PyOS_InputHook is not called when waiting for input() in Windows

[yhlam]

BPO	31546
Nosy	@pfmoore, @tjguk, @zware, @zooba, @ZackerySpytz, @yhlam, @miss-islington
PRs	bpo-31546: fix input hook integration on windows #7978 [3.7] bpo-31546: Fix input hook integration (GH-7978) #7990 [3.6] bpo-31546: Fix input hook integration (GH-7978) #7991
Files	test_tk.py: TK test script py35_call_stack.png: Python 3.5 call stack py36_call_stack.png: Python 3.6 call stack

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-07-23.15:44:37.548>
created_at = <Date 2017-09-21.16:13:02.342>
labels = ['type-bug', '3.7', 'OS-windows']
title = 'PyOS_InputHook is not called when waiting for input() in Windows'
updated_at = <Date 2019-07-23.15:44:37.548>
user = 'https://github.com/yhlam'

bugs.python.org fields:

activity = <Date 2019-07-23.15:44:37.548>
actor = 'steve.dower'
assignee = 'none'
closed = True
closed_date = <Date 2019-07-23.15:44:37.548>
closer = 'steve.dower'
components = ['Windows']
creation = <Date 2017-09-21.16:13:02.342>
creator = 'yhlam'
dependencies = []
files = ['47160', '47161', '47162']
hgrepos = []
issue_num = 31546
keywords = ['patch']
message_count = 12.0
messages = ['302701', '302702', '302703', '302705', '302707', '304785', '305567', '305568', '320674', '320680', '320681', '348067']
nosy_count = 7.0
nosy_names = ['paul.moore', 'tim.golden', 'zach.ware', 'steve.dower', 'ZackerySpytz', 'yhlam', 'miss-islington']
pr_nums = ['7978', '7990', '7991']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31546'
versions = ['Python 3.6', 'Python 3.7']

[yhlam]

Since python 3.6, PyOS_InputHook is not called when waiting for IO in Windows.

This causes issues with GUI framework like tkinter that relys on PyOS_InputHook to handle user interaction.

I attached a test script. When running the script with python 3.5, the tkinter window will show up properly. But if you run the script with python 3.6, the tkinter window will be frozen.

I believe the issue is introduced in commit 3929499. In commit 3929499, _PyOS_WindowsConsoleReadline is added as the new Windows implementation of PyOS_StdioReadline. Originally, PyOS_StdioReadline calls my_fgets to read input, and my_fgets will call PyOS_InputHook before the calling the real fgets. However, _PyOS_WindowsConsoleReadline calls ReadConsoleW instead of my_fgets to read input, and PyOS_InputHook is never called.

The bug is first reported in matplotlib.
matplotlib/matplotlib#9206 (comment)

[yhlam]

Attach python 3.5 call stack of the test script

[yhlam]

Attach python 3.6 call stack of the test script

[zooba]

You're right, we're missing this section of code:

    if (PyOS_InputHook != NULL)
        (void)(PyOS_InputHook)();

Since we just call it and ignore anything it does, it should be safe enough to add it immediately before the ReadConsoleW call (inside the loop).

[zooba]

(Belongs inside Parser/myreadline.c in the _PyOS_WindowsConsoleReadline function)

[yhlam]

As the fix seems simple, any chance this bug can be fixed in next python 3.6 maintenance release? It is the major roadblock for my application to upgrade to python 3.6. Thanks

[zooba]

The fix is simple, just need someone to do a PR. (I might get to it eventually, but I'm working on other things right now.)

[zooba]

And yes, I think this is fine for 3.6.

[zooba]

New changeset 9b9d58f by Steve Dower (Thomas A Caswell) in branch 'master':
bpo-31546: Fix input hook integration (GH-7978)
9b9d58f

[miss-islington]

New changeset 0ebd1bc by Miss Islington (bot) in branch '3.6':
bpo-31546: Fix input hook integration (GH-7978)
0ebd1bc

[zooba]

New changeset 9d92524 by Steve Dower (Miss Islington (bot)) in branch '3.7':
bpo-31546: Fix input hook integration (GH-7978)
9d92524

[ZackerySpytz]

Can this issue be closed? PR 7978 was merged and backported.