test the interactions between IMT and tbb::global_control

core/imt/test/CMakeLists.txt

@@ -4,4 +4,4 @@
 # For the licensing terms see $ROOTSYS/LICENSE.
 # For the list of contributors see $ROOTSYS/README/CREDITS.
 
-ROOT_ADD_GTEST(testImt testRTaskArena.cxx testTFuture.cxx testTTaskGroup.cxx LIBRARIES Imt ${TBB_LIBRARIES})
+ROOT_ADD_GTEST(testImt testRTaskArena.cxx testTBBGlobalControl.cxx testTFuture.cxx testTTaskGroup.cxx LIBRARIES Imt ${TBB_LIBRARIES})

core/imt/test/testTBBGlobalControl.cxx

@@ -0,0 +1,55 @@
+#include "TROOT.h"
+#include "ROOT/RTaskArena.hxx"
+#include "ROOT/TThreadExecutor.hxx"
+#include "ROOTUnitTestSupport.h"
+#include "gtest/gtest.h"
+#include "tbb/global_control.h"
+
+#ifdef R__USE_IMT
+
+const unsigned maxConcurrency = ROOT::Internal::LogicalCPUBandwithControl();
+
+TEST(TBBGlobalControl, RTaskArena)
+{
+   if (maxConcurrency <= 1)
+      return; // skip this test on systems with only 1 core
+   auto gTAInstance = ROOT::Internal::GetGlobalTaskArena(maxConcurrency);
+   tbb::global_control c(tbb::global_control::max_allowed_parallelism, 1u);
+   gTAInstance.reset();
+   ROOT_EXPECT_WARNING(gTAInstance = ROOT::Internal::GetGlobalTaskArena(maxConcurrency);,
+                       "RTaskArenaWrapper",
+                       "tbb::global_control is active, limiting the number of parallel workers"
+                       "from this task arena available for execution.");
+}
+
+TEST(TBBGlobalControl, TThreadExecutor)
+{
+   // ***See them pass***
+   ROOT::TThreadExecutor executor{maxConcurrency};
+   executor.Map([]() { return 1; }, 10); // ParallelFor
+   std::vector<double> vd{0., 1., 2.};
+   executor.Reduce(vd, std::plus<double>{}); // ParallelReduce double
+   std::vector<float> vf{0., 1., 2.};
+   executor.Reduce(vf, std::plus<float>{}); // ParallelReduce float
+
+   tbb::global_control c(tbb::global_control::max_allowed_parallelism, 1u);
+
+   if (maxConcurrency <= 1)
+      return; // skip this test on systems with only 1 core
+   // ***See them warn***
+   ROOT_EXPECT_WARNING(executor.Map([]() { return 1; }, 10), "TThreadExecutor::ParallelFor",
+                       "tbb::global_control is limiting the number of parallel workers."
+                       " Proceeding with 1 threads this time");
+
+   // ParallelReduce double
+   ROOT_EXPECT_WARNING(executor.Reduce(vd, std::plus<double>{}), "TThreadExecutor::ParallelReduce",
+                       "tbb::global_control is limiting the number of parallel workers."
+                       " Proceeding with 1 threads this time");
+
+   // ParallelReduce float
+   ROOT_EXPECT_WARNING(executor.Reduce(vf, std::plus<float>{}), "TThreadExecutor::ParallelReduce",
+                       "tbb::global_control is limiting the number of parallel workers."
+                       " Proceeding with 1 threads this time");
+}
+
+#endif