Valgrind "definitely lost" backtrace

Richard Kimberly Heck rikiheck at
Fri Feb 14 16:19:45 UTC 2020

On 2/14/20 8:55 AM, Pavel Sanda wrote:
> On Thu, Feb 13, 2020 at 09:58:15PM -0500, Scott Kostyshak wrote:
>> The corresponding line of TocModel.cpp:362 is the line with "new" below:
>>   // First, fill in the toc models.
>>   iterator mod_it = models_.find(type);
>>   if (mod_it == models_.end())
>>   	mod_it = models_.insert(type, new TocModel(this));
>>   mod_it.value()->reset(toc.second);
>> Note that models_ is declared as follow:
>>   QHash<QString, TocModel *> models_;
>> Is it the responsibility of the QHash's destructor to call delete on all
>> of the TocModel * of its elements? Where is the problem likely to be?
> Without looking how insert() is defined my guess is that it just copies
> the whole object created by new TocModel(this) (not using pointer to it),
> so once you leave this statement there is no handle for temporarily created
> object and mem leak occurs.

QHash::insert does make a copy, but it makes a copy of the pointer: It's
a QHash<QString, TocModel *>, right? So we still have access to the
created object. The code is here:

I doubt that it is QHash's responsibility to call delete on these
pointers, but the whole point of this change (see 6ad1b1cd0) was not to
recreate all the objects every time we reset the TocModel. I.e., the
pointers don't change. We just clear the objects to which they point and
then reuse them.

I'm puzzled. Is it possible that valgrind just thinks that we lose
access to this object, for the sorts of reasons Pavel gave?

That said, I am getting a weird warning in QtCreator about the loop
variable itself involving a copy:

/cvs/lyx/lyx-devel/src/frontends/qt/TocModel.cpp:356: warning: loop
variable 'toc' has type 'const pair<std::string, shared_ptr<lyx::Toc> >
&' (aka 'const pair<basic_string<char>, shared_ptr<vector<lyx::TocItem>
> > &') but is initialized with type 'const std::pair<const
std::shared_ptr<std::vector<lyx::TocItem, std::allocator<lyx::TocItem> >
> >' resulting in a copy

/cvs/lyx/lyx-devel/src/frontends/qt/TocModel.cpp:356: use non-reference
type 'pair<std::string, shared_ptr<lyx::Toc> >' (aka
'pair<basic_string<char>, shared_ptr<vector<lyx::TocItem> > >') to keep
the copy or type 'const std::pair<const
std::shared_ptr<std::vector<lyx::TocItem, std::allocator<lyx::TocItem> >
> > &' to prevent copying

Unsurprisingly, that goes away if I just change the loop variable to
'auto'. I've made that change in master. Probably won't help but....


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