最低要求c++17 static inline实现head only

    1. #pragma once
    3. #include <atomic>
    5. template<typename Traits>
    6. class AllocImpl;
    9. template<typename Traits>
    10. inline auto Next() {
    11. return AllocImpl<Traits>::Next();
    12. }
    17. template<typename Traits>
    18. class AllocImpl {
    19. public:
    20.     using Type = typename Traits::Type;
    22.     static Type Next() {
    23.         if (current < max) {
    24.             return current++;
    25.         }
    26.         return SlowNext();
    27.     }
    29. private:
    30.     static Type SlowNext();
    32. private:
    33.     static inline std::atomic<Type> global{Traits::kMin};
    35.     static inline thread_local Type current = 0;
    36.     static inline thread_local Type max = 0;
    37. };
    39. template<typename Traits>
    40. typename AllocImpl<Traits>::Type AllocImpl<Traits>::SlowNext() {
    41.     static_assert(Traits::kMin < Traits::kMax);
    42.     static_assert(Traits::kBatchSize > 0);
    43.     static_assert(Traits::kMin + Traits::kBatchSize < Traits::kMax,
    44.         "Not supported due to implementation limitations.");
    45.     static_assert(Traits::kBatchSize > 1,
    46.         "Not supported due to implementation limitations.");
    48.     // Get more IDs from global counter...
    49.     Type read, next;
    50.     do {
    51.         read = global.load(std::memory_order_relaxed);
    52.         current = read;
    53.         if (read > Traits::kMax - Traits::kBatchSize /* Overflowing */) {
    54.             next = Traits::kMin;
    55.             max = Traits::kMax;
    56.         }
    57.         else {
    58.             next = read + Traits::kBatchSize;
    59.             max = next;
    60.         }
    61.     } while (
    62.         !global.compare_exchange_weak(read, next, std::memory_order_relaxed));
    64.     // ... and retry.
    65.     return Next();
    66. }

    使用时指定1个traits.

    1. struct ClientIdAllocTraits {
    2.     using Type = std::uint64_t;
    3.     static constexpr const Type kMin = 0;
    4.     static constexpr const Type kMax = 999999999999999;
    5.     static constexpr const Type kBatchSize = 200;
    6. };
    8. int main()
    9. {
    10.     while (true) {
    11.         std::cout << Next<ClientIdAllocTraits>() << std::endl;
    12.     }
    13.     return 0;
    14. }