77 lines
2.3 KiB
C++
77 lines
2.3 KiB
C++
template<typename Iterator,typename MatchType>
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Iterator parallel_find(Iterator first,Iterator last,MatchType match)
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{
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struct find_element
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{
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void operator()(Iterator begin,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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{
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for(;(begin!=end) && !done_flag->load();++begin)
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{
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if(*begin==match)
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{
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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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{
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try
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{
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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=
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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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{
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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(find_element(),
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block_start,block_end,match,
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&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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{
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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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