[Rd] Moderating consequences of garbage collection when in C

[Martin Morgan]

On 11/14/2011 01:12 PM, dhinds at sonic.net wrote:
> Martin Morgan<mtmorgan at fhcrc.org>  wrote:
>> >  On 11/14/2011 11:47 AM,dhinds at sonic.net  wrote:
>>> >  >  dhinds at sonic.net  wrote:
>>>> >  >>  Martin Morgan<mtmorgan at fhcrc.org>   wrote:
>>> >  >
>>> >  >  I had done some google searches on this issue, since it seemed like it
>>> >  >  should not be too uncommon, but the only other hit I could come up
>>> >  >  with was a thread from 2006:
>>> >  >
>>> >  >  https://stat.ethz.ch/pipermail/r-devel/2006-November/043446.html
>>> >  >
>>> >  >  In any case, one issue with your suggested workaround is that it
>>> >  >  requires knowing how much additional storage is needed, which may be
>>> >  >  an expensive operation to determine.  I've just tried implementing a
>>> >  >  different approach, which is to define two new functions to either
>>> >  >  disable or enable GC.  The function to disable GC first invokes
>>> >  >  R_gc_full() to shrink the heap as much as possible, then sets a flag.
>>> >  >  Then in R_gc_internal(), I first check that flag, and if it is set, I
>>> >  >  call AdjustHeapSize(size_needed) and exit immediately.
>> >  I think this is a better approach; mine seriously understated the
>> >  complexity of figuring out required size.
>>> >  >  These calls could be used to bracket any code section that expects to
>>> >  >  make lots of calls to R's memory allocator.  The down side is that
>>> >  >  this approach requires that all paths out of such a code section
>>> >  >  (including error handling) need to take care to unset the GC-disabled
>>> >  >  flag.  I think I would want to hear from someone on the R team about
>>> >  >  whether they think this is a good idea.
>>> >  >
>> >  Another place where this comes up is during package load, especially for
>> >  packages with many S4 instances.
> Do you know if this is all happening inside a C function that could
> handle disabling and enabling GC?  Or would it require doing this at
> the R level?  For testing, I am turning GC on and off at the R level

Generally complicated operations across multiple function calls. 
Something like

   f = function() {
     state <- gcdisable(TRUE)
     on.exit(gcdisable(state))
     as.character(1:10000000)
   }

might be used.

Martin
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