enable specifying number of threads via environment variable

Author: jjallaire

R/hooks.R

@@ -26,7 +26,12 @@ mallocDllInfo <- NULL
    library.dynam("RcppParallel", pkgname, libname)
 
    # set default thread options
-   setThreadOptions()
+   numThreads <- "auto"
+   numThreadsEnv <- Sys.getenv("RCPP_PARALLEL_NUM_THREADS", unset = NA)
+   if (!is.na(numThreadsEnv))
+      setThreadOptions(numThreads = as.integer(numThreadsEnv))
+   else
+      setThreadOptions(numThreads = "auto")
 }
 
 .onUnload <- function(libpath) {