text: /*
   * Copyright (c) Facebook, Inc. and its affiliates.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #pragma once
  
  #include <string>
  
  #include <folly/synchronization/Hazptr.h>
  
  namespace folly {
  
  /** Wide CAS.
   */
  template <typename T, template <typename> class Atom = std::atomic>
  class HazptrWideCAS {
    struct Node : public hazptr_obj_base<Node, Atom> {
      T val_;
      explicit Node(T v = {}) : val_(v) {}
    };
  
    Atom<Node*> node_;
  
   public:
    HazptrWideCAS() : node_(new Node()) {}
  
    ~HazptrWideCAS() { delete node_.load(std::memory_order_relaxed); }
  
    bool cas(T& u, T& v) {
      Node* n = new Node(v);
      hazptr_holder<Atom> hptr;
      Node* p;
      while (true) {
        p = hptr.get_protected(node_);
        if (p->val_ != u) {
          delete n;
          return false;
        }
        if (node_.compare_exchange_weak(
                p, n, std::memory_order_relaxed, std::memory_order_release)) {
          break;
        }
      }
      hptr.reset();
      p->retire();
      return true;
    }
  };
  
  } // namespace folly
  