#include <iostream>
#include <vector>
#include <list>
#include <algorithm>

#include <TROOT.h>
#include <TFile.h>
#include <TString.h>
#include <TEventList.h>
#include <TTree.h>
#include <TThread.h>

using namespace std;

TString INPUTFILE = "RunAndEventTree.root";
TString TREENAME = "GoodEventList";
const Int_t NTHREADS = 4;

TFile *inFile; 
TTree *inTree;
TEventList *eventList[NTHREADS];

Float_t runNumber, eventNumber;

void *threadFunction(void *a){

  Int_t *args = (Int_t*)a;
  Int_t threadIndex = args[0];
  Int_t rNum = args[1];

  TThread::Lock();
  cout <<"This is thread: " <<threadIndex 
       <<" Looking for run number: " <<rNum <<endl;

  TThread::UnLock();

  //The line below is the problem
  //Try moving it into the Lock/UnLock block above to see that it works
  //____________________________________________________________________
  inTree->Draw(Form(">>elist_%d",threadIndex),Form("RunNum==%d",rNum));
  //____________________________________________________________________

  eventList[threadIndex] = (TEventList*)gDirectory->Get(Form("elist_%d",threadIndex));
  eventList[threadIndex]->Print();

  return 0;

}


void drawFromThreads(){

  inFile = new TFile(INPUTFILE,"READ");
  inTree = (TTree*)inFile->Get(TREENAME);

  inTree->SetBranchAddress("RunNum",&runNumber);
  inTree->SetBranchAddress("EventNum",&eventNumber);

  //First create a vector of all the run numbers
  std::vector<long> runNumberVec;
  Long64_t nEntries = inTree->GetEntries();
  for (Int_t i=0; i<nEntries; i++){
   inTree->GetEntry(i);
   runNumberVec.push_back((long)runNumber);
  }

  //Each entry in the input tree has a run number and event number
  //so there will be duplicate run numbers in the run vector
  //thus sort the run vector and remove duplicates
  std::vector<long>::iterator it;
  std::sort(runNumberVec.begin(),runNumberVec.end());
  it = std::unique(runNumberVec.begin(),runNumberVec.end());
  runNumberVec.resize(std::distance(runNumberVec.begin(),it));

  cout <<"The Number of Unique RUN NUMBERS is: " <<runNumberVec.size() <<endl;

  //There should be another control structure around this thread block to 
  //loop through all the run numbers in runNumberVec, but for proof of principle this
  //will do for now :)
  TThread *thread[NTHREADS];
  Int_t threadArgs[NTHREADS][2];
  for (Int_t i=0; i<NTHREADS; i++){
    threadArgs[i][0] = i;
    threadArgs[i][1] = runNumberVec[i];
    thread[i] = new TThread(Form("thread_%d",i),threadFunction, (void *)threadArgs[i]);
    thread[i]->Run();
  }

  for (Int_t i=0; i<NTHREADS; i++)
    thread[i]->Join();

}