ton/tdactor/benchmark/third_party/HazardPointers.h

/******************************************************************************
 * Copyright (c) 2014-2016, Pedro Ramalhete, Andreia Correia
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
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 *       derived from this software without specific prior written permission.

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#ifndef _HAZARD_POINTERS_H_
#define _HAZARD_POINTERS_H_

#include <atomic>
#include <vector>
#include <iostream>

namespace ConcurrencyFreaks {
template <typename T>
class HazardPointers {
 private:
  static const int HP_MAX_THREADS = 128;
  static const int HP_MAX_HPS = 4;  // This is named 'K' in the HP paper
  static const int CLPAD = 128 / sizeof(std::atomic<T*>);
  static const int HP_THRESHOLD_R = 0;                         // This is named 'R' in the HP paper
  static const int MAX_RETIRED = HP_MAX_THREADS * HP_MAX_HPS;  // Maximum number of retired objects per thread

  const int maxHPs;
  const int maxThreads;

  std::atomic<T*>* hp[HP_MAX_THREADS];
  // It's not nice that we have a lot of empty vectors, but we need padding to avoid false sharing
  std::vector<T*> retiredList[HP_MAX_THREADS * CLPAD];

 public:
  HazardPointers(int maxHPs = HP_MAX_HPS, int maxThreads = HP_MAX_THREADS) : maxHPs{maxHPs}, maxThreads{maxThreads} {
    for (int ithread = 0; ithread < HP_MAX_THREADS; ithread++) {
      hp[ithread] =
          new std::atomic<T*>[CLPAD *
                              2];  // We allocate four cache lines to allow for many hps and without false sharing
      for (int ihp = 0; ihp < HP_MAX_HPS; ihp++) {
        hp[ithread][ihp].store(nullptr, std::memory_order_relaxed);
      }
    }
  }

  ~HazardPointers() {
    for (int ithread = 0; ithread < HP_MAX_THREADS; ithread++) {
      delete[] hp[ithread];
      // Clear the current retired nodes
      for (unsigned iret = 0; iret < retiredList[ithread * CLPAD].size(); iret++) {
        delete retiredList[ithread * CLPAD][iret];
      }
    }
  }

  /**
     * Progress Condition: wait-free bounded (by maxHPs)
     */
  void clear(const int tid) {
    for (int ihp = 0; ihp < maxHPs; ihp++) {
      hp[tid][ihp].store(nullptr, std::memory_order_release);
    }
  }

  /**
     * Progress Condition: wait-free population oblivious
     */
  void clearOne(int ihp, const int tid) {
    hp[tid][ihp].store(nullptr, std::memory_order_release);
  }

  /**
     * Progress Condition: lock-free
     */
  T* protect(int index, const std::atomic<T*>& atom, const int tid) {
    T* n = nullptr;
    T* ret;
    while ((ret = atom.load()) != n) {
      hp[tid][index].store(ret);
      n = ret;
    }
    return ret;
  }

  /**
     * This returns the same value that is passed as ptr, which is sometimes useful
     * Progress Condition: wait-free population oblivious
     */
  T* protectPtr(int index, T* ptr, const int tid) {
    hp[tid][index].store(ptr);
    return ptr;
  }

  /**
     * This returns the same value that is passed as ptr, which is sometimes useful
     * Progress Condition: wait-free population oblivious
     */
  T* protectRelease(int index, T* ptr, const int tid) {
    hp[tid][index].store(ptr, std::memory_order_release);
    return ptr;
  }

  /**
     * Progress Condition: wait-free bounded (by the number of threads squared)
     */
  void retire(T* ptr, const int tid) {
    retiredList[tid * CLPAD].push_back(ptr);
    if (retiredList[tid * CLPAD].size() < HP_THRESHOLD_R)
      return;
    for (unsigned iret = 0; iret < retiredList[tid * CLPAD].size();) {
      auto obj = retiredList[tid * CLPAD][iret];
      bool canDelete = true;
      for (int tid = 0; tid < maxThreads && canDelete; tid++) {
        for (int ihp = maxHPs - 1; ihp >= 0; ihp--) {
          if (hp[tid][ihp].load() == obj) {
            canDelete = false;
            break;
          }
        }
      }
      if (canDelete) {
        retiredList[tid * CLPAD].erase(retiredList[tid * CLPAD].begin() + iret);
        delete obj;
        continue;
      }
      iret++;
    }
  }
};
}  // namespace ConcurrencyFreaks

#endif /* _HAZARD_POINTERS_H_ */