thread/src/shared_mutex.cpp

// Copyright Howard Hinnant 2007-2010.
// Copyright Vicente J. Botet Escriba 2012.
// Use, modification and distribution are subject to the
// Boost Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#include <boost/thread/v2/shared_mutex.hpp>
#include <boost/thread/locks.hpp>

namespace boost
{

  namespace thread_v2
  {

    // shared_mutex

    shared_mutex::shared_mutex()
    : state_(0)
    {
    }

    shared_mutex::~shared_mutex()
    {
      boost::lock_guard<mutex_t> _(mut_);
    }

    // Exclusive ownership

    void
    shared_mutex::lock()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      while (state_ & write_entered_)
        gate1_.wait(lk);
      state_ |= write_entered_;
      while (state_ & n_readers_)
        gate2_.wait(lk);
    }

    bool
    shared_mutex::try_lock()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      if (state_ == 0)
      {
        state_ = write_entered_;
        return true;
      }
      return false;
    }

    void
    shared_mutex::unlock()
    {
      boost::lock_guard<mutex_t> _(mut_);
      state_ = 0;
      gate1_.notify_all();
    }

    // Shared ownership

    void
    shared_mutex::lock_shared()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      while ((state_ & write_entered_) || (state_ & n_readers_) == n_readers_)
        gate1_.wait(lk);
      count_t num_readers = (state_ & n_readers_) + 1;
      state_ &= ~n_readers_;
      state_ |= num_readers;
    }

    bool
    shared_mutex::try_lock_shared()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      count_t num_readers = state_ & n_readers_;
      if (!(state_ & write_entered_) && num_readers != n_readers_)
      {
        ++num_readers;
        state_ &= ~n_readers_;
        state_ |= num_readers;
        return true;
      }
      return false;
    }

    void
    shared_mutex::unlock_shared()
    {
      boost::lock_guard<mutex_t> _(mut_);
      count_t num_readers = (state_ & n_readers_) - 1;
      state_ &= ~n_readers_;
      state_ |= num_readers;
      if (state_ & write_entered_)
      {
        if (num_readers == 0)
          gate2_.notify_one();
      }
      else
      {
        if (num_readers == n_readers_ - 1)
          gate1_.notify_one();
      }
    }

    // upgrade_mutex

    upgrade_mutex::upgrade_mutex()
    : gate1_(),
      gate2_(),
      state_(0)
    {
    }

    upgrade_mutex::~upgrade_mutex()
    {
      boost::lock_guard<mutex_t> _(mut_);
    }

    // Exclusive ownership

    void
    upgrade_mutex::lock()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      while (state_ & (write_entered_ | upgradable_entered_))
        gate1_.wait(lk);
      state_ |= write_entered_;
      while (state_ & n_readers_)
        gate2_.wait(lk);
    }

    bool
    upgrade_mutex::try_lock()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      if (state_ == 0)
      {
        state_ = write_entered_;
        return true;
      }
      return false;
    }

    void
    upgrade_mutex::unlock()
    {
      boost::lock_guard<mutex_t> _(mut_);
      state_ = 0;
      gate1_.notify_all();
    }

    // Shared ownership

    void
    upgrade_mutex::lock_shared()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      while ((state_ & write_entered_) || (state_ & n_readers_) == n_readers_)
        gate1_.wait(lk);
      count_t num_readers = (state_ & n_readers_) + 1;
      state_ &= ~n_readers_;
      state_ |= num_readers;
    }

    bool
    upgrade_mutex::try_lock_shared()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      count_t num_readers = state_ & n_readers_;
      if (!(state_ & write_entered_) && num_readers != n_readers_)
      {
        ++num_readers;
        state_ &= ~n_readers_;
        state_ |= num_readers;
        return true;
      }
      return false;
    }

    void
    upgrade_mutex::unlock_shared()
    {
      boost::lock_guard<mutex_t> _(mut_);
      count_t num_readers = (state_ & n_readers_) - 1;
      state_ &= ~n_readers_;
      state_ |= num_readers;
      if (state_ & write_entered_)
      {
        if (num_readers == 0)
          gate2_.notify_one();
      }
      else
      {
        if (num_readers == n_readers_ - 1)
          gate1_.notify_one();
      }
    }

    // Upgrade ownership

    void
    upgrade_mutex::lock_upgrade()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      while ((state_ & (write_entered_ | upgradable_entered_)) ||
          (state_ & n_readers_) == n_readers_)
        gate1_.wait(lk);
      count_t num_readers = (state_ & n_readers_) + 1;
      state_ &= ~n_readers_;
      state_ |= upgradable_entered_ | num_readers;
    }

    bool
    upgrade_mutex::try_lock_upgrade()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      count_t num_readers = state_ & n_readers_;
      if (!(state_ & (write_entered_ | upgradable_entered_))
          && num_readers != n_readers_)
      {
        ++num_readers;
        state_ &= ~n_readers_;
        state_ |= upgradable_entered_ | num_readers;
        return true;
      }
      return false;
    }

    void
    upgrade_mutex::unlock_upgrade()
    {
      {
        boost::lock_guard<mutex_t> _(mut_);
        count_t num_readers = (state_ & n_readers_) - 1;
        state_ &= ~(upgradable_entered_ | n_readers_);
        state_ |= num_readers;
      }
      gate1_.notify_all();
    }

    // Shared <-> Exclusive

    bool
    upgrade_mutex::try_unlock_shared_and_lock()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      if (state_ == 1)
      {
        state_ = write_entered_;
        return true;
      }
      return false;
    }

    void
    upgrade_mutex::unlock_and_lock_shared()
    {
      {
        boost::lock_guard<mutex_t> _(mut_);
        state_ = 1;
      }
      gate1_.notify_all();
    }

    // Shared <-> Upgrade

    bool
    upgrade_mutex::try_unlock_shared_and_lock_upgrade()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      if (!(state_ & (write_entered_ | upgradable_entered_)))
      {
        state_ |= upgradable_entered_;
        return true;
      }
      return false;
    }

    void
    upgrade_mutex::unlock_upgrade_and_lock_shared()
    {
      {
        boost::lock_guard<mutex_t> _(mut_);
        state_ &= ~upgradable_entered_;
      }
      gate1_.notify_all();
    }

    // Upgrade <-> Exclusive

    void
    upgrade_mutex::unlock_upgrade_and_lock()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      count_t num_readers = (state_ & n_readers_) - 1;
      state_ &= ~(upgradable_entered_ | n_readers_);
      state_ |= write_entered_ | num_readers;
      while (state_ & n_readers_)
        gate2_.wait(lk);
    }

    bool
    upgrade_mutex::try_unlock_upgrade_and_lock()
    {
      boost::unique_lock<mutex_t> lk(mut_);
      if (state_ == (upgradable_entered_ | 1))
      {
        state_ = write_entered_;
        return true;
      }
      return false;
    }

    void
    upgrade_mutex::unlock_and_lock_upgrade()
    {
      {
        boost::lock_guard<mutex_t> _(mut_);
        state_ = upgradable_entered_ | 1;
      }
      gate1_.notify_all();
    }

  } // thread_v2
} // boost