[R] Processing repeated images and memory recovery by GC

[Steve Rowley]

I have a question about repeated image processing and recovering memory via
garbage collection.

A couple images are displayed simultaneously for analysis, using
split.screen().  I'm looping over a large collection of images, using
jpeg/readJPEG(), png/readPNG(), and caTools/read.gif() to load an image
into memory from a file.  Then I use erase.screen() to erase the previous
image, use plot() to set up a plotting area, and display the image with
rasterImage().  Then the user elects some processing, and we move on to the
next image(s).

I'm very carefully not holding references to any of the previous images.
GC is indeed happening, but memory quickly fills up.  It certainly *looks*
as though the image memory is not being released: printing out trace info
using mem_used()[[1]] says memory use increases with each image, by about
the image size.  Forcing periodic GC's, measuring memory used before and
after, shows that no memory is recovered.

Some questions:

(1) Is it known that processing images in this way will lead to allocating
memory that is not recovered by GC?

(2) Are there any tools you'd recommend to see exactly *what* is filling up
memory, just in case it's not previous images, but some other problem?

This is R 4.4.2 (for now).  Running MacOS on an ARM processor.
___________
Steve Rowley <sgr using alum.mit.edu> Zoom: 839 529 4589
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