Kevin,
On Mar 18, 2009, at 12:08 , Kevin Hendricks wrote:
I don't think so, because IMHO it makes no sense - you're missing
the main point that R is not thread safe. There are ways to use
threads from within R very cautiously (see Luke's parallelized
vector math operations for R for example). There are many good
methods to use threads in general (pthreads, OpenMP, GCD, ...) and
you can do that as long as you don't use memory allocation in R and
don't call any R functions that may do that (which is most of
them ;)). Making R thread-safe is not really an issue of a
threading toolkit...
Memory allocation does not necessarily make a function non-reentrant
unless non-shared static variables are involved. There are a number
of thread-safe malloc implementations. I admit, I have not
looked at the R-internals in a long time.
I'm not talking about system-level memory allocation, but at R level
which uses a garbage collector that is not thread safe and it does
involve global variables. However, I'm not the right person to comment
on those issues in detail, but just be assured that several people
very well versed in the R internals have already looked at this (see
below).
In addition, there are many more issues in R, because a lot of
concepts in R just assume sequential operation (graphics devices,
global options, hooks etc. - see below).
Based on converting code to be thread safe when I helped port the
JDK to Linux, I was amazed about how much code was already reentrant
capable and therefore basically thread-safe (or could be made so
with small effort - adding a few locks). In fact the original JVM
(jdk 1.0) had a "green-threads" implementation that basically ended
up adding wrappers to most of the memory allocation and io system
calls system calls to make the whole thing work.
How much of the code itself is now reentrant safe - I noticed that
some of the R-internal routines actually used reentrant code and
even recursion? How hard would it be to make the internal object/
memory allocation scheme thread-safe? As you noted there are many
posix threads (pthreads) implmentations out there.
Is there any official effort underway to make R thread-safe?
I know that Duncan TL was looking into this since he did the job for S
while ago, but I'm not sure how far he got. Luke Tierney has written
up some thoughts on the issue and despite the document being quite
dated I think it's still very applicable to today's R:
http://www.stat.uiowa.edu/~luke/R/thrgui/thrgui.pdf
Cheers,
Simon
If so, are they looking for volunteers. Would making R fully thread-
safe really make that much sense given you can parallelize vector/
matrix operations now (as you noted) which probably provides the
most bang for the buck.
Thanks,
Kevin
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