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Finally, officially support shielded REPL-ing! 

It's been a long time prepped and now finally implemented!

Offer a `shield: bool` argument from our async `._debug` APIs:
- `await tractor.pause(shield=True)`,
- `await tractor.post_mortem(shield=True)`

^-These-^ can now be used inside cancelled `trio.CancelScope`s,
something very handy when introspecting complex (distributed) system
tear/shut-downs particularly under remote error or (inter-peer)
cancellation conditions B)

Thanks to previous prepping in a prior attempt and various patches from
the rigorous rework of `.devx._debug` internals around typed msg specs,
there ain't much that was needed!

Impl deats
- obvi passthrough `shield` from the public API endpoints (was already
  done from a prior attempt).
- put ad-hoc internal `with trio.CancelScope(shield=shield):` around all
  checkpoints inside `._pause()` for both the root-process and subactor
  case branches.

Add a fairly rigorous example, `examples/debugging/shielded_pause.py`
with a wrapping `pexpect` test, `test_debugger.test_shield_pause()` and
ensure it covers as many cases as i can think of offhand:

- multiple `.pause()` entries in a loop despite parent scope
  cancellation in a subactor RPC task which itself spawns a sub-task.
- a `trio.Nursery.parent_task` which raises, is handled and
  tries to enter and unshielded `.post_mortem()`, which of course
  internally raises `Cancelled` in a `._pause()` checkpoint, so we catch
  the `Cancelled` again and then debug the debugger's internal
  cancellation with specific checks for the particular raising
  checkpoint-LOC.
- do ^- the latter -^ for both subactor and root cases to ensure we
  can debug `._pause()` itself when it tries to REPL engage from
  a cancelled task scope Bo
runtime_to_msgspec
Tyler Goodlet 2024-05-30 17:52:24 -04:00
parent 13ea500a44
commit 8ea0f08386
3 changed files with 199 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

88
examples/debugging/shielded_pause.py 100644
View File

@ -0,0 +1,88 @@
import trio
import tractor
async def cancellable_pause_loop(
task_status: trio.TaskStatus[trio.CancelScope] = trio.TASK_STATUS_IGNORED
):
with trio.CancelScope() as cs:
task_status.started(cs)
for _ in range(3):
try:
# ON first entry, there is no level triggered
# cancellation yet, so this cp does a parent task
# ctx-switch so that this scope raises for the NEXT
# checkpoint we hit.
await trio.lowlevel.checkpoint()
await tractor.pause()
cs.cancel()
# parent should have called `cs.cancel()` by now
await trio.lowlevel.checkpoint()
except trio.Cancelled:
print('INSIDE SHIELDED PAUSE')
await tractor.pause(shield=True)
else:
# should raise it again, bubbling up to parent
print('BUBBLING trio.Cancelled to parent task-nursery')
await trio.lowlevel.checkpoint()
async def pm_on_cancelled():
async with trio.open_nursery() as tn:
tn.cancel_scope.cancel()
try:
await trio.sleep_forever()
except trio.Cancelled:
# should also raise `Cancelled` since
# we didn't pass `shield=True`.
try:
await tractor.post_mortem(hide_tb=False)
except trio.Cancelled as taskc:
# should enter just fine, in fact it should
# be debugging the internals of the previous
# sin-shield call above Bo
await tractor.post_mortem(
hide_tb=False,
shield=True,
)
raise taskc
else:
raise RuntimeError('Dint cancel as expected!?')
async def cancelled_before_pause(
):
'''
Verify that using a shielded pause works despite surrounding
cancellation called state in the calling task.
'''
async with trio.open_nursery() as tn:
cs: trio.CancelScope = await tn.start(cancellable_pause_loop)
await trio.sleep(0.1)
assert cs.cancelled_caught
await pm_on_cancelled()
async def main():
async with tractor.open_nursery(
debug_mode=True,
) as n:
portal: tractor.Portal = await n.run_in_actor(
cancelled_before_pause,
)
await portal.result()
# ensure the same works in the root actor!
await pm_on_cancelled()
if __name__ == '__main__':
trio.run(main)

79
tests/test_debugger.py
View File

@ -1234,6 +1234,81 @@ def test_post_mortem_api(
child.expect(pexpect.EOF)
def test_shield_pause(
spawn,
):
'''
Verify the `tractor.pause()/.post_mortem()` API works inside an
already cancelled `trio.CancelScope` and that you can step to the
next checkpoint wherein the cancelled will get raised.
'''
child = spawn('shielded_pause')
# First entry is via manual `.post_mortem()`
child.expect(PROMPT)
assert_before(
child,
[
_pause_msg,
"cancellable_pause_loop'",
"('cancelled_before_pause'", # actor name
]
)
# since 3 tries in ex. shield pause loop
for i in range(3):
child.sendline('c')
child.expect(PROMPT)
assert_before(
child,
[
_pause_msg,
"INSIDE SHIELDED PAUSE",
"('cancelled_before_pause'", # actor name
]
)
# back inside parent task that opened nursery
child.sendline('c')
child.expect(PROMPT)
assert_before(
child,
[
_crash_msg,
"('cancelled_before_pause'", # actor name
"Failed to engage debugger via `_pause()`",
"trio.Cancelled",
"raise Cancelled._create()",
# we should be handling a taskc inside
# the first `.port_mortem()` sin-shield!
'await DebugStatus.req_finished.wait()',
]
)
# same as above but in the root actor's task
child.sendline('c')
child.expect(PROMPT)
assert_before(
child,
[
_crash_msg,
"('root'", # actor name
"Failed to engage debugger via `_pause()`",
"trio.Cancelled",
"raise Cancelled._create()",
# handling a taskc inside the first unshielded
# `.port_mortem()`.
# BUT in this case in the root-proc path ;)
'wait Lock._debug_lock.acquire()',
]
)
child.sendline('c')
child.expect(pexpect.EOF)
# TODO: needs ANSI code stripping tho, see `assert_before()` # above!
def test_correct_frames_below_hidden():
'''
@ -1255,7 +1330,3 @@ def test_cant_pause_from_paused_task():
'''
...
def test_shield_pause():
...

15
tractor/devx/_debug.py
View File

@ -1600,12 +1600,14 @@ async def _pause(
f'REPL: {Lock.repl}\n'
# TODO: use `._frame_stack` scanner to find the @api_frame
)
with trio.CancelScope(shield=shield):
await trio.lowlevel.checkpoint()
return
# XXX: since we need to enter pdb synchronously below,
# we have to release the lock manually from pdb completion
# callbacks. Can't think of a nicer way then this atm.
with trio.CancelScope(shield=shield):
if Lock._debug_lock.locked():
log.warning(
'attempting to shield-acquire active TTY lock owned by\n'
@ -1614,7 +1616,7 @@ async def _pause(
# must shield here to avoid hitting a ``Cancelled`` and
# a child getting stuck bc we clobbered the tty
with trio.CancelScope(shield=True):
# with trio.CancelScope(shield=True):
await Lock._debug_lock.acquire()
else:
# may be cancelled
@ -1659,6 +1661,7 @@ async def _pause(
f'{task.name}@{actor.uid} already has TTY lock\n'
f'ignoring..'
)
with trio.CancelScope(shield=shield):
await trio.lowlevel.checkpoint()
return
@ -1671,6 +1674,7 @@ async def _pause(
f'{task}@{actor.uid} already has TTY lock\n'
f'waiting for release..'
)
with trio.CancelScope(shield=shield):
await DebugStatus.repl_release.wait()
await trio.sleep(0.1)
@ -1683,6 +1687,7 @@ async def _pause(
'Waiting for previous request to complete..\n'
)
with trio.CancelScope(shield=shield):
await DebugStatus.req_finished.wait()
# this **must** be awaited by the caller and is done using the
@ -1721,6 +1726,7 @@ async def _pause(
'Starting request task\n'
f'|_{task}\n'
)
with trio.CancelScope(shield=shield):
req_ctx: Context = await actor._service_n.start(
partial(
request_root_stdio_lock,
@ -2147,6 +2153,13 @@ async def post_mortem(
**_pause_kwargs,
) -> None:
'''
`tractor`'s builtin async equivalient of `pdb.post_mortem()`
which can be used inside exception handlers.
It's also used for the crash handler when `debug_mode == True` ;)
'''
__tracebackhide__: bool = hide_tb
tb: TracebackType = tb or sys.exc_info()[2]