R extension memory leak detection question

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 at 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

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