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arena.c
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arena.c
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#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include "assert.h"
#include "except.h"
#include "arena.h"
#define T Arena_T
#define MAX_ALLOC_ONCE_TIME (10 * 1024)
#define THRESHOLD (10)
const Except_T Arena_NewFailed =
{ "Arena Creation Failed" };
const Except_T Arena_Failed =
{ "Arena Allocation Failed" };
struct T {
T prev;
unsigned int threshold;
char *avail;
char *limit;
};
union align {
int i;
long l;
long *lp;
void (*func)(void);
void *p;
double d;
long double ld;
};
union header {
struct T b;
union align ba;
};
static T freechunks;
static int nfree;
T Arena_new(int threshold)
{
T arena;
assert(threshold >= 0);
arena = malloc(sizeof (*arena));
if (arena == NULL)
RAISE(Arena_NewFailed);
arena->threshold = (THRESHOLD > threshold) ?
THRESHOLD : threshold;
arena->prev = NULL;
arena->avail = arena->limit = NULL;
return arena;
}
void Arena_dispose(T *ap)
{
assert(ap && *ap);
free(*ap);
*ap = NULL;
}
void *Arena_alloc(T arena, long nbytes,
const char *file, int line)
{
T ptr;
char *limit;
//The flag to record if the return address is newly allocated.
int flag = 0;
assert(arena);
assert(nbytes > 0);
/*
* Adjust nbytes to alignment size.
* */
nbytes = ((nbytes + sizeof(union align) - 1)/
(sizeof(union align))) * (sizeof(union align));
/*
* Check the chain first.
* */
ptr = arena;
while (ptr && (ptr->limit - ptr->avail < nbytes)) {
ptr = ptr->prev;
}
/*
* If not block is large enough in the chain,
* then we check the free chain.
* */
if (ptr == NULL) {
ptr = freechunks;
while (ptr && (ptr->limit - ptr->avail < nbytes)) {
ptr = ptr->prev;
}
//ptr != NULL, means we find a block suitable
if (ptr != NULL) {
freechunks = freechunks->prev;
nfree--;
limit = ptr->limit;
flag = 1;
}
}
/*
* If not block suitable in both chain and free chain,
* we need to allocate a new block.
* */
if (ptr == NULL) {
long m = sizeof(union header);
if (nbytes < MAX_ALLOC_ONCE_TIME)
m += MAX_ALLOC_ONCE_TIME;
else
m += nbytes;
ptr = malloc(m);
if (ptr == NULL) {
if (file == NULL)
RAISE(Arena_Failed);
else
Except_raise(&Arena_Failed, file, line);
}
limit = (char *)ptr + m;
flag = 1;
}
if (flag == 1) {//newly allocated or from the free chain
*ptr = *arena;
arena->avail = (char *)((union header *)ptr + 1);
arena->limit = limit;
arena->prev = ptr;
arena->avail += nbytes;
return (arena->avail - nbytes);
} else {//From the previous block
ptr->avail += nbytes;
return (ptr->avail - nbytes);
}
}
void *Arena_calloc(T arena, long count, long bytes,
const char *file, int line)
{
void *ptr;
assert(count > 0);
ptr = Arena_alloc(arena, count * bytes, file, line);
memset(ptr, '\0', count * bytes);
return ptr;
}
void Arena_free(T arena)
{
assert(arena);
while (arena->prev) {
/*
* tmp->prev = arena->prev->prev;
* tmp->avail = arena->prev->avail;
* tmp->limit = arena->prev->limit;
* */
struct T tmp = *(arena->prev);
if (nfree < arena->threshold) {
arena->prev->prev = freechunks;
freechunks = arena->prev;
nfree++;
freechunks->avail = (char *)((union header *)freechunks + 1);
freechunks->limit = arena->limit;
} else {
free(arena->prev);
}
*arena = tmp;
}
assert(arena->limit == NULL);
assert(arena->avail == NULL);
}
void Arena_exit(T *arena)
{
T p, q;
assert(arena && *arena);
Arena_free(*arena);
for (p = freechunks; p; p = q) {
q = p->prev;
free(p);
}
free(*arena);
}