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gc.c
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gc.c
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#include "gc.h"
#include "arena.h"
#include "internal.h"
#include "common.h"
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#ifdef _WIN32
#include <windows.h>
static inline void *gc_mmap(size_t size) {
return VirtualAlloc(NULL, size, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
}
static inline void gc_munmap(void *ptr, size_t size) {
(void)size;
VirtualFree(ptr, 0, MEM_RELEASE);
}
#else
#include <sys/mman.h>
static inline void *gc_mmap(size_t size) {
void *p = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
return (p == MAP_FAILED) ? NULL : p;
}
static inline void gc_munmap(void *ptr, size_t size) {
munmap(ptr, size);
}
#endif
#define MCO_API extern
#include "minicoro.h"
static uint8_t *gc_scratch_buf = NULL;
static size_t gc_scratch_size = 0;
static time_t gc_last_run_time = 0;
static bool gc_throttled = false;
void js_gc_throttle(bool enabled) { gc_throttled = enabled; }
#define FWD_EMPTY ((jsoff_t)~0)
#define FWD_TOMBSTONE ((jsoff_t)~1)
#ifdef _WIN32
#define RELEASE_PAGES(p, sz) VirtualAlloc(p, sz, MEM_RESET, PAGE_READWRITE)
#else
#define RELEASE_PAGES(p, sz) madvise(p, sz, MADV_DONTNEED)
#endif
typedef struct {
jsoff_t *old_offs;
jsoff_t *new_offs;
size_t count;
size_t capacity;
size_t mask;
} gc_forward_table_t;
typedef struct {
jsoff_t *items;
size_t count;
size_t capacity;
} gc_work_queue_t;
typedef struct {
ant_t *js;
uint8_t *new_mem;
uint8_t *mark_bits;
gc_forward_table_t fwd;
gc_work_queue_t work;
jsoff_t new_brk;
jsoff_t new_size;
bool failed;
} gc_ctx_t;
static jsval_t gc_update_val(gc_ctx_t *ctx, jsval_t val);
static inline void mark_set(gc_ctx_t *ctx, jsoff_t off) {
jsoff_t idx = off >> 3;
ctx->mark_bits[idx >> 3] |= (1 << (idx & 7));
}
static inline size_t next_pow2(size_t n) {
n--;
n |= n >> 1; n |= n >> 2; n |= n >> 4;
n |= n >> 8; n |= n >> 16;
#if SIZE_MAX > 0xFFFFFFFF
n |= n >> 32;
#endif
return n + 1;
}
static bool fwd_init(gc_forward_table_t *fwd, size_t estimated) {
size_t cap = next_pow2(estimated < 64 ? 64 : estimated);
size_t size = cap * sizeof(jsoff_t);
fwd->old_offs = (jsoff_t *)gc_mmap(size);
fwd->new_offs = (jsoff_t *)gc_mmap(size);
if (!fwd->old_offs || !fwd->new_offs) {
if (fwd->old_offs) gc_munmap(fwd->old_offs, size);
if (fwd->new_offs) gc_munmap(fwd->new_offs, size);
return false;
}
for (size_t i = 0; i < cap; i++) fwd->old_offs[i] = FWD_EMPTY;
fwd->count = 0;
fwd->capacity = cap;
fwd->mask = cap - 1;
return true;
}
static bool fwd_grow(gc_forward_table_t *fwd) {
size_t new_cap = fwd->capacity * 2;
size_t new_mask = new_cap - 1;
size_t new_size = new_cap * sizeof(jsoff_t);
size_t old_size = fwd->capacity * sizeof(jsoff_t);
jsoff_t *new_old = (jsoff_t *)gc_mmap(new_size);
jsoff_t *new_new = (jsoff_t *)gc_mmap(new_size);
if (!new_old || !new_new) {
if (new_old) gc_munmap(new_old, new_size);
if (new_new) gc_munmap(new_new, new_size);
return false;
}
for (size_t i = 0; i < new_cap; i++) new_old[i] = FWD_EMPTY;
for (size_t i = 0; i < fwd->capacity; i++) {
jsoff_t key = fwd->old_offs[i];
if (key == FWD_EMPTY || key == FWD_TOMBSTONE) continue;
size_t h = (key >> 3) & new_mask;
while (new_old[h] != FWD_EMPTY) h = (h + 1) & new_mask;
new_old[h] = key;
new_new[h] = fwd->new_offs[i];
}
gc_munmap(fwd->old_offs, old_size);
gc_munmap(fwd->new_offs, old_size);
fwd->old_offs = new_old;
fwd->new_offs = new_new;
fwd->capacity = new_cap;
fwd->mask = new_mask;
return true;
}
static inline bool fwd_add(gc_forward_table_t *fwd, jsoff_t old_off, jsoff_t new_off) {
if (fwd->count * 100 >= fwd->capacity * GC_FWD_LOAD_FACTOR) {
if (!fwd_grow(fwd)) return false;
}
size_t h = (old_off >> 3) & fwd->mask;
while (fwd->old_offs[h] != FWD_EMPTY && fwd->old_offs[h] != FWD_TOMBSTONE) {
if (fwd->old_offs[h] == old_off) {
fwd->new_offs[h] = new_off;
return true;
}
h = (h + 1) & fwd->mask;
}
fwd->old_offs[h] = old_off;
fwd->new_offs[h] = new_off;
fwd->count++;
return true;
}
static inline jsoff_t fwd_lookup(gc_forward_table_t *fwd, jsoff_t old_off) {
size_t h = (old_off >> 3) & fwd->mask;
for (size_t i = 0; i < fwd->capacity; i++) {
jsoff_t key = fwd->old_offs[h];
if (key == FWD_EMPTY) return (jsoff_t)~0;
if (key == old_off) return fwd->new_offs[h];
h = (h + 1) & fwd->mask;
}
return (jsoff_t)~0;
}
static void fwd_free(gc_forward_table_t *fwd) {
size_t size = fwd->capacity * sizeof(jsoff_t);
if (fwd->old_offs) gc_munmap(fwd->old_offs, size);
if (fwd->new_offs) gc_munmap(fwd->new_offs, size);
fwd->old_offs = NULL;
fwd->new_offs = NULL;
fwd->count = 0;
fwd->capacity = 0;
}
static bool work_init(gc_work_queue_t *work, size_t initial) {
size_t size = initial * sizeof(jsoff_t);
work->items = (jsoff_t *)gc_mmap(size);
if (!work->items) return false;
work->count = 0;
work->capacity = initial;
return true;
}
static inline bool work_push(gc_work_queue_t *work, jsoff_t off) {
if (work->count >= work->capacity) {
size_t new_cap = work->capacity * 2;
size_t new_size = new_cap * sizeof(jsoff_t);
size_t old_size = work->capacity * sizeof(jsoff_t);
jsoff_t *new_items = (jsoff_t *)gc_mmap(new_size);
if (!new_items) return false;
memcpy(new_items, work->items, work->count * sizeof(jsoff_t));
gc_munmap(work->items, old_size);
work->items = new_items;
work->capacity = new_cap;
}
work->items[work->count++] = off;
return true;
}
static inline jsoff_t work_pop(gc_work_queue_t *work) {
if (work->count == 0) return (jsoff_t)~0;
return work->items[--work->count];
}
static void work_free(gc_work_queue_t *work) {
size_t size = work->capacity * sizeof(jsoff_t);
if (work->items) gc_munmap(work->items, size);
work->items = NULL;
work->count = 0;
work->capacity = 0;
}
static inline jsoff_t gc_loadoff(uint8_t *mem, jsoff_t off) {
jsoff_t val;
memcpy(&val, &mem[off], sizeof(val));
return val;
}
static inline jsval_t gc_loadval(uint8_t *mem, jsoff_t off) {
jsval_t val;
memcpy(&val, &mem[off], sizeof(val));
return val;
}
static inline void gc_saveoff(uint8_t *mem, jsoff_t off, jsoff_t val) {
memcpy(&mem[off], &val, sizeof(val));
}
static inline void gc_saveval(uint8_t *mem, jsoff_t off, jsval_t val) {
memcpy(&mem[off], &val, sizeof(val));
}
static jsoff_t gc_alloc(gc_ctx_t *ctx, size_t size) {
size = (size + 7) / 8 * 8;
if (ctx->new_brk + size > ctx->new_size) {
ctx->failed = true;
return (jsoff_t)~0;
}
jsoff_t off = ctx->new_brk;
ctx->new_brk += (jsoff_t)size;
return off;
}
static inline bool gc_is_tagged(jsval_t v) {
return (v >> 53) == NANBOX_PREFIX_CHK;
}
static inline uint8_t gc_vtype(jsval_t v) {
return gc_is_tagged(v) ? ((v >> NANBOX_TYPE_SHIFT) & NANBOX_TYPE_MASK) : 255;
}
static inline size_t gc_vdata(jsval_t v) {
return (size_t)(v & NANBOX_DATA_MASK);
}
static inline jsval_t gc_mkval(uint8_t type, uint64_t data) {
return NANBOX_PREFIX | ((jsval_t)(type & NANBOX_TYPE_MASK) << NANBOX_TYPE_SHIFT) | (data & NANBOX_DATA_MASK);
}
static jsoff_t gc_copy_string(gc_ctx_t *ctx, jsoff_t old_off) {
if (old_off >= ctx->js->brk) return old_off;
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
if (new_off != (jsoff_t)~0) return new_off;
jsoff_t header = gc_loadoff(ctx->js->mem, old_off);
if ((header & 3) != T_STR) return old_off;
bool is_rope_str = (header & ROPE_FLAG) != 0;
jsoff_t size;
if (is_rope_str) {
size = sizeof(rope_node_t);
} else size = esize(header);
if (size == (jsoff_t)~0) return old_off;
new_off = gc_alloc(ctx, size);
if (new_off == (jsoff_t)~0) return old_off;
memcpy(&ctx->new_mem[new_off], &ctx->js->mem[old_off], size);
if (!fwd_add(&ctx->fwd, old_off, new_off)) ctx->failed = true;
mark_set(ctx, old_off);
if (is_rope_str) {
jsval_t left, right, cached;
memcpy(&left, &ctx->js->mem[old_off + offsetof(rope_node_t, left)], sizeof(jsval_t));
memcpy(&right, &ctx->js->mem[old_off + offsetof(rope_node_t, right)], sizeof(jsval_t));
memcpy(&cached, &ctx->js->mem[old_off + offsetof(rope_node_t, cached)], sizeof(jsval_t));
jsval_t new_left = gc_update_val(ctx, left);
jsval_t new_right = gc_update_val(ctx, right);
jsval_t new_cached = gc_update_val(ctx, cached);
memcpy(&ctx->new_mem[new_off + offsetof(rope_node_t, left)], &new_left, sizeof(jsval_t));
memcpy(&ctx->new_mem[new_off + offsetof(rope_node_t, right)], &new_right, sizeof(jsval_t));
memcpy(&ctx->new_mem[new_off + offsetof(rope_node_t, cached)], &new_cached, sizeof(jsval_t));
}
return new_off;
}
static jsoff_t gc_copy_bigint(gc_ctx_t *ctx, jsoff_t old_off) {
if (old_off >= ctx->js->brk) return old_off;
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
if (new_off != (jsoff_t)~0) return new_off;
jsoff_t header = gc_loadoff(ctx->js->mem, old_off);
size_t total = (header >> 4) + sizeof(jsoff_t);
total = (total + 7) / 8 * 8;
new_off = gc_alloc(ctx, total);
if (new_off == (jsoff_t)~0) return old_off;
memcpy(&ctx->new_mem[new_off], &ctx->js->mem[old_off], total);
if (!fwd_add(&ctx->fwd, old_off, new_off)) ctx->failed = true;
mark_set(ctx, old_off);
return new_off;
}
static jsoff_t gc_reserve_object(gc_ctx_t *ctx, jsoff_t old_off) {
if (old_off >= ctx->js->brk) return old_off;
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
if (new_off != (jsoff_t)~0) return new_off;
jsoff_t header = gc_loadoff(ctx->js->mem, old_off);
if ((header & 3) != T_OBJ) return old_off;
jsoff_t size = esize(header);
if (size == (jsoff_t)~0) return old_off;
new_off = gc_alloc(ctx, size);
if (new_off == (jsoff_t)~0) return old_off;
memcpy(&ctx->new_mem[new_off], &ctx->js->mem[old_off], size);
if (!fwd_add(&ctx->fwd, old_off, new_off)) ctx->failed = true;
mark_set(ctx, old_off);
if (!work_push(&ctx->work, old_off)) ctx->failed = true;
return new_off;
}
static jsoff_t gc_reserve_prop(gc_ctx_t *ctx, jsoff_t old_off) {
if (old_off >= ctx->js->brk) return old_off;
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
if (new_off != (jsoff_t)~0) return new_off;
jsoff_t header = gc_loadoff(ctx->js->mem, old_off);
if ((header & 3) != T_PROP) return old_off;
jsoff_t size = esize(header);
if (size == (jsoff_t)~0) return old_off;
new_off = gc_alloc(ctx, size);
if (new_off == (jsoff_t)~0) return old_off;
memcpy(&ctx->new_mem[new_off], &ctx->js->mem[old_off], size);
if (!fwd_add(&ctx->fwd, old_off, new_off)) ctx->failed = true;
mark_set(ctx, old_off);
if (!work_push(&ctx->work, old_off)) ctx->failed = true;
return new_off;
}
static void gc_process_prop(gc_ctx_t *ctx, jsoff_t old_off) {
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
if (new_off == (jsoff_t)~0) return;
jsoff_t header = gc_loadoff(ctx->js->mem, old_off);
jsoff_t next_prop = header & ~(3ULL | FLAGMASK);
if (next_prop != 0 && next_prop < ctx->js->brk) {
jsoff_t new_next = gc_reserve_prop(ctx, next_prop);
jsoff_t new_header = (new_next & ~3ULL) | (header & (3ULL | FLAGMASK));
gc_saveoff(ctx->new_mem, new_off, new_header);
}
bool is_slot = (header & SLOTMASK) != 0;
if (!is_slot) {
jsoff_t key_off = gc_loadoff(ctx->js->mem, old_off + sizeof(jsoff_t));
if (key_off < ctx->js->brk) {
jsoff_t new_key = gc_copy_string(ctx, key_off);
gc_saveoff(ctx->new_mem, new_off + sizeof(jsoff_t), new_key);
}
}
jsval_t val = gc_loadval(ctx->js->mem, old_off + sizeof(jsoff_t) + sizeof(jsoff_t));
jsval_t new_val = gc_update_val(ctx, val);
gc_saveval(ctx->new_mem, new_off + sizeof(jsoff_t) + sizeof(jsoff_t), new_val);
}
static void gc_process_object(gc_ctx_t *ctx, jsoff_t old_off) {
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
if (new_off == (jsoff_t)~0) return;
jsoff_t header = gc_loadoff(ctx->js->mem, old_off);
jsoff_t first_prop = header & ~(3ULL | FLAGMASK);
if (first_prop != 0 && first_prop < ctx->js->brk) {
jsoff_t new_first = gc_reserve_prop(ctx, first_prop);
jsoff_t new_header = (new_first & ~3ULL) | (header & (3ULL | FLAGMASK));
gc_saveoff(ctx->new_mem, new_off, new_header);
}
jsoff_t parent_off = gc_loadoff(ctx->js->mem, old_off + sizeof(jsoff_t));
if (parent_off < ctx->js->brk) {
jsoff_t new_parent = gc_reserve_object(ctx, parent_off);
gc_saveoff(ctx->new_mem, new_off + sizeof(jsoff_t), new_parent);
}
jsoff_t tail_off = gc_loadoff(ctx->js->mem, old_off + sizeof(jsoff_t) + sizeof(jsoff_t));
if (tail_off != 0 && tail_off < ctx->js->brk) {
jsoff_t new_tail = fwd_lookup(&ctx->fwd, tail_off);
if (new_tail == (jsoff_t)~0) new_tail = gc_reserve_prop(ctx, tail_off);
gc_saveoff(ctx->new_mem, new_off + sizeof(jsoff_t) + sizeof(jsoff_t), new_tail);
}
}
static void gc_drain_work_queue(gc_ctx_t *ctx) {
jsoff_t off;
while ((off = work_pop(&ctx->work)) != (jsoff_t)~0) {
jsoff_t header = gc_loadoff(ctx->js->mem, off);
switch (header & 3) {
case T_OBJ: gc_process_object(ctx, off); break;
case T_PROP: gc_process_prop(ctx, off); break;
default: break;
}
}
}
static jsval_t gc_update_val(gc_ctx_t *ctx, jsval_t val) {
if (!gc_is_tagged(val)) return val;
uint8_t type = gc_vtype(val);
jsoff_t old_off = (jsoff_t)gc_vdata(val);
switch (type) {
case T_OBJ:
case T_FUNC:
case T_ARR:
case T_PROMISE:
case T_GENERATOR: {
if (old_off >= ctx->js->brk) return val;
jsoff_t new_off = gc_reserve_object(ctx, old_off);
if (new_off != (jsoff_t)~0) return gc_mkval(type, new_off);
break;
}
case T_STR: {
if (old_off >= ctx->js->brk) return val;
jsoff_t new_off = gc_copy_string(ctx, old_off);
if (new_off != (jsoff_t)~0) return gc_mkval(type, new_off);
break;
}
case T_PROP: {
if (old_off >= ctx->js->brk) return val;
jsoff_t new_off = gc_reserve_prop(ctx, old_off);
if (new_off != (jsoff_t)~0) return gc_mkval(type, new_off);
break;
}
case T_BIGINT: {
if (old_off >= ctx->js->brk) return val;
jsoff_t new_off = gc_copy_bigint(ctx, old_off);
if (new_off != (jsoff_t)~0) return gc_mkval(type, new_off);
break;
}
default: break;
}
return val;
}
static jsoff_t gc_fwd_off_callback(void *ctx_ptr, jsoff_t old_off) {
gc_ctx_t *ctx = (gc_ctx_t *)ctx_ptr;
if (old_off == 0) return 0;
if (old_off >= ctx->js->brk) return old_off;
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
if (new_off != (jsoff_t)~0) return new_off;
static const void *dispatch[] = { &&l_obj, &&l_prop, &&l_str, &&l_default };
jsoff_t header = gc_loadoff(ctx->js->mem, old_off);
goto *dispatch[header & 3];
l_obj: new_off = gc_reserve_object(ctx, old_off); goto l_done;
l_prop: new_off = gc_reserve_prop(ctx, old_off); goto l_done;
l_str: new_off = gc_copy_string(ctx, old_off); goto l_done;
l_default: return old_off;
l_done: return (new_off != (jsoff_t)~0) ? new_off : old_off;
}
static jsval_t gc_fwd_val_callback(void *ctx_ptr, jsval_t val) {
gc_ctx_t *ctx = (gc_ctx_t *)ctx_ptr;
return gc_update_val(ctx, val);
}
static jsoff_t gc_apply_off_callback(void *ctx_ptr, jsoff_t old_off) {
gc_ctx_t *ctx = (gc_ctx_t *)ctx_ptr;
if (old_off == 0) return 0;
if (old_off >= ctx->js->brk) return old_off;
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
return (new_off != (jsoff_t)~0) ? new_off : old_off;
}
static jsval_t gc_apply_val(gc_ctx_t *ctx, jsval_t val) {
if (!gc_is_tagged(val)) return val;
uint8_t type = gc_vtype(val);
jsoff_t old_off = (jsoff_t)gc_vdata(val);
if (old_off >= ctx->js->brk) return val;
switch (type) {
case T_OBJ:
case T_FUNC:
case T_ARR:
case T_PROMISE:
case T_GENERATOR:
case T_STR:
case T_PROP:
case T_BIGINT: {
jsoff_t new_off = fwd_lookup(&ctx->fwd, old_off);
if (new_off != (jsoff_t)~0) return gc_mkval(type, new_off);
break;
}
default: break;
}
return val;
}
static jsval_t gc_apply_val_callback(void *ctx_ptr, jsval_t val) {
gc_ctx_t *ctx = (gc_ctx_t *)ctx_ptr;
return gc_apply_val(ctx, val);
}
static jsoff_t gc_weak_off_callback(void *ctx_ptr, jsoff_t old_off) {
gc_ctx_t *ctx = (gc_ctx_t *)ctx_ptr;
if (old_off >= ctx->js->brk) return old_off;
return fwd_lookup(&ctx->fwd, old_off);
}
size_t js_gc_compact(ant_t *js) {
if (!js || js->brk == 0) return 0;
if (js->brk < 2 * 1024 * 1024) return 0;
mco_coro *running = mco_running();
int in_coroutine = (running != NULL && running->stack_base != NULL);
if (in_coroutine) {
js->needs_gc = true;
return 0;
}
time_t now = time(NULL);
if (now != (time_t)-1 && gc_last_run_time != 0) {
double elapsed = difftime(now, gc_last_run_time);
double cooldown;
if (js->brk > 64 * 1024 * 1024) cooldown = 0.5;
else if (js->brk > 16 * 1024 * 1024) cooldown = 1.0;
else if (js->brk > 4 * 1024 * 1024) cooldown = 2.0;
else cooldown = 4.0;
if (elapsed >= 0.0
&& elapsed < cooldown
&& js->gc_alloc_since < js->brk / 4
) return 0;
}
if (now != (time_t)-1) gc_last_run_time = now;
size_t old_brk = js->brk;
size_t new_size = js->size;
if (new_size > gc_scratch_size) {
if (gc_scratch_buf) gc_munmap(gc_scratch_buf, gc_scratch_size);
gc_scratch_buf = (uint8_t *)gc_mmap(new_size);
gc_scratch_size = gc_scratch_buf ? new_size : 0;
}
if (!gc_scratch_buf) return 0;
uint8_t *new_mem = gc_scratch_buf;
size_t bitmap_size = (js->brk / 8 + 7) / 8 + 1;
uint8_t *mark_bits = (uint8_t *)calloc(1, bitmap_size);
if (!mark_bits) return 0;
size_t estimated_objs = js->brk / 64;
if (estimated_objs < 256) estimated_objs = 256;
gc_ctx_t ctx;
ctx.js = js;
ctx.new_mem = new_mem;
ctx.new_brk = 0;
ctx.new_size = (jsoff_t)new_size;
ctx.mark_bits = mark_bits;
if (!fwd_init(&ctx.fwd, estimated_objs)) {
free(mark_bits);
return 0;
}
if (!work_init(&ctx.work, estimated_objs / 4 < 64 ? 64 : estimated_objs / 4)) {
fwd_free(&ctx.fwd);
free(mark_bits);
return 0;
}
ctx.failed = false;
if (js->brk > 0) {
jsoff_t header_at_0 = gc_loadoff(js->mem, 0);
if ((header_at_0 & 3) == T_OBJ) gc_reserve_object(&ctx, 0);
}
js_gc_reserve_roots(js,
gc_fwd_off_callback,
gc_fwd_val_callback,
&ctx
); gc_drain_work_queue(&ctx);
if (ctx.failed) {
free(mark_bits);
work_free(&ctx.work);
fwd_free(&ctx.fwd);
return 0;
}
js_gc_update_roots(js,
gc_apply_off_callback,
gc_weak_off_callback,
gc_apply_val_callback,
&ctx);
memcpy(js->mem, new_mem, ctx.new_brk);
js->brk = ctx.new_brk;
free(mark_bits);
work_free(&ctx.work);
fwd_free(&ctx.fwd);
if (gc_scratch_buf && gc_scratch_size > 0) {
RELEASE_PAGES(gc_scratch_buf, gc_scratch_size);
}
size_t new_brk = ctx.new_brk;
size_t old_size = js->size;
if (new_brk < old_size / 2 && old_size > ARENA_GROW_INCREMENT) {
size_t target = ((new_brk * 2 + ARENA_GROW_INCREMENT - 1) / ARENA_GROW_INCREMENT) * ARENA_GROW_INCREMENT;
if (target < ARENA_GROW_INCREMENT) target = ARENA_GROW_INCREMENT;
if (target < old_size) { ant_arena_decommit(js->mem, old_size, target); js->size = (jsoff_t)target; }
}
return (old_brk > new_brk ? old_brk - new_brk : 0);
}
void js_gc_maybe(ant_t *js) {
jsoff_t thresh = js->brk / 4;
jsoff_t min_thresh = gc_throttled
? 8 * 1024 * 1024
: 2 * 1024 * 1024;
jsoff_t max_thresh = gc_throttled
? 64 * 1024 * 1024
: 16 * 1024 * 1024;
if (thresh < min_thresh) thresh = min_thresh;
if (thresh > max_thresh) thresh = max_thresh;
if (js->gc_alloc_since > thresh || js->needs_gc) {
js->needs_gc = false;
if (js_gc_compact(js) > 0) js->gc_alloc_since = 0;
}
}

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