[Rd] Memory "leak" in readChar (PR#1483)

[ripley@stats.ox.ac.uk]

Yes, we know of a couple of other leaks, which will be fixed for 1.6.0
(and perhaps 1.5.1).

BDR

On Mon, 29 Apr 2002, H C Pumphrey wrote:

>
> A few days ago, I wrote
> > >
> > > The function readChar() appears to have some type of problem with
> > >memory  allocation.
>
> On Fri, 26 Apr 2002 ripley@stats.ox.ac.uk wrote:
>
> > It's not really a memory leak, more that R_alloc was at the time
> > incorrectly documented and do_readchar needs to reset vmax.
> [snip]
> > I'll put the two-line fix in for 1.5.0.
>
> I originally said that this problem didn't occur in readBin(). That seems
> to be true if you are reading 8-byte data.  However, I stressed this a bit
> harder, and found that if you use the size=4 keyword then the problem
> _does_ appear with readBin(). I enclose an example below.
>
> Apologies if the original bug report was misleading and again, many thanks
>
> Hugh
>
>
>
> ## Stress read/write of files in binary mode to see if there is a
> ## memory problem. Now, readBin seems to be innocent if the default
> ## (8-byte) reals are used, but there is a problem reading 4-bute reals.
>
> nrecs <-2000
> ntries <- 100
> npts <- 300
> gunge <- 1:npts
> ## Write a test file
> stream <- file("/tmp/gunge")
> open(stream,open="wb")
> for(irec in 1:nrecs){
>   writeBin(gunge,"numeric",size=4)
> }
> close(stream)
>
> ## Read in the file ntries times. In real applications one would be reading
> ## ntries _different_ files and calculating some summary statistics
> for(itry in 1:ntries){
>   stream <- file("/tmp/gunge")
>   open(stream,open="rb")
>   if(itry %% 10== 0) print(itry)
>   for(irec in 1:nrecs){
>     ## Seems to be worse if reads are in several small chunks
>     ##
>     bunge <- readBin(stream,"numeric",10,size=4)
>     bunge <- readBin(stream,"numeric",20,size=4)
>     bunge <- readBin(stream,"numeric",10,size=4)
>     bunge <- readBin(stream,"numeric",20,size=4)
>     bunge <- readBin(stream,"numeric",npts-60,size=4)
>
>   }
>   close(stream)
> }
>
>
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> Dr. Hugh C. Pumphrey             | Tel. 0131-650-6026,Fax:0131-650-5780
> Institute for Meteorology        | Replace 0131 with +44-131 if outside UK
> The University of Edinburgh      | Email hcp@met.ed.ac.uk
> EDINBURGH EH9 3JZ, Scotland      | URL: http://www.met.ed.ac.uk/~hcp
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>
>

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


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