When is m2w64-libwinpthread-git needed? Is it related to OpenMP?

[mfansler]

Your question:

The Knowledge Base for maintainers omits any mention of Windows in the OpenMP section. While it seems like there is no such corresponding package, I have noticed a pattern of linking analysis errors for win-64 builds of R packages. Specifically, I've repeatedly observed R packages using OpenMP, where the win-64 versions of these builds result in linking against m2w64-libwinpthread-git.

Example error from r-rxode2random build

ERROR (r-rxode2random,lib/R/library/rxode2random/libs/x64/rxode2random.dll): Needed DSO Library/mingw-w64/bin/libwinpthread-1.dll found in ['m2w64-libwinpthread-git']
  ERROR (r-rxode2random,lib/R/library/rxode2random/libs/x64/rxode2random.dll): .. but ['m2w64-libwinpthread-git'] not in reqs/run, (i.e. it is overlinking) (likely) or a missing dependency (less likely)

I have been resolving this with adding {{ native }}libwinpthread-git as a run dependency, but perhaps this should be being added elsewhere (as {{ posix }}libwinpthread-git?) whenever a build is using OpenMP flags. Note that I lack familiarity with how win-64 builds are handling -fopenmp flag, and this is merely an empirical pattern I've happened across in a dozen or so packages.

Is there any guidance we could give for when a {{ native }}libwinpthread-git is expected to be needed? Is the association with OpenMP appropriate?

Even if there is no direct OpenMP association, at the least it would be helpful if there were some explanation for why Windows is never mentioned in the OpenMP section of the Knowledge Base.