[Rd] R/C++/memory leaks

Thomas Lumley tlumley at u.washington.edu
Mon Feb 26 22:42:25 CET 2007

On Mon, 26 Feb 2007, Hin-Tak Leung wrote:

> Read the help page of gc(). You need to run it with reset=TRUE for
> the usage to drop back to original. i.e. gc(reset=TRUE). gc() on its
> own doesn't quite do what you think it would do.

This is almost completely incorrect (apart from the advice to read the 
help page).  The setting for reset= has absolutely no effect on R's memory 
use. It just clears the internal variable that has kept track of the 
highest memory use so far.


> Ernest Turro wrote:
>> Dear all,
>> 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 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.
>> 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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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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