options.R

#' Thread options for RcppParallel
#' 
#' Set thread options (number of threads to use for task scheduling and stack
#' size per-thread) for RcppParallel.
#' 
#' RcppParallel is automatically initialized with the default number of threads
#' and thread stack size when it loads. You can call `setThreadOptions()` at
#' any time to change the defaults.
#' 
#' The `parallelFor()` and `parallelReduce()` also accept `numThreads` as
#' an argument, if you'd like to control the number of threads specifically
#' to be made available for a particular parallel function call. Note that
#' this value is advisory, and TBB may choose a smaller number of threads
#' if the number of requested threads cannot be honored on the system.
#' 
#' @aliases setThreadOptions defaultNumThreads
#' 
#' @param numThreads
#' Number of threads to use for task scheduling. Call `defaultNumThreads()`
#' to determine the the default value used for "auto".
#' 
#' @param stackSize
#' Stack size (in bytes) to use for worker threads. The
#' default used for "auto" is 2MB on 32-bit systems and 4MB on 64-bit systems
#' (note that this parameter has no effect on Windows).
#' 
#' @return
#' `defaultNumThreads()` returns the default number of threads used by
#' RcppParallel, if another value isn't specified either via
#' `setThreadOptions()` or explicitly in calls to `parallelFor()` and
#' `parallelReduce()`.
#'
#' @examples
#' 
#' \dontrun{
#' library(RcppParallel)
#' setThreadOptions(numThreads = 4)
#' defaultNumThreads()
#' }
#' 
#' @export setThreadOptions
setThreadOptions<-function(numThreads="auto",
stackSize="auto")
{
# validate and resolve numThreads
if (identical(numThreads, "auto"))
numThreads<--1L
elseif (!is.numeric(numThreads))
 stop("numThreads must be an integer")
else
numThreads<- as.integer(numThreads)

# validate and resolve stackSize
if (identical(stackSize, "auto"))
stackSize<-0L
elseif (!is.numeric(stackSize))
 stop("stackSize must be an integer")
else
stackSize<- as.integer(stackSize)

# set RCPP_PARALLEL_NUM_THREADS
if (numThreads==-1L)
 Sys.unsetenv("RCPP_PARALLEL_NUM_THREADS")
else
 Sys.setenv(RCPP_PARALLEL_NUM_THREADS=numThreads)

# set RCPP_PARALLEL_STACK_SIZE
if (stackSize==0L)
 Sys.unsetenv("RCPP_PARALLEL_STACK_SIZE")
else
 Sys.setenv(RCPP_PARALLEL_STACK_SIZE=stackSize)
}

#' @rdname setThreadOptions
#' @export
defaultNumThreads<-function() {
 .Call("defaultNumThreads", PACKAGE="RcppParallel")
}

isUsingTbb<-function() {
backend<- Sys.getenv("RCPP_PARALLEL_BACKEND", "tbb")
 identical(backend, "tbb")
}