Nick Coghlan added the comment:
Greg Smith & I are looking at this at the core dev sprint, and we think some
variant of the "atomic until" idea should work, but there's a prerequisite
change to the way "async with" works: the "GET_AWAITABLE" opcodes need to be
avoided in this case, as they call __await__, and hence may run arbitrary
Python code.
We can't see any immediate barriers to moving those calls up into
BEFORE_ASYNC_WITH, such that what ends up on the eval loop's stack is the
already resolved iterable for use by YIELD FROM, rather than combining
GET_AWAITABLE+YIELD_FROM the way a normal await expression does.
That would then give the preamble:
BEFORE_ASYNC_WITH (resolves __aenter__ and __aexit__ to iterables)
LOAD_CONST 0
YIELD_FROM (need to skip signal processing here)
SETUP_ASYNC_WITH
And the postamble:
POP_BLOCK (need to skip signal processing until YIELD_FROM)
LOAD_CONST 0
WITH_CLEANUP_START
LOAD_CONST 0
YIELD_FROM
WITH_CLEANUP_FINISH
We also agree that adding some kind of test injection hook (potentially limited
to pydebug builds, depending on exactly how it works) is likely to be a
necessary to be able to test this.
----------
stage: -> test needed
type: -> behavior
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<http://bugs.python.org/issue29988>
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