gcc/memory-block.h

   1 /* Shared pool of memory blocks for pool allocators.
   2    Copyright (C) 2015-2020 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 3, or (at your option)
   9 any later version.
  10
  11 GCC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20
  21 #ifndef MEMORY_BLOCK_H
  22 #define MEMORY_BLOCK_H
  23
  24 /* Shared pool which allows other memory pools to reuse each others' allocated
  25    memory blocks instead of calling free/malloc again.  */
  26 class memory_block_pool
  27 {
  28 public:
  29   /* Blocks have fixed size.  This is necessary for sharing.  */
  30   static const size_t block_size = 64 * 1024;
  31   /* Number of blocks we keep in the freelists.  */
  32   static const size_t freelist_size = 1024 * 1024 / block_size;
  33
  34   memory_block_pool ();
  35
  36   static inline void *allocate () ATTRIBUTE_MALLOC;
  37   static inline void release (void *);
  38   static void trim (int nblocks = freelist_size);
  39   void reduce_free_list (int);
  40
  41 private:
  42   /* memory_block_pool singleton instance, defined in memory-block.cc.  */
  43   static memory_block_pool instance;
  44
  45   struct block_list
  46   {
  47     block_list *m_next;
  48   };
  49
  50   /* Free list.  */
  51   block_list *m_blocks;
  52 };
  53
  54 /* Allocate a single block.  Reuse a previously returned block, if possible.  */
  55 inline void *
  56 memory_block_pool::allocate ()
  57 {
  58   if (instance.m_blocks == NULL)
  59     return XNEWVEC (char, block_size);
  60
  61   void *result = instance.m_blocks;
  62   instance.m_blocks = instance.m_blocks->m_next;
  63   VALGRIND_DISCARD (VALGRIND_MAKE_MEM_UNDEFINED (result, block_size));
  64   return result;
  65 }
  66
  67 /* Return UNCAST_BLOCK to the pool.  */
  68 inline void
  69 memory_block_pool::release (void *uncast_block)
  70 {
  71   block_list *block = new (uncast_block) block_list;
  72   block->m_next = instance.m_blocks;
  73   instance.m_blocks = block;
  74
  75   VALGRIND_DISCARD (VALGRIND_MAKE_MEM_NOACCESS ((char *)uncast_block
  76                                                 + sizeof (block_list),
  77                                                 block_size
  78                                                 - sizeof (block_list)));
  79 }
  80
  81 extern void *mempool_obstack_chunk_alloc (size_t) ATTRIBUTE_MALLOC;
  82 extern void mempool_obstack_chunk_free (void *);
  83
  84 #endif /* MEMORY_BLOCK_H */