1 /*
2 *
3 * Copyright (c) 2004
4 * John Maddock
5 *
6 * Use, modification and distribution are subject to the
7 * Boost Software License, Version 1.0. (See accompanying file
8 * LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
9 *
10 */
11
12 /*
13 * LOCATION: see http://www.boost.org for most recent version.
14 * FILE object_cache.hpp
15 * VERSION see <boost/version.hpp>
16 * DESCRIPTION: Implements a generic object cache.
17 */
18
19 #ifndef BOOST_REGEX_OBJECT_CACHE_HPP
20 #define BOOST_REGEX_OBJECT_CACHE_HPP
21
22 #include <boost/regex/config.hpp>
23 #include <boost/shared_ptr.hpp>
24 #include <map>
25 #include <list>
26 #include <stdexcept>
27 #include <string>
28 #ifdef BOOST_HAS_THREADS
29 #include <boost/regex/pending/static_mutex.hpp>
30 #endif
31
32 namespace boost{
33
34 template <class Key, class Object>
35 class object_cache
36 {
37 public:
38 typedef std::pair< ::boost::shared_ptr<Object const>, Key const*> value_type;
39 typedef std::list<value_type> list_type;
40 typedef typename list_type::iterator list_iterator;
41 typedef std::map<Key, list_iterator> map_type;
42 typedef typename map_type::iterator map_iterator;
43 typedef typename list_type::size_type size_type;
44 static boost::shared_ptr<Object const> get(const Key& k, size_type l_max_cache_size);
45
46 private:
47 static boost::shared_ptr<Object const> do_get(const Key& k, size_type l_max_cache_size);
48
49 struct data
50 {
51 list_type cont;
52 map_type index;
53 };
54
55 // Needed by compilers not implementing the resolution to DR45. For reference,
56 // see http://www.open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#45.
57 friend struct data;
58 };
59
60 #ifdef BOOST_MSVC
61 #pragma warning(push)
62 #pragma warning(disable: 4702)
63 #endif
64 template <class Key, class Object>
get(const Key & k,size_type l_max_cache_size)65 boost::shared_ptr<Object const> object_cache<Key, Object>::get(const Key& k, size_type l_max_cache_size)
66 {
67 #ifdef BOOST_HAS_THREADS
68 static boost::static_mutex mut = BOOST_STATIC_MUTEX_INIT;
69 boost::static_mutex::scoped_lock l(mut);
70 if (l)
71 {
72 return do_get(k, l_max_cache_size);
73 }
74 //
75 // what do we do if the lock fails?
76 // for now just throw, but we should never really get here...
77 //
78 ::boost::throw_exception(std::runtime_error("Error in thread safety code: could not acquire a lock"));
79 #if defined(BOOST_NO_UNREACHABLE_RETURN_DETECTION) || defined(BOOST_NO_EXCEPTIONS)
80 return boost::shared_ptr<Object>();
81 #endif
82 #else
83 return do_get(k, l_max_cache_size);
84 #endif
85 }
86 #ifdef BOOST_MSVC
87 #pragma warning(pop)
88 #endif
89
90 template <class Key, class Object>
do_get(const Key & k,size_type l_max_cache_size)91 boost::shared_ptr<Object const> object_cache<Key, Object>::do_get(const Key& k, size_type l_max_cache_size)
92 {
93 typedef typename object_cache<Key, Object>::data object_data;
94 typedef typename map_type::size_type map_size_type;
95 static object_data s_data;
96
97 //
98 // see if the object is already in the cache:
99 //
100 map_iterator mpos = s_data.index.find(k);
101 if(mpos != s_data.index.end())
102 {
103 //
104 // Eureka!
105 // We have a cached item, bump it up the list and return it:
106 //
107 if(--(s_data.cont.end()) != mpos->second)
108 {
109 // splice out the item we want to move:
110 list_type temp;
111 temp.splice(temp.end(), s_data.cont, mpos->second);
112 // and now place it at the end of the list:
113 s_data.cont.splice(s_data.cont.end(), temp, temp.begin());
114 BOOST_REGEX_ASSERT(*(s_data.cont.back().second) == k);
115 // update index with new position:
116 mpos->second = --(s_data.cont.end());
117 BOOST_REGEX_ASSERT(&(mpos->first) == mpos->second->second);
118 BOOST_REGEX_ASSERT(&(mpos->first) == s_data.cont.back().second);
119 }
120 return s_data.cont.back().first;
121 }
122 //
123 // if we get here then the item is not in the cache,
124 // so create it:
125 //
126 boost::shared_ptr<Object const> result(new Object(k));
127 //
128 // Add it to the list, and index it:
129 //
130 s_data.cont.push_back(value_type(result, static_cast<Key const*>(0)));
131 s_data.index.insert(std::make_pair(k, --(s_data.cont.end())));
132 s_data.cont.back().second = &(s_data.index.find(k)->first);
133 map_size_type s = s_data.index.size();
134 BOOST_REGEX_ASSERT(s_data.index[k]->first.get() == result.get());
135 BOOST_REGEX_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
136 BOOST_REGEX_ASSERT(s_data.index.find(k)->first == k);
137 if(s > l_max_cache_size)
138 {
139 //
140 // We have too many items in the list, so we need to start
141 // popping them off the back of the list, but only if they're
142 // being held uniquely by us:
143 //
144 list_iterator pos = s_data.cont.begin();
145 list_iterator last = s_data.cont.end();
146 while((pos != last) && (s > l_max_cache_size))
147 {
148 if(pos->first.unique())
149 {
150 list_iterator condemmed(pos);
151 ++pos;
152 // now remove the items from our containers,
153 // then order has to be as follows:
154 BOOST_REGEX_ASSERT(s_data.index.find(*(condemmed->second)) != s_data.index.end());
155 s_data.index.erase(*(condemmed->second));
156 s_data.cont.erase(condemmed);
157 --s;
158 }
159 else
160 ++pos;
161 }
162 BOOST_REGEX_ASSERT(s_data.index[k]->first.get() == result.get());
163 BOOST_REGEX_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
164 BOOST_REGEX_ASSERT(s_data.index.find(k)->first == k);
165 }
166 return result;
167 }
168
169 }
170
171 #endif
172