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

[hcp@met.ed.ac.uk]

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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