context.open_stream()``.
+    This is the type returned to a local task which entered either
+    ``Portal.open_stream_from()`` or ``Context.open_stream()``.
 
     Termination rules:
 
@@ -69,7 +70,7 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
     '''
     def __init__(
         self,
-        ctx: Context,  # typing: ignore # noqa
+        ctx: 'Context',  # typing: ignore # noqa
         rx_chan: trio.MemoryReceiveChannel,
         _broadcaster: Optional[BroadcastReceiver] = None,
 
@@ -82,9 +83,6 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
         self._eoc: bool = False
         self._closed: bool = False
 
-    def ctx(self) -> Context:
-        return self._ctx
-
     # delegate directly to underlying mem channel
     def receive_nowait(self):
         msg = self._rx_chan.receive_nowait()
@@ -100,6 +98,9 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
         if self._eoc:
             raise trio.EndOfChannel
 
+        if self._closed:
+            raise trio.ClosedResourceError('This stream was closed')
+
         try:
             msg = await self._rx_chan.receive()
             return msg['yield']
@@ -113,6 +114,9 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
             # - 'error'
             # possibly just handle msg['stop'] here!
 
+            if self._closed:
+                raise trio.ClosedResourceError('This stream was closed')
+
             if msg.get('stop') or self._eoc:
                 log.debug(f"{self} was stopped at remote end")
 
@@ -192,7 +196,6 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
             return
 
         self._eoc = True
-        self._closed = True
 
         # NOTE: this is super subtle IPC messaging stuff:
         # Relay stop iteration to far end **iff** we're
@@ -209,12 +212,8 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
 
         # In the bidirectional case, `Context.open_stream()` will create
         # the `Actor._cids2qs` entry from a call to
-        # `Actor.get_context()` and will send the stop message in
+        # `Actor.get_context()` and will call us here to send the stop
-        # ``__aexit__()`` on teardown so it **does not** need to be
+        # msg in ``__aexit__()`` on teardown.
-        # called here.
-        if not self._ctx._portal:
-            # Only for 2 way streams can we can send stop from the
-            # caller side.
         try:
             # NOTE: if this call is cancelled we expect this end to
             # handle as though the stop was never sent (though if it
@@ -231,7 +230,14 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
             # the underlying channel may already have been pulled
             # in which case our stop message is meaningless since
             # it can't traverse the transport.
-                log.debug(f'Channel for {self} was already closed')
+            ctx = self._ctx
+            log.warning(
+                f'Stream was already destroyed?\n'
+                f'actor: {ctx.chan.uid}\n'
+                f'ctx id: {ctx.cid}'
+            )
+
+        self._closed = True
 
         # Do we close the local mem chan ``self._rx_chan`` ??!?
 
@@ -312,15 +318,15 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
         async with self._broadcaster.subscribe() as bstream:
             assert bstream.key != self._broadcaster.key
             assert bstream._recv == self._broadcaster._recv
+
+            # NOTE: we patch on a `.send()` to the bcaster so that the
+            # caller can still conduct 2-way streaming using this
+            # ``bstream`` handle transparently as though it was the msg
+            # stream instance.
+            bstream.send = self.send  # type: ignore
+
             yield bstream
 
-
-class MsgStream(ReceiveMsgStream, trio.abc.Channel):
-    '''
-    Bidirectional message stream for use within an inter-actor actor
-    ``Context```.
-
-    '''
     async def send(
         self,
         data: Any
@@ -384,7 +390,7 @@ class Context:
     # only set on the callee side
     _scope_nursery: Optional[trio.Nursery] = None
 
-    _backpressure: bool = True
+    _backpressure: bool = False
 
     async def send_yield(self, data: Any) -> None:
 
@@ -597,30 +603,23 @@ class Context:
         async with MsgStream(
             ctx=self,
             rx_chan=ctx._recv_chan,
-        ) as rchan:
+        ) as stream:
 
             if self._portal:
-                self._portal._streams.add(rchan)
+                self._portal._streams.add(stream)
 
             try:
                 self._stream_opened = True
 
-                # ensure we aren't cancelled before delivering
+                # XXX: do we need this?
-                # the stream
+                # ensure we aren't cancelled before yielding the stream
                 # await trio.lowlevel.checkpoint()
-                yield rchan
+                yield stream
 
-                # XXX: Make the stream "one-shot use".  On exit, signal
+                # NOTE: Make the stream "one-shot use".  On exit, signal
                 # ``trio.EndOfChannel``/``StopAsyncIteration`` to the
                 # far end.
-                try:
+                await stream.aclose()
-                    await self.send_stop()
-                except trio.BrokenResourceError:
-                    log.warning(
-                        f"Couldn't close: stream already broken?\n"
-                        f'actor: {self.chan.uid}\n'
-                        f'ctx id: {self.cid}'
-                    )
 
             finally:
                 if self._portal:

tractor/_supervise.py

@@ -302,7 +302,7 @@ async def _open_and_supervise_one_cancels_all_nursery(
 ) -> typing.AsyncGenerator[ActorNursery, None]:
 
     # TODO: yay or nay?
-    # __tracebackhide__ = True
+    __tracebackhide__ = True
 
     # the collection of errors retreived from spawned sub-actors
     errors: dict[tuple[str, str], BaseException] = {}

tractor/trionics/_broadcast.py

@@ -23,7 +23,6 @@ from __future__ import annotations
 from abc import abstractmethod
 from collections import deque
 from contextlib import asynccontextmanager
-from dataclasses import dataclass
 from functools import partial
 from operator import ne
 from typing import Optional, Callable, Awaitable, Any, AsyncIterator, Protocol
@@ -33,7 +32,10 @@ import trio
 from trio._core._run import Task
 from trio.abc import ReceiveChannel
 from trio.lowlevel import current_task
+from msgspec import Struct
+from tractor.log import get_logger
 
+log = get_logger(__name__)
 
 # A regular invariant generic type
 T = TypeVar("T")
@@ -86,8 +88,7 @@ class Lagged(trio.TooSlowError):
     '''
 
 
-@dataclass
+class BroadcastState(Struct):
-class BroadcastState:
     '''
     Common state to all receivers of a broadcast.
 
@@ -110,7 +111,35 @@ class BroadcastState:
     eoc: bool = False
 
     # If the broadcaster was cancelled, we might as well track it
-    cancelled: bool = False
+    cancelled: dict[int, Task] = {}
+
+    def statistics(self) -> dict[str, Any]:
+        '''
+        Return broadcast receiver group "statistics" like many of
+        ``trio``'s internal task-sync primitives.
+
+        '''
+        key: int | None
+        ev: trio.Event | None
+
+        subs = self.subs
+        if self.recv_ready is not None:
+            key, ev = self.recv_ready
+        else:
+            key = ev = None
+
+        qlens: dict[int, int] = {}
+        for tid, sz in subs.items():
+            qlens[tid] = sz if sz != -1 else 0
+
+        return {
+            'open_consumers': len(subs),
+            'queued_len_by_task': qlens,
+            'max_buffer_size': self.maxlen,
+            'tasks_waiting': ev.statistics().tasks_waiting if ev else 0,
+            'tasks_cancelled': self.cancelled,
+            'next_value_receiver_id': key,
+        }
 
 
 class BroadcastReceiver(ReceiveChannel):
@@ -128,23 +157,40 @@ class BroadcastReceiver(ReceiveChannel):
         rx_chan: AsyncReceiver,
         state: BroadcastState,
         receive_afunc: Optional[Callable[[], Awaitable[Any]]] = None,
+        raise_on_lag: bool = True,
 
     ) -> None:
 
         # register the original underlying (clone)
         self.key = id(self)
         self._state = state
+
+        # each consumer has an int count which indicates
+        # which index contains the next value that the task has not yet
+        # consumed and thus should read. In the "up-to-date" case the
+        # consumer task must wait for a new value from the underlying
+        # receiver and we use ``-1`` as the sentinel for this state.
         state.subs[self.key] = -1
 
         # underlying for this receiver
         self._rx = rx_chan
         self._recv = receive_afunc or rx_chan.receive
         self._closed: bool = False
+        self._raise_on_lag = raise_on_lag
 
-    async def receive(self) -> ReceiveType:
+    def receive_nowait(
+        self,
+        _key: int | None = None,
+        _state: BroadcastState | None = None,
 
-        key = self.key
+    ) -> Any:
-        state = self._state
+        '''
+        Sync version of `.receive()` which does all the low level work
+        of receiving from the underlying/wrapped receive channel.
+
+        '''
+        key = _key or self.key
+        state = _state or self._state
 
         # TODO: ideally we can make some way to "lock out" the
         # underlying receive channel in some way such that if some task
@@ -177,32 +223,47 @@ class BroadcastReceiver(ReceiveChannel):
                 # return this value."
                 # https://docs.rs/tokio/1.11.0/tokio/sync/broadcast/index.html#lagging
 
+                mxln = state.maxlen
+                lost = seq - mxln
+
                 # decrement to the last value and expect
                 # consumer to either handle the ``Lagged`` and come back
                 # or bail out on its own (thus un-subscribing)
-                state.subs[key] = state.maxlen - 1
+                state.subs[key] = mxln - 1
 
                 # this task was overrun by the producer side
                 task: Task = current_task()
-                raise Lagged(f'Task {task.name} was overrun')
+                msg = f'Task `{task.name}` overrun and dropped `{lost}` values'
+
+                if self._raise_on_lag:
+                    raise Lagged(msg)
+                else:
+                    log.warning(msg)
+                    return self.receive_nowait(_key, _state)
 
             state.subs[key] -= 1
             return value
 
-        # current task already has the latest value **and** is the
+        raise trio.WouldBlock
-        # first task to begin waiting for a new one
+
-        if state.recv_ready is None:
+    async def _receive_from_underlying(
+        self,
+        key: int,
+        state: BroadcastState,
+
+    ) -> ReceiveType:
 
         if self._closed:
             raise trio.ClosedResourceError
 
         event = trio.Event()
+        assert state.recv_ready is None
         state.recv_ready = key, event
 
+        try:
             # if we're cancelled here it should be
             # fine to bail without affecting any other consumers
             # right?
-            try:
             value = await self._recv()
 
             # items with lower indices are "newer"
@@ -220,7 +281,6 @@ class BroadcastReceiver(ReceiveChannel):
             # already retreived the last value
 
             # XXX: which of these impls is fastest?
-
             # subs = state.subs.copy()
             # subs.pop(key)
 
@@ -251,54 +311,85 @@ class BroadcastReceiver(ReceiveChannel):
             # consumers will be awoken with a sequence of -1
             # and will potentially try to rewait the underlying
             # receiver instead of just cancelling immediately.
-                self._state.cancelled = True
+            self._state.cancelled[key] = current_task()
             if event.statistics().tasks_waiting:
                 event.set()
             raise
 
         finally:
-
             # Reset receiver waiter task event for next blocking condition.
             # this MUST be reset even if the above ``.recv()`` call
             # was cancelled to avoid the next consumer from blocking on
             # an event that won't be set!
             state.recv_ready = None
 
+    async def receive(self) -> ReceiveType:
+        key = self.key
+        state = self._state
+
+        try:
+            return self.receive_nowait(
+                _key=key,
+                _state=state,
+            )
+        except trio.WouldBlock:
+            pass
+
+        # current task already has the latest value **and** is the
+        # first task to begin waiting for a new one so we begin blocking
+        # until rescheduled with the a new value from the underlying.
+        if state.recv_ready is None:
+            return await self._receive_from_underlying(key, state)
+
         # This task is all caught up and ready to receive the latest
-        # value, so queue sched it on the internal event.
+        # value, so queue/schedule it to be woken on the next internal
+        # event.
         else:
-            seq = state.subs[key]
+            while state.recv_ready is not None:
-            assert seq == -1  # sanity
+                # seq = state.subs[key]
+                # assert seq == -1  # sanity
                 _, ev = state.recv_ready
                 await ev.wait()
+                try:
+                    return self.receive_nowait(
+                        _key=key,
+                        _state=state,
+                    )
+                except trio.WouldBlock:
+                    if self._closed:
+                        raise trio.ClosedResourceError
 
-            # NOTE: if we ever would like the behaviour where if the
+                    subs = state.subs
-            # first task to recv on the underlying is cancelled but it
+                    if (
-            # still DOES trigger the ``.recv_ready``, event we'll likely need
+                        len(subs) == 1
-            # this logic:
+                        and key in subs
+                        # or cancelled
+                    ):
+                        # XXX: we are the last and only user of this BR so
+                        # likely it makes sense to unwind back to the
+                        # underlying?
+                        # import tractor
+                        # await tractor.breakpoint()
+                        log.warning(
+                            f'Only one sub left for {self}?\n'
+                            'We can probably unwind from breceiver?'
+                        )
 
-            if seq > -1:
-                # stuff from above..
-                seq = state.subs[key]
-
-                value = state.queue[seq]
-                state.subs[key] -= 1
-                return value
-
-            elif seq == -1:
                     # XXX: In the case where the first task to allocate the
-                # ``.recv_ready`` event is cancelled we will be woken with
+                    # ``.recv_ready`` event is cancelled we will be woken
-                # a non-incremented sequence number and thus will read the
+                    # with a non-incremented sequence number (the ``-1``
-                # oldest value if we use that. Instead we need to detect if
+                    # sentinel) and thus will read the oldest value if we
-                # we have not been incremented and then receive again.
+                    # use that. Instead we need to detect if we have not
-                return await self.receive()
+                    # been incremented and then receive again.
+                    # return await self.receive()
 
-            else:
+            return await self._receive_from_underlying(key, state)
-                raise ValueError(f'Invalid sequence {seq}!?')
 
     @asynccontextmanager
     async def subscribe(
         self,
+        raise_on_lag: bool = True,
+
     ) -> AsyncIterator[BroadcastReceiver]:
         '''
         Subscribe for values from this broadcast receiver.
@@ -316,6 +407,7 @@ class BroadcastReceiver(ReceiveChannel):
             rx_chan=self._rx,
             state=state,
             receive_afunc=self._recv,
+            raise_on_lag=raise_on_lag,
         )
         # assert clone in state.subs
         assert br.key in state.subs
@@ -352,7 +444,8 @@ def broadcast_receiver(
 
     recv_chan: AsyncReceiver,
     max_buffer_size: int,
-    **kwargs,
+    receive_afunc: Optional[Callable[[], Awaitable[Any]]] = None,
+    raise_on_lag: bool = True,
 
 ) -> BroadcastReceiver:
 
@@ -363,5 +456,6 @@ def broadcast_receiver(
             maxlen=max_buffer_size,
             subs={},
         ),
-        **kwargs,
+        receive_afunc=receive_afunc,
+        raise_on_lag=raise_on_lag,
     )