parallel_for.h

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#ifndef META_PARALLEL_FOR_H_
#define META_PARALLEL_FOR_H_

#include <algorithm>
#include <iterator>
#include <thread>
#include <vector>

#include "parallel/thread_pool.h"

namespace meta
{
namespace parallel
{

template <class Iterator, class Function>
void parallel_for(Iterator begin, Iterator end, Function func)
{
    thread_pool pool;
    parallel_for(begin, end, pool, func);
}

template <class Iterator, class Function>
void parallel_for(Iterator begin, Iterator end, thread_pool& pool,
                  Function func)
{
    auto block_size = std::distance(begin, end)
                      / std::thread::hardware_concurrency();

    Iterator last = begin;
    if (block_size > 0)
    {
        std::advance(last,
                     (std::thread::hardware_concurrency() - 1) * block_size);
    }
    else
    {
        last = end;
        block_size = 1;
    }

    std::vector<std::future<void>> futures;
    // first p - 1 groups
    for (; begin != last; std::advance(begin, block_size))
    {
        futures.emplace_back(pool.submit_task([=]()
        {
            auto mylast = begin;
            std::advance(mylast, block_size);
            std::for_each(begin, mylast, func);
        }));
    }
    // last group
    futures.emplace_back(pool.submit_task([=]()
    { std::for_each(begin, end, func); }));
    for (auto& fut : futures)
        fut.get();
}
}
}

#endif