Sweden-Number/ipc/shm_fragment.c

179 lines
5.3 KiB
C

/***************************************************************************
* Copyright 1995, Technion, Israel Institute of Technology
* Electrical Eng, Software Lab.
* Author: Michael Veksler.
***************************************************************************
* File: shm_fragment.c
* Purpose: Data fragments and free list items. Allocate and free blocks.
***************************************************************************
*/
#include <stdio.h> /* for debugging only */
#include <stddebug.h>
#include <debug.h> /* for "stddeb" */
#include "shm_fragment.h"
#include "shm_block.h"
/******************************************************************************
*
* Free list: all fragments are ordered according to memory location.
* new fragments are inserted in this way.
*
******************************************************************************
*/
#define FRAG_PTR(block,ofs) ((struct shm_fragment *) ((char *) block + ofs) )
#define NEXT_FRAG(block,ofs) ( FRAG_PTR(block,ofs)->info.next )
/* setup first item in the free list */
void shm_FragmentInit(struct shm_block *block,int first, int size)
{
struct shm_fragment *fragment;
/* round up to nearest 16 byte boundary */
first=(first+15)& ~15;
block->free_list=first;
/* make all the block (exluding the header) free */
fragment= FRAG_PTR(block, first);
block->free= fragment->size= size-first;
fragment->info.next=0;
}
void shm_FragPtrFree(struct shm_block *block, void *ptr)
{
/* ptr points to fragment->info.data, find pointer to fragment,
* find the offset of this pointer in block.
*/
if (ptr)
shm_FragmentFree(block, PTR2REL(block, ptr));
}
void shm_FragmentFree(struct shm_block *block, int fragment_ofs)
{
struct shm_fragment *fragment=NULL;
int prev;
int next;
fragment_ofs-=(int )&fragment->info.data;
fragment= FRAG_PTR(block, fragment_ofs);
block->free+=fragment->size;
/* scan free list to find candidates for merging with fragment */
for (prev=0, next=block->free_list;
(next!=0) && (fragment_ofs > next) ;
prev=next, next=NEXT_FRAG(block,next) )
;
/* insert fragment between, prev and next
* prev==0: fragment will be the first item in free list
* next==0: fragment will be the last item in free list
*/
/* update fragment (point to next, or merge with next) */
if ( fragment_ofs+fragment->size == next ) {
/* merge with the next free block */
fragment->size+= FRAG_PTR(block,next)->size;
fragment->info.next=FRAG_PTR(block,next)->info.next;
} else
/* fragment should be inserted before the next fragment or end of */
/* list. (not merged) */
fragment->info.next=next;
/* now fragment has all the information about the rest of the list */
/* upate prev fragment (point or merge with fragment) */
if (prev==0) /* first item in free list */
block->free_list=fragment_ofs;
else if ( prev+FRAG_PTR(block,prev)->size == fragment_ofs ) {
/* merge fragment with previous fragment */
FRAG_PTR(block,prev)->size+= fragment->size;
FRAG_PTR(block,prev)->info.next=fragment->info.next;
} else
/* insert fragment after previous fragment */
FRAG_PTR(block,prev)->info.next=fragment_ofs;
}
/* use "first fit" algorithm,
* return: offset to data in fragment.
*/
int shm_FragmentAlloc(struct shm_block *block, int size)
{
int prev;
int candidate;
struct shm_fragment *fragment;
struct shm_fragment *ret_fragment;
if (size <= 0)
return NIL;
/* add size of "fragment->size" */
size+= (char *)&fragment->info.data - (char *)fragment ;
/* round "size" to nearest 16 byte value */
size= (size+15) & ~15;
if (size > block->free)
return NIL;
/* scan free list to find candidates for allocation */
for (prev=0, candidate=block->free_list;
candidate!=0 ;
prev=candidate, candidate= fragment->info.next )
{
fragment=FRAG_PTR(block,candidate);
if (fragment->size >= size)
break;
}
if (candidate == 0)
return NIL;
block->free-=size;
if (fragment->size == size) {
if (prev == 0)
block->free_list= fragment->info.next;
else
FRAG_PTR(block,prev)->info.next= fragment->info.next;
return PTR2REL(block, &fragment->info.data);
}
/* fragment->size > size */
/* Split fragment in two, return one part, put the other in free list. */
/* The part that starts at the old location - will stay in the free list. */
fragment->size -= size;
ret_fragment=FRAG_PTR(block, candidate + fragment->size);
ret_fragment->size= size;
return PTR2REL(block, ret_fragment->info.data);
}
/* like shm_FragmentAlloc, returns pointer instead of offset */
char *shm_FragPtrAlloc(struct shm_block *block, int size)
{
int ofs;
ofs= shm_FragmentAlloc(block,size);
if (ofs == NIL)
return NULL;
else
return (char *) REL2PTR(block, ofs);
}
/* This is used for debugging only */
void shm_print_free_list(struct shm_block *block)
{
struct shm_fragment *fragment;
int item;
item=block->free_list;
if (item==0) {
fprintf(stddeb,"no free fragments");
} else {
for (; item ; item=fragment->info.next) {
fragment=FRAG_PTR(block,item);
fprintf(stddeb,"{0x%04x,0x%04x} ",item,fragment->size);
}
}
fprintf(stddeb," [total free=%04x]\n",block->free);
fflush(stddeb);
}