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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) 1995-2021, 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/RCanvas.hxx"
#include "TRandom3.h"
#include "TEnv.h"
#include "TROOT.h"
#include <thread>
#include <iostream>
// macro must be here while cling is not capable to load
// library automatically for outlined function see ROOT-10336
using namespace ROOT::Experimental;
void draw_canvas(const std::string &title, RColor col)
// Create histograms
RAxisConfig xaxis(100, -10., 10.);
auto pHist = std::make_shared<RH1D>(xaxis);
auto pHist2 = std::make_shared<RH1D>(xaxis);
TRandom3 random;
Float_t px, py;
for (int n = 0; n < 10000; ++n) {
random.Rannor(px, py);
pHist->Fill(px - 2);
pHist2->Fill(py + 2);
// Create a canvas to be displayed.
auto canvas = RCanvas::Create(title);
canvas->Draw(pHist)->line.color = col;
canvas->Draw(pHist2)->line.color = RColor::kBlue;
int maxloop = 100;
std::cout << title << " started" <<std::endl;
for (int loop = 0; loop < maxloop; ++loop) {
for (int n = 0; n < 10000; ++n) {
random.Rannor(px, py);
pHist->Fill(px - 2);
pHist2->Fill(py + 2);
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
void rcanvas_mt(bool block_main_thread = true)
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");
// create instance in main thread, used to assign thread id as well
std::thread thrd1(draw_canvas, "First canvas", RColor::kRed);
std::thread thrd2(draw_canvas, "Second canvas", RColor::kBlue);
std::thread thrd3(draw_canvas, "Third canvas", RColor::kGreen);
if (block_main_thread) {
// wait until threads execution finished
} else {
// detach threads and return to CLING
float Float_t
Definition: RtypesCore.h:57
Definition: Rtypes.h:472
@ kRed
Definition: Rtypes.h:66
@ kGreen
Definition: Rtypes.h:66
@ kBlue
Definition: Rtypes.h:66
R__EXTERN TEnv * gEnv
Definition: TEnv.h:170
virtual void SetValue(const char *name, const char *value, EEnvLevel level=kEnvChange, const char *type=nullptr)
Set the value of a resource or create a new resource.
Definition: TEnv.cxx:736
Random number generator class based on M.
Definition: TRandom3.h:27
virtual void Rannor(Float_t &a, Float_t &b)
Return 2 numbers distributed following a gaussian with mean=0 and sigma=1.
Definition: TRandom.cxx:500
const Int_t n
Definition: legend1.C:16
void EnableThreadSafety()
Enables the global mutex to make ROOT thread safe/aware.
Definition: TROOT.cxx:493
This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback is welcome!
Sergey Linev s.lin.nosp@m.ev@g.nosp@m.si.de

Definition in file rcanvas_mt.cxx.