text: /*
   *
   * Copyright (c) 2004
   * John Maddock
   *
   * 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)
   *
   */
  
   /*
    *   LOCATION:    see http://www.boost.org for most recent version.
    *   FILE         object_cache.hpp
    *   VERSION      see <boost/version.hpp>
    *   DESCRIPTION: Implements a generic object cache.
    */
  
  #ifndef BOOST_REGEX_OBJECT_CACHE_HPP
  #define BOOST_REGEX_OBJECT_CACHE_HPP
  
  #include <map>
  #include <list>
  #include <stdexcept>
  #include <string>
  #include <boost/config.hpp>
  #include <boost/shared_ptr.hpp>
  #ifdef BOOST_HAS_THREADS
  #include <boost/regex/pending/static_mutex.hpp>
  #endif
  
  namespace boost{
  
  template <class Key, class Object>
  class object_cache
  {
  public:
     typedef std::pair< ::boost::shared_ptr<Object const>, Key const*> value_type;
     typedef std::list<value_type> list_type;
     typedef typename list_type::iterator list_iterator;
     typedef std::map<Key, list_iterator> map_type;
     typedef typename map_type::iterator map_iterator;
     typedef typename list_type::size_type size_type;
     static boost::shared_ptr<Object const> get(const Key& k, size_type l_max_cache_size);
  
  private:
     static boost::shared_ptr<Object const> do_get(const Key& k, size_type l_max_cache_size);
  
     struct data
     {
        list_type   cont;
        map_type    index;
     };
  
     // Needed by compilers not implementing the resolution to DR45. For reference,
     // see http://www.open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#45.
     friend struct data;
  };
  
  template <class Key, class Object>
  boost::shared_ptr<Object const> object_cache<Key, Object>::get(const Key& k, size_type l_max_cache_size)
  {
  #ifdef BOOST_HAS_THREADS
     static boost::static_mutex mut = BOOST_STATIC_MUTEX_INIT;
  
     boost::static_mutex::scoped_lock l(mut);
     if(l)
     {
        return do_get(k, l_max_cache_size);
     }
     //
     // what do we do if the lock fails?
     // for now just throw, but we should never really get here...
     //
     ::boost::throw_exception(std::runtime_error("Error in thread safety code: could not acquire a lock"));
  #if defined(BOOST_NO_UNREACHABLE_RETURN_DETECTION) || defined(BOOST_NO_EXCEPTIONS)
     return boost::shared_ptr<Object>();
  #endif
  #else
     return do_get(k, l_max_cache_size);
  #endif
  }
  
  template <class Key, class Object>
  boost::shared_ptr<Object const> object_cache<Key, Object>::do_get(const Key& k, size_type l_max_cache_size)
  {
     typedef typename object_cache<Key, Object>::data object_data;
     typedef typename map_type::size_type map_size_type;
     static object_data s_data;
  
     //
     // see if the object is already in the cache:
     //
     map_iterator mpos = s_data.index.find(k);
     if(mpos != s_data.index.end())
     {
        //
        // Eureka! 
        // We have a cached item, bump it up the list and return it:
        //
        if(--(s_data.cont.end()) != mpos->second)
        {
           // splice out the item we want to move:
           list_type temp;
           temp.splice(temp.end(), s_data.cont, mpos->second);
           // and now place it at the end of the list:
           s_data.cont.splice(s_data.cont.end(), temp, temp.begin());
           BOOST_ASSERT(*(s_data.cont.back().second) == k);
           // update index with new position:
           mpos->second = --(s_data.cont.end());
           BOOST_ASSERT(&(mpos->first) == mpos->second->second);
           BOOST_ASSERT(&(mpos->first) == s_data.cont.back().second);
        }
        return s_data.cont.back().first;
     }
     //
     // if we get here then the item is not in the cache,
     // so create it:
     //
     boost::shared_ptr<Object const> result(new Object(k));
     //
     // Add it to the list, and index it:
     //
     s_data.cont.push_back(value_type(result, static_cast<Key const*>(0)));
     s_data.index.insert(std::make_pair(k, --(s_data.cont.end())));
     s_data.cont.back().second = &(s_data.index.find(k)->first);
     map_size_type s = s_data.index.size();
     BOOST_ASSERT(s_data.index[k]->first.get() == result.get());
     BOOST_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
     BOOST_ASSERT(s_data.index.find(k)->first == k);
     if(s > l_max_cache_size)
     {
        //
        // We have too many items in the list, so we need to start
        // popping them off the back of the list, but only if they're
        // being held uniquely by us:
        //
        list_iterator pos = s_data.cont.begin();
        list_iterator last = s_data.cont.end();
        while((pos != last) && (s > l_max_cache_size))
        {
           if(pos->first.unique())
           {
              list_iterator condemmed(pos);
              ++pos;
              // now remove the items from our containers, 
              // then order has to be as follows:
              BOOST_ASSERT(s_data.index.find(*(condemmed->second)) != s_data.index.end());
              s_data.index.erase(*(condemmed->second));
              s_data.cont.erase(condemmed); 
              --s;
           }
           else
              ++pos;
        }
        BOOST_ASSERT(s_data.index[k]->first.get() == result.get());
        BOOST_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
        BOOST_ASSERT(s_data.index.find(k)->first == k);
     }
     return result;
  }
  
  }
  
  #endif
  