[Rd] R/C++/memory leaks

Simon Urbanek simon.urbanek at r-project.org
Mon Feb 26 17:58:15 CET 2007


On Feb 25, 2007, at 12:37 PM, Ernest Turro wrote:

> I have wrapped a C++ function in an R package. I allocate/ 
> deallocate memory using C++ 'new' and 'delete'. In order to allow  
> user interrupts without memory leaks

How do you allow for user interrupts? R doesn't allow interrupts  
while in .C/.Call on purpose, so it's up to your code to handle  
interrupts properly. This also implies that you can use the regular  
methods for error recovery available in your language and handle the  
interrupt yourself by freeing the memory as needed, your code  
shouldn't return to R until it has cleaned everything up ...

> I've moved all the delete statements required after an interrupt to  
> a separate C++ function freeMemory(), which is called using on.exit 
> () just before the .C() call.

This sounds a bit dangerous - how can the separate function know  
about the previous call and the state it was in before the interrupt  
(save for hard-wiring everything into one instance)? Again, the  
crucial part is the interrupt handling in your code - it may fail to  
release some objects...

@Ross [see follow-up]: R_RegisterCFinalizerEx is called on R exit if  
desired (see arguments). However, I don't think this is relevant to  
the discussed issue as a process termination frees all its memory.  
Moreover I don't think Ernest wants to wrap all his classes to R  
objects - we're not talking about the GC here, it is supposed to be C+ 
+ internal issue.


> I am concerned about the following. In square brackets you see R's
> total virtual memory use (VIRT in `top`):
> 1) Load library and data [178MB] (if I run gc(), then [122MB])
> 2) Just before .C [223MB]
> 3) Just before freeing memory [325MB]
> 4) Just after freeing memory [288MB]
> 5) After running gc() [230MB]
> So although the freeMemory function works (frees 37MB), R ends up
> using 100MB more after the function call than before it. ls() only
> returns the data object so no new objects have been added to the
> workspace.
> Do any of you have any idea what could be eating this memory?
> Many thanks,
> Ernest
> PS: it is not practical to use R_alloc et al because C++ allocation/
> deallocation involves constructors/destructors and because the C++
> code is also compiled into a standalone binary (I would rather avoid
> maintaining two separate versions).
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