gdb/dwarf2/index-cache.h

   1 /* Caching of GDB/DWARF index files.
   2
   3    Copyright (C) 2018-2024 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #ifndef DWARF_INDEX_CACHE_H
  21 #define DWARF_INDEX_CACHE_H
  22
  23 #include "gdbsupport/array-view.h"
  24
  25 class dwarf2_per_bfd;
  26 class index_cache;
  27
  28 /* Base of the classes used to hold the resources of the indices loaded from
  29    the cache (e.g. mmapped files).  */
  30
  31 struct index_cache_resource
  32 {
  33   virtual ~index_cache_resource () = 0;
  34 };
  35
  36 /* Information to be captured in the main thread, and to be used by worker
  37    threads during store ().  */
  38
  39 struct index_cache_store_context
  40 {
  41   index_cache_store_context (const index_cache &ic, dwarf2_per_bfd *per_bfd);
  42
  43   /* Store the index in the cache.  */
  44   void store () const;
  45
  46 private:
  47   /* Captured value of enabled ().  */
  48   bool m_enabled;
  49
  50   /* Captured value of index cache directory.  */
  51   std::string m_dir;
  52
  53   /* The per-bfd object that we're caching.  */
  54   dwarf2_per_bfd *m_per_bfd;
  55
  56   /* Captured value of build id.  */
  57   std::string m_build_id_str;
  58
  59   /* Captured value of dwz build id.  */
  60   std::optional<std::string> m_dwz_build_id_str;
  61 };
  62
  63 /* Class to manage the access to the DWARF index cache.  */
  64
  65 class index_cache
  66 {
  67   friend struct index_cache_store_context;
  68 public:
  69   /* Change the directory used to save/load index files.  */
  70   void set_directory (std::string dir);
  71
  72   /* Return true if the usage of the cache is enabled.  */
  73   bool enabled () const
  74   {
  75     return m_enabled;
  76   }
  77
  78   /* Enable the cache.  */
  79   void enable ();
  80
  81   /* Disable the cache.  */
  82   void disable ();
  83
  84   /* Look for an index file matching BUILD_ID.  If found, return the contents
  85      as an array_view and store the underlying resources (allocated memory,
  86      mapped file, etc) in RESOURCE.  The returned array_view is valid as long
  87      as RESOURCE is not destroyed.
  88
  89      If no matching index file is found, return an empty array view.  */
  90   gdb::array_view<const gdb_byte>
  91   lookup_gdb_index (const bfd_build_id *build_id,
  92                     std::unique_ptr<index_cache_resource> *resource);
  93
  94   /* Return the number of cache hits.  */
  95   unsigned int n_hits () const
  96   { return m_n_hits; }
  97
  98   /* Record a cache hit.  */
  99   void hit ()
 100   {
 101     if (enabled ())
 102       m_n_hits++;
 103   }
 104
 105   /* Return the number of cache misses.  */
 106   unsigned int n_misses () const
 107   { return m_n_misses; }
 108
 109   /* Record a cache miss.  */
 110   void miss ()
 111   {
 112     if (enabled ())
 113       m_n_misses++;
 114   }
 115
 116 private:
 117
 118   /* Compute the absolute filename where the index of the objfile with build
 119      id BUILD_ID will be stored.  SUFFIX is appended at the end of the
 120      filename.  */
 121   std::string make_index_filename (const bfd_build_id *build_id,
 122                                    const char *suffix) const;
 123
 124   /* The base directory where we are storing and looking up index files.  */
 125   std::string m_dir;
 126
 127   /* Whether the cache is enabled.  */
 128   bool m_enabled = false;
 129
 130   /* Number of cache hits and misses during this GDB session.  */
 131   unsigned int m_n_hits = 0;
 132   unsigned int m_n_misses = 0;
 133 };
 134
 135 /* The global instance of the index cache.  */
 136 extern index_cache global_index_cache;
 137
 138 #endif /* DWARF_INDEX_CACHE_H */