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concurrentfill.cxx
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1/// \file
2/// \ingroup tutorial_v7
3///
4/// \macro_code
5///
6/// \date 2015-07-09
7/// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
8/// is welcome!
9/// \author Axel Naumann <axel@cern.ch>
10
11/*************************************************************************
12 * Copyright (C) 1995-2015, Rene Brun and Fons Rademakers. *
13 * All rights reserved. *
14 * *
15 * For the licensing terms see $ROOTSYS/LICENSE. *
16 * For the list of contributors see $ROOTSYS/README/CREDITS. *
17 *************************************************************************/
18
19#include "ROOT/RHist.hxx"
21
22#include <iostream>
23#include <future>
24#include <random>
25
26using namespace ROOT;
27
28double wasteCPUTime(std::mt19937 &gen)
29{
30 // Simulate number crunching through gen and ridiculous num bits
31 return std::generate_canonical<double, 100>(gen) + std::generate_canonical<double, 100>(gen) +
32 std::generate_canonical<double, 100>(gen) + std::generate_canonical<double, 100>(gen) +
33 std::generate_canonical<double, 100>(gen);
34}
35
37
38/// This function is called within each thread: it spends some CPU time and then
39/// fills a number into the histogram, through the Filler_t. This is repeated
40/// several times.
41void theTask(Filler_t filler)
42{
43 std::mt19937 gen;
44
45 for (int i = 0; i < 3000000; ++i)
46 filler.Fill({wasteCPUTime(gen), wasteCPUTime(gen)});
47}
48
49/// This example fills a histogram concurrently, from several threads.
50void concurrentHistFill(Experimental::RH2D &hist)
51{
52 // RHistConcurrentFillManager allows multiple threads to fill the histogram
53 // concurrently.
54 //
55 // Details: each thread's Fill() calls are buffered. once the buffer is full,
56 // the RHistConcurrentFillManager locks and flushes the buffer into the
57 // histogram.
59
60 std::array<std::thread, 8> threads;
61
62 // Let the threads fill the histogram concurrently.
63 for (auto &thr: threads) {
64 // Each thread calls fill(), passing a dedicated filler per thread.
65 thr = std::thread(theTask, fillMgr.MakeFiller());
66 }
67
68 // Join them.
69 for (auto &thr: threads)
70 thr.join();
71}
72
73void concurrentfill()
74{
75 // This histogram will be filled from several threads.
76 Experimental::RH2D hist{{100, 0., 1.}, {{0., 1., 2., 3., 10.}}};
77
78 concurrentHistFill(hist);
79
80 std::cout << hist.GetEntries() << '\n';
81}
void Fill(const CoordArray_t &x, Weight_t weight=1.)
Manages the synchronization of calls to FillN().
Buffers a thread's Fill calls and submits them to the RHistConcurrentFillManager.
Histogram class for histograms with DIMENSIONS dimensions, where each bin count is stored by a value ...
Definition RHist.hxx:53
int64_t GetEntries() const noexcept
Get the number of entries this histogram was filled with.
Definition RHist.hxx:169
tbb::task_arena is an alias of tbb::interface7::task_arena, which doesn't allow to forward declare tb...