[Python-Dev] bpo-33257: seeking advice & approval on the course of action

[Ivan Pozdeev]

On 14.05.2018 21:58, Terry Reedy wrote:
> On 5/14/2018 12:20 PM, Chris Barker via Python-Dev wrote:
>> On Wed, May 2, 2018 at 8:21 PM, Terry Reedy <tjreedy at udel.edu 
>> <mailto:tjreedy at udel.edu>> wrote:
>>
>>     On 5/2/2018 4:38 PM, Ivan Pozdeev via Python-Dev wrote:
>>
>>         The bottom line is: Tkinter is currently broken
>>
>>
>>     This is way over-stated.  Many modules have bugs, somethings in
>>     features more central to their main purpose.
>>
>> I'll suggest a re-statement:
>>
>> tkinter is not thread safe,
>
> Still over-stated.  If one uses tcl/tk compiled with thread support, 
> tkinter *is* thread-safe.  This is 'as far as I know' from running 
> posted 'failing' examples (possible with bug fixes) with 3.5+ on 
> Windows, which is installed with tcl/tk 8.6, which defaults to 
> thread-safe.
>
This means that you didn't (yet) read the letter that I attached to 
https://bugs.python.org/issue33479 .
Reciting the relevant section:

===
The reality is that with neither flavor of Tcl is Tkinter completely 
thread-safe, but with threaded flavor, it's more so:

* with nonthreaded Tcl, making concurrent Tcl calls leads to crashes due 
to incorrect management of the "Tcl lock" as per 
https://bugs.python.org/issue33257
* with threaded Tcl, the only issue that I found so far is that a few 
APIs must be called from the interpreter's thread 
(https://bugs.python.org/issue33412#msg316152; so far, I know 
`mainloop()` and `destroy()` to be this) -- while most can be called 
from anywhere. Whether the exceptions are justified is a matter of 
discussion (e.g. at first glance, `destroy()` can be fixed).
===
> Tkinter was intended to also be thread-safe when using tcl/tk without 
> thread support, which was the default for tcl/tk 8.5 and before. The 
> posted examples can fail on 2.x on Windows, which comes with tcl/tk 
> 8.5 or before. _tkinter.c has some different #ifdefs for the two 
> situations.
>
>> and yet it is documented as being thread safe
>
> True in https://docs.python.org/3/library/tk.html
> Unspecified in https://docs.python.org/3/library/tkinter.html
>
>> This is either a bug(s) in the implementation or the docs.
>
> Both
>
>> So what are the solutions?
>>
>> 1) fix the docs -- unless tkInter is made thread safe really soon, 
>> and fixes are back-ported, this seems like a no brainer -- at least 
>> temporarily.
>
> https://bugs.python.org/issue33479 'Document tkinter and threads'
>
>> 2) fix the issues that make tkInter not thread safe
>
> with non-thread tcl/tk.
>
> https://bugs.python.org/issue33257 has a patch that might improve the 
> situation for one type of call.  Fixing everything might not be 
> possible.  AFAIK, there are currently no tests of thread safety.
>

-- 
Regards,
Ivan