_tkinter should use Python PyMem_Malloc() instead of Tcl ckalloc()

[vstinner]

BPO	22336
Nosy	@vstinner, @serhiy-storchaka
Files	pymem.patch tkinter_pymem_2.patch tkinter_pymem_3.patch

^{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 2014-09-11.15:52:36.190>
created_at = <Date 2014-09-04.15:46:10.949>
labels = ['type-feature', 'expert-tkinter']
title = '_tkinter should use Python PyMem_Malloc() instead of Tcl ckalloc()'
updated_at = <Date 2014-09-11.15:53:44.381>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2014-09-11.15:53:44.381>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2014-09-11.15:52:36.190>
closer = 'python-dev'
components = ['Tkinter']
creation = <Date 2014-09-04.15:46:10.949>
creator = 'vstinner'
dependencies = []
files = ['36533', '36596', '36599']
hgrepos = []
issue_num = 22336
keywords = ['patch']
message_count = 10.0
messages = ['226363', '226365', '226366', '226753', '226764', '226771', '226779', '226782', '226784', '226785']
nosy_count = 4.0
nosy_names = ['vstinner', 'python-dev', 'serhiy.storchaka', 'David.Edelsohn']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue22336'
versions = ['Python 3.5']

[vstinner]

The PyMem_Malloc(size) function has a well defined behaviour: if size is 0, a pointer different than NULL is returned. It looks like ckalloc(size) returns NULL if the size is NULL: see issue bpo-21951 (bug on AIX).

Moreover, memory allocated by ckalloc() is not traced by the new tracemalloc module!

Attached patch replaces calls to ckalloc() and ckfree() with PyMem_Malloc() and PyMem_Free(). It may fix the issue bpo-21951 on AIX.

There is still a call to ckfree() in Tkapp_SplitList(). This memory block is allocated internally by Tcl, not directly by _tkinter.c.

[vstinner]

   PyMem_Free(FREECAST argv);

FREECAST can be dropped here, PyMem_Free() always takes a void* pointer.

[serhiy-storchaka]

Event structs (Tkapp_CallEvent, VarEvent, CommandEvent) must have been allocated by the caller using Tcl_Alloc or ckalloc (see man Tcl_ThreadQueueEvent).

[serhiy-storchaka]

Here is updated patch which is synchronized with the tip after changes made in bpo-21951 and addresses my comments.

[vstinner]

I read tkinter_pymem_2.patch.

Remaining calls to ckalloc():

• they are only used to allocate events passed later to Tcl_ThreadQueueEvent(). Tcl_ThreadQueueEvent doc explicitly says that the memory must be allocated by Tcl_Alloc or ckalloc, so it's correct (PyMem cannot be used).

Remaining calls to ckfree():

• Tkapp_SplitList() calls ckfree() on memory allocated by Tcl_SplitList(), it's correct.

• Tkapp_CallDeallocArgs() ckfree() on memory allocated by PyMem_Malloc() => wrong (see my review on Rietveld).

[serhiy-storchaka]

• Tkapp_CallDeallocArgs() ckfree() on memory allocated by PyMem_Malloc() =>
  wrong

Oh, you are right, thanks.

(see my review on Rietveld).

Perhaps you forgot to press the "Publish" button.

[vstinner]

tkinter_pymem_3.patch looks good to me.

[serhiy-storchaka]

And to me too. Please commit it, this is mainly your patch.

[python-dev]

New changeset 9f1d3e6e6ce6 by Victor Stinner in branch 'default':
Closes bpo-22336: attemptckalloc() with PyMem_Malloc() in _tkinter
http://hg.python.org/cpython/rev/9f1d3e6e6ce6

[vstinner]

And to me too. Please commit it, this is mainly your patch.

Ok, thanks, done.