Branch data     Line data    Source code

       1                 :             : // Copyright 2026 HPActor Contributors
       2                 :             : //
       3                 :             : // Licensed under the Apache License, Version 2.0 (the "License");
       4                 :             : // you may not use this file except in compliance with the License.
       5                 :             : // You may obtain a copy of the License at
       6                 :             : //
       7                 :             : //     http://www.apache.org/licenses/LICENSE-2.0
       8                 :             : //
       9                 :             : // Unless required by applicable law or agreed to in writing, software
      10                 :             : // distributed under the License is distributed on an "AS IS" BASIS,
      11                 :             : // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      12                 :             : // See the License for the specific language governing permissions and
      13                 :             : // limitations under the License.
      14                 :             : 
      15                 :             : #pragma once
      16                 :             : 
      17                 :             : #include <atomic>
      18                 :             : #include <cstddef>
      19                 :             : #include <cstdint>
      20                 :             : #include <vector>
      21                 :             : 
      22                 :             : namespace hpactor::metrics {
      23                 :             : 
      24                 :             : // Lock-free MPSC ring buffer. Multi-producer, single-consumer.
      25                 :             : // Capacity must be a power of two.
      26                 :             : // Producer: try_push(value) writes the slot then CAS-claims it with a release fence.
      27                 :             : // Consumer: drain(callback) reads all committed slots since last drain.
      28                 :             : template <typename T, size_t Capacity = 65536>
      29                 :             : class MpscRingBuffer {
      30                 :             :     static_assert((Capacity & (Capacity - 1)) == 0,
      31                 :             :                   "Capacity must be a power of two");
      32                 :             : 
      33                 :             : public:
      34                 :             :     static constexpr size_t kDefaultCapacity = Capacity;
      35                 :             : 
      36                 :         232 :     MpscRingBuffer() : buffer_(Capacity) {}
      37                 :             : 
      38                 :             :     // Producer: write the value, then CAS-claim the slot with a release fence
      39                 :             :     // to ensure the write is visible before the consumer sees the increment.
      40                 :        6655 :     bool try_push(const T& value) noexcept {
      41                 :       13310 :         uint64_t w = write_cursor_.load(std::memory_order_relaxed);
      42                 :             :         do {
      43                 :       19692 :             if (w - read_cursor_.load(std::memory_order_acquire) >= Capacity) {
      44                 :           1 :                 events_lost_.fetch_add(1, std::memory_order_relaxed);
      45                 :           1 :                 return false;
      46                 :             :             }
      47                 :       19690 :         } while (!write_cursor_.compare_exchange_weak(
      48                 :             :             w, w + 1, std::memory_order_acquire, std::memory_order_relaxed));
      49                 :        6654 :         buffer_[w & mask_] = value;
      50                 :             :         std::atomic_thread_fence(std::memory_order_release);
      51                 :        6654 :         return true;
      52                 :             :     }
      53                 :             : 
      54                 :             :     // Consumer: drain all committed slots since last drain.
      55                 :             :     template <typename Fn>
      56                 :        3148 :     size_t drain(Fn&& callback) {
      57                 :        3148 :         uint64_t r = read_cursor_.load(std::memory_order_relaxed);
      58                 :        6296 :         uint64_t w = write_cursor_.load(std::memory_order_acquire);
      59                 :             :         std::atomic_thread_fence(std::memory_order_acquire);
      60                 :        3148 :         size_t count = 0;
      61                 :        8165 :         while (r < w) {
      62                 :        5017 :             callback(buffer_[r & mask_]);
      63                 :        5017 :             ++r;
      64                 :        5017 :             ++count;
      65                 :             :         }
      66                 :        3148 :         read_cursor_.store(r, std::memory_order_release);
      67                 :        3148 :         return count;
      68                 :             :     }
      69                 :             : 
      70                 :           0 :     uint64_t events_lost() const noexcept {
      71                 :           0 :         return events_lost_.load(std::memory_order_relaxed);
      72                 :             :     }
      73                 :             : 
      74                 :           6 :     size_t size() const noexcept {
      75                 :           6 :         uint64_t w = write_cursor_.load(std::memory_order_acquire);
      76                 :           6 :         uint64_t r = read_cursor_.load(std::memory_order_relaxed);
      77                 :           6 :         return static_cast<size_t>(w - r);
      78                 :             :     }
      79                 :             : 
      80                 :           4 :     bool empty() const noexcept { return size() == 0; }
      81                 :             : 
      82                 :             : private:
      83                 :             :     static constexpr size_t mask_ = Capacity - 1;
      84                 :             :     alignas(64) std::atomic<uint64_t> write_cursor_{0};
      85                 :             :     alignas(64) std::atomic<uint64_t> read_cursor_{0};
      86                 :             :     alignas(64) std::atomic<uint64_t> events_lost_{0};
      87                 :             :     std::vector<T> buffer_;
      88                 :             : };
      89                 :             : 
      90                 :             : } // namespace hpactor::metrics