[Rd] R extension memory leak detection question

[Lionel Henry]

> Still, memory leaks are possible if the program forgets about a
> pointer to some piece of memory no longer needed, and keeps that
> pointer in say some global structure. Such memory leaks would not be
> found using address sanitizer.

We had a few cases of this in the past. Given the difficulty of
tracing the leaking references, we wrote this package for taking
snapshots of the R heap and finding dominators and shortest paths
between nodes:

Repo: https://github.com/r-lib/memtools
Vignette: https://memtools.r-lib.org/articles/memtools.html

One issue that complicates taking snapshots is that R doesn't expose
the GC roots. In practice, only the precious list is needed I think.
Would you consider a patch that allows retrieving the precious list
for debugging purposes via a `.Internal()` call?

Best,
Lionel


On 3/15/21, Tomas Kalibera <tomas.kalibera using gmail.com> wrote:
> On 3/12/21 7:43 PM, xiaoyan yu wrote:
>> I am writing C++ program based on R extensions and also try to test the
>> program with google address sanitizer.
>>
>> I thought if I don't protect the variable from the allocation API such as
>> Rf_allocVector, there will be a memory leak. However, the address
>> sanitizer
>> didn't report it. Is my understanding correct? Or I will see the memory
>> leak only if I compile R source code with the address sanitizer.
>
> Yes, you should use special options for compilation and linking to use
> address sanitizer. See Writing R Extensions, section 4.3.3.
>
> If you allocate an R object using Rf_allocVector(), but don't protect
> it, it means this object is available for the garbage collector to
> reclaim. So it is not a memory leak.
>
> Memory leaks with a garbage collector are much less common than without,
> because if the program loses a pointer to some piece of memory, that
> piece will automatically be reclaimed (not leaked). Still, memory leaks
> are possible if the program forgets about a pointer to some piece of
> memory no longer needed, and keeps that pointer in say some global
> structure. Such memory leaks would not be found using address sanitizer.
>
> Address sanitizer/Undefined behavior sanitizer can sometimes find errors
> caused by that the program forgets to protect an R object, but this is
> relatively rare, as they don't understand R heap specifically, so you
> cannot assume that if you create such example, the error will always be
> found.
>
> Best
> Tomas
>
>>
>>   Please help!
>>
>> Thanks,
>> Xiaoyan
>>
>> 	[[alternative HTML version deleted]]
>>
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