interprocess_upgradable_mutex.hpp

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   //The exclusive lock must block in the first gate
   //if an exclusive or upgradable lock has been acquired
   while (this->m_ctrl.exclusive_in || this->m_ctrl.upgradable_in){
      if(!this->m_first_gate.timed_wait(lock, abs_time))
         return !(this->m_ctrl.exclusive_in || this->m_ctrl.upgradable_in);
   }

   //Mark that exclusive lock has been acquired
   this->m_ctrl.exclusive_in = 1;

   //Prepare rollback
   exclusive_rollback rollback(this->m_ctrl, this->m_first_gate);

   //Now wait until all readers are gone
   while (this->m_ctrl.num_upr_shar){
      if(!this->m_second_gate.timed_wait(lock, abs_time)){
         return !(this->m_ctrl.num_upr_shar);
      }
   }
   rollback.release();
   return true;
}

inline void interprocess_upgradable_mutex::unlock()
{
   scoped_lock_t lock(m_mut);
   this->m_ctrl.exclusive_in = 0;
   this->m_first_gate.notify_all();
}

//Upgradable locking

inline void interprocess_upgradable_mutex::lock_upgradable()
{
   scoped_lock_t lock(m_mut);

   //The upgradable lock must block in the first gate
   //if an exclusive or upgradable lock has been acquired
   //or there are too many sharable locks
   while(this->m_ctrl.exclusive_in || this->m_ctrl.upgradable_in
         || this->m_ctrl.num_upr_shar == constants::max_readers){
      this->m_first_gate.wait(lock);
   }

   //Mark that upgradable lock has been acquired
   //And add upgradable to the sharable count
   this->m_ctrl.upgradable_in = 1;
   ++this->m_ctrl.num_upr_shar;
}

inline bool interprocess_upgradable_mutex::try_lock_upgradable()
{
   scoped_lock_t lock(m_mut, try_to_lock);

   //The upgradable lock must fail
   //if an exclusive or upgradable lock has been acquired
   //or there are too many sharable locks
   if(!lock.owns() 
      || this->m_ctrl.exclusive_in 
      || this->m_ctrl.upgradable_in 
      || this->m_ctrl.num_upr_shar == constants::max_readers){
      return false;
   }

   //Mark that upgradable lock has been acquired
   //And add upgradable to the sharable count
   this->m_ctrl.upgradable_in = 1;
   ++this->m_ctrl.num_upr_shar;
   return true;
}

inline bool interprocess_upgradable_mutex::timed_lock_upgradable
   (const boost::posix_time::ptime &abs_time)
{
   if(abs_time == boost::posix_time::pos_infin){
      this->lock_upgradable();
      return true;
   }
   scoped_lock_t lock(m_mut, abs_time);
   if(!lock.owns())   return false;

   //The upgradable lock must block in the first gate
   //if an exclusive or upgradable lock has been acquired
   //or there are too many sharable locks
   while(this->m_ctrl.exclusive_in 
         || this->m_ctrl.upgradable_in
         || this->m_ctrl.num_upr_shar == constants::max_readers){
      if(!this->m_first_gate.timed_wait(lock, abs_time)){
         return!(this->m_ctrl.exclusive_in 
               || this->m_ctrl.upgradable_in
               || this->m_ctrl.num_upr_shar == constants::max_readers);
      }
   }

   //Mark that upgradable lock has been acquired
   //And add upgradable to the sharable count
   this->m_ctrl.upgradable_in = 1;
   ++this->m_ctrl.num_upr_shar;
   return true;
}

inline void interprocess_upgradable_mutex::unlock_upgradable()
{
   scoped_lock_t lock(m_mut);
   //Mark that upgradable lock has been acquired
   //And add upgradable to the sharable count
   this->m_ctrl.upgradable_in = 0;
   --this->m_ctrl.num_upr_shar;
   this->m_first_gate.notify_all();
}

//Sharable locking

inline void interprocess_upgradable_mutex::lock_sharable()
{
   scoped_lock_t lock(m_mut);

   //The sharable lock must block in the first gate
   //if an exclusive lock has been acquired
   //or there are too many sharable locks
   while(this->m_ctrl.exclusive_in
        || this->m_ctrl.num_upr_shar == constants::max_readers){
      this->m_first_gate.wait(lock);
   }

   //Increment sharable count
   ++this->m_ctrl.num_upr_shar;
}

inline bool interprocess_upgradable_mutex::try_lock_sharable()
{
   scoped_lock_t lock(m_mut, try_to_lock);

   //The sharable lock must fail
   //if an exclusive lock has been acquired
   //or there are too many sharable locks
   if(!lock.owns()
      || this->m_ctrl.exclusive_in
      || this->m_ctrl.num_upr_shar == constants::max_readers){
      return false;
   }

   //Increment sharable count
   ++this->m_ctrl.num_upr_shar;
   return true;
}

inline bool interprocess_upgradable_mutex::timed_lock_sharable
   (const boost::posix_time::ptime &abs_time)
{
   if(abs_time == boost::posix_time::pos_infin){
      this->lock_sharable();
      return true;
   }
   scoped_lock_t lock(m_mut, abs_time);
   if(!lock.owns())   return false;

   //The sharable lock must block in the first gate
   //if an exclusive lock has been acquired
   //or there are too many sharable locks
   while (this->m_ctrl.exclusive_in
         || this->m_ctrl.num_upr_shar == constants::max_readers){
      if(!this->m_first_gate.timed_wait(lock, abs_time)){
         return!(this->m_ctrl.exclusive_in
               || this->m_ctrl.num_upr_shar == constants::max_readers);
      }
   }

   //Increment sharable count
   ++this->m_ctrl.num_upr_shar;
   return true;
}

inline void interprocess_upgradable_mutex::unlock_sharable()
{
   scoped_lock_t lock(m_mut);
   //Decrement sharable count
   --this->m_ctrl.num_upr_shar;
   if (this->m_ctrl.num_upr_shar == 0){
      this->m_second_gate.notify_one();
   }
   //Check if there are blocked sharables because of
   //there were too many sharables
   else if(this->m_ctrl.num_upr_shar == (constants::max_readers-1)){
      this->m_first_gate.notify_all();
   }
}

//Downgrading

inline void interprocess_upgradable_mutex::unlock_and_lock_upgradable()
{
   scoped_lock_t lock(m_mut);
   //Unmark it as exclusive
   this->m_ctrl.exclusive_in     = 0;
   //Mark it as upgradable
   this->m_ctrl.upgradable_in    = 1;
   //The sharable count should be 0 so increment it
   this->m_ctrl.num_upr_shar   = 1;
   //Notify readers that they can enter
   m_first_gate.notify_all();
}

inline void interprocess_upgradable_mutex::unlock_and_lock_sharable()
{
   scoped_lock_t lock(m_mut);
   //Unmark it as exclusive
   this->m_ctrl.exclusive_in   = 0;
   //The sharable count should be 0 so increment it
   this->m_ctrl.num_upr_shar   = 1;
   //Notify readers that they can enter
   m_first_gate.notify_all();
}

inline void interprocess_upgradable_mutex::unlock_upgradable_and_lock_sharable()
{
   scoped_lock_t lock(m_mut);
   //Unmark it as upgradable (we don't have to decrement count)
   this->m_ctrl.upgradable_in    = 0;
   //Notify readers/upgradable that they can enter
   m_first_gate.notify_all();
}

//Upgrading

inline void interprocess_upgradable_mutex::unlock_upgradable_and_lock()
{
   scoped_lock_t lock(m_mut);
   //Simulate unlock_upgradable() without
   //notifying sharables.
   this->m_ctrl.upgradable_in = 0;
   --this->m_ctrl.num_upr_shar;   
   //Execute the second half of exclusive locking
   this->m_ctrl.exclusive_in = 1;

   //Prepare rollback
   upgradable_to_exclusive_rollback rollback(m_ctrl);

   while (this->m_ctrl.num_upr_shar){
      this->m_second_gate.wait(lock);
   }
   rollback.release();
}

inline bool interprocess_upgradable_mutex::try_unlock_upgradable_and_lock()
{
   scoped_lock_t lock(m_mut, try_to_lock);
   //Check if there are no readers
   if(!lock.owns()
      || this->m_ctrl.num_upr_shar != 1){
      return false;
   }
   //Now unlock upgradable and mark exclusive
   this->m_ctrl.upgradable_in = 0;
   --this->m_ctrl.num_upr_shar;   
   this->m_ctrl.exclusive_in = 1;
   return true;
}

inline bool interprocess_upgradable_mutex::timed_unlock_upgradable_and_lock
   (const boost::posix_time::ptime &abs_time)
{
   scoped_lock_t lock(m_mut, abs_time);
   if(!lock.owns())   return false;

   //Simulate unlock_upgradable() without
   //notifying sharables.
   this->m_ctrl.upgradable_in = 0;
   --this->m_ctrl.num_upr_shar;   
   //Execute the second half of exclusive locking
   this->m_ctrl.exclusive_in = 1;

   //Prepare rollback
   upgradable_to_exclusive_rollback rollback(m_ctrl);

   while (this->m_ctrl.num_upr_shar){
      if(!this->m_second_gate.timed_wait(lock, abs_time)){
         return !(this->m_ctrl.num_upr_shar);
      }
   }
   rollback.release();
   return true;
}

inline bool interprocess_upgradable_mutex::try_unlock_sharable_and_lock()
{
   scoped_lock_t lock(m_mut, try_to_lock);

   //If we can't lock or any has there is any exclusive, upgradable 
   //or sharable mark return false;
   if(!lock.owns() 
      || this->m_ctrl.exclusive_in 
      || this->m_ctrl.upgradable_in
      || this->m_ctrl.num_upr_shar != 1){
      return false;
   }
   this->m_ctrl.exclusive_in = 1;
   this->m_ctrl.num_upr_shar = 0;
   return true;
}

inline bool interprocess_upgradable_mutex::try_unlock_sharable_and_lock_upgradable()
{
   scoped_lock_t lock(m_mut, try_to_lock);

   //The upgradable lock must fail
   //if an exclusive or upgradable lock has been acquired
   if(!lock.owns()
      || this->m_ctrl.exclusive_in 
      || this->m_ctrl.upgradable_in){
      return false;
   }

   //Mark that upgradable lock has been acquired
   this->m_ctrl.upgradable_in = 1;
   return true;
}

/// @endcond

}  //namespace interprocess {
}  //namespace boost {


#include <boost/interprocess/detail/config_end.hpp>

#endif   //BOOST_INTERPROCESS_UPGRADABLE_MUTEX_HPP