Parallel.hpp

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#pragma once
 
#include <SDL3/SDL.h>
 
#include <algorithm>
#include <atomic>
#include <cstdlib>
 
#if defined(GROUP2_HAVE_TBB)
#include <execution>
#endif
 
namespace group2::perf
{

inline std::atomic<bool> parallelEnabled{true};

inline constexpr std::size_t k_parallelThreshold = 64;

inline void initParallelFromEnv()
{
    const char* p = std::getenv("GROUP2_SERVER_PARALLEL");
    const bool wantOff = p != nullptr && (p[0] == '0' || p[0] == 'f' || p[0] == 'F' || p[0] == 'n' || p[0] == 'N');
    const bool wantOn = !wantOff;
    parallelEnabled.store(wantOn, std::memory_order_release);
#if defined(GROUP2_HAVE_TBB)
    SDL_Log("[perf] parallel kernels: %s (TBB-backed; default ON, set GROUP2_SERVER_PARALLEL=0 to disable)",
            wantOn ? "ENABLED" : "disabled");
#else
    SDL_Log("[perf] parallel kernels: sequential fallback (TBB not linked)");
#endif
}

template <class Iter, class Fn>
inline void parallelFor(Iter begin, Iter end, Fn&& fn)
{
#if defined(GROUP2_HAVE_TBB)
    const auto distance = std::distance(begin, end);
    if (parallelEnabled.load(std::memory_order_relaxed) && static_cast<std::size_t>(distance) >= k_parallelThreshold) {
        std::for_each(std::execution::par_unseq, begin, end, std::forward<Fn>(fn));
        return;
    }
#endif
    std::for_each(begin, end, std::forward<Fn>(fn));
}
 
} // namespace group2::perf