shared_mutex.hpp

Boost provides free peer-reviewed portable C++ source libraries. We emphasize libraries that work

                        new_state.exclusive_waiting_blocked=true;
                    }
                    else
                    {
                        new_state.exclusive=true;
                    }

                    state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                    if(current_state==old_state)
                    {
                        break;
                    }
                    old_state=current_state;
                }

                if(!old_state.shared_count && !old_state.exclusive)
                {
                    return true;
                }
                unsigned long const wait_res=detail::win32::WaitForMultipleObjects(2,semaphores,true,::boost::detail::get_milliseconds_until(wait_until));
                if(wait_res==detail::win32::timeout)
                {
                    for(;;)
                    {
                        state_data new_state=old_state;
                        if(new_state.shared_count || new_state.exclusive)
                        {
                            if(new_state.exclusive_waiting)
                            {
                                if(!--new_state.exclusive_waiting)
                                {
                                    new_state.exclusive_waiting_blocked=false;
                                }
                            }
                        }
                        else
                        {
                            new_state.exclusive=true;
                        }

                        state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                        if(current_state==old_state)
                        {
                            break;
                        }
                        old_state=current_state;
                    }
                    if(!old_state.shared_count && !old_state.exclusive)
                    {
                        return true;
                    }
                    return false;
                }
                BOOST_ASSERT(wait_res<2);
            }
        }

        void unlock()
        {
            state_data old_state=state;
            for(;;)
            {
                state_data new_state=old_state;
                new_state.exclusive=false;
                if(new_state.exclusive_waiting)
                {
                    --new_state.exclusive_waiting;
                    new_state.exclusive_waiting_blocked=false;
                }
                new_state.shared_waiting=0;

                state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                if(current_state==old_state)
                {
                    break;
                }
                old_state=current_state;
            }
            release_waiters(old_state);
        }

        void lock_upgrade()
        {
            for(;;)
            {
                state_data old_state=state;
                for(;;)
                {
                    state_data new_state=old_state;
                    if(new_state.exclusive || new_state.exclusive_waiting_blocked || new_state.upgrade)
                    {
                        ++new_state.shared_waiting;
                    }
                    else
                    {
                        ++new_state.shared_count;
                        new_state.upgrade=true;
                    }

                    state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                    if(current_state==old_state)
                    {
                        break;
                    }
                    old_state=current_state;
                }

                if(!(old_state.exclusive|| old_state.exclusive_waiting_blocked|| old_state.upgrade))
                {
                    return;
                }
                    
                BOOST_VERIFY(!detail::win32::WaitForSingleObject(unlock_sem,detail::win32::infinite));
            }
        }

        bool try_lock_upgrade()
        {
            state_data old_state=state;
            for(;;)
            {
                state_data new_state=old_state;
                if(new_state.exclusive || new_state.exclusive_waiting_blocked || new_state.upgrade)
                {
                    return false;
                }
                else
                {
                    ++new_state.shared_count;
                    new_state.upgrade=true;
                }
                
                state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                if(current_state==old_state)
                {
                    break;
                }
                old_state=current_state;
            }
            return true;
        }

        void unlock_upgrade()
        {
            state_data old_state=state;
            for(;;)
            {
                state_data new_state=old_state;
                new_state.upgrade=false;
                bool const last_reader=!--new_state.shared_count;
                
                if(last_reader)
                {
                    if(new_state.exclusive_waiting)
                    {
                        --new_state.exclusive_waiting;
                        new_state.exclusive_waiting_blocked=false;
                    }
                    new_state.shared_waiting=0;
                }
                
                state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                if(current_state==old_state)
                {
                    if(last_reader)
                    {
                        release_waiters(old_state);
                    }
                    break;
                }
                old_state=current_state;
            }
        }

        void unlock_upgrade_and_lock()
        {
            state_data old_state=state;
            for(;;)
            {
                state_data new_state=old_state;
                bool const last_reader=!--new_state.shared_count;
                
                if(last_reader)
                {
                    new_state.upgrade=false;
                    new_state.exclusive=true;
                }
                
                state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                if(current_state==old_state)
                {
                    if(!last_reader)
                    {
                        BOOST_VERIFY(!detail::win32::WaitForSingleObject(upgrade_sem,detail::win32::infinite));
                    }
                    break;
                }
                old_state=current_state;
            }
        }

        void unlock_and_lock_upgrade()
        {
            state_data old_state=state;
            for(;;)
            {
                state_data new_state=old_state;
                new_state.exclusive=false;
                new_state.upgrade=true;
                ++new_state.shared_count;
                if(new_state.exclusive_waiting)
                {
                    --new_state.exclusive_waiting;
                    new_state.exclusive_waiting_blocked=false;
                }
                new_state.shared_waiting=0;

                state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                if(current_state==old_state)
                {
                    break;
                }
                old_state=current_state;
            }
            release_waiters(old_state);
        }
        
        void unlock_and_lock_shared()
        {
            state_data old_state=state;
            for(;;)
            {
                state_data new_state=old_state;
                new_state.exclusive=false;
                ++new_state.shared_count;
                if(new_state.exclusive_waiting)
                {
                    --new_state.exclusive_waiting;
                    new_state.exclusive_waiting_blocked=false;
                }
                new_state.shared_waiting=0;

                state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                if(current_state==old_state)
                {
                    break;
                }
                old_state=current_state;
            }
            release_waiters(old_state);
        }
        
        void unlock_upgrade_and_lock_shared()
        {
            state_data old_state=state;
            for(;;)
            {
                state_data new_state=old_state;
                new_state.upgrade=false;
                if(new_state.exclusive_waiting)
                {
                    --new_state.exclusive_waiting;
                    new_state.exclusive_waiting_blocked=false;
                }
                new_state.shared_waiting=0;

                state_data const current_state=interlocked_compare_exchange(&state,new_state,old_state);
                if(current_state==old_state)
                {
                    break;
                }
                old_state=current_state;
            }
            release_waiters(old_state);
        }
        
    };
}

#include <boost/config/abi_suffix.hpp>

#endif