mcas_helper.h

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/*
The MIT License (MIT)

Copyright (c) 2015 University of Central Florida's Computer Software Engineering
Scalable & Secure Systems (CSE - S3) Lab

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
#ifndef TERVEL_MCAS_MCAS_HELPER_H_
#define TERVEL_MCAS_MCAS_HELPER_H_

#include <tervel/util/info.h>
#include <tervel/util/descriptor.h>
#include <tervel/util/memory/hp/hazard_pointer.h>
#include <tervel/util/memory/rc/descriptor_util.h>

#include <tervel/algorithms/wf/mcas/mcas.h>
#include <tervel/algorithms/wf/mcas/mcas_casrow.h>

namespace tervel {
namespace algorithms {
namespace wf {
namespace mcas {

template<class T>
class MCAS;
template<class T>
class CasRow;

template<class T>
class Helper : public util::Descriptor {
 public:
  Helper<T>(MCAS<T> *mcas_op, CasRow<T> *cas_row)
    : cas_row_(cas_row), mcas_op_(mcas_op) {}

  using util::Descriptor::on_watch;
  bool on_watch(std::atomic<void *> *address, void * value) {
    typedef util::memory::hp::HazardPointer::SlotID t_SlotID;
    bool success = util::memory::hp::HazardPointer::watch(
          t_SlotID::SHORTUSE, mcas_op_, address, value);

    if (success) {
      /* Success, means that the MCAS object referenced by this Helper can not
       * be freed while we check to make sure this Helper is assocaited with
       * it. */
      Helper<T> *curr_mch = cas_row_->helper_.load();
      if (curr_mch == nullptr) {
         if (cas_row_->helper_.compare_exchange_strong(curr_mch, this)) {
           /* If this passed then curr_mch == nullptr, so we set it to be ==
            * this */
            curr_mch = this;
         }
      }

      assert(cas_row_->helper_.load() == curr_mch);

      if (curr_mch != this) {
        /* This Helper was placed in error, remove it and replace it with the
         * logic value of this object (expected_value)
         */
        address->compare_exchange_strong(value, cas_row_->expected_value_);
        success = false;
      }
      /* No longer need HP protection, if we have RC protection on an associated
       * Helper. If we don't it, the value at this address must have changed and
       * we don't need it either way.
       */
      util::memory::hp::HazardPointer::unwatch(t_SlotID::SHORTUSE);
    }  // End Successfull watch

    if (success) {
      assert(cas_row_->helper_.load() != nullptr);
      assert(util::memory::rc::is_watched(this));
      assert(util::memory::hp::HazardPointer::is_watched(mcas_op_));
    }

    return success;
  };


  using util::Descriptor::complete;
  void * complete(void *value, std::atomic<void *> *address) {
    assert(cas_row_->helper_.load());
    assert(util::memory::rc::is_watched(this));
    assert(util::memory::hp::HazardPointer::is_watched(this->mcas_op_));
    Helper<T>* temp_null = nullptr;
    this->cas_row_->helper_.compare_exchange_strong(temp_null, this);

    bool success = false;
    if (temp_null == nullptr || temp_null == this) {
      /* This implies it was successfully associated
         So call the complete function of the MCAS operation */
      success = this->mcas_op_->mcas_complete(this->cas_row_);
      if (util::RecursiveAction::recursive_return()) {
        /* If the thread is performing a recursive return back to its own
           operation, then just return null, it will be ignored. */
        return nullptr;
      }
    }

    if (success) {
    /* If the MCAS op was successfull then remove the Helper by replacing
        it with the new_value */
      address->compare_exchange_strong(value,
          reinterpret_cast<void *>(this->cas_row_->new_value_));
    } else {
      /*Otherwise remove the Helper by replacing it with the expected_value*/
      address->compare_exchange_strong(value,
          reinterpret_cast<void *>(this->cas_row_->expected_value_));
    }
    // Return the new current value of the position
    return address->load();
  };

  using util::Descriptor::get_logical_value;
  void * get_logical_value() {
    if (this->mcas_op_->state_ ==  MCAS<T>::MCasState::PASS) {
      return this->cas_row_->new_value_;
    }

    return this->cas_row_->expected_value_;
  }

 private:
  // The Row in the MCAS operation this MCH was placed for
  CasRow<T> *cas_row_;
  // The MCAS which contains the cas_row_
  MCAS<T> *mcas_op_;
};  // Helper



}  // namespace mcas
}  // namespace wf
}  // namespace algorithms
}  // namespace tervel

#endif  // TERVEL_MCAS_MCAS_HELPER_H_