provide back-compat class defn

Author: kevinushey

.Rbuildignore

@@ -4,6 +4,7 @@
 ^\.Rprofile$
 ^\.Rproj\.user$
 ^appveyor\.yml$
+^check$
 ^doc$
 ^gen$
 ^libs$

.gitignore

@@ -3,6 +3,7 @@
 .Rhistory
 .RData
 .DS_Store
+check
 inst/doc
 inst/lib
 inst/libs

inst/include/RcppParallel.h

@@ -18,14 +18,13 @@
 #endif
 
 #if RCPP_PARALLEL_USE_TBB
-#if defined(WINNT) && defined(__aarch64__) && !defined(TBB_USE_GCC_BUILTINS)
-#define TBB_USE_GCC_BUILTINS 1
-#endif
+# if defined(WINNT) && defined(__aarch64__) && !defined(TBB_USE_GCC_BUILTINS)
+#  define TBB_USE_GCC_BUILTINS 1
+# endif
 # include "RcppParallel/TBB.h"
 #endif
 
 #include "RcppParallel/Backend.h"
-
 #include "RcppParallel/RVector.h"
 #include "RcppParallel/RMatrix.h"
 

inst/include/RcppParallel/TBB.h

@@ -10,6 +10,37 @@
 #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 {
+
+#ifndef __TBB_task_scheduler_init_H
+#define __TBB_task_scheduler_init_H
+
+class task_scheduler_init {
+   
+public:
+   task_scheduler_init(
+      int number_of_threads = -1,
+      std::size_t stack_size = 0)
+   {
+   }
+   
+   static int default_num_threads()
+   {
+      return tbb::this_task_arena::max_concurrency();
+   }
+   
+   static const int automatic = -1;
+   static const int deferred = -2;
+ 
+};
+
+#endif
+
+} // end namespace tbb
+
 
 namespace RcppParallel {