source/ps/CStrIntern.cpp

   1 /* Copyright (C) 2021 Wildfire Games.
   2  * This file is part of 0 A.D.
   3  *
   4  * 0 A.D. is free software: you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation, either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * 0 A.D. is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include "precompiled.h"
  19
  20 #include "CStrIntern.h"
  21
  22 #include "lib/fnv_hash.h"
  23 #include "ps/CLogger.h"
  24 #include "ps/ThreadUtil.h"
  25
  26 #include <unordered_map>
  27
  28 class CStrInternInternals
  29 {
  30 public:
  31         CStrInternInternals(const char* str, size_t len)
  32                 : data(str, str+len), hash(fnv_hash(str, len))
  33         {
  34 //              LOGWARNING("New interned string '%s'", data.c_str());
  35         }
  36
  37         bool operator==(const CStrInternInternals& b) const
  38         {
  39                 // Compare hash first for quick rejection of inequal strings
  40                 return (hash == b.hash && data == b.data);
  41         }
  42
  43         const std::string data;
  44         const u32 hash; // fnv_hash of data
  45
  46 private:
  47         CStrInternInternals& operator=(const CStrInternInternals&);
  48 };
  49
  50 // Interned strings are stored in a hash table, indexed by string:
  51
  52 using StringsKey = std::string;
  53
  54 struct StringsKeyHash
  55 {
  56         size_t operator()(const StringsKey& key) const
  57         {
  58                 return fnv_hash(key.c_str(), key.length());
  59         }
  60 };
  61
  62 // To avoid std::string memory allocations when GetString does lookups in the
  63 // hash table of interned strings, we make use of std::unordered_map's ability
  64 // to do lookups with a functionally equivalent proxy object:
  65
  66 struct StringsKeyProxy
  67 {
  68         const char* str;
  69         size_t len;
  70 };
  71
  72 struct StringsKeyProxyHash
  73 {
  74         size_t operator()(const StringsKeyProxy& key) const
  75         {
  76                 return fnv_hash(key.str, key.len);
  77         }
  78 };
  79
  80 struct StringsKeyProxyEq
  81 {
  82         bool operator()(const StringsKeyProxy& proxy, const StringsKey& key) const
  83         {
  84                 return (proxy.len == key.length() && memcmp(proxy.str, key.c_str(), proxy.len) == 0);
  85         }
  86 };
  87
  88 static std::unordered_map<StringsKey, std::shared_ptr<CStrInternInternals>, StringsKeyHash> g_Strings;
  89
  90 #define X(id) CStrIntern str_##id(#id);
  91 #define X2(id, str) CStrIntern str_##id(str);
  92 #include "CStrInternStatic.h"
  93 #undef X
  94 #undef X2
  95
  96 static CStrInternInternals* GetString(const char* str, size_t len)
  97 {
  98         // g_Strings is not thread-safe, so complain if anyone is using this
  99         // type in non-main threads. (If that's desired, g_Strings should be changed
 100         // to be thread-safe, preferably without sacrificing performance.)
 101         ENSURE(Threading::IsMainThread());
 102
 103         std::unordered_map<StringsKey, std::shared_ptr<CStrInternInternals> >::iterator it = g_Strings.find(str);
 104
 105         if (it != g_Strings.end())
 106                 return it->second.get();
 107
 108         std::shared_ptr<CStrInternInternals> internals = std::make_shared<CStrInternInternals>(str, len);
 109         g_Strings.insert(std::make_pair(internals->data, internals));
 110         return internals.get();
 111 }
 112
 113 CStrIntern::CStrIntern()
 114 {
 115         *this = str__emptystring;
 116 }
 117
 118 CStrIntern::CStrIntern(const char* str)
 119 {
 120         m = GetString(str, strlen(str));
 121 }
 122
 123 CStrIntern::CStrIntern(const std::string& str)
 124 {
 125         m = GetString(str.c_str(), str.length());
 126 }
 127
 128 u32 CStrIntern::GetHash() const
 129 {
 130         return m->hash;
 131 }
 132
 133 const char* CStrIntern::c_str() const
 134 {
 135         return m->data.c_str();
 136 }
 137
 138 size_t CStrIntern::length() const
 139 {
 140         return m->data.length();
 141 }
 142
 143 bool CStrIntern::empty() const
 144 {
 145         return m->data.empty();
 146 }
 147
 148 const std::string& CStrIntern::string() const
 149 {
 150         return m->data;
 151 }