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Diffstat (limited to 'include/my_stack_alloc.h')
| -rw-r--r-- | include/my_stack_alloc.h | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/include/my_stack_alloc.h b/include/my_stack_alloc.h new file mode 100644 index 00000000..95e746d6 --- /dev/null +++ b/include/my_stack_alloc.h @@ -0,0 +1,92 @@ +/* Copyright 2019 MariaDB corporation AB + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; version 2 of the License. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA +*/ + +#ifndef _my_stack_alloc_h +#define _my_stack_alloc_h + +/* + Do allocation through alloca if there is enough stack available. + If not, use my_malloc() instead. + + The idea is that to be able to alloc as much as possible through the + stack. To ensure this, we have two different limits, on for big + blocks and one for small blocks. This will enable us to continue to + do allocation for small blocks even when there is less stack space + available. + This is for example used by Aria when traversing the b-tree and the code + needs to allocate one b-tree page and a few keys for each recursion. Even + if there is not space to allocate the b-tree pages on stack we can still + continue to allocate the keys. +*/ + +/* + Default suggested allocations +*/ + +/* Allocate big blocks as long as there is this much left */ +#define STACK_ALLOC_BIG_BLOCK 1024*64 + +/* Allocate small blocks as long as there is this much left */ +#define STACK_ALLOC_SMALL_BLOCK 1024*32 + +/* Allocate small blocks as long as there is this much left */ +#define STACK_ALLOC_SMALL_BLOCK_SIZE 4096 + +/* + Allocate a block on stack or through malloc. + The 'must_be_freed' variable will be set to 1 if malloc was called. + 'must_be_freed' must be a variable on the stack! +*/ + +#ifdef HAVE_ALLOCA +#define alloc_on_stack(stack_end, res, must_be_freed, size) \ +do \ +{ \ + size_t alloc_size= (size); \ + size_t stack_left= available_stack_size(&alloc_size, (stack_end)); \ + if (stack_left > alloc_size && \ + (STACK_ALLOC_BIG_BLOCK < stack_left - alloc_size || \ + ((STACK_ALLOC_SMALL_BLOCK < stack_left - alloc_size) && \ + (STACK_ALLOC_SMALL_BLOCK_SIZE <= alloc_size)))) \ + { \ + (must_be_freed)= 0; \ + (res)= alloca(size); \ + } \ + else \ + { \ + (must_be_freed)= 1; \ + (res)= my_malloc(PSI_INSTRUMENT_ME, size, MYF(MY_THREAD_SPECIFIC | MY_WME)); \ + } \ +} while(0) +#else +#define alloc_on_stack(stack_end, res, must_be_freed, size) \ + do { \ + (must_be_freed)= 1; \ + (res)= my_malloc(PSI_INSTRUMENT_ME, size, MYF(MY_THREAD_SPECIFIC | MY_WME)); \ + } while(0) +#endif /* HAVE_ALLOCA */ + + +/* + Free memory allocated by stack_alloc +*/ + +static inline void stack_alloc_free(void *res, my_bool must_be_freed) +{ + if (must_be_freed) + my_free(res); +} +#endif /* _my_stack_alloc_h */ |