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gc.c
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/*
* This file is part of the MicroPython project, http://micropython.org/
*
* The MIT License (MIT)
*
* Copyright (c) 2013, 2014 Damien P. George
* Copyright (c) 2014 Paul Sokolovsky
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include "py/gc.h"
#include "py/runtime.h"
#if MICROPY_ENABLE_GC
#if MICROPY_DEBUG_VERBOSE // print debugging info
#define DEBUG_PRINT (1)
#define DEBUG_printf DEBUG_printf
#else // don't print debugging info
#define DEBUG_PRINT (0)
#define DEBUG_printf(...) (void)0
#endif
// make this 1 to dump the heap each time it changes
#define EXTENSIVE_HEAP_PROFILING (0)
// make this 1 to zero out swept memory to more eagerly
// detect untraced object still in use
#define CLEAR_ON_SWEEP (0)
#define WORDS_PER_BLOCK ((MICROPY_BYTES_PER_GC_BLOCK) / MP_BYTES_PER_OBJ_WORD)
#define BYTES_PER_BLOCK (MICROPY_BYTES_PER_GC_BLOCK)
// ATB = allocation table byte
// 0b00 = FREE -- free block
// 0b01 = HEAD -- head of a chain of blocks
// 0b10 = TAIL -- in the tail of a chain of blocks
// 0b11 = MARK -- marked head block
#define AT_FREE (0)
#define AT_HEAD (1)
#define AT_TAIL (2)
#define AT_MARK (3)
#define BLOCKS_PER_ATB (4)
#define ATB_MASK_0 (0x03)
#define ATB_MASK_1 (0x0c)
#define ATB_MASK_2 (0x30)
#define ATB_MASK_3 (0xc0)
#define ATB_0_IS_FREE(a) (((a) & ATB_MASK_0) == 0)
#define ATB_1_IS_FREE(a) (((a) & ATB_MASK_1) == 0)
#define ATB_2_IS_FREE(a) (((a) & ATB_MASK_2) == 0)
#define ATB_3_IS_FREE(a) (((a) & ATB_MASK_3) == 0)
#if MICROPY_GC_SPLIT_HEAP
#define NEXT_AREA(area) (area->next)
#else
#define NEXT_AREA(area) (NULL)
#endif
#define BLOCK_SHIFT(block) (2 * ((block) & (BLOCKS_PER_ATB - 1)))
#define ATB_GET_KIND(area, block) (((area)->gc_alloc_table_start[(block) / BLOCKS_PER_ATB] >> BLOCK_SHIFT(block)) & 3)
#define ATB_ANY_TO_FREE(area, block) do { area->gc_alloc_table_start[(block) / BLOCKS_PER_ATB] &= (~(AT_MARK << BLOCK_SHIFT(block))); } while (0)
#define ATB_FREE_TO_HEAD(area, block) do { area->gc_alloc_table_start[(block) / BLOCKS_PER_ATB] |= (AT_HEAD << BLOCK_SHIFT(block)); } while (0)
#define ATB_FREE_TO_TAIL(area, block) do { area->gc_alloc_table_start[(block) / BLOCKS_PER_ATB] |= (AT_TAIL << BLOCK_SHIFT(block)); } while (0)
#define ATB_HEAD_TO_MARK(area, block) do { area->gc_alloc_table_start[(block) / BLOCKS_PER_ATB] |= (AT_MARK << BLOCK_SHIFT(block)); } while (0)
#define ATB_MARK_TO_HEAD(area, block) do { area->gc_alloc_table_start[(block) / BLOCKS_PER_ATB] &= (~(AT_TAIL << BLOCK_SHIFT(block))); } while (0)
#define BLOCK_FROM_PTR(area, ptr) (((byte *)(ptr) - area->gc_pool_start) / BYTES_PER_BLOCK)
#define PTR_FROM_BLOCK(area, block) (((block) * BYTES_PER_BLOCK + (uintptr_t)area->gc_pool_start))
#if MICROPY_ENABLE_FINALISER
// FTB = finaliser table byte
// if set, then the corresponding block may have a finaliser
#define BLOCKS_PER_FTB (8)
#define FTB_GET(area, block) ((area->gc_finaliser_table_start[(block) / BLOCKS_PER_FTB] >> ((block) & 7)) & 1)
#define FTB_SET(area, block) do { area->gc_finaliser_table_start[(block) / BLOCKS_PER_FTB] |= (1 << ((block) & 7)); } while (0)
#define FTB_CLEAR(area, block) do { area->gc_finaliser_table_start[(block) / BLOCKS_PER_FTB] &= (~(1 << ((block) & 7))); } while (0)
#endif
#if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
#define GC_ENTER() mp_thread_mutex_lock(&MP_STATE_MEM(gc_mutex), 1)
#define GC_EXIT() mp_thread_mutex_unlock(&MP_STATE_MEM(gc_mutex))
#else
#define GC_ENTER()
#define GC_EXIT()
#endif
// TODO waste less memory; currently requires that all entries in alloc_table have a corresponding block in pool
STATIC void gc_setup_area(mp_state_mem_area_t *area, void *start, void *end) {
// calculate parameters for GC (T=total, A=alloc table, F=finaliser table, P=pool; all in bytes):
// T = A + F + P
// F = A * BLOCKS_PER_ATB / BLOCKS_PER_FTB
// P = A * BLOCKS_PER_ATB * BYTES_PER_BLOCK
// => T = A * (1 + BLOCKS_PER_ATB / BLOCKS_PER_FTB + BLOCKS_PER_ATB * BYTES_PER_BLOCK)
size_t total_byte_len = (byte *)end - (byte *)start;
#if MICROPY_ENABLE_FINALISER
area->gc_alloc_table_byte_len = total_byte_len * MP_BITS_PER_BYTE / (MP_BITS_PER_BYTE + MP_BITS_PER_BYTE * BLOCKS_PER_ATB / BLOCKS_PER_FTB + MP_BITS_PER_BYTE * BLOCKS_PER_ATB * BYTES_PER_BLOCK);
#else
area->gc_alloc_table_byte_len = total_byte_len / (1 + MP_BITS_PER_BYTE / 2 * BYTES_PER_BLOCK);
#endif
area->gc_alloc_table_start = (byte *)start;
#if MICROPY_ENABLE_FINALISER
size_t gc_finaliser_table_byte_len = (area->gc_alloc_table_byte_len * BLOCKS_PER_ATB + BLOCKS_PER_FTB - 1) / BLOCKS_PER_FTB;
area->gc_finaliser_table_start = area->gc_alloc_table_start + area->gc_alloc_table_byte_len;
#endif
size_t gc_pool_block_len = area->gc_alloc_table_byte_len * BLOCKS_PER_ATB;
area->gc_pool_start = (byte *)end - gc_pool_block_len * BYTES_PER_BLOCK;
area->gc_pool_end = end;
#if MICROPY_ENABLE_FINALISER
assert(area->gc_pool_start >= area->gc_finaliser_table_start + gc_finaliser_table_byte_len);
#endif
// clear ATBs
memset(area->gc_alloc_table_start, 0, area->gc_alloc_table_byte_len);
#if MICROPY_ENABLE_FINALISER
// clear FTBs
memset(area->gc_finaliser_table_start, 0, gc_finaliser_table_byte_len);
#endif
area->gc_last_free_atb_index = 0;
#if MICROPY_GC_SPLIT_HEAP
area->next = NULL;
#endif
}
void gc_init(void *start, void *end) {
// align end pointer on block boundary
end = (void *)((uintptr_t)end & (~(BYTES_PER_BLOCK - 1)));
DEBUG_printf("Initializing GC heap: %p..%p = " UINT_FMT " bytes\n", start, end, (byte *)end - (byte *)start);
gc_setup_area(&MP_STATE_MEM(area), start, end);
// set last free ATB index to start of heap
#if MICROPY_GC_SPLIT_HEAP
MP_STATE_MEM(gc_last_free_area) = &MP_STATE_MEM(area);
#endif
// unlock the GC
MP_STATE_THREAD(gc_lock_depth) = 0;
// allow auto collection
MP_STATE_MEM(gc_auto_collect_enabled) = 1;
#if MICROPY_GC_ALLOC_THRESHOLD
// by default, maxuint for gc threshold, effectively turning gc-by-threshold off
MP_STATE_MEM(gc_alloc_threshold) = (size_t)-1;
MP_STATE_MEM(gc_alloc_amount) = 0;
#endif
#if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
mp_thread_mutex_init(&MP_STATE_MEM(gc_mutex));
#endif
DEBUG_printf("GC layout:\n");
DEBUG_printf(" alloc table at %p, length " UINT_FMT " bytes, " UINT_FMT " blocks\n", MP_STATE_MEM(gc_alloc_table_start), MP_STATE_MEM(gc_alloc_table_byte_len), MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB);
#if MICROPY_ENABLE_FINALISER
DEBUG_printf(" finaliser table at %p, length " UINT_FMT " bytes, " UINT_FMT " blocks\n", MP_STATE_MEM(gc_finaliser_table_start), gc_finaliser_table_byte_len, gc_finaliser_table_byte_len * BLOCKS_PER_FTB);
#endif
DEBUG_printf(" pool at %p, length " UINT_FMT " bytes, " UINT_FMT " blocks\n", MP_STATE_MEM(gc_pool_start), gc_pool_block_len * BYTES_PER_BLOCK, gc_pool_block_len);
}
#if MICROPY_GC_SPLIT_HEAP
void gc_add(void *start, void *end) {
// Place the area struct at the start of the area.
mp_state_mem_area_t *area = (mp_state_mem_area_t *)start;
start = (void *)((uintptr_t)start + sizeof(mp_state_mem_area_t));
end = (void *)((uintptr_t)end & (~(BYTES_PER_BLOCK - 1)));
DEBUG_printf("Adding GC heap: %p..%p = " UINT_FMT " bytes\n", start, end, (byte *)end - (byte *)start);
// Init this area
gc_setup_area(area, start, end);
// Find the last registered area in the linked list
mp_state_mem_area_t *prev_area = &MP_STATE_MEM(area);
while (prev_area->next != NULL) {
prev_area = prev_area->next;
}
// Add this area to the linked list
prev_area->next = area;
}
#endif
void gc_lock(void) {
// This does not need to be atomic or have the GC mutex because:
// - each thread has its own gc_lock_depth so there are no races between threads;
// - a hard interrupt will only change gc_lock_depth during its execution, and
// upon return will restore the value of gc_lock_depth.
MP_STATE_THREAD(gc_lock_depth)++;
}
void gc_unlock(void) {
// This does not need to be atomic, See comment above in gc_lock.
MP_STATE_THREAD(gc_lock_depth)--;
}
bool gc_is_locked(void) {
return MP_STATE_THREAD(gc_lock_depth) != 0;
}
#if MICROPY_GC_SPLIT_HEAP
// Returns the area to which this pointer belongs, or NULL if it isn't
// allocated on the GC-managed heap.
STATIC inline mp_state_mem_area_t *gc_get_ptr_area(const void *ptr) {
if (((uintptr_t)(ptr) & (BYTES_PER_BLOCK - 1)) != 0) { // must be aligned on a block
return NULL;
}
for (mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
if (ptr >= (void *)area->gc_pool_start // must be above start of pool
&& ptr < (void *)area->gc_pool_end) { // must be below end of pool
return area;
}
}
return NULL;
}
#endif
// ptr should be of type void*
#define VERIFY_PTR(ptr) ( \
((uintptr_t)(ptr) & (BYTES_PER_BLOCK - 1)) == 0 /* must be aligned on a block */ \
&& ptr >= (void *)MP_STATE_MEM(area).gc_pool_start /* must be above start of pool */ \
&& ptr < (void *)MP_STATE_MEM(area).gc_pool_end /* must be below end of pool */ \
)
#ifndef TRACE_MARK
#if DEBUG_PRINT
#define TRACE_MARK(block, ptr) DEBUG_printf("gc_mark(%p)\n", ptr)
#else
#define TRACE_MARK(block, ptr)
#endif
#endif
// Take the given block as the topmost block on the stack. Check all it's
// children: mark the unmarked child blocks and put those newly marked
// blocks on the stack. When all children have been checked, pop off the
// topmost block on the stack and repeat with that one.
#if MICROPY_GC_SPLIT_HEAP
STATIC void gc_mark_subtree(mp_state_mem_area_t *area, size_t block)
#else
STATIC void gc_mark_subtree(size_t block)
#endif
{
// Start with the block passed in the argument.
size_t sp = 0;
for (;;) {
MICROPY_GC_HOOK_LOOP
#if !MICROPY_GC_SPLIT_HEAP
mp_state_mem_area_t * area = &MP_STATE_MEM(area);
#endif
// work out number of consecutive blocks in the chain starting with this one
size_t n_blocks = 0;
do {
n_blocks += 1;
} while (ATB_GET_KIND(area, block + n_blocks) == AT_TAIL);
// check this block's children
void **ptrs = (void **)PTR_FROM_BLOCK(area, block);
for (size_t i = n_blocks * BYTES_PER_BLOCK / sizeof(void *); i > 0; i--, ptrs++) {
MICROPY_GC_HOOK_LOOP
void *ptr = *ptrs;
// If this is a heap pointer that hasn't been marked, mark it and push
// it's children to the stack.
#if MICROPY_GC_SPLIT_HEAP
mp_state_mem_area_t *ptr_area = gc_get_ptr_area(ptr);
if (!ptr_area) {
// Not a heap-allocated pointer (might even be random data).
continue;
}
#else
if (!VERIFY_PTR(ptr)) {
continue;
}
mp_state_mem_area_t *ptr_area = area;
#endif
size_t ptr_block = BLOCK_FROM_PTR(ptr_area, ptr);
if (ATB_GET_KIND(ptr_area, ptr_block) != AT_HEAD) {
// This block is already marked.
continue;
}
// An unmarked head. Mark it, and push it on gc stack.
TRACE_MARK(ptr_block, ptr);
ATB_HEAD_TO_MARK(ptr_area, ptr_block);
if (sp < MICROPY_ALLOC_GC_STACK_SIZE) {
MP_STATE_MEM(gc_block_stack)[sp] = ptr_block;
#if MICROPY_GC_SPLIT_HEAP
MP_STATE_MEM(gc_area_stack)[sp] = ptr_area;
#endif
sp += 1;
} else {
MP_STATE_MEM(gc_stack_overflow) = 1;
}
}
// Are there any blocks on the stack?
if (sp == 0) {
break; // No, stack is empty, we're done.
}
// pop the next block off the stack
sp -= 1;
block = MP_STATE_MEM(gc_block_stack)[sp];
#if MICROPY_GC_SPLIT_HEAP
area = MP_STATE_MEM(gc_area_stack)[sp];
#endif
}
}
STATIC void gc_deal_with_stack_overflow(void) {
while (MP_STATE_MEM(gc_stack_overflow)) {
MP_STATE_MEM(gc_stack_overflow) = 0;
// scan entire memory looking for blocks which have been marked but not their children
for (mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
for (size_t block = 0; block < area->gc_alloc_table_byte_len * BLOCKS_PER_ATB; block++) {
MICROPY_GC_HOOK_LOOP
// trace (again) if mark bit set
if (ATB_GET_KIND(area, block) == AT_MARK) {
#if MICROPY_GC_SPLIT_HEAP
gc_mark_subtree(area, block);
#else
gc_mark_subtree(block);
#endif
}
}
}
}
}
STATIC void gc_sweep(void) {
#if MICROPY_PY_GC_COLLECT_RETVAL
MP_STATE_MEM(gc_collected) = 0;
#endif
// free unmarked heads and their tails
int free_tail = 0;
for (mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
for (size_t block = 0; block < area->gc_alloc_table_byte_len * BLOCKS_PER_ATB; block++) {
MICROPY_GC_HOOK_LOOP
switch (ATB_GET_KIND(area, block)) {
case AT_HEAD:
#if MICROPY_ENABLE_FINALISER
if (FTB_GET(area, block)) {
mp_obj_base_t *obj = (mp_obj_base_t *)PTR_FROM_BLOCK(area, block);
if (obj->type != NULL) {
// if the object has a type then see if it has a __del__ method
mp_obj_t dest[2];
mp_load_method_maybe(MP_OBJ_FROM_PTR(obj), MP_QSTR___del__, dest);
if (dest[0] != MP_OBJ_NULL) {
// load_method returned a method, execute it in a protected environment
#if MICROPY_ENABLE_SCHEDULER
mp_sched_lock();
#endif
mp_call_function_1_protected(dest[0], dest[1]);
#if MICROPY_ENABLE_SCHEDULER
mp_sched_unlock();
#endif
}
}
// clear finaliser flag
FTB_CLEAR(area, block);
}
#endif
free_tail = 1;
DEBUG_printf("gc_sweep(%p)\n", (void *)PTR_FROM_BLOCK(area, block));
#if MICROPY_PY_GC_COLLECT_RETVAL
MP_STATE_MEM(gc_collected)++;
#endif
// fall through to free the head
MP_FALLTHROUGH
case AT_TAIL:
if (free_tail) {
ATB_ANY_TO_FREE(area, block);
#if CLEAR_ON_SWEEP
memset((void *)PTR_FROM_BLOCK(area, block), 0, BYTES_PER_BLOCK);
#endif
}
break;
case AT_MARK:
ATB_MARK_TO_HEAD(area, block);
free_tail = 0;
break;
}
}
}
}
void gc_collect_start(void) {
GC_ENTER();
MP_STATE_THREAD(gc_lock_depth)++;
#if MICROPY_GC_ALLOC_THRESHOLD
MP_STATE_MEM(gc_alloc_amount) = 0;
#endif
MP_STATE_MEM(gc_stack_overflow) = 0;
// Trace root pointers. This relies on the root pointers being organised
// correctly in the mp_state_ctx structure. We scan nlr_top, dict_locals,
// dict_globals, then the root pointer section of mp_state_vm.
void **ptrs = (void **)(void *)&mp_state_ctx;
size_t root_start = offsetof(mp_state_ctx_t, thread.dict_locals);
size_t root_end = offsetof(mp_state_ctx_t, vm.qstr_last_chunk);
gc_collect_root(ptrs + root_start / sizeof(void *), (root_end - root_start) / sizeof(void *));
#if MICROPY_ENABLE_PYSTACK
// Trace root pointers from the Python stack.
ptrs = (void **)(void *)MP_STATE_THREAD(pystack_start);
gc_collect_root(ptrs, (MP_STATE_THREAD(pystack_cur) - MP_STATE_THREAD(pystack_start)) / sizeof(void *));
#endif
}
// Address sanitizer needs to know that the access to ptrs[i] must always be
// considered OK, even if it's a load from an address that would normally be
// prohibited (due to being undefined, in a red zone, etc).
#if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8))
__attribute__((no_sanitize_address))
#endif
static void *gc_get_ptr(void **ptrs, int i) {
return ptrs[i];
}
void gc_collect_root(void **ptrs, size_t len) {
#if !MICROPY_GC_SPLIT_HEAP
mp_state_mem_area_t *area = &MP_STATE_MEM(area);
#endif
for (size_t i = 0; i < len; i++) {
MICROPY_GC_HOOK_LOOP
void *ptr = gc_get_ptr(ptrs, i);
#if MICROPY_GC_SPLIT_HEAP
mp_state_mem_area_t *area = gc_get_ptr_area(ptr);
if (!area) {
continue;
}
#else
if (!VERIFY_PTR(ptr)) {
continue;
}
#endif
size_t block = BLOCK_FROM_PTR(area, ptr);
if (ATB_GET_KIND(area, block) == AT_HEAD) {
// An unmarked head: mark it, and mark all its children
ATB_HEAD_TO_MARK(area, block);
#if MICROPY_GC_SPLIT_HEAP
gc_mark_subtree(area, block);
#else
gc_mark_subtree(block);
#endif
}
}
}
void gc_collect_end(void) {
gc_deal_with_stack_overflow();
gc_sweep();
#if MICROPY_GC_SPLIT_HEAP
MP_STATE_MEM(gc_last_free_area) = &MP_STATE_MEM(area);
#endif
for (mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
area->gc_last_free_atb_index = 0;
}
MP_STATE_THREAD(gc_lock_depth)--;
GC_EXIT();
}
void gc_sweep_all(void) {
GC_ENTER();
MP_STATE_THREAD(gc_lock_depth)++;
MP_STATE_MEM(gc_stack_overflow) = 0;
gc_collect_end();
}
void gc_info(gc_info_t *info) {
GC_ENTER();
info->total = 0;
info->used = 0;
info->free = 0;
info->max_free = 0;
info->num_1block = 0;
info->num_2block = 0;
info->max_block = 0;
for (mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
bool finish = false;
info->total += area->gc_pool_end - area->gc_pool_start;
for (size_t block = 0, len = 0, len_free = 0; !finish;) {
size_t kind = ATB_GET_KIND(area, block);
switch (kind) {
case AT_FREE:
info->free += 1;
len_free += 1;
len = 0;
break;
case AT_HEAD:
info->used += 1;
len = 1;
break;
case AT_TAIL:
info->used += 1;
len += 1;
break;
case AT_MARK:
// shouldn't happen
break;
}
block++;
finish = (block == area->gc_alloc_table_byte_len * BLOCKS_PER_ATB);
// Get next block type if possible
if (!finish) {
kind = ATB_GET_KIND(area, block);
}
if (finish || kind == AT_FREE || kind == AT_HEAD) {
if (len == 1) {
info->num_1block += 1;
} else if (len == 2) {
info->num_2block += 1;
}
if (len > info->max_block) {
info->max_block = len;
}
if (finish || kind == AT_HEAD) {
if (len_free > info->max_free) {
info->max_free = len_free;
}
len_free = 0;
}
}
}
}
info->used *= BYTES_PER_BLOCK;
info->free *= BYTES_PER_BLOCK;
GC_EXIT();
}
void *gc_alloc(size_t n_bytes, unsigned int alloc_flags) {
bool has_finaliser = alloc_flags & GC_ALLOC_FLAG_HAS_FINALISER;
size_t n_blocks = ((n_bytes + BYTES_PER_BLOCK - 1) & (~(BYTES_PER_BLOCK - 1))) / BYTES_PER_BLOCK;
DEBUG_printf("gc_alloc(" UINT_FMT " bytes -> " UINT_FMT " blocks)\n", n_bytes, n_blocks);
// check for 0 allocation
if (n_blocks == 0) {
return NULL;
}
// check if GC is locked
if (MP_STATE_THREAD(gc_lock_depth) > 0) {
return NULL;
}
GC_ENTER();
mp_state_mem_area_t *area;
size_t i;
size_t end_block;
size_t start_block;
size_t n_free;
int collected = !MP_STATE_MEM(gc_auto_collect_enabled);
#if MICROPY_GC_ALLOC_THRESHOLD
if (!collected && MP_STATE_MEM(gc_alloc_amount) >= MP_STATE_MEM(gc_alloc_threshold)) {
GC_EXIT();
gc_collect();
collected = 1;
GC_ENTER();
}
#endif
for (;;) {
#if MICROPY_GC_SPLIT_HEAP
area = MP_STATE_MEM(gc_last_free_area);
#else
area = &MP_STATE_MEM(area);
#endif
// look for a run of n_blocks available blocks
for (; area != NULL; area = NEXT_AREA(area), i = 0) {
n_free = 0;
for (i = area->gc_last_free_atb_index; i < area->gc_alloc_table_byte_len; i++) {
byte a = area->gc_alloc_table_start[i];
// *FORMAT-OFF*
if (ATB_0_IS_FREE(a)) { if (++n_free >= n_blocks) { i = i * BLOCKS_PER_ATB + 0; goto found; } } else { n_free = 0; }
if (ATB_1_IS_FREE(a)) { if (++n_free >= n_blocks) { i = i * BLOCKS_PER_ATB + 1; goto found; } } else { n_free = 0; }
if (ATB_2_IS_FREE(a)) { if (++n_free >= n_blocks) { i = i * BLOCKS_PER_ATB + 2; goto found; } } else { n_free = 0; }
if (ATB_3_IS_FREE(a)) { if (++n_free >= n_blocks) { i = i * BLOCKS_PER_ATB + 3; goto found; } } else { n_free = 0; }
// *FORMAT-ON*
}
// No free blocks found on this heap. Mark this heap as
// filled, so we won't try to find free space here again until
// space is freed.
#if MICROPY_GC_SPLIT_HEAP
if (n_blocks == 1) {
area->gc_last_free_atb_index = (i + 1) / BLOCKS_PER_ATB; // or (size_t)-1
}
#endif
}
GC_EXIT();
// nothing found!
if (collected) {
return NULL;
}
DEBUG_printf("gc_alloc(" UINT_FMT "): no free mem, triggering GC\n", n_bytes);
gc_collect();
collected = 1;
GC_ENTER();
}
// found, ending at block i inclusive
found:
// get starting and end blocks, both inclusive
end_block = i;
start_block = i - n_free + 1;
// Set last free ATB index to block after last block we found, for start of
// next scan. To reduce fragmentation, we only do this if we were looking
// for a single free block, which guarantees that there are no free blocks
// before this one. Also, whenever we free or shink a block we must check
// if this index needs adjusting (see gc_realloc and gc_free).
if (n_free == 1) {
#if MICROPY_GC_SPLIT_HEAP
MP_STATE_MEM(gc_last_free_area) = area;
#endif
area->gc_last_free_atb_index = (i + 1) / BLOCKS_PER_ATB;
}
// mark first block as used head
ATB_FREE_TO_HEAD(area, start_block);
// mark rest of blocks as used tail
// TODO for a run of many blocks can make this more efficient
for (size_t bl = start_block + 1; bl <= end_block; bl++) {
ATB_FREE_TO_TAIL(area, bl);
}
// get pointer to first block
// we must create this pointer before unlocking the GC so a collection can find it
void *ret_ptr = (void *)(area->gc_pool_start + start_block * BYTES_PER_BLOCK);
DEBUG_printf("gc_alloc(%p)\n", ret_ptr);
#if MICROPY_GC_ALLOC_THRESHOLD
MP_STATE_MEM(gc_alloc_amount) += n_blocks;
#endif
GC_EXIT();
#if MICROPY_GC_CONSERVATIVE_CLEAR
// be conservative and zero out all the newly allocated blocks
memset((byte *)ret_ptr, 0, (end_block - start_block + 1) * BYTES_PER_BLOCK);
#else
// zero out the additional bytes of the newly allocated blocks
// This is needed because the blocks may have previously held pointers
// to the heap and will not be set to something else if the caller
// doesn't actually use the entire block. As such they will continue
// to point to the heap and may prevent other blocks from being reclaimed.
memset((byte *)ret_ptr + n_bytes, 0, (end_block - start_block + 1) * BYTES_PER_BLOCK - n_bytes);
#endif
#if MICROPY_ENABLE_FINALISER
if (has_finaliser) {
// clear type pointer in case it is never set
((mp_obj_base_t *)ret_ptr)->type = NULL;
// set mp_obj flag only if it has a finaliser
GC_ENTER();
FTB_SET(area, start_block);
GC_EXIT();
}
#else
(void)has_finaliser;
#endif
#if EXTENSIVE_HEAP_PROFILING
gc_dump_alloc_table();
#endif
return ret_ptr;
}
/*
void *gc_alloc(mp_uint_t n_bytes) {
return _gc_alloc(n_bytes, false);
}
void *gc_alloc_with_finaliser(mp_uint_t n_bytes) {
return _gc_alloc(n_bytes, true);
}
*/
// force the freeing of a piece of memory
// TODO: freeing here does not call finaliser
void gc_free(void *ptr) {
if (MP_STATE_THREAD(gc_lock_depth) > 0) {
// TODO how to deal with this error?
return;
}
GC_ENTER();
DEBUG_printf("gc_free(%p)\n", ptr);
if (ptr == NULL) {
// free(NULL) is a no-op
GC_EXIT();
return;
}
// get the GC block number corresponding to this pointer
mp_state_mem_area_t *area;
#if MICROPY_GC_SPLIT_HEAP
area = gc_get_ptr_area(ptr);
assert(area);
#else
assert(VERIFY_PTR(ptr));
area = &MP_STATE_MEM(area);
#endif
size_t block = BLOCK_FROM_PTR(area, ptr);
assert(ATB_GET_KIND(area, block) == AT_HEAD);
#if MICROPY_ENABLE_FINALISER
FTB_CLEAR(area, block);
#endif
#if MICROPY_GC_SPLIT_HEAP
if (MP_STATE_MEM(gc_last_free_area) != area) {
// We freed something but it isn't the current area. Reset the
// last free area to the start for a rescan. Note that this won't
// give much of a performance hit, since areas that are completely
// filled will likely be skipped (the gc_last_free_atb_index
// points to the last block).
// The reason why this is necessary is because it is not possible
// to see which area came first (like it is possible to adjust
// gc_last_free_atb_index based on whether the freed block is
// before the last free block).
MP_STATE_MEM(gc_last_free_area) = &MP_STATE_MEM(area);
}
#endif
// set the last_free pointer to this block if it's earlier in the heap
if (block / BLOCKS_PER_ATB < area->gc_last_free_atb_index) {
area->gc_last_free_atb_index = block / BLOCKS_PER_ATB;
}
// free head and all of its tail blocks
do {
ATB_ANY_TO_FREE(area, block);
block += 1;
} while (ATB_GET_KIND(area, block) == AT_TAIL);
GC_EXIT();
#if EXTENSIVE_HEAP_PROFILING
gc_dump_alloc_table();
#endif
}
size_t gc_nbytes(const void *ptr) {
GC_ENTER();
mp_state_mem_area_t *area;
#if MICROPY_GC_SPLIT_HEAP
area = gc_get_ptr_area(ptr);
#else
if (VERIFY_PTR(ptr)) {
area = &MP_STATE_MEM(area);
} else {
area = NULL;
}
#endif
if (area) {
size_t block = BLOCK_FROM_PTR(area, ptr);
if (ATB_GET_KIND(area, block) == AT_HEAD) {
// work out number of consecutive blocks in the chain starting with this on
size_t n_blocks = 0;
do {
n_blocks += 1;
} while (ATB_GET_KIND(area, block + n_blocks) == AT_TAIL);
GC_EXIT();
return n_blocks * BYTES_PER_BLOCK;
}
}
// invalid pointer
GC_EXIT();
return 0;
}
#if 0
// old, simple realloc that didn't expand memory in place
void *gc_realloc(void *ptr, mp_uint_t n_bytes) {
mp_uint_t n_existing = gc_nbytes(ptr);
if (n_bytes <= n_existing) {
return ptr;
} else {
bool has_finaliser;
if (ptr == NULL) {
has_finaliser = false;
} else {
#if MICROPY_ENABLE_FINALISER
has_finaliser = FTB_GET(BLOCK_FROM_PTR((mp_uint_t)ptr));
#else
has_finaliser = false;
#endif
}
void *ptr2 = gc_alloc(n_bytes, has_finaliser);
if (ptr2 == NULL) {
return ptr2;
}
memcpy(ptr2, ptr, n_existing);
gc_free(ptr);
return ptr2;
}
}
#else // Alternative gc_realloc impl
void *gc_realloc(void *ptr_in, size_t n_bytes, bool allow_move) {
// check for pure allocation
if (ptr_in == NULL) {
return gc_alloc(n_bytes, false);
}
// check for pure free
if (n_bytes == 0) {
gc_free(ptr_in);
return NULL;
}
if (MP_STATE_THREAD(gc_lock_depth) > 0) {
return NULL;
}
void *ptr = ptr_in;
GC_ENTER();
// get the GC block number corresponding to this pointer
mp_state_mem_area_t *area;
#if MICROPY_GC_SPLIT_HEAP
area = gc_get_ptr_area(ptr);
assert(area);
#else
assert(VERIFY_PTR(ptr));
area = &MP_STATE_MEM(area);
#endif
size_t block = BLOCK_FROM_PTR(area, ptr);
assert(ATB_GET_KIND(area, block) == AT_HEAD);
// compute number of new blocks that are requested
size_t new_blocks = (n_bytes + BYTES_PER_BLOCK - 1) / BYTES_PER_BLOCK;
// Get the total number of consecutive blocks that are already allocated to
// this chunk of memory, and then count the number of free blocks following
// it. Stop if we reach the end of the heap, or if we find enough extra
// free blocks to satisfy the realloc. Note that we need to compute the
// total size of the existing memory chunk so we can correctly and
// efficiently shrink it (see below for shrinking code).
size_t n_free = 0;
size_t n_blocks = 1; // counting HEAD block
size_t max_block = area->gc_alloc_table_byte_len * BLOCKS_PER_ATB;
for (size_t bl = block + n_blocks; bl < max_block; bl++) {
byte block_type = ATB_GET_KIND(area, bl);
if (block_type == AT_TAIL) {
n_blocks++;
continue;
}
if (block_type == AT_FREE) {
n_free++;
if (n_blocks + n_free >= new_blocks) {
// stop as soon as we find enough blocks for n_bytes
break;
}
continue;
}
break;
}
// return original ptr if it already has the requested number of blocks
if (new_blocks == n_blocks) {
GC_EXIT();
return ptr_in;
}
// check if we can shrink the allocated area
if (new_blocks < n_blocks) {
// free unneeded tail blocks
for (size_t bl = block + new_blocks, count = n_blocks - new_blocks; count > 0; bl++, count--) {
ATB_ANY_TO_FREE(area, bl);
}
#if MICROPY_GC_SPLIT_HEAP
if (MP_STATE_MEM(gc_last_free_area) != area) {
// See comment in gc_free.
MP_STATE_MEM(gc_last_free_area) = &MP_STATE_MEM(area);
}
#endif
// set the last_free pointer to end of this block if it's earlier in the heap
if ((block + new_blocks) / BLOCKS_PER_ATB < area->gc_last_free_atb_index) {
area->gc_last_free_atb_index = (block + new_blocks) / BLOCKS_PER_ATB;
}
GC_EXIT();
#if EXTENSIVE_HEAP_PROFILING
gc_dump_alloc_table();
#endif
return ptr_in;
}
// check if we can expand in place
if (new_blocks <= n_blocks + n_free) {
// mark few more blocks as used tail
for (size_t bl = block + n_blocks; bl < block + new_blocks; bl++) {
assert(ATB_GET_KIND(area, bl) == AT_FREE);
ATB_FREE_TO_TAIL(area, bl);
}
GC_EXIT();
#if MICROPY_GC_CONSERVATIVE_CLEAR
// be conservative and zero out all the newly allocated blocks
memset((byte *)ptr_in + n_blocks * BYTES_PER_BLOCK, 0, (new_blocks - n_blocks) * BYTES_PER_BLOCK);
#else
// zero out the additional bytes of the newly allocated blocks (see comment above in gc_alloc)
memset((byte *)ptr_in + n_bytes, 0, new_blocks * BYTES_PER_BLOCK - n_bytes);
#endif
#if EXTENSIVE_HEAP_PROFILING
gc_dump_alloc_table();
#endif
return ptr_in;
}
#if MICROPY_ENABLE_FINALISER
bool ftb_state = FTB_GET(area, block);
#else
bool ftb_state = false;
#endif
GC_EXIT();
if (!allow_move) {
// not allowed to move memory block so return failure
return NULL;
}
// can't resize inplace; try to find a new contiguous chain
void *ptr_out = gc_alloc(n_bytes, ftb_state);
// check that the alloc succeeded
if (ptr_out == NULL) {
return NULL;
}
DEBUG_printf("gc_realloc(%p -> %p)\n", ptr_in, ptr_out);
memcpy(ptr_out, ptr_in, n_blocks * BYTES_PER_BLOCK);
gc_free(ptr_in);
return ptr_out;