use RCPP_PARALLEL_NUM_THREADS for default num threads

Author: kevinushey

R/options.R

@@ -22,28 +22,20 @@ setThreadOptions <- function(numThreads = "auto", stackSize = "auto") {
    else
       stackSize <- as.integer(stackSize)
 
-   # Call setThreadOptions if using tbb
-   if (!is.null(dllInfo) && isUsingTbb())
-      setTbbThreadOptions(numThreads, stackSize)
-   
+   # set RCPP_PARALLEL_NUM_THREADS
    if (numThreads == -1L)
       Sys.unsetenv("RCPP_PARALLEL_NUM_THREADS")
    else
       Sys.setenv(RCPP_PARALLEL_NUM_THREADS = numThreads)
-}
-
-setTbbThreadOptions <- function(numThreads, stackSize) {
-   .Call(
-      "setThreadOptions",
-      as.integer(numThreads),
-      as.integer(stackSize),
-      PACKAGE = "RcppParallel"
-   )
+   
+   # set RCPP_PARALLEL_STACK_SIZE
+   if (stackSize == 0L)
+      Sys.unsetenv("RCPP_PARALLEL_STACK_SIZE")
+   else
+      Sys.setenv(RCPP_PARALLEL_STACK_SIZE = stackSize)
+   
 }
 
 defaultNumThreads <- function() {
-   .Call(
-      "defaultNumThreads",
-      PACKAGE = "RcppParallel"
-   )
+   .Call("defaultNumThreads", PACKAGE = "RcppParallel")
 }

inst/include/RcppParallel/TBB.h

@@ -178,6 +178,31 @@ class TBBArenaParallelReduceExecutor
    std::size_t end_;
    std::size_t grainSize_;
 };
+
+int tbbResolveNumThreads(int numThreads)
+{
+   // if the user has explicitly set the value away from the default,
+   // then we can just honor their request
+   if (numThreads != -1)
+      return numThreads;
+   
+   // otherwise, try reading the default from RCPP_PARALLEL_NUM_THREADS.
+   // if that is unset, we'll let tbb decide
+   const char* var = getenv("RCPP_PARALLEL_NUM_THREADS");
+   if (var == NULL)
+      return tbb::task_arena::automatic;
+   
+   // try to convert the string to a number
+   errno = 0;
+   char* end;
+   long threads = strtol(var, &end, 10);
+   
+   // if an error occurred during conversion, just use default
+   if (errno != 0)
+      threads = tbb::task_arena::automatic;
+   
+   return threads;
+}
 
 } // anonymous namespace
 
@@ -188,7 +213,7 @@ inline void tbbParallelFor(std::size_t begin,
                            std::size_t grainSize = 1,
                            int numThreads = -1)
 {
-   tbb::task_arena arena(numThreads == -1 ? tbb::task_arena::automatic : numThreads);
+   tbb::task_arena arena(tbbResolveNumThreads(numThreads));
    tbb::task_group group;
 
    TBBArenaParallelForExecutor executor(group, worker, begin, end, grainSize);
@@ -202,7 +227,7 @@ inline void tbbParallelReduce(std::size_t begin,
                               std::size_t grainSize = 1,
                               int numThreads = -1)
 {
-   tbb::task_arena arena(numThreads == -1 ? tbb::task_arena::automatic : numThreads);
+   tbb::task_arena arena(tbbResolveNumThreads(numThreads));
    tbb::task_group group;
 
    TBBArenaParallelReduceExecutor<Reducer> executor(group, reducer, begin, end, grainSize);

src/init.cpp

@@ -6,11 +6,9 @@
 
 /* .Call calls */
 extern "C" SEXP defaultNumThreads();
-extern "C" SEXP setThreadOptions(SEXP, SEXP);
 
 static const R_CallMethodDef CallEntries[] = {
    {"defaultNumThreads", (DL_FUNC) &defaultNumThreads, 0},
-   {"setThreadOptions",  (DL_FUNC) &setThreadOptions,  2},
    {NULL, NULL, 0}
 };
 

src/options.cpp

@@ -8,35 +8,6 @@
 #include <string>
 #include <exception>
 
-#include <tbb/task_scheduler_init.h>
-
-extern "C" SEXP setThreadOptions(SEXP numThreadsSEXP, SEXP stackSizeSEXP) {
-
-   static tbb::task_scheduler_init* s_pTaskScheduler = NULL;
-   if (s_pTaskScheduler != NULL)
-      return Rf_ScalarLogical(0);
-
-   int numThreads = Rf_asInteger(numThreadsSEXP);
-   int stackSize = Rf_asInteger(stackSizeSEXP);
-
-   try
-   {
-      s_pTaskScheduler = new tbb::task_scheduler_init(numThreads, stackSize);
-   }
-   catch(const std::exception& e)
-   {
-      const char* fmt = "Error loading TBB: %s\n";
-      Rf_error(fmt, e.what());
-   }
-   catch(...)
-   {
-      const char* fmt = "Error loading TBB: %s\n";
-      Rf_error(fmt, "(Unknown error)");
-   }
-
-   return Rf_ScalarLogical(1);
-}
-
 extern "C" SEXP defaultNumThreads() {
    SEXP threadsSEXP = Rf_allocVector(INTSXP, 1);
    INTEGER(threadsSEXP)[0] = tbb::task_scheduler_init::default_num_threads();
@@ -47,10 +18,6 @@ extern "C" SEXP defaultNumThreads() {
 
 #include <tthread/tinythread.h>
 
-extern "C" SEXP setThreadOptions(SEXP numThreadsSEXP, SEXP stackSizeSEXP) {
-   return R_NilValue;   
-}
-
 extern "C" SEXP defaultNumThreads() {
    SEXP threadsSEXP = Rf_allocVector(INTSXP, 1);
    INTEGER(threadsSEXP)[0] = tthread::thread::hardware_concurrency();