Enable building with the system tbb library

[bryteise]

I'd like to build against the system tbb instead of the embedded tbb provided by the source package. Looking at the build process this seems like a bigger patch though. Would that be something you would consider adding?

[eddelbuettel]

Tough. In general, we can support this -- I once enabled just that for nloptr.

But this is a much larger and complicated package so I am not sure. Call to be made by @kevinushey.

[kevinushey]

Seems possible in theory. We load TBB when RcppParallel is loaded here:

RcppParallel/R/hooks.R

Lines 7 to 23 in b216ba2

	# load tbb and tbbmalloc on supported platforms
	tbb <- tbbLibPath()
	if (!is.null(tbb)) {
	if (!file.exists(tbb)) {
	warning(paste("TBB library", tbb, "not found."))
	} else {
	dllInfo <<- dyn.load(tbb, local = FALSE, now = TRUE)
	}
	}
	tbbMalloc <- tbbLibPath("malloc")
	if (!is.null(tbbMalloc)) {
	if (!file.exists(tbbMalloc)) {
	warning(paste("TBB malloc library", tbbMalloc, "not found."))
	} else {
	mallocDllInfo <<- dyn.load(tbbMalloc, local = FALSE, now = TRUE)
	}
	}

We'd just have to swap out those paths for something separately provided / requested by the user.

However, I'm not sure if TBB is intended to be used in this way, or if things could subtly break.

[bryteise]

I patched tbbLibPath to just return the path to the system installed libtbb as a workaround to avoid shipping the vendored libtbb. Currently my project's opencv is linking against the system libtbb without issue. Things often are a little trickier when dlopening though as RccpParallel does since you won't see library version mismatches at build time.

[eddelbuettel]

Keep at it. This will be worthwhile.

[dsteuer]

Hunting for a solution of a different issue I came around the debian patch for using the system tbb.
https://salsa.debian.org/r-pkg-team/r-cran-rcppparallel/-/blob/master/debian/patches/use_debian_packaged_libtbb.patch

Would you advise against using of the system's tbb? Otherwise I would build for OpenSUSE just like debian does.

[eddelbuettel]

It is not my package, hence not my call. In general, I like using system libs, but there is a risk of a delta.

[kevinushey]

I wouldn't advise against it, I just haven't tested it yet. I'd like to eventually do this properly but haven't yet been able to carve out the time to do it (but would gladly accept a PR)