45 lines
1.3 KiB
C++
45 lines
1.3 KiB
C++
template<typename Iterator,typename Func>
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void 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=
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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::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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{
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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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[=]()
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{
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std::for_each(block_start,block_end,f);
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});
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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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{
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futures[i].get();
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}
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}
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