gecko-dev/db/common/db_salloc.c
1998-10-15 03:56:37 +00:00

302 lines
7.2 KiB
C

/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996, 1997, 1998
* Sleepycat Software. All rights reserved.
*/
#include "config.h"
#ifndef lint
static const char sccsid[] = "@(#)db_salloc.c 10.13 (Sleepycat) 5/10/98";
#endif /* not lint */
#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#include <errno.h>
#include <string.h>
#endif
#include "db_int.h"
#include "shqueue.h"
#include "common_ext.h"
/*
* Implement shared memory region allocation, using simple first-fit algorithm.
* The model is that we take a "chunk" of shared memory store and begin carving
* it up into areas, similarly to how malloc works. We do coalescing on free.
*
* The "len" field in the __data struct contains the length of the free region
* (less the size_t bytes that holds the length). We use the address provided
* by the caller to find this length, which allows us to free a chunk without
* requiring that the caller pass in the length of the chunk they're freeing.
*/
SH_LIST_HEAD(__head);
struct __data {
size_t len;
SH_LIST_ENTRY links;
};
/*
* __db_shalloc_init --
* Initialize the area as one large chunk.
*
* PUBLIC: void __db_shalloc_init __P((void *, size_t));
*/
void
__db_shalloc_init(area, size)
void *area;
size_t size;
{
struct __data *elp;
struct __head *hp;
hp = area;
SH_LIST_INIT(hp);
elp = (struct __data *)(hp + 1);
elp->len = size - sizeof(struct __head) - sizeof(elp->len);
SH_LIST_INSERT_HEAD(hp, elp, links, __data);
}
/*
* __db_shalloc --
* Allocate some space from the shared region.
*
* PUBLIC: int __db_shalloc __P((void *, size_t, size_t, void *));
*/
int
__db_shalloc(p, len, align, retp)
void *p, *retp;
size_t len, align;
{
struct __data *elp;
size_t *sp;
void *rp;
/*
* We never allocate less than the size of a struct __data, align
* to less than a size_t boundary, or align to something that's not
* a multiple of a size_t.
*/
if (len < sizeof(struct __data))
len = sizeof(struct __data);
align = align <= sizeof(size_t) ?
sizeof(size_t) : ALIGN(align, sizeof(size_t));
/* Walk the list, looking for a slot. */
for (elp = SH_LIST_FIRST((struct __head *)p, __data);
elp != NULL;
elp = SH_LIST_NEXT(elp, links, __data)) {
/*
* Calculate the value of the returned pointer if we were to
* use this chunk.
* + Find the end of the chunk.
* + Subtract the memory the user wants.
* + Find the closest previous correctly-aligned address.
*/
rp = (u_int8_t *)elp + sizeof(size_t) + elp->len;
rp = (u_int8_t *)rp - len;
rp = (u_int8_t *)((ALIGNTYPE)rp & ~(align - 1));
/*
* Rp may now point before elp->links, in which case the chunk
* was too small, and we have to try again.
*/
if ((u_int8_t *)rp < (u_int8_t *)&elp->links)
continue;
*(void **)retp = rp;
#define SHALLOC_FRAGMENT 32
/*
* If there are at least SHALLOC_FRAGMENT additional bytes of
* memory, divide the chunk into two chunks.
*/
if ((u_int8_t *)rp >=
(u_int8_t *)&elp->links + SHALLOC_FRAGMENT) {
sp = rp;
*--sp = elp->len -
((u_int8_t *)rp - (u_int8_t *)&elp->links);
elp->len -= *sp + sizeof(size_t);
return (0);
}
/*
* Otherwise, we return the entire chunk, wasting some amount
* of space to keep the list compact. However, because the
* address we're returning to the user may not be the address
* of the start of the region for alignment reasons, set the
* size_t length fields back to the "real" length field to a
* flag value, so that we can find the real length during free.
*/
#define ILLEGAL_SIZE 1
SH_LIST_REMOVE(elp, links, __data);
for (sp = rp; (u_int8_t *)--sp >= (u_int8_t *)&elp->links;)
*sp = ILLEGAL_SIZE;
return (0);
}
/* Nothing found large enough; need to grow the region. */
return (ENOMEM);
}
/*
* __db_shalloc_free --
* Free a shared memory allocation.
*
* PUBLIC: void __db_shalloc_free __P((void *, void *));
*/
void
__db_shalloc_free(regionp, ptr)
void *regionp, *ptr;
{
struct __data *elp, *lastp, *newp;
struct __head *hp;
size_t free_size, *sp;
int merged;
/*
* Step back over flagged length fields to find the beginning of
* the object and its real size.
*/
for (sp = (size_t *)ptr; sp[-1] == ILLEGAL_SIZE; --sp)
;
ptr = sp;
newp = (struct __data *)((u_int8_t *)ptr - sizeof(size_t));
free_size = newp->len;
/* Trash the returned memory. */
#ifdef DIAGNOSTIC
memset(ptr, 0xff, free_size);
#endif
/*
* Walk the list, looking for where this entry goes.
*
* We keep the free list sorted by address so that coalescing is
* trivial.
*
* XXX
* Probably worth profiling this to see how expensive it is.
*/
hp = (struct __head *)regionp;
for (elp = SH_LIST_FIRST(hp, __data), lastp = NULL;
elp != NULL && (void *)elp < (void *)ptr;
lastp = elp, elp = SH_LIST_NEXT(elp, links, __data))
;
/*
* Elp is either NULL (we reached the end of the list), or the slot
* after the one that's being returned. Lastp is either NULL (we're
* returning the first element of the list) or the element before the
* one being returned.
*
* Check for coalescing with the next element.
*/
merged = 0;
if ((u_int8_t *)ptr + free_size == (u_int8_t *)elp) {
newp->len += elp->len + sizeof(size_t);
SH_LIST_REMOVE(elp, links, __data);
if (lastp != NULL)
SH_LIST_INSERT_AFTER(lastp, newp, links, __data);
else
SH_LIST_INSERT_HEAD(hp, newp, links, __data);
merged = 1;
}
/* Check for coalescing with the previous element. */
if (lastp != NULL && (u_int8_t *)lastp +
lastp->len + sizeof(size_t) == (u_int8_t *)newp) {
lastp->len += newp->len + sizeof(size_t);
/*
* If we have already put the new element into the list take
* it back off again because it's just been merged with the
* previous element.
*/
if (merged)
SH_LIST_REMOVE(newp, links, __data);
merged = 1;
}
if (!merged)
if (lastp == NULL)
SH_LIST_INSERT_HEAD(hp, newp, links, __data);
else
SH_LIST_INSERT_AFTER(lastp, newp, links, __data);
}
/*
* __db_shalloc_count --
* Return the amount of memory on the free list.
*
* PUBLIC: size_t __db_shalloc_count __P((void *));
*/
size_t
__db_shalloc_count(addr)
void *addr;
{
struct __data *elp;
size_t count;
count = 0;
for (elp = SH_LIST_FIRST((struct __head *)addr, __data);
elp != NULL;
elp = SH_LIST_NEXT(elp, links, __data))
count += elp->len;
return (count);
}
/*
* __db_shsizeof --
* Return the size of a shalloc'd piece of memory.
*
* PUBLIC: size_t __db_shsizeof __P((void *));
*/
size_t
__db_shsizeof(ptr)
void *ptr;
{
struct __data *elp;
size_t *sp;
/*
* Step back over flagged length fields to find the beginning of
* the object and its real size.
*/
for (sp = (size_t *)ptr; sp[-1] == ILLEGAL_SIZE; --sp)
;
elp = (struct __data *)((u_int8_t *)sp - sizeof(size_t));
return (elp->len);
}
/*
* __db_shalloc_dump --
*
* PUBLIC: void __db_shalloc_dump __P((void *, FILE *));
*/
void
__db_shalloc_dump(addr, fp)
void *addr;
FILE *fp;
{
struct __data *elp;
/* Make it easy to call from the debugger. */
if (fp == NULL)
fp = stderr;
fprintf(fp, "%s\nMemory free list\n", DB_LINE);
for (elp = SH_LIST_FIRST((struct __head *)addr, __data);
elp != NULL;
elp = SH_LIST_NEXT(elp, links, __data))
fprintf(fp, "%#lx: %lu\t", (u_long)elp, (u_long)elp->len);
fprintf(fp, "\n");
}