40 lines
1.2 KiB
C++
40 lines
1.2 KiB
C++
template <typename Iterator, typename Func>
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void
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parallel_for_each(Iterator first, Iterator last, Func f)
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{
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unsigned long const length = std::distance(first, last);
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if (!length)
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return;
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unsigned long const min_per_thread = 25;
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unsigned long const max_threads =
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(length + min_per_thread - 1) / min_per_thread;
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unsigned long const hardware_threads = std::thread::hardware_concurrency();
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unsigned long const num_threads =
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std::min(hardware_threads != 0 ? hardware_threads : 2, max_threads);
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unsigned long const block_size = length / num_threads;
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std::vector<std::future<void>> futures(num_threads - 1);
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std::vector<std::thread> threads(num_threads - 1);
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join_threads joiner(threads);
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Iterator block_start = first;
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for (unsigned long i = 0; i < (num_threads - 1); ++i) {
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Iterator block_end = block_start;
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std::advance(block_end, block_size);
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std::packaged_task<void(void)> task(
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[=]() { std::for_each(block_start, block_end, f); });
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futures[i] = task.get_future();
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threads[i] = std::thread(std::move(task));
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block_start = block_end;
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}
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std::for_each(block_start, last, f);
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for (unsigned long i = 0; i < (num_threads - 1); ++i) {
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futures[i].get();
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}
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}
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