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       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                 :             : #include <hpactor/sched/a2ws.hpp>
      16                 :             : 
      17                 :             : namespace hpactor::sched {
      18                 :             : 
      19                 :         107 : A2WS::A2WS(uint32_t num_workers, uint32_t pool_size)
      20                 :         214 :     : num_workers_(num_workers), pool_size_(pool_size), workers_(num_workers),
      21                 :         214 :       victim_hints_(num_workers) {
      22                 :             :     // Initialize victim hints to point to self + 1 (start scanning from next
      23                 :             :     // worker)
      24                 :         215 :     for (uint32_t i = 0; i < num_workers; ++i) {
      25                 :         108 :         victim_hints_[i].store((i + 1) % num_workers, std::memory_order_relaxed);
      26                 :             :     }
      27                 :         107 : }
      28                 :             : 
      29                 :       63033 : uint32_t A2WS::get_victim(uint32_t thief_index) {
      30                 :             :     // Simple round-robin with hint
      31                 :       63033 :     uint32_t hint = victim_hints_[thief_index].load(std::memory_order_relaxed);
      32                 :       63033 :     return hint;
      33                 :             : }
      34                 :             : 
      35                 :       63020 : void A2WS::record_attempt(uint32_t thief, uint32_t victim, bool success) {
      36                 :       63020 :     workers_[thief].steal_attempts.fetch_add(1, std::memory_order_relaxed);
      37                 :             : 
      38                 :       63020 :     if (success) {
      39                 :           1 :         workers_[thief].steal_successes.fetch_add(1, std::memory_order_relaxed);
      40                 :             :     }
      41                 :             : 
      42                 :             :     // Update victim hint based on result
      43                 :             :     // If steal failed, advance to next potential victim
      44                 :       63020 :     uint32_t current_hint = victim_hints_[thief].load(std::memory_order_relaxed);
      45                 :       63020 :     uint32_t next_hint = (victim + 1) % num_workers_;
      46                 :             : 
      47                 :       63020 :     if (!success) {
      48                 :             :         // Failed steal - try next victim
      49                 :       63019 :         victim_hints_[thief].store(next_hint, std::memory_order_relaxed);
      50                 :             :     } else {
      51                 :             :         // Success - stick with current victim for now
      52                 :             :         // Could also use adaptive logic to prefer victims with history of
      53                 :             :         // success
      54                 :             :     }
      55                 :             : 
      56                 :             :     (void)thief;        // Currently unused in victim selection
      57                 :             :     (void)current_hint; // Currently unused
      58                 :       63020 : }
      59                 :             : 
      60                 :          16 : void A2WS::record_steal(uint32_t thief, uint32_t victim) {
      61                 :          16 :     if (same_pool(thief, victim)) {
      62                 :          15 :         workers_[thief].local_steals.fetch_add(1, std::memory_order_relaxed);
      63                 :             :     } else {
      64                 :           1 :         workers_[thief].remote_steals.fetch_add(1, std::memory_order_relaxed);
      65                 :             :     }
      66                 :          16 : }
      67                 :             : 
      68                 :           4 : void A2WS::get_victim_pool(uint32_t worker, uint32_t& start, uint32_t& end) const {
      69                 :           4 :     uint32_t pool_id = worker / pool_size_;
      70                 :           4 :     start = pool_id * pool_size_;
      71                 :           4 :     end = std::min(start + pool_size_, num_workers_);
      72                 :           4 : }
      73                 :             : 
      74                 :          21 : bool A2WS::same_pool(uint32_t a, uint32_t b) const {
      75                 :          21 :     return (a / pool_size_) == (b / pool_size_);
      76                 :             : }
      77                 :             : 
      78                 :             : } // namespace hpactor::sched