69 lines
1.9 KiB
C++
69 lines
1.9 KiB
C++
template <typename Iterator, typename MatchType>
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Iterator
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parallel_find(Iterator first, Iterator last, MatchType match)
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{
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struct find_element {
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void operator()(Iterator begin,
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Iterator end,
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MatchType match,
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std::promise<Iterator>* result,
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std::atomic<bool>* done_flag)
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{
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try {
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for (; (begin != end) && !done_flag->load(); ++begin) {
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if (*begin == match) {
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result->set_value(begin);
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done_flag->store(true);
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return;
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}
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}
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}
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catch (...) {
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try {
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result->set_exception(std::current_exception());
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done_flag->store(true);
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}
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catch (...) {
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}
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}
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}
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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 last;
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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::promise<Iterator> result;
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std::atomic<bool> done_flag(false);
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std::vector<std::thread> threads(num_threads - 1);
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{
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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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threads[i] = std::thread(
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find_element(), block_start, block_end, match, &result, &done_flag);
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block_start = block_end;
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}
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find_element()(block_start, last, match, &result, &done_flag);
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}
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if (!done_flag.load()) {
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return last;
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}
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return result.get_future().get();
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}
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