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76 lines
2.3 KiB
C++
76 lines
2.3 KiB
C++
// Copyright 2015-2018 Hans Dembinski
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//
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt
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// or copy at http://www.boost.org/LICENSE_1_0.txt)
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//[ guide_custom_storage
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#include <array>
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#include <atomic>
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#include <boost/histogram.hpp>
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#include <boost/histogram/algorithm/sum.hpp>
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#include <cassert>
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#include <chrono>
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#include <functional>
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#include <thread>
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#include <vector>
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namespace bh = boost::histogram;
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template <typename Histogram>
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void fill(Histogram& h) {
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for (unsigned i = 0; i < 1000; ++i) { h(i % 10); }
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}
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/*
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std::atomic has deleted copy ctor, we need to wrap it in a type with a
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potentially unsafe copy ctor. It can be used in a thread-safe way if some
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rules are followed, see below.
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*/
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template <typename T>
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class copyable_atomic : public std::atomic<T> {
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public:
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using std::atomic<T>::atomic;
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copyable_atomic() = default;
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// this is potentially not thread-safe
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copyable_atomic(const copyable_atomic& rhs) { this->operator=(rhs); }
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// this is potentially not thread-safe
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copyable_atomic& operator=(const copyable_atomic& rhs) {
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if (this != &rhs) { std::atomic<T>::operator=(rhs.load()); }
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return *this;
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}
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};
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int main() {
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/*
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Create histogram with container of atomic counters for parallel filling
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in several threads. You cannot use std::atomic here, because std::atomic
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types are not copyable. Using the copyable_atomic as a work-around is safe,
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if the storage does not change size while it is filled. This means that
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growing axis types are not allowed.
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*/
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auto h = bh::make_histogram_with(std::vector<copyable_atomic<std::size_t>>(),
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bh::axis::integer<>(0, 10));
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/*
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The histogram storage may not be resized in either thread. This is the case
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if you do not use growing axis types. Some notes regarding std::thread.
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- The templated fill function must be instantiated when passed to
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std::thread, do we pass fill<decltype(h)>.
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- std::thread copies the argument. To avoid filling two copies of the
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histogram, we need to pass it via std::ref.
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*/
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std::thread t1(fill<decltype(h)>, std::ref(h));
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std::thread t2(fill<decltype(h)>, std::ref(h));
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t1.join();
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t2.join();
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assert(bh::algorithm::sum(h) == 2000);
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}
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//]
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