rcanvas_mt.cxx File Reference

Detailed Description

This macro demonstrate usage of ROOT7 graphics from many threads Three different canvases in three different threads are started and regularly updated.

Extra thread created in background and used to run http protocol, in/out websocket communications and process http requests Main application thread (CLING interactive session) remains fully functional

 
/*************************************************************************
 * Copyright (C) 1995-2025, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
 
#include "ROOT/RWebWindowsManager.hxx"
#include "ROOT/RCanvas.hxx"
#include "ROOT/TObjectDrawable.hxx"
 
#include "TRandom3.h"
#include "TEnv.h"
#include "TROOT.h"
#include "TH1.h"
#include "TColor.h"
 
#include <thread>
#include <iostream>
 
using namespace ROOT::Experimental;
 
void draw_canvas(const std::string &title, Int_t col1)
{
   // Create histograms
   auto hist1 = new TH1D("hist1", "hist1", 100, -10, 10);
   auto hist2 = new TH1D("hist2", "hist2", 100, -10, 10);
 
   hist1->SetLineColor(col1);
   hist2->SetLineColor(kBlue);
 
   TRandom3 random;
   Float_t px, py;
 
   for (int n = 0; n < 10000; ++n) {
      random.Rannor(px, py);
      hist1->Fill(px - 2);
      hist2->Fill(py + 2);
   }
 
   // Create a canvas to be displayed.
   auto canvas = RCanvas::Create(title);
 
   canvas->Draw<TObjectDrawable>(hist1, "");
   canvas->Draw<TObjectDrawable>(hist2, "same");
 
   int maxloop = 100;
 
   canvas->Show();
 
   std::cout << title << " started" << std::endl;
 
   for (int loop = 0; loop < maxloop; ++loop) {
 
      for (int n = 0; n < 10000; ++n) {
         random.Rannor(px, py);
         hist1->Fill(px - 2);
         hist2->Fill(py + 2);
      }
 
      canvas->Modified();
 
      canvas->Update();
      canvas->Run(0.2); // let run canvas code for next 0.5 seconds
 
      // if (loop == 0)
      //    canvas->SaveAs(title + "_first.png");
      // if (loop == maxloop - 1)
      //    canvas->SaveAs(title + "_last.png");
   }
 
   std::cout << title << " completed" << std::endl;
 
   // remove from global list, will be destroyed with thread exit
   canvas->Remove();
}
 
void rcanvas_mt(bool block_main_thread = true)
{
   TDirectory::TContext ctx{nullptr}; // Don't register histograms to the current directory
 
   if (block_main_thread) {
      // let use special http thread to process requests, do not need main thread
      // required while gSystem->ProcessEvents() will be blocked
      gEnv->SetValue("WebGui.HttpThrd", "yes");
 
      // let create special threads for data sending, optional
      gEnv->SetValue("WebGui.SenderThrds", "yes");
   }
 
   ROOT::EnableThreadSafety();
 
   // create instance in main thread, used to assign thread id as well
   ROOT::RWebWindowsManager::Instance();
 
   std::thread thrd1(draw_canvas, "First canvas", kRed);
   std::thread thrd2(draw_canvas, "Second canvas", kBlue);
   std::thread thrd3(draw_canvas, "Third canvas", kGreen);
 
   if (block_main_thread) {
      // wait until threads execution finished
      thrd1.join();
      thrd2.join();
      thrd3.join();
   } else {
      // detach threads and return to CLING
      thrd1.detach();
      thrd2.detach();
      thrd3.detach();
   }
}

Date

2018-08-16

Warning

This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback is welcome!

Author

Sergey Linev

Definition in file rcanvas_mt.cxx.