gdb/dwarf2/index-cache.h

   1 /* Caching of GDB/DWARF index files.
   2
   3    Copyright (C) 2018-2023 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   friend class index_cache;
  44
  45   index_cache_store_context (const index_cache &ic, dwarf2_per_bfd *per_bfd);
  46
  47 private:
  48   /* Captured value of enabled ().  */
  49   bool m_enabled;
  50
  51   /* Captured value of build id.  */
  52   std::string build_id_str;
  53
  54   /* Captured value of dwz build id.  */
  55   std::optional<std::string> dwz_build_id_str;
  56 };
  57
  58 /* Class to manage the access to the DWARF index cache.  */
  59
  60 class index_cache
  61 {
  62   friend struct index_cache_store_context;
  63 public:
  64   /* Change the directory used to save/load index files.  */
  65   void set_directory (std::string dir);
  66
  67   /* Return true if the usage of the cache is enabled.  */
  68   bool enabled () const
  69   {
  70     return m_enabled;
  71   }
  72
  73   /* Enable the cache.  */
  74   void enable ();
  75
  76   /* Disable the cache.  */
  77   void disable ();
  78
  79   /* Store an index for the specified object file in the cache.  */
  80   void store (dwarf2_per_bfd *per_bfd,
  81               const index_cache_store_context &);
  82
  83   /* Look for an index file matching BUILD_ID.  If found, return the contents
  84      as an array_view and store the underlying resources (allocated memory,
  85      mapped file, etc) in RESOURCE.  The returned array_view is valid as long
  86      as RESOURCE is not destroyed.
  87
  88      If no matching index file is found, return an empty array view.  */
  89   gdb::array_view<const gdb_byte>
  90   lookup_gdb_index (const bfd_build_id *build_id,
  91                     std::unique_ptr<index_cache_resource> *resource);
  92
  93   /* Return the number of cache hits.  */
  94   unsigned int n_hits () const
  95   { return m_n_hits; }
  96
  97   /* Record a cache hit.  */
  98   void hit ()
  99   {
 100     if (enabled ())
 101       m_n_hits++;
 102   }
 103
 104   /* Return the number of cache misses.  */
 105   unsigned int n_misses () const
 106   { return m_n_misses; }
 107
 108   /* Record a cache miss.  */
 109   void miss ()
 110   {
 111     if (enabled ())
 112       m_n_misses++;
 113   }
 114
 115 private:
 116
 117   /* Compute the absolute filename where the index of the objfile with build
 118      id BUILD_ID will be stored.  SUFFIX is appended at the end of the
 119      filename.  */
 120   std::string make_index_filename (const bfd_build_id *build_id,
 121                                    const char *suffix) const;
 122
 123   /* The base directory where we are storing and looking up index files.  */
 124   std::string m_dir;
 125
 126   /* Whether the cache is enabled.  */
 127   bool m_enabled = false;
 128
 129   /* Number of cache hits and misses during this GDB session.  */
 130   unsigned int m_n_hits = 0;
 131   unsigned int m_n_misses = 0;
 132 };
 133
 134 /* The global instance of the index cache.  */
 135 extern index_cache global_index_cache;
 136
 137 #endif /* DWARF_INDEX_CACHE_H */