temp file race conditions when invoking tile() in parallel

[achubaty]

Calling tile() in a parallel (i.e., multiple concurrent tile calls) produces the following problems:

1. python 'missing file' errors on the nodes due to disappearance of the g2ttmp directory.

g2t_tmp_dir <- file.path(tempdir(), "g2ttmp")
## and later
unlink(g2t_tmp_dir, recursive = TRUE, force = TRUE)
...

In order to make this work, each nodes needs its own tmpdir. The following change does the trick, provided the rasters are all of the supported type:

g2t_tmp_dir <- tempfile("g2ttmp_")

2. attempts to use the same temp file when rasters are not one of the supported filetypes:

## this fliename is hardcoded to be the same for all nodes :(
file <- file.path(tempdir(), "tmp_raster.tif")

Unfortunately this is a more involved fix because that file name is hardcoded in multiple places outside of tile(), so would need to pass the temp file name through every other function that checks for that file. Otherwise, I'd use tempfile("tmp_raster_", fileext = ".tif") here too.

[leonawicz]

This request I agree it would be great for parallel processing. I don't have time to dig into this one myself very soon. But if you can make a PR, I can review it, at least to get the process started.

Are you suggesting append a random string of characters to g2t_tmp_dir <- file.path(tempdir(), "g2ttmp_")?

It sounds like (2) can be addressed independently from (1).

Regards,
Matt

[achubaty]

Yes, sorry I just edited my OP.

For 1) I suggest g2t_tmp_dir <- tempfile("g2ttmp_") to add the random characters; 2) can be done separately.

I have (1) implemented in my fork and I am testing with some of my projects. Will PR when I'm happy with it (though note my fork also implements #19).

[leonawicz]

Thank you! That sounds good to me, feel free to combine it all in one PR.

[achubaty]

update: changes for number 1 seem fine -- it's number 2 that's biting me still.

[leonawicz]

@achubaty Hi Alex, it's been a while; I know this was merged, but are we good to close the issue or is there still something outstanding?
Regards,
Matt

[achubaty]

Hi Matt, the first part is completed, but I haven't come back to deal with the second part of this issue ('attempts to use the same temp file when rasters are not one of the supported filetypes') - so this piece is still outstanding.

[achubaty]

@leonawicz Hi again, I started working on this but encountered an issue when running tests using the latest raster package. So this is currently a work in progress.

[leonawicz]

Hi, yeah I encountered a similar problem with a couple unit tests involving raster stacks last week and had to skip them for now.

There may be an option to remove raster from the package, exclusively in favor of terra, but I don't have the bandwidth to look into that and it would be a whole separate issue. Even the packaged test files created in data-raw/data.R use raster.

My next goal is to at least republish to CRAN the current version on master, to address critical dependency issues #22

If we can fold in completion of this issue with the next release, that would be a bonus, but it's also fine if we don't.

[leonawicz]

CRAN submission is offline until August 7. I will submit afterward. But everything looks to be passing. :)

[achubaty]

Hi, yeah I encountered a similar problem with a couple unit tests involving raster stacks last week and had to skip them for now.

There may be an option to remove raster from the package, exclusively in favor of terra, but I don't have the bandwidth to look into that and it would be a whole separate issue. Even the packaged test files created in data-raw/data.R use raster.

My next goal is to at least republish to CRAN the current version on master, to address critical dependency issues #22

If we can fold in completion of this issue with the next release, that would be a bonus, but it's also fine if we don't.

@leonawicz this has been fixed upstream in raster