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 "dwarf2/index-common.h"
  24 #include "gdbsupport/array-view.h"
  25 #include "symfile.h"
  26
  27 class dwarf2_per_bfd;
  28 class index_cache;
  29
  30 /* Base of the classes used to hold the resources of the indices loaded from
  31    the cache (e.g. mmapped files).  */
  32
  33 struct index_cache_resource
  34 {
  35   virtual ~index_cache_resource () = 0;
  36 };
  37
  38 /* Information to be captured in the main thread, and to be used by worker
  39    threads during store ().  */
  40
  41 struct index_cache_store_context
  42 {
  43   index_cache_store_context (const index_cache &ic, dwarf2_per_bfd *per_bfd);
  44
  45   /* Store the index in the cache.  */
  46   void store () const;
  47
  48 private:
  49   /* Captured value of enabled ().  */
  50   bool m_enabled;
  51
  52   /* Captured value of index cache directory.  */
  53   std::string m_dir;
  54
  55   /* The per-bfd object that we're caching.  */
  56   dwarf2_per_bfd *m_per_bfd;
  57
  58   /* Captured value of build id.  */
  59   std::string m_build_id_str;
  60
  61   /* Captured value of dwz build id.  */
  62   std::optional<std::string> m_dwz_build_id_str;
  63 };
  64
  65 /* Class to manage the access to the DWARF index cache.  */
  66
  67 class index_cache
  68 {
  69   friend struct index_cache_store_context;
  70 public:
  71   /* Change the directory used to save/load index files.  */
  72   void set_directory (std::string dir);
  73
  74   /* Return true if the usage of the cache is enabled.  */
  75   bool enabled () const
  76   {
  77     return m_enabled;
  78   }
  79
  80   /* Enable the cache.  */
  81   void enable ();
  82
  83   /* Disable the cache.  */
  84   void disable ();
  85
  86   /* Look for an index file matching BUILD_ID.  If found, return the contents
  87      as an array_view and store the underlying resources (allocated memory,
  88      mapped file, etc) in RESOURCE.  The returned array_view is valid as long
  89      as RESOURCE is not destroyed.
  90
  91      If no matching index file is found, return an empty array view.  */
  92   gdb::array_view<const gdb_byte>
  93   lookup_gdb_index (const bfd_build_id *build_id,
  94                     std::unique_ptr<index_cache_resource> *resource);
  95
  96   /* Return the number of cache hits.  */
  97   unsigned int n_hits () const
  98   { return m_n_hits; }
  99
 100   /* Record a cache hit.  */
 101   void hit ()
 102   {
 103     if (enabled ())
 104       m_n_hits++;
 105   }
 106
 107   /* Return the number of cache misses.  */
 108   unsigned int n_misses () const
 109   { return m_n_misses; }
 110
 111   /* Record a cache miss.  */
 112   void miss ()
 113   {
 114     if (enabled ())
 115       m_n_misses++;
 116   }
 117
 118 private:
 119
 120   /* Compute the absolute filename where the index of the objfile with build
 121      id BUILD_ID will be stored.  SUFFIX is appended at the end of the
 122      filename.  */
 123   std::string make_index_filename (const bfd_build_id *build_id,
 124                                    const char *suffix) const;
 125
 126   /* The base directory where we are storing and looking up index files.  */
 127   std::string m_dir;
 128
 129   /* Whether the cache is enabled.  */
 130   bool m_enabled = false;
 131
 132   /* Number of cache hits and misses during this GDB session.  */
 133   unsigned int m_n_hits = 0;
 134   unsigned int m_n_misses = 0;
 135 };
 136
 137 /* The global instance of the index cache.  */
 138 extern index_cache global_index_cache;
 139
 140 #endif /* DWARF_INDEX_CACHE_H */