RMINC breaks parallel::parSapply() when using parallel::makeForkCluster() in R 4.1.3

[dnmacdon]

In R 4.1.3, I've noticed the following issue. It does not occur when using 3.5.1. Note that no RMINC functions are used - merely loading RMINC causes this to break.

This works:

library(parallel)
cl <- makeForkCluster( 2 )
result <- parSapply (cl, X=1:1000, FUN=function(x) x)
stopCluster(cl)

This does not:

library(parallel)
library(RMINC)
cl <- makeForkCluster( 2 )
result <- parSapply (cl, X=1:1000, FUN=function(x) x)
stopCluster(cl)

Fails with: Error in serialize(data, node$con, xdr = FALSE) : ignoring SIGPIPE signal