#include "TROOT.h"
#include "Math/MinimizerOptions.h"
#include "TH1.h"
#include "TF1.h"
#include "TRandom3.h"
#include <thread>
using std::thread;
using std::vector; 

void a(int type = 0){
   ROOT::EnableThreadSafety();
   TH1::AddDirectory(kFALSE);
   if (type) {
      ROOT::Math::MinimizerOptions::SetDefaultMinimizer("Minuit"); // but also the default minimiser is thread unsafe
      printf("Using TMinuit \n");
   }
   else {
      ROOT::Math::MinimizerOptions::SetDefaultMinimizer("Minuit2"); // but also the default minimiser is thread unsafe
      printf("Using Minuit2 \n");      
   }
   vector<thread> threads;
   //gSystem->Load("libMinuit2");
 
   auto gaus = (TF1*) gROOT->GetFunction("gaus");
   for (int i=0;i<8;++i){
      auto f = [&](){
         int ithread = i; 
         TF1* myGaus;
         {
         R__LOCKGUARD(gGlobalMutex);
         //std::cout << "creating TF1 class " << std::endl;
         myGaus = new TF1(*gaus);
         //std::cout << "TF1 class created" << std::endl;
         }
         //TCanvas c; // W/o this, another problem is detected.
         TRandom3 rndm(0);
         TH1F h("h","h",100,-3,3);
         for (int j=0;j<1000;++j){
            h.Fill(rndm.Gaus(0,1));
         }
         auto r = h.Fit(myGaus,"Q0SL");
         {
            R__LOCKGUARD(gGlobalMutex);
            std::cout << "result for thread " << ithread << std::endl;
            r->Print();
         }
         delete myGaus;
      };
      threads.emplace_back(f);
   }
   for (auto&& t : threads) t.join();
}
int main(int argc, char ** argv) {
   if (argc > 1) 
      a(1);
   else
      a(0);
}