GH-106897: Add RERAISE event to sys.monitoring.

[markshannon]

Fixes the imbalance between RAISE and EXCEPTION_HANDLED events.

• Issue: No sys.monitoring RAISE event emitted when exception is re-raised (3.12b4) #106897

[markshannon]

@gaogaotiantian would you mind reviewing this?

[gaogaotiantian]

If I understand the monitoring system correctly, for all the exceptions raised, we want to balance it so each RAISE or RERAISE event(except for StopIteration) should match a PY_UNWIND or an EXCEPTION_HANDLED event right?

Consider the following code:

import sys
import asyncio

E = sys.monitoring.events

sys.monitoring.use_tool_id(0, "test")
 
async def async_generator():
    for i in range(1):
        raise ZeroDivisionError
        yield i
 
async def main():
    sys.monitoring.register_callback(0, E.EXCEPTION_HANDLED, lambda *args: print(f"EXCEPTION_HANDLED {args}"))
    sys.monitoring.register_callback(0, E.RAISE, lambda *args: print(f"RAISE {args}"))
    sys.monitoring.register_callback(0, E.RERAISE, lambda *args: print(f"RERAISE {args}"))
    sys.monitoring.register_callback(0, E.PY_UNWIND, lambda *args: print(f"PY_UNWIND {args}"))
    sys.monitoring.set_events(0, E.EXCEPTION_HANDLED | E.RAISE | E.RERAISE | E.PY_UNWIND)
    try:
        async for item in async_generator():
            print(item)
    except Exception:
        pass
    sys.monitoring.set_events(0, 0)
 
asyncio.run(main())

It prints

RAISE (<code object async_generator at 0x7f54aaeb5230, file "/home/gaogaotiantian/programs/cpython/example.py", line 10>, 44, ZeroDivisionError())
EXCEPTION_HANDLED (<code object async_generator at 0x7f54aaeb5230, file "/home/gaogaotiantian/programs/cpython/example.py", line 10>, 50, ZeroDivisionError())
RERAISE (<code object async_generator at 0x7f54aaeb5230, file "/home/gaogaotiantian/programs/cpython/example.py", line 10>, 52, ZeroDivisionError())
PY_UNWIND (<code object async_generator at 0x7f54aaeb5230, file "/home/gaogaotiantian/programs/cpython/example.py", line 10>, 52)
RAISE (<code object main at 0x5600748fdbc0, file "/home/gaogaotiantian/programs/cpython/example.py", line 17>, 610, ZeroDivisionError())
EXCEPTION_HANDLED (<code object main at 0x5600748fdbc0, file "/home/gaogaotiantian/programs/cpython/example.py", line 17>, 656, ZeroDivisionError())
EXCEPTION_HANDLED (<code object main at 0x5600748fdbc0, file "/home/gaogaotiantian/programs/cpython/example.py", line 17>, 660, ZeroDivisionError())

Maybe because we should add monitor_reraise (or maybe monitor_raise?) in END_ASYNC_FOR? The exception from the coroutine seems to be raised again.

[markshannon]

Thanks for spotting that.

[iritkatriel]

I'm confused about error reporting from do_raise. If there is no exception set, it sets an exception and returns 0. What does that mean?

[markshannon]

do_raise returns 0 if it raises, and 1 if it reraises.
Historical reasons probably 🤷

[miss-islington]

Thanks @markshannon for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[miss-islington]

Sorry, @markshannon, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 766d2518ae8384c6bd7f82727defeb86847ccf64 3.12

[bedevere-bot]

GH-107346 is a backport of this pull request to the 3.12 branch.