mirror of
https://github.com/boostorg/histogram.git
synced 2025-05-09 23:04:07 +00:00
77 lines
2.2 KiB
C++
77 lines
2.2 KiB
C++
// Copyright 2015-2018 Hans Dembinski
|
|
//
|
|
// Distributed under the Boost Software License, Version 1.0.
|
|
// (See accompanying file LICENSE_1_0.txt
|
|
// or copy at http://www.boost.org/LICENSE_1_0.txt)
|
|
|
|
//[ guide_parallel_filling
|
|
|
|
#include <atomic>
|
|
#include <boost/histogram.hpp>
|
|
#include <boost/histogram/algorithm/sum.hpp>
|
|
#include <cassert>
|
|
#include <functional>
|
|
#include <thread>
|
|
#include <vector>
|
|
|
|
// dummy fill function, to be executed in parallel by several threads
|
|
template <typename Histogram>
|
|
void fill(Histogram& h) {
|
|
for (unsigned i = 0; i < 1000; ++i) { h(i % 10); }
|
|
}
|
|
|
|
/*
|
|
std::atomic has deleted copy ctor, we need to wrap it in a type with a
|
|
potentially unsafe copy ctor. It can be used in a thread-safe way if some
|
|
rules are followed, see below.
|
|
*/
|
|
template <typename T>
|
|
class copyable_atomic : public std::atomic<T> {
|
|
public:
|
|
using std::atomic<T>::atomic;
|
|
|
|
// zero-initialize the atomic T
|
|
copyable_atomic() noexcept : std::atomic<T>(T()) {}
|
|
|
|
// this is potentially not thread-safe, see below
|
|
copyable_atomic(const copyable_atomic& rhs) : std::atomic<T>() { this->operator=(rhs); }
|
|
|
|
// this is potentially not thread-safe, see below
|
|
copyable_atomic& operator=(const copyable_atomic& rhs) {
|
|
if (this != &rhs) { std::atomic<T>::store(rhs.load()); }
|
|
return *this;
|
|
}
|
|
};
|
|
|
|
int main() {
|
|
using namespace boost::histogram;
|
|
|
|
/*
|
|
Create histogram with container of atomic counters for parallel filling in
|
|
several threads. You cannot use bare std::atomic here, because std::atomic
|
|
types are not copyable. Using the copyable_atomic as a work-around is safe,
|
|
if the storage does not change size while it is filled. This means that
|
|
growing axis types are not allowed.
|
|
*/
|
|
auto h = make_histogram_with(std::vector<copyable_atomic<std::size_t>>(),
|
|
axis::integer<>(0, 10));
|
|
|
|
/*
|
|
The histogram storage may not be resized in either thread.
|
|
This is the case, if you do not use growing axis types.
|
|
*/
|
|
auto fill_h = [&h]() { fill(h); };
|
|
std::thread t1(fill_h);
|
|
std::thread t2(fill_h);
|
|
std::thread t3(fill_h);
|
|
std::thread t4(fill_h);
|
|
t1.join();
|
|
t2.join();
|
|
t3.join();
|
|
t4.join();
|
|
|
|
assert(algorithm::sum(h) == 4000);
|
|
}
|
|
|
|
//]
|