Myles, can you please, provide more details such as exact versions of your macOS and well as details on the hardware you are using? I cannot reproduce the problem - it works perfectly fine for me on M3 running macOS 26.0.1 so it would be good to know what the conditions for failure are.
Thanks, Simon > On 15 Jan 2026, at 06:05, Myles Lewis via R-SIG-Mac <[email protected]> > wrote: > > I wanted to report an issue with R 4.5.2 for arm64, which is caused by the > change in the default BLAS from R�s standard BLAS library to using Apple > Accelerate vecLib BLAS library by default. In 4.5.1 and earlier, R for macOS > ships with the standard R BLAS. To change to vecLib, users had to > deliberately invoke this using a terminal command to change a symlink: > https://cran.r-project.org/bin/macosx/RMacOSX-FAQ.html#Which-BLAS-is-used-and-how-can-it-be-changed_003f > > However, R 4.5.2 for arm64 now defaults to vecLib. For intel macOS, 4.5.2 > stays with the standard R BLAS. VecLib BLAS has a problem with > parallelisation using mclapply() which now gives a warning and returns NULL > if mc.cores >= 2 and vecLib is invoked e.g. by the use of crossprod(). Here�s > a short reprex: > > system("readlink > /Library/Frameworks/R.framework/Resources/lib/libRblas.dylib") > # R 4.5.2 arm64: libRblas.vecLib.dylib > # R 4.5.1 arm64: libRblas.0.dylib > > N <- 200 > M <- 4000 > X <- matrix(rnorm(N*M),N) > > library(parallel) > > # ok > res <- mclapply(1:4, function(i) {crossprod(X + i)}, mc.cores = 1) > > # ok in R 4.5.1 > # not ok in R 4.5.2 arm64 (but works if M is smaller) > res <- mclapply(1:4, function(i) {crossprod(X + i)}, mc.cores = 2) > # gives warning and `res` contains NULL > > The same error occurs on Intel & arm Macs with any version of R if the BLAS > is switched to VecLib by symlink. > > My question is whether R for arm64 should go back to standard R BLAS by > default. Otherwise, users may find that functions which invoke the BLAS e.g. > lm() may crash unexpectedly and return NULL when parallelised using mclapply > (a fairly common situation in lots of packages). > > Thanks, > Myles Lewis > > > [[alternative HTML version deleted]] > > _______________________________________________ > R-SIG-Mac mailing list > [email protected] > https://stat.ethz.ch/mailman/listinfo/r-sig-mac _______________________________________________ R-SIG-Mac mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-mac
