[issue24017] Implemenation of the PEP 492 - Coroutines with async and await syntax

[Yury Selivanov]

Yury Selivanov added the comment:

Nick, Guido,

Attached is a patch that fixes a refleak in 'async with' implementation.

The problem is related to WITH_CLEANUP_START/WITH_CLEANUP_FINISH opcodes.

For regular 'with' statements, these opcodes go one after another (essentially, it was one opcode before 'async with').

For 'async with' statements, we have a GET_AWAITABLE/YIELD_FROM pair between them.

Now, if an error occurred during running a GET_AWAITABLE or a YIELD_FROM opcode, WITH_CLEANUP_FINISH was unreachable.  All blocks were correctly unwound by the eval loop, but exception object got too many DECREFS.

My solution is to continue using WITH_CLEANUP_START/WITH_CLEANUP_FINISH opcodes, but use SETUP_EXCEPT to guard them and nested YIELD_FROM and GET_AWAITABLE.

In case of an exception, I propose to use another new opcode -- ASYNC_WITH_CLEANUP_EXCEPT.  It unwinds the block set up by SETUP_EXCEPT, restores exception, NULLifies a copy of exception in the stack and does 'goto error', letting eval loop do the rest.

"./python.exe -m test -R3:3 test_coroutines" with this patch reports no refleaks.  I also updates test_coroutines with a lot of new 'async with' tests, I think that I got all usecases covered.

Please take a look at the patch, I want to commit it as soon as possible.

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Added file: http://bugs.python.org/file39354/with.patch

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