166 lines
5.3 KiB
Plaintext
166 lines
5.3 KiB
Plaintext
/*
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*
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* Copyright (c) 2004
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* John Maddock
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*
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* Use, modification and distribution are subject to the
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* Boost Software License, Version 1.0. (See accompanying file
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* LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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*
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*/
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/*
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* LOCATION: see http://www.boost.org for most recent version.
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* FILE object_cache.hpp
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* VERSION see <boost/version.hpp>
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* DESCRIPTION: Implements a generic object cache.
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*/
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#ifndef BOOST_REGEX_OBJECT_CACHE_HPP
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#define BOOST_REGEX_OBJECT_CACHE_HPP
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#include <map>
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#include <list>
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#include <stdexcept>
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#include <string>
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#include <boost/config.hpp>
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#include <boost/shared_ptr.hpp>
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#ifdef BOOST_HAS_THREADS
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#include <boost/regex/pending/static_mutex.hpp>
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#endif
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namespace boost{
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template <class Key, class Object>
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class object_cache
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{
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public:
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typedef std::pair< ::boost::shared_ptr<Object const>, Key const*> value_type;
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typedef std::list<value_type> list_type;
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typedef typename list_type::iterator list_iterator;
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typedef std::map<Key, list_iterator> map_type;
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typedef typename map_type::iterator map_iterator;
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typedef typename list_type::size_type size_type;
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static boost::shared_ptr<Object const> get(const Key& k, size_type l_max_cache_size);
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private:
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static boost::shared_ptr<Object const> do_get(const Key& k, size_type l_max_cache_size);
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struct data
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{
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list_type cont;
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map_type index;
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};
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// Needed by compilers not implementing the resolution to DR45. For reference,
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// see http://www.open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#45.
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friend struct data;
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};
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template <class Key, class Object>
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boost::shared_ptr<Object const> object_cache<Key, Object>::get(const Key& k, size_type l_max_cache_size)
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{
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#ifdef BOOST_HAS_THREADS
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static boost::static_mutex mut = BOOST_STATIC_MUTEX_INIT;
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boost::static_mutex::scoped_lock l(mut);
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if(l)
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{
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return do_get(k, l_max_cache_size);
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}
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//
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// what do we do if the lock fails?
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// for now just throw, but we should never really get here...
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//
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::boost::throw_exception(std::runtime_error("Error in thread safety code: could not acquire a lock"));
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#if defined(BOOST_NO_UNREACHABLE_RETURN_DETECTION) || defined(BOOST_NO_EXCEPTIONS)
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return boost::shared_ptr<Object>();
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#endif
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#else
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return do_get(k, l_max_cache_size);
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#endif
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}
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template <class Key, class Object>
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boost::shared_ptr<Object const> object_cache<Key, Object>::do_get(const Key& k, size_type l_max_cache_size)
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{
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typedef typename object_cache<Key, Object>::data object_data;
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typedef typename map_type::size_type map_size_type;
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static object_data s_data;
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//
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// see if the object is already in the cache:
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//
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map_iterator mpos = s_data.index.find(k);
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if(mpos != s_data.index.end())
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{
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//
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// Eureka!
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// We have a cached item, bump it up the list and return it:
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//
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if(--(s_data.cont.end()) != mpos->second)
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{
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// splice out the item we want to move:
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list_type temp;
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temp.splice(temp.end(), s_data.cont, mpos->second);
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// and now place it at the end of the list:
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s_data.cont.splice(s_data.cont.end(), temp, temp.begin());
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BOOST_ASSERT(*(s_data.cont.back().second) == k);
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// update index with new position:
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mpos->second = --(s_data.cont.end());
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BOOST_ASSERT(&(mpos->first) == mpos->second->second);
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BOOST_ASSERT(&(mpos->first) == s_data.cont.back().second);
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}
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return s_data.cont.back().first;
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}
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//
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// if we get here then the item is not in the cache,
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// so create it:
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//
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boost::shared_ptr<Object const> result(new Object(k));
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//
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// Add it to the list, and index it:
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//
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s_data.cont.push_back(value_type(result, static_cast<Key const*>(0)));
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s_data.index.insert(std::make_pair(k, --(s_data.cont.end())));
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s_data.cont.back().second = &(s_data.index.find(k)->first);
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map_size_type s = s_data.index.size();
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BOOST_ASSERT(s_data.index[k]->first.get() == result.get());
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BOOST_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
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BOOST_ASSERT(s_data.index.find(k)->first == k);
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if(s > l_max_cache_size)
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{
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//
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// We have too many items in the list, so we need to start
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// popping them off the back of the list, but only if they're
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// being held uniquely by us:
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//
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list_iterator pos = s_data.cont.begin();
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list_iterator last = s_data.cont.end();
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while((pos != last) && (s > l_max_cache_size))
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{
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if(pos->first.unique())
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{
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list_iterator condemmed(pos);
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++pos;
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// now remove the items from our containers,
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// then order has to be as follows:
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BOOST_ASSERT(s_data.index.find(*(condemmed->second)) != s_data.index.end());
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s_data.index.erase(*(condemmed->second));
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s_data.cont.erase(condemmed);
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--s;
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}
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else
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++pos;
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}
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BOOST_ASSERT(s_data.index[k]->first.get() == result.get());
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BOOST_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
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BOOST_ASSERT(s_data.index.find(k)->first == k);
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}
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return result;
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}
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}
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#endif
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