fixalloc.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <assert.h>

struct memnode {
	struct memnode * next;
};

struct fixalloc {
	struct memnode *freelist;
	int nodesz;
	int cap;
	int used;
	int freed;
};

struct fixalloc *
fixalloc_create(int nodesz, int cap) {
	struct fixalloc * pool = malloc(sizeof(*pool));
	pool->freelist = NULL;
	pool->nodesz = nodesz;
	pool->used = 0;
	pool->freed = 0;
	pool->cap = cap;
	return pool;
}

void
fixalloc_release(struct fixalloc *pool) {
	free(pool);
}

void *
fixalloc_alloc(struct fixalloc *pool) {
	pool->used++;
	if (pool->freelist) {
		struct memnode * ret = pool->freelist;
		pool->freelist = ret->next;
		return ret;
	}
	return malloc(pool->nodesz);
}

void
fixalloc_free(struct fixalloc *pool, void *p) {
	assert(p != NULL);
	assert(pool->used > 0);
	struct memnode *n = p;
	--pool->used;
	++pool->freed;
	n->next = pool->freelist;
	pool->freelist = n;
}

void
fixalloc_collect(struct fixalloc *pool, int ti) {
	int total = pool->used + pool->freed;
	int n = total - pool->cap;
	if (n > pool->freed)
		n = pool->freed;
	if (n <= 0)
		return;
	clock_t ct = clock();
	int i;
	for (i=0;i<n;i++) {
		struct memnode * p = pool->freelist;
		pool->freelist = p->next;
		free(p);
		clock_t t = clock() - ct;
		if (t * 1000 / CLOCKS_PER_SEC > ti)
			break;
	}
	pool->freed -= i;
}