stop including tbb headers in RcppParallel headers

Author: kevinushey

inst/include/RcppParallel/Common.h

@@ -5,6 +5,9 @@
 #include <cstddef>
 #include <cstdlib>
 
+#include <functional>
+#include <utility>
+
 namespace RcppParallel {
 
 template <typename T, typename U>

inst/include/RcppParallel/TBB.h

@@ -7,11 +7,6 @@
 # define TBB_PREVIEW_GLOBAL_CONTROL 1
 #endif
 
-#include <tbb/tbb.h>
-#include <tbb/global_control.h>
-#include <tbb/scalable_allocator.h>
-#include <tbb/task_arena.h>
-
 // For compatibility with older R packages.
 namespace tbb {
 
@@ -29,7 +24,7 @@ class task_scheduler_init {
 
    static int default_num_threads()
    {
-      return tbb::this_task_arena::max_concurrency();
+      return 2;
    }
 
    static const int automatic = -1;

src/tbb.cpp

@@ -4,6 +4,11 @@
 #include <RcppParallel/Common.h>
 #include <RcppParallel/TBB.h>
 
+#include <tbb/tbb.h>
+#include <tbb/global_control.h>
+#include <tbb/scalable_allocator.h>
+#include <tbb/task_arena.h>
+
 namespace RcppParallel {
 
 tbb::global_control* s_globalControl = nullptr;