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gc.c
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gc.c
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#include <stdio.h>
#include <stdlib.h>
#include "agent.h"
#include "cbcvm.h"
#include "error.h"
#include "eval.h"
#include "gc.h"
#include "hashmap.h"
#include "module.h"
#include "value.h"
#define DEBUG_LOG(MSG, ...) ({ \
if (cb_options.debug_gc) \
printf("GC: " MSG "\n", ##__VA_ARGS__); \
})
#define GC_HINT_THRESHOLD (1 << 14)
#define GC_INITIAL_THRESHOLD (1 << 16)
#define GC_HEAP_GROW_FACTOR 16
static struct cb_gc_header *allocated = NULL;
static size_t amount_allocated = 0;
static size_t next_allocation_threshold = GC_INITIAL_THRESHOLD;
static size_t hint = 0;
inline void cb_gc_register(struct cb_gc_header *obj, size_t size,
cb_deinit_fn *deinit_fn)
{
obj->deinit = deinit_fn;
obj->mark = 0;
obj->size = size;
obj->next = allocated;
allocated = obj;
amount_allocated += size;
}
inline int cb_gc_should_collect(void)
{
return hint > GC_HINT_THRESHOLD
|| amount_allocated > next_allocation_threshold;
}
inline void cb_gc_mark(struct cb_gc_header *obj)
{
obj->mark = 1;
}
inline int cb_gc_is_marked(struct cb_gc_header *obj)
{
return obj->mark;
}
struct mark_queue_node {
struct cb_value *val;
struct mark_queue_node *next;
};
static struct mark_queue_node *mark_queue = NULL;
void cb_gc_queue_mark(struct cb_value *obj)
{
struct mark_queue_node *node;
node = malloc(sizeof(struct mark_queue_node));
node->next = mark_queue;
node->val = obj;
mark_queue = node;
}
static void evaluate_mark_queue(void)
{
struct mark_queue_node *tmp;
while (mark_queue) {
tmp = mark_queue;
mark_queue = tmp->next;
if (!cb_value_is_marked(tmp->val))
cb_value_mark(tmp->val);
free(tmp);
}
}
struct cext_root {
struct cext_root *prev, *next;
struct cb_value value;
};
static struct cext_root *cext_root = NULL;
struct cext_root *cb_gc_hold(struct cb_value value)
{
struct cext_root *node = malloc(sizeof(struct cext_root));
node->prev = NULL;
node->next = cext_root;
node->value = value;
cext_root = node;
return node;
}
void cb_gc_release(struct cext_root *node)
{
if (node->prev)
node->prev->next = node->next;
if (node->next)
node->next->prev = node->prev;
if (node == cext_root)
cext_root = node->next;
free(node);
}
static void mark(void)
{
struct cb_module *mod;
/* Roots:
* - stack
* - globals
* - vm state error
* - functions in frames
*/
DEBUG_LOG("marking stack values");
for (struct cb_value *val = cb_vm_state.stack;
val < cb_vm_state.stack_top; val += 1)
cb_value_mark(val);
DEBUG_LOG("marking module global scopes");
if (cb_vm_state.modules) {
for (unsigned i = 0; i < cb_agent_modspec_count(); i += 1) {
mod = &cb_vm_state.modules[i];
if (!mod || !mod->spec)
continue;
cb_str name = cb_agent_get_string(cb_modspec_name(
mod->spec));
DEBUG_LOG("marking %s global scope", cb_strptr(&name));
cb_hashmap_mark_contents(mod->global_scope);
}
}
DEBUG_LOG("marking error");
cb_error_mark();
DEBUG_LOG("marking frame functions");
for (struct cb_frame *f = cb_vm_state.frame; f; f = f->parent) {
if (CB_VALUE_IS_USER_FN(&f->func))
cb_value_mark(&f->func);
}
DEBUG_LOG("marking c ext roots");
for (struct cext_root *node = cext_root; node; node = node->next)
cb_value_mark(&node->value);
evaluate_mark_queue();
}
static void sweep(void)
{
struct cb_gc_header *current, *tmp, **prev_ptr;
current = allocated;
prev_ptr = &allocated;
while (current) {
tmp = current;
current = current->next;
if (!tmp->mark) {
*prev_ptr = tmp->next;
if (tmp->deinit)
tmp->deinit(tmp);
DEBUG_LOG("freeing object at %p", tmp);
amount_allocated -= tmp->size;
free(tmp);
} else {
DEBUG_LOG("not freeing object at %p", tmp);
tmp->mark = 0;
prev_ptr = &tmp->next;
}
}
}
void cb_gc_collect(void)
{
size_t before = amount_allocated;
DEBUG_LOG("start; allocated=%zu", amount_allocated);
hint = 0;
mark();
sweep();
next_allocation_threshold = amount_allocated * GC_HEAP_GROW_FACTOR;
DEBUG_LOG("end; allocated=%zu, collected=%zu, next collection at %zu",
amount_allocated, before - amount_allocated,
next_allocation_threshold);
}