{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "7eb68a0d",
   "metadata": {},
   "source": [
    "# mtbb_fillHistos\n",
    "Fill histograms in parallel and write them on file\n",
    "with a multithreaded approach using\n",
    "TThreadExecutor and TExecutor::Map.\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "**Author:** Danilo Piparo  \n",
    "<i><small>This notebook tutorial was automatically generated with <a href= \"https://github.com/root-project/root/blob/master/documentation/doxygen/converttonotebook.py\">ROOTBOOK-izer</a> from the macro found in the ROOT repository  on Tuesday, May 19, 2026 at 08:11 PM.</small></i>"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "33839635",
   "metadata": {
    "collapsed": false,
    "execution": {
     "iopub.execute_input": "2026-05-19T20:11:14.008502Z",
     "iopub.status.busy": "2026-05-19T20:11:14.008259Z",
     "iopub.status.idle": "2026-05-19T20:11:14.334710Z",
     "shell.execute_reply": "2026-05-19T20:11:14.333760Z"
    }
   },
   "outputs": [],
   "source": [
    "const UInt_t nNumbers = 20000000U;\n",
    "\n",
    "const UInt_t nThreads = 4U;"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "420e4c88",
   "metadata": {},
   "source": [
    "We define our work item"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "3debc206",
   "metadata": {
    "collapsed": false,
    "execution": {
     "iopub.execute_input": "2026-05-19T20:11:14.343004Z",
     "iopub.status.busy": "2026-05-19T20:11:14.342873Z",
     "iopub.status.idle": "2026-05-19T20:11:14.575962Z",
     "shell.execute_reply": "2026-05-19T20:11:14.557387Z"
    }
   },
   "outputs": [],
   "source": [
    "auto workItem = [](UInt_t workerID) {\n",
    "   // One generator, file and ntuple per worker\n",
    "   TRandom3 workerRndm(workerID); // Change the seed\n",
    "   TFile f(Form(\"myFile_mtbb001_%u.root\", workerID), \"RECREATE\");\n",
    "   TH1F h(Form(\"myHisto_%u\", workerID), \"The Histogram\", 64, -4, 4);\n",
    "   for (UInt_t i = 0; i < nNumbers; ++i) {\n",
    "      h.Fill(workerRndm.Gaus());\n",
    "   }\n",
    "   h.Write();\n",
    "   return 0;\n",
    "};"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "c38e39c2",
   "metadata": {},
   "source": [
    "Create the pool of threads"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "6e899b5c",
   "metadata": {
    "collapsed": false,
    "execution": {
     "iopub.execute_input": "2026-05-19T20:11:14.580395Z",
     "iopub.status.busy": "2026-05-19T20:11:14.580250Z",
     "iopub.status.idle": "2026-05-19T20:11:14.787082Z",
     "shell.execute_reply": "2026-05-19T20:11:14.786633Z"
    }
   },
   "outputs": [],
   "source": [
    "ROOT::TThreadExecutor pool(nThreads);"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "332ba117",
   "metadata": {},
   "source": [
    "Fill the pool with work"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "9d0235e6",
   "metadata": {
    "collapsed": false,
    "execution": {
     "iopub.execute_input": "2026-05-19T20:11:14.796198Z",
     "iopub.status.busy": "2026-05-19T20:11:14.796065Z",
     "iopub.status.idle": "2026-05-19T20:11:15.774533Z",
     "shell.execute_reply": "2026-05-19T20:11:15.773831Z"
    }
   },
   "outputs": [],
   "source": [
    "pool.Map(workItem, ROOT::TSeqI(nThreads));\n",
    "return 0;"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d9d84a25",
   "metadata": {},
   "source": [
    "Draw all canvases "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "794690f0",
   "metadata": {
    "collapsed": false,
    "execution": {
     "iopub.execute_input": "2026-05-19T20:11:15.776543Z",
     "iopub.status.busy": "2026-05-19T20:11:15.776388Z",
     "iopub.status.idle": "2026-05-19T20:11:15.979826Z",
     "shell.execute_reply": "2026-05-19T20:11:15.979226Z"
    }
   },
   "outputs": [],
   "source": [
    "gROOT->GetListOfCanvases()->Draw()"
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "ROOT C++",
   "language": "c++",
   "name": "root"
  },
  "language_info": {
   "codemirror_mode": "text/x-c++src",
   "file_extension": ".C",
   "mimetype": " text/x-c++src",
   "name": "c++"
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 },
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 "nbformat_minor": 5
}