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cyclone/gc.c
Justin Ethier 730434bb14 Added header comment block.
2016-02-14 22:35:04 -05:00

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/**
* Cyclone Scheme
* https://github.com/justinethier/cyclone
*
* Copyright (c) 2015-2016, Justin Ethier
* All rights reserved.
*
* Heap garbage collector used by the Cyclone runtime for major collections.
*
* Tracing GC algorithm is based on the one from "Implementing an on-the-fly
* garbage collector for Java", by Domani et al.
*
* The heap implementation (alloc / sweep, etc) is based on code from Chibi Scheme.
*
* Note there is also a minor GC (in runtime.c) that collects objects allocated
* on the stack, based on "Cheney on the MTA" (but without the copying collector).
*/
#include <ck_array.h>
#include <ck_pr.h>
#include "cyclone/types.h"
#include <time.h>
////////////////////
// Global variables
// Note: will need to use atomics and/or locking to access any
// variables shared between threads
static int gc_color_mark = 1; // Black, is swapped during GC
static int gc_color_clear = 3; // White, is swapped during GC
// unfortunately this had to be split up; const colors are located in types.h
static int gc_status_col = STATUS_SYNC1;
static int gc_stage = STAGE_RESTING;
// Does not need sync, only used by collector thread
static void **mark_stack = NULL;
static int mark_stack_len = 0;
static int mark_stack_i = 0;
// Lock to protect the heap from concurrent modifications
static pthread_mutex_t heap_lock;
// Cached heap statistics
// Note this assumes a single overall heap "chain". Code would need to
// be modified to support multiple independent heaps
static int cached_heap_free_size = 0;
static int cached_heap_total_size = 0;
// Data for each individual mutator thread
ck_array_t Cyc_mutators, old_mutators;
static pthread_mutex_t mutators_lock;
static void my_free(void *p, size_t m, bool d)
{
free(p);
return;
}
static void *my_malloc(size_t b)
{
return malloc(b);
}
static void *my_realloc(void *r, size_t a, size_t b, bool d)
{
return realloc(r, b);
}
static struct ck_malloc my_allocator = {
.malloc = my_malloc,
.free = my_free,
.realloc = my_realloc
};
/////////////
// Functions
// Perform one-time initialization before mutators can be executed
void gc_initialize()
{
if (ck_array_init(&Cyc_mutators, CK_ARRAY_MODE_SPMC, &my_allocator, 10) == 0){
fprintf(stderr, "Unable to initialize mutator array\n");
exit(1);
}
if (ck_array_init(&old_mutators, CK_ARRAY_MODE_SPMC, &my_allocator, 10) == 0){
fprintf(stderr, "Unable to initialize mutator array\n");
exit(1);
}
// Initialize collector's mark stack
mark_stack_len = 128;
mark_stack = vpbuffer_realloc(mark_stack, &(mark_stack_len));
// Here is as good a place as any to do this...
if (pthread_mutex_init(&(heap_lock), NULL) != 0) {
fprintf(stderr, "Unable to initialize heap_lock mutex\n");
exit(1);
}
if (pthread_mutex_init(&(mutators_lock), NULL) != 0) {
fprintf(stderr, "Unable to initialize mutators_lock mutex\n");
exit(1);
}
}
// Add data for a new mutator
void gc_add_mutator(gc_thread_data *thd)
{
pthread_mutex_lock(&mutators_lock);
if (ck_array_put_unique(&Cyc_mutators, (void *)thd) < 0) {
fprintf(stderr, "Unable to allocate memory for a new thread, exiting\n");
exit(1);
}
ck_array_commit(&Cyc_mutators);
pthread_mutex_unlock(&mutators_lock);
}
// Remove selected mutator from the mutator list.
// This is done for terminated threads. Note data is queued to be
// freed, to prevent accidentally freeing it while the collector
// thread is potentially accessing it.
void gc_remove_mutator(gc_thread_data *thd)
{
pthread_mutex_lock(&mutators_lock);
if (!ck_array_remove(&Cyc_mutators, (void *)thd)) {
fprintf(stderr, "Unable to remove thread data, exiting\n");
exit(1);
}
ck_array_commit(&Cyc_mutators);
// Place on list of old mutators to cleanup
if (ck_array_put_unique(&old_mutators, (void *)thd) < 0) {
fprintf(stderr, "Unable to add thread data to GC list, existing\n");
exit(1);
}
ck_array_commit(&old_mutators);
pthread_mutex_unlock(&mutators_lock);
}
void gc_free_old_thread_data()
{
ck_array_iterator_t iterator;
gc_thread_data *m;
int freed = 0;
pthread_mutex_lock(&mutators_lock);
CK_ARRAY_FOREACH(&old_mutators, &iterator, &m){
//printf("JAE DEBUG - freeing old thread data...");
gc_thread_data_free(m);
if (!ck_array_remove(&old_mutators, (void *)m)) {
fprintf(stderr, "Error removing old mutator data\n");
exit(1);
}
freed = 1;
//printf(" done\n");
}
if (freed) {
ck_array_commit(&old_mutators);
//printf("commited old mutator data deletions\n");
}
pthread_mutex_unlock(&mutators_lock);
}
gc_heap *gc_heap_create(size_t size, size_t max_size, size_t chunk_size)
{
gc_free_list *free, *next;
gc_heap *h;
// TODO: mmap?
h = malloc(gc_heap_pad_size(size));
if (!h) return NULL;
h->size = size;
//h->free_size = size;
cached_heap_total_size += size;
cached_heap_free_size += size;
h->chunk_size = chunk_size;
h->max_size = max_size;
h->data = (char *) gc_heap_align(sizeof(h->data) + (unsigned int)&(h->data));
h->next = NULL;
free = h->free_list = (gc_free_list *)h->data;
next = (gc_free_list *)(((char *) free) + gc_heap_align(gc_free_chunk_size));
free->size = 0; // First one is just a dummy record
free->next = next;
next->size = size - gc_heap_align(gc_free_chunk_size);
next->next = NULL;
#if GC_DEBUG_PRINTFS
fprintf(stderr, "DEBUG h->data addr: %p\n", &(h->data));
fprintf(stderr, "DEBUG h->data addr: %p\n", h->data);
fprintf(stderr, ("heap: %p-%p data: %p-%p size: %d\n"),
h, ((char*)h)+gc_heap_pad_size(size), h->data, h->data + size, size);
fprintf(stderr, ("first: %p end: %p\n"),
(object)gc_heap_first_block(h), (object)gc_heap_end(h));
fprintf(stderr, ("free1: %p-%p free2: %p-%p\n"),
free, ((char*)free)+free->size, next, ((char*)next)+next->size);
#endif
return h;
}
// Copy given object into given heap object
char *gc_copy_obj(object dest, char *obj, gc_thread_data *thd)
{
// NOTE: no additional type checking because this is called from gc_move
// which already does that
switch(type_of(obj)){
case cons_tag: {
list hp = dest;
hp->hdr.mark = thd->gc_alloc_color;
type_of(hp) = cons_tag;
car(hp) = car(obj);
cdr(hp) = cdr(obj);
return (char *)hp;
}
case macro_tag: {
macro_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = macro_tag;
hp->fn = ((macro) obj)->fn;
hp->num_args = ((macro) obj)->num_args;
return (char *)hp;
}
case closure0_tag: {
closure0_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = closure0_tag;
hp->fn = ((closure0) obj)->fn;
hp->num_args = ((closure0) obj)->num_args;
return (char *)hp;
}
case closure1_tag: {
closure1_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = closure1_tag;
hp->fn = ((closure1) obj)->fn;
hp->num_args = ((closure1) obj)->num_args;
hp->elt1 = ((closure1) obj)->elt1;
return (char *)hp;
}
case closure2_tag: {
closure2_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = closure2_tag;
hp->fn = ((closure2) obj)->fn;
hp->num_args = ((closure2) obj)->num_args;
hp->elt1 = ((closure2) obj)->elt1;
hp->elt2 = ((closure2) obj)->elt2;
return (char *)hp;
}
case closure3_tag: {
closure3_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = closure3_tag;
hp->fn = ((closure3) obj)->fn;
hp->num_args = ((closure3) obj)->num_args;
hp->elt1 = ((closure3) obj)->elt1;
hp->elt2 = ((closure3) obj)->elt2;
hp->elt3 = ((closure3) obj)->elt3;
return (char *)hp;
}
case closure4_tag: {
closure4_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = closure4_tag;
hp->fn = ((closure4) obj)->fn;
hp->num_args = ((closure4) obj)->num_args;
hp->elt1 = ((closure4) obj)->elt1;
hp->elt2 = ((closure4) obj)->elt2;
hp->elt3 = ((closure4) obj)->elt3;
hp->elt4 = ((closure4) obj)->elt4;
return (char *)hp;
}
case closureN_tag: {
int i;
closureN_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = closureN_tag;
hp->fn = ((closureN) obj)->fn;
hp->num_args = ((closureN) obj)->num_args;
hp->num_elt = ((closureN) obj)-> num_elt;
hp->elts = (object *)(((char *)hp) + sizeof(closureN_type));
for (i = 0; i < hp->num_elt; i++) {
hp->elts[i] = ((closureN) obj)->elts[i];
}
return (char *)hp;
}
case vector_tag: {
int i;
vector_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = vector_tag;
hp->num_elt = ((vector) obj)-> num_elt;
hp->elts = (object *)(((char *)hp) + sizeof(vector_type));
for (i = 0; i < hp->num_elt; i++) {
hp->elts[i] = ((vector) obj)->elts[i];
}
return (char *)hp;
}
case string_tag: {
char *s;
string_type *hp = dest;
s = ((char *)hp) + sizeof(string_type);
memcpy(s, string_str(obj), string_len(obj) + 1);
mark(hp) = thd->gc_alloc_color;
type_of(hp) = string_tag;
string_len(hp) = string_len(obj);
string_str(hp) = s;
return (char *)hp;
}
case integer_tag: {
integer_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = integer_tag;
hp->value = ((integer_type *) obj)->value;
return (char *)hp;
}
case double_tag: {
double_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = double_tag;
hp->value = ((double_type *) obj)->value;
return (char *)hp;
}
case port_tag: {
port_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = port_tag;
hp->fp = ((port_type *) obj)->fp;
hp->mode = ((port_type *) obj)->mode;
return (char *)hp;
}
case cvar_tag: {
cvar_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = cvar_tag;
hp->pvar = ((cvar_type *) obj)->pvar;
return (char *)hp;
}
case mutex_tag: {
mutex_type *hp = dest;
mark(hp) = thd->gc_alloc_color;
type_of(hp) = mutex_tag;
// NOTE: don't copy mutex itself, caller will do that (this is a special case)
return (char *)hp;
}
case forward_tag:
return (char *)forward(obj);
case eof_tag:
case primitive_tag:
case boolean_tag:
case symbol_tag:
break;
default:
fprintf(stderr, "gc_copy_obj: bad tag obj=%p obj.tag=%ld\n",(object) obj, type_of(obj));
exit(1);
}
return (char *)obj;
}
int gc_grow_heap(gc_heap *h, size_t size, size_t chunk_size)
{
size_t cur_size, new_size;
gc_heap *h_last, *h_new;
pthread_mutex_lock(&heap_lock);
h_last = gc_heap_last(h);
cur_size = h_last->size;
// JAE - For now, just add a new page
new_size = cur_size; //gc_heap_align(((cur_size > size) ? cur_size : size) * 2);
h_new = gc_heap_create(new_size, h_last->max_size, chunk_size);
h_last->next = h_new;
pthread_mutex_unlock(&heap_lock);
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - grew heap\n");
#endif
return (h_new != NULL);
}
void *gc_try_alloc(gc_heap *h, size_t size, char *obj, gc_thread_data *thd)
{
gc_free_list *f1, *f2, *f3;
pthread_mutex_lock(&heap_lock);
for (; h; h = h->next) { // All heaps
// TODO: chunk size (ignoring for now)
for (f1 = h->free_list, f2 = f1->next; f2; f1 = f2, f2 = f2->next) { // all free in this heap
if (f2->size >= size) { // Big enough for request
// TODO: take whole chunk or divide up f2 (using f3)?
if (f2->size >= (size + gc_heap_align(1) /* min obj size */)) {
f3 = (gc_free_list *) (((char *)f2) + size);
f3->size = f2->size - size;
f3->next = f2->next;
f1->next = f3;
} else { /* Take the whole chunk */
f1->next = f2->next;
}
// Copy object into heap now to avoid any uninitialized memory issues
gc_copy_obj(f2, obj, thd);
//h->free_size -= gc_allocated_bytes(obj, NULL, NULL);
cached_heap_free_size -= gc_allocated_bytes(obj, NULL, NULL);
pthread_mutex_unlock(&heap_lock);
return f2;
}
}
}
pthread_mutex_unlock(&heap_lock);
return NULL;
}
void *gc_alloc(gc_heap *h, size_t size, char *obj, gc_thread_data *thd, int *heap_grown)
{
void *result = NULL;
size_t max_freed = 0, sum_freed = 0, total_size;
// TODO: check return value, if null (could not alloc) then
// run a collection and check how much free space there is. if less
// the allowed ratio, try growing heap.
// then try realloc. if cannot alloc now, then throw out of memory error
size = gc_heap_align(size);
result = gc_try_alloc(h, size, obj, thd);
if (!result) {
// A vanilla mark&sweep collector would collect now, but unfortunately
// we can't do that because we have to go through multiple stages, some
// of which are asynchronous. So... no choice but to grow the heap.
gc_grow_heap(h, size, 0);
*heap_grown = 1;
result = gc_try_alloc(h, size, obj, thd);
if (!result) {
fprintf(stderr, "out of memory error allocating %d bytes\n", size);
exit(1); // could throw error, but OOM is a major issue, so...
}
}
#if GC_DEBUG_TRACE
fprintf(stderr, "alloc %p size = %d, obj=%p, tag=%ld, mark=%d\n", result, size, obj, type_of(obj), mark(((object)result)));
// Debug check, should no longer be necessary
//if (is_value_type(result)) {
// printf("Invalid allocated address - is a value type %p\n", result);
//}
#endif
return result;
}
size_t gc_allocated_bytes(object obj, gc_free_list *q, gc_free_list *r)
{
tag_type t;
#if GC_SAFETY_CHECKS
if (is_value_type(obj)) {
fprintf(stderr,
"gc_allocated_bytes - passed value type %p q=[%p, %d] r=[%p, %d]\n",
obj, q, q->size, r, r->size);
exit(1);
}
#endif
t = type_of(obj);
if (t == cons_tag) return gc_heap_align(sizeof(cons_type));
if (t == macro_tag) return gc_heap_align(sizeof(macro_type));
if (t == closure0_tag) return gc_heap_align(sizeof(closure0_type));
if (t == closure1_tag) return gc_heap_align(sizeof(closure1_type));
if (t == closure2_tag) return gc_heap_align(sizeof(closure2_type));
if (t == closure3_tag) return gc_heap_align(sizeof(closure3_type));
if (t == closure4_tag) return gc_heap_align(sizeof(closure4_type));
if (t == closureN_tag){
return gc_heap_align(sizeof(closureN_type) + sizeof(object) * ((closureN_type *)obj)->num_elt);
}
if (t == vector_tag){
return gc_heap_align(sizeof(vector_type) + sizeof(object) * ((vector_type *)obj)->num_elt);
}
if (t == string_tag){
return gc_heap_align(sizeof(string_type) + string_len(obj) + 1);
}
if (t == integer_tag) return gc_heap_align(sizeof(integer_type));
if (t == double_tag) return gc_heap_align(sizeof(double_type));
if (t == port_tag) return gc_heap_align(sizeof(port_type));
if (t == cvar_tag) return gc_heap_align(sizeof(cvar_type));
if (t == mutex_tag) return gc_heap_align(sizeof(mutex_type));
fprintf(stderr, "gc_allocated_bytes: unexpected object %p of type %ld\n", obj, t);
exit(1);
return 0;
}
gc_heap *gc_heap_last(gc_heap *h)
{
while (h->next)
h = h->next;
return h;
}
size_t gc_heap_total_size(gc_heap *h)
{
size_t total_size = 0;
pthread_mutex_lock(&heap_lock);
while(h) {
total_size += h->size;
h = h->next;
}
pthread_mutex_unlock(&heap_lock);
return total_size;
}
//size_t gc_heap_total_free_size(gc_heap *h)
//{
// size_t total_size = 0;
// pthread_mutex_lock(&heap_lock);
// while(h) {
// total_size += h->free_size;
// h = h->next;
// }
// pthread_mutex_unlock(&heap_lock);
// return total_size;
//}
size_t gc_sweep(gc_heap *h, size_t *sum_freed_ptr)
{
size_t freed, max_freed=0, heap_freed = 0, sum_freed=0, size;
object p, end;
gc_free_list *q, *r, *s;
//
// Lock the heap to prevent issues with allocations during sweep
// It sucks to have to use a coarse-grained lock like this, but let's
// be safe and prevent threading issues right now. Once the new GC
// works we can go back and try to speed things up (if possible)
// by using more fine-grained locking. Can also profile to see
// how much time is even spent sweeping
//
pthread_mutex_lock(&heap_lock);
for (; h; h = h->next) { // All heaps
#if GC_DEBUG_TRACE
fprintf(stderr, "sweep heap %p, size = %d\n", h, h->size);
#endif
p = gc_heap_first_block(h);
q = h->free_list;
end = gc_heap_end(h);
while (p < end) {
// find preceding/succeeding free list pointers for p
for (r = q->next; r && ((char *)r < (char *)p); q=r, r=r->next);
if ((char *)r == (char *)p) { // this is a free block, skip it
p = (object) (((char *)p) + r->size);
#if GC_DEBUG_TRACE
fprintf(stderr, "skip free block %p size = %d\n", p, r->size);
#endif
continue;
}
size = gc_heap_align(gc_allocated_bytes(p, q, r));
#if GC_SAFETY_CHECKS
if (!is_object_type(p)) {
fprintf(stderr, "sweep: invalid object at %p", p);
exit(1);
}
if ((char *)q + q->size > (char *)p) {
fprintf(stderr, "bad size at %p < %p + %u", p, q, q->size);
exit(1);
}
if (r && ((char *)p) + size > (char *)r) {
fprintf(stderr, "sweep: bad size at %p + %d > %p", p, size, r);
exit(1);
}
#endif
if (mark(p) == gc_color_clear) {
#if GC_DEBUG_VERBOSE
fprintf(stderr, "sweep is freeing unmarked obj: %p with tag %ld\n", p, type_of(p));
#endif
mark(p) = gc_color_blue; // Needed?
if (type_of(p) == mutex_tag) {
#if GC_DEBUG_VERBOSE
fprintf(stderr, "pthread_mutex_destroy from sweep\n");
#endif
if (pthread_mutex_destroy(&(((mutex)p)->lock)) != 0) {
fprintf(stderr, "Error destroying mutex\n");
exit(1);
}
}
// free p
heap_freed += size;
if (((((char *)q) + q->size) == (char *)p) && (q != h->free_list)) {
/* merge q with p */
if (r && r->size && ((((char *)p)+size) == (char *)r)) {
// ... and with r
q->next = r->next;
freed = q->size + size + r->size;
p = (object) (((char *)p) + size + r->size);
} else {
freed = q->size + size;
p = (object) (((char *)p) + size);
}
q->size = freed;
} else {
s = (gc_free_list *)p;
if (r && r->size && ((((char *)p) + size) == (char *)r)) {
// merge p with r
s->size = size + r->size;
s->next = r->next;
q->next = s;
freed = size + r->size;
} else {
s->size = size;
s->next = r;
q->next = s;
freed = size;
}
p = (object) (((char *)p) + freed);
}
if (freed > max_freed)
max_freed = freed;
} else {
//#if GC_DEBUG_VERBOSE
// fprintf(stderr, "sweep: object is marked %p\n", p);
//#endif
p = (object)(((char *)p) + size);
}
}
//h->free_size += heap_freed;
cached_heap_free_size += heap_freed;
sum_freed += heap_freed;
heap_freed = 0;
}
pthread_mutex_unlock(&heap_lock);
if (sum_freed_ptr) *sum_freed_ptr = sum_freed;
return max_freed;
}
void gc_thr_grow_move_buffer(gc_thread_data *d)
{
if (!d) return;
if (d->moveBufLen == 0) { // Special case
d->moveBufLen = 128;
d->moveBuf = NULL;
} else {
d->moveBufLen *= 2;
}
d->moveBuf = realloc(d->moveBuf, d->moveBufLen * sizeof(void *));
#if GC_DEBUG_TRACE
fprintf(stderr, "grew moveBuffer, len = %d\n", d->moveBufLen);
#endif
}
void gc_thr_add_to_move_buffer(gc_thread_data *d, int *alloci, object obj)
{
if (*alloci == d->moveBufLen) {
gc_thr_grow_move_buffer(d);
}
d->moveBuf[*alloci] = obj;
(*alloci)++;
}
// Generic buffer functions
void **vpbuffer_realloc(void **buf, int *len)
{
return realloc(buf, (*len) * sizeof(void *));
}
void **vpbuffer_add(void **buf, int *len, int i, void *obj)
{
if (i == *len) {
*len *= 2;
buf = vpbuffer_realloc(buf, len);
}
buf[i] = obj;
return buf;
}
void vpbuffer_free(void **buf)
{
free(buf);
}
// END heap definitions
// Tri-color GC section
/////////////////////////////////////////////
// GC functions called by the Mutator threads
/**
* Determine if object lives on the thread's stack
*/
int gc_is_stack_obj(gc_thread_data *thd, object obj)
{
char tmp;
object low_limit = &tmp;
object high_limit = thd->stack_start;
return (check_overflow(low_limit, obj) &&
check_overflow(obj, high_limit));
}
/**
* Write barrier for updates to heap-allocated objects
* The key for this barrier is to identify stack objects that contain
* heap references, so they can be marked to avoid collection.
*/
void gc_mut_update(gc_thread_data *thd, object old_obj, object value)
{
int status = ck_pr_load_int(&gc_status_col),
stage = ck_pr_load_int(&gc_stage);
if (ck_pr_load_int(&(thd->gc_status)) != STATUS_ASYNC) {
pthread_mutex_lock(&(thd->lock));
gc_mark_gray(thd, old_obj);
if (gc_is_stack_obj(thd, value)) {
// Set object to be marked after moved to heap by next GC.
// This avoids having to recursively examine the stack now,
// which we have to do anyway during minor GC.
grayed(value) = 1;
} else {
// Value is on the heap, mark gray right now
gc_mark_gray(thd, value);
}
pthread_mutex_unlock(&(thd->lock));
} else if (stage == STAGE_TRACING) {
//fprintf(stderr, "DEBUG - GC async tracing marking heap obj %p ", old_obj);
//Cyc_display(old_obj, stderr);
//fprintf(stderr, "\n");
pthread_mutex_lock(&(thd->lock));
gc_mark_gray(thd, old_obj);
pthread_mutex_unlock(&(thd->lock));
#if GC_DEBUG_VERBOSE
if (is_object_type(old_obj) && mark(old_obj) == gc_color_clear) {
fprintf(stderr, "added to mark buffer (trace) from write barrier %p:mark %d:", old_obj, mark(old_obj));
Cyc_display(old_obj, stderr);
fprintf(stderr, "\n");
}
#endif
}
}
void gc_mut_cooperate(gc_thread_data *thd, int buf_len)
{
int i, status_c, status_m;
#if GC_DEBUG_VERBOSE
int debug_print = 0;
#endif
// Handle any pending marks from write barrier
pthread_mutex_lock(&(thd->lock));
thd->last_write += thd->pending_writes;
thd->pending_writes = 0;
pthread_mutex_unlock(&(thd->lock));
// I think below is thread safe, but this code is tricky.
// Worst case should be that some work is done twice if there is
// a race condition
//
// TODO: should use an atomic comparison here
status_c = ck_pr_load_int(&gc_status_col);
status_m = ck_pr_load_int(&(thd->gc_status));
if (status_m != status_c) {
ck_pr_cas_int(&(thd->gc_status), status_m, status_c);
if (status_m == STATUS_ASYNC) {
// Async is done, so clean up old mark data from the last collection
pthread_mutex_lock(&(thd->lock));
thd->last_write = 0;
thd->last_read = 0;
thd->pending_writes = 0;
pthread_mutex_unlock(&(thd->lock));
}
else if (status_m == STATUS_SYNC2) {
#if GC_DEBUG_VERBOSE
debug_print = 1;
#endif
// Mark thread "roots":
// Begin my marking current continuation, which may have already
// been on the heap prior to latest minor GC
pthread_mutex_lock(&(thd->lock));
gc_mark_gray(thd, thd->gc_cont);
for (i = 0; i < thd->gc_num_args; i++) {
gc_mark_gray(thd, thd->gc_args[i]);
}
// Also, mark everything the collector moved to the heap
for (i = 0; i < buf_len; i++) {
gc_mark_gray(thd, thd->moveBuf[i]);
}
pthread_mutex_unlock(&(thd->lock));
thd->gc_alloc_color = ck_pr_load_int(&gc_color_mark);
}
}
#if GC_DEBUG_VERBOSE
if (debug_print) {
fprintf(stderr, "coop mark gc_cont %p\n", thd->gc_cont);
for (i = 0; i < thd->gc_num_args; i++) {
fprintf(stderr, "coop mark gc_args[%d] %p\n", i, thd->gc_args[i]);
}
for (i = 0; i < buf_len; i++) {
fprintf(stderr, "coop mark from move buf %i %p\n", i, thd->moveBuf[i]);
}
}
#endif
// Initiate collection cycle if free space is too low.
// Threshold is intentially low because we have to go through an
// entire handshake/trace/sweep cycle, ideally without growing heap.
if (ck_pr_load_int(&gc_stage) == STAGE_RESTING &&
(cached_heap_free_size < (cached_heap_total_size * 0.50))){
#if GC_DEBUG_TRACE
fprintf(stdout, "Less than 50%% of the heap is free, initiating collector\n");
#endif
ck_pr_cas_int(&gc_stage, STAGE_RESTING, STAGE_CLEAR_OR_MARKING);
}
}
/////////////////////////////////////////////
// Collector functions
/**
* Mark the given object gray if it is on the heap.
* Note marking is done implicitly by placing it in a buffer,
* to avoid repeated re-scanning.
*
* This function must be executed once the thread lock has been acquired.
*/
void gc_mark_gray(gc_thread_data *thd, object obj)
{
// From what I can tell, no other thread would be modifying
// either object type or mark. Both should be stable once the object is placed
// into the heap, with the collector being the only thread that changes marks.
if (is_object_type(obj) && mark(obj) == gc_color_clear) { // TODO: sync??
// Place marked object in a buffer to avoid repeated scans of the heap.
// TODO:
// Note that ideally this should be a lock-free data structure to make the
// algorithm more efficient. So this code (and the corresponding collector
// trace code) should be converted at some point.
thd->mark_buffer = vpbuffer_add(thd->mark_buffer,
&(thd->mark_buffer_len),
thd->last_write,
obj);
(thd->last_write)++; // Already locked, just do it...
}
}
/**
* Add a pending write to the mark buffer.
* These are pended because they are written in a batch during minor GC.
* To prevent race conditions we wait until all of the writes are made before
* updating last write.
*
* TODO: figure out a new name for this function.
*/
void gc_mark_gray2(gc_thread_data *thd, object obj)
{
if (is_object_type(obj) && mark(obj) == gc_color_clear) {
thd->mark_buffer = vpbuffer_add(thd->mark_buffer,
&(thd->mark_buffer_len),
(thd->last_write + thd->pending_writes),
obj);
thd->pending_writes++;
}
}
void gc_collector_trace()
{
ck_array_iterator_t iterator;
gc_thread_data *m;
int clean = 0;
while (!clean) {
clean = 1;
CK_ARRAY_FOREACH(&Cyc_mutators, &iterator, &m){
// TODO: ideally, want to use a lock-free data structure to prevent
// having to use a mutex here. see corresponding code in gc_mark_gray
pthread_mutex_lock(&(m->lock));
while (m->last_read < m->last_write) {
clean = 0;
#if GC_DEBUG_VERBOSE
fprintf(stderr, "gc_mark_black mark buffer %p, last_read = %d last_write = %d\n",
(m->mark_buffer)[m->last_read],
m->last_read, m->last_write);
#endif
gc_mark_black((m->mark_buffer)[m->last_read]);
gc_empty_collector_stack();
(m->last_read)++; // Inc here to prevent off-by-one error
}
pthread_mutex_unlock(&(m->lock));
// Try checking the condition once more after giving the
// mutator a chance to respond, to prevent exiting early.
// This is experimental, not sure if it is necessary
if (clean) {
pthread_mutex_lock(&(m->lock));
if (m->last_read < m->last_write) {
fprintf(stderr, "JAE DEBUG - might have exited trace early\n");
clean = 0;
}
else if (m->pending_writes) {
clean = 0;
}
pthread_mutex_unlock(&(m->lock));
}
}
}
}
// TODO: seriously consider changing the mark() macro to color(),
// and sync up the header variable. that would make all of this code
// bit clearer...
void gc_mark_black(object obj)
{
// TODO: is sync required to get colors? probably not on the collector
// thread (at least) since colors are only changed once during the clear
// phase and before the first handshake.
int markColor = ck_pr_load_int(&gc_color_mark);
if (is_object_type(obj) && mark(obj) != markColor) {
// Gray any child objects
// Note we probably should use some form of atomics/synchronization
// for cons and vector types, as these pointers could change.
switch(type_of(obj)) {
case cons_tag: {
gc_collector_mark_gray(obj, car(obj));
gc_collector_mark_gray(obj, cdr(obj));
break;
}
case closure1_tag:
gc_collector_mark_gray(obj, ((closure1) obj)->elt1);
break;
case closure2_tag:
gc_collector_mark_gray(obj, ((closure2) obj)->elt1);
gc_collector_mark_gray(obj, ((closure2) obj)->elt2);
case closure3_tag:
gc_collector_mark_gray(obj, ((closure3) obj)->elt1);
gc_collector_mark_gray(obj, ((closure3) obj)->elt2);
gc_collector_mark_gray(obj, ((closure3) obj)->elt3);
case closure4_tag:
gc_collector_mark_gray(obj, ((closure4) obj)->elt1);
gc_collector_mark_gray(obj, ((closure4) obj)->elt2);
gc_collector_mark_gray(obj, ((closure4) obj)->elt3);
gc_collector_mark_gray(obj, ((closure4) obj)->elt4);
break;
case closureN_tag: {
int i, n = ((closureN) obj)->num_elt;
for (i = 0; i < n; i++) {
gc_collector_mark_gray(obj, ((closureN) obj)->elts[i]);
}
break;
}
case vector_tag: {
int i, n = ((vector) obj)->num_elt;
for (i = 0; i < n; i++) {
gc_collector_mark_gray(obj, ((vector) obj)->elts[i]);
}
break;
}
case cvar_tag: {
cvar_type *c = (cvar_type *)obj;
object pvar = *(c->pvar);
if (pvar) {
gc_collector_mark_gray(obj, pvar);
}
break;
}
default:
break;
}
if (mark(obj) != gc_color_red) {
// Only blacken objects on the heap
mark(obj) = markColor;
}
#if GC_DEBUG_VERBOSE
if (mark(obj) != gc_color_red) {
fprintf(stderr, "marked %p %d\n", obj, markColor);
} else {
fprintf(stderr, "not marking stack obj %p %d\n", obj, markColor);
}
#endif
}
}
void gc_collector_mark_gray(object parent, object obj)
{
// "Color" objects gray by adding them to the mark stack for further processing.
//
// Note that stack objects are always colored red during creation, so
// they should never be added to the mark stack. Which would be bad because it
// could lead to stack corruption.
if (is_object_type(obj) && mark(obj) == gc_color_clear) {
mark_stack = vpbuffer_add(mark_stack, &mark_stack_len, mark_stack_i++, obj);
#if GC_DEBUG_VERBOSE
fprintf(stderr, "mark gray parent = %p (%ld) obj = %p\n", parent, type_of(parent), obj);
#endif
}
}
void gc_empty_collector_stack()
{
// Mark stack is only used by the collector thread, so no sync needed
while (mark_stack_i > 0) { // not empty
mark_stack_i--;
//#if GC_DEBUG_VERBOSE
// fprintf(stderr, "gc_mark_black mark stack %p \n",
// mark_stack[mark_stack_i]);
//#endif
gc_mark_black(mark_stack[mark_stack_i]);
}
}
void gc_handshake(gc_status_type s)
{
gc_post_handshake(s);
gc_wait_handshake();
}
void gc_post_handshake(gc_status_type s)
{
int status = ck_pr_load_int(&gc_status_col);
while (!ck_pr_cas_int(&gc_status_col, status, s)){}
}
void gc_wait_handshake()
{
ck_array_iterator_t iterator;
gc_thread_data *m;
int statusm, statusc, thread_status, i, buf_len;
struct timespec tim;
tim.tv_sec = 0;
tim.tv_nsec = 1000000; // 1 millisecond
CK_ARRAY_FOREACH(&Cyc_mutators, &iterator, &m) {
while (1) {
// TODO: use an atomic comparison
statusc = ck_pr_load_int(&gc_status_col);
statusm = ck_pr_load_int(&(m->gc_status));
if (statusc == statusm) {
// Handshake succeeded, check next mutator
break;
}
thread_status = ck_pr_load_int((int *)&(m->thread_state));
if (thread_status == CYC_THREAD_STATE_BLOCKED ||
thread_status == CYC_THREAD_STATE_BLOCKED_COOPERATING) {
if (statusm == STATUS_ASYNC) { // Prev state
ck_pr_cas_int(&(m->gc_status), statusm, statusc);
// Async is done, so clean up old mark data from the last collection
pthread_mutex_lock(&(m->lock));
m->last_write = 0;
m->last_read = 0;
m->pending_writes = 0;
pthread_mutex_unlock(&(m->lock));
}else if (statusm == STATUS_SYNC1) {
ck_pr_cas_int(&(m->gc_status), statusm, statusc);
} else if (statusm == STATUS_SYNC2) {
//printf("DEBUG - is mutator still blocked?\n");
// Check again, if thread is still blocked we need to cooperate
if (ck_pr_cas_int((int *)&(m->thread_state),
CYC_THREAD_STATE_BLOCKED,
CYC_THREAD_STATE_BLOCKED_COOPERATING)
||
ck_pr_cas_int((int *)&(m->thread_state),
CYC_THREAD_STATE_BLOCKED_COOPERATING,
CYC_THREAD_STATE_BLOCKED_COOPERATING)
) {
//printf("DEBUG - update mutator GC status\n");
ck_pr_cas_int(&(m->gc_status), statusm, statusc);
pthread_mutex_lock(&(m->lock));
//printf("DEBUG - collector is cooperating for blocked mutator\n");
buf_len = gc_minor(m, m->stack_limit, m->stack_start, m->gc_cont, NULL, 0);
// Mark thread "roots", based on code from mutator's cooperator
gc_mark_gray(m, m->gc_cont);
//for (i = 0; i < m->gc_num_args; i++) {
// gc_mark_gray(m, m->gc_args[i]);
//}
// Also, mark everything the collector moved to the heap
for (i = 0; i < buf_len; i++) {
gc_mark_gray(m, m->moveBuf[i]);
}
m->gc_alloc_color = ck_pr_load_int(&gc_color_mark);
pthread_mutex_unlock(&(m->lock));
}
}
} else if (thread_status == CYC_THREAD_STATE_TERMINATED) {
// Thread is no longer running
break;
}
// At least for now, just give up quantum and come back to
// this quickly to test again. This probably could be more
// efficient.
nanosleep(&tim, NULL);
}
}
}
/////////////////////////////////////////////
// GC Collection cycle
void debug_dump_globals();
// Main collector function
void gc_collector()
{
int old_clear, old_mark;
size_t freed = 0, max_freed = 0, total_size, total_free;
#if GC_DEBUG_TRACE
time_t sweep_start = time(NULL);
#endif
//clear :
ck_pr_cas_int(&gc_stage, STAGE_RESTING, STAGE_CLEAR_OR_MARKING);
// exchange values of markColor and clearColor
old_clear = ck_pr_load_int(&gc_color_clear);
old_mark = ck_pr_load_int(&gc_color_mark);
while(!ck_pr_cas_int(&gc_color_clear, old_clear, old_mark)){}
while(!ck_pr_cas_int(&gc_color_mark, old_mark, old_clear)){}
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - swap clear %d / mark %d\n", gc_color_clear, gc_color_mark);
#endif
gc_handshake(STATUS_SYNC1);
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - after handshake sync 1\n");
#endif
//mark :
gc_handshake(STATUS_SYNC2);
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - after handshake sync 2\n");
#endif
ck_pr_cas_int(&gc_stage, STAGE_CLEAR_OR_MARKING, STAGE_TRACING);
gc_post_handshake(STATUS_ASYNC);
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - after post_handshake async\n");
#endif
gc_mark_globals();
gc_wait_handshake();
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - after wait_handshake async\n");
#endif
//trace :
gc_collector_trace();
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - after trace\n");
//debug_dump_globals();
#endif
ck_pr_cas_int(&gc_stage, STAGE_TRACING, STAGE_SWEEPING);
//
//sweep :
max_freed = gc_sweep(gc_get_heap(), &freed);
total_size = cached_heap_total_size; //gc_heap_total_size(gc_get_heap());
total_free = cached_heap_free_size; //gc_heap_total_free_size(gc_get_heap());
if (total_free < (total_size * 0.10)) {
#if GC_DEBUG_TRACE
fprintf(stdout, "Less than 10%% of the heap is free, growing it\n",
total_free, total_size);
#endif
gc_grow_heap(gc_get_heap(), 0, 0);
}
#if GC_DEBUG_TRACE
fprintf(stderr, "sweep done, total_size = %d, total_free = %d, freed = %d, max_freed = %d, elapsed = %ld\n",
total_size, total_free,
freed, max_freed, time(NULL) - sweep_start);
#endif
#if GC_DEBUG_TRACE
fprintf(stderr, "cleaning up any old thread data\n");
#endif
gc_free_old_thread_data();
// Idle the GC thread
ck_pr_cas_int(&gc_stage, STAGE_SWEEPING, STAGE_RESTING);
}
void *collector_main(void *arg)
{
int stage;
struct timespec tim;
tim.tv_sec = 0;
//JAE TODO: this is still not good enough, seems memory grows still grows fast with this.
//alternatively, may want to consider shrinking the heap if possible after a collection, if it is
//sparse enough (would be difficult to do without relocations, though
tim.tv_nsec = 100 * NANOSECONDS_PER_MILLISECOND;
while (1) {
stage = ck_pr_load_int(&gc_stage);
if (stage != STAGE_RESTING) {
gc_collector();
}
nanosleep(&tim, NULL);
}
return NULL;
}
static pthread_t collector_thread;
void gc_start_collector()
{
if (pthread_create(&collector_thread, NULL, collector_main, &collector_thread)) {
fprintf(stderr, "Error creating collector thread\n");
exit(1);
}
}
/////////////////////////////////////////////
// END tri-color marking section
/////////////////////////////////////////////
// Initialize runtime data structures for a thread.
// Must be called on the target thread itself during startup,
// to verify stack limits are setup correctly.
void gc_thread_data_init(gc_thread_data *thd, int mut_num, char *stack_base, long stack_size)
{
char stack_ref;
thd->stack_start = stack_base;
#if STACK_GROWS_DOWNWARD
thd->stack_limit = stack_base - stack_size;
#else
thd->stack_limit = stack_base + stack_size;
#endif
if (check_overflow(stack_base, &stack_ref)){
fprintf(stderr,
"Error: recompile with STACK_GROWS_DOWNWARD set to %d\n",
(1 - STACK_GROWS_DOWNWARD));
exit(1);
}
thd->stack_traces = calloc(MAX_STACK_TRACES, sizeof(char *));
thd->stack_trace_idx = 0;
thd->stack_prev_frame = NULL;
thd->mutations = NULL;
thd->exception_handler_stack = NULL;
// thd->thread = NULL;
thd->thread_state = CYC_THREAD_STATE_NEW;
//thd->mutator_num = mut_num;
thd->jmp_start = malloc(sizeof(jmp_buf));
thd->gc_args = malloc(sizeof(object) * NUM_GC_ANS);
thd->gc_num_args = 0;
thd->moveBufLen = 0;
gc_thr_grow_move_buffer(thd);
thd->gc_alloc_color = ck_pr_load_int(&gc_color_clear);
thd->gc_status = ck_pr_load_int(&gc_status_col);
thd->pending_writes = 0;
thd->last_write = 0;
thd->last_read = 0;
thd->mark_buffer = NULL;
thd->mark_buffer_len = 128;
thd->mark_buffer = vpbuffer_realloc(thd->mark_buffer, &(thd->mark_buffer_len));
if (pthread_mutex_init(&(thd->lock), NULL) != 0) {
fprintf(stderr, "Unable to initialize thread mutex\n");
exit(1);
}
}
void gc_thread_data_free(gc_thread_data *thd)
{
if (thd) {
if (pthread_mutex_destroy(&thd->lock) != 0) {
// TODO: can only destroy the lock if it is unlocked. need to make sure we
// can guarantee that is the case prior to making this call
// On the other hand, can we just use sleep and a loop to retry??
fprintf(stderr, "Thread mutex is locked, unable to free\n");
exit(1);
}
if (thd->jmp_start) free(thd->jmp_start);
if (thd->gc_args) free(thd->gc_args);
if (thd->moveBuf) free(thd->moveBuf);
if (thd->mark_buffer) free(thd->mark_buffer);
if (thd->stack_traces) free(thd->stack_traces);
if (thd->mutations) {
clear_mutations(thd);
}
free(thd);
}
}
/**
* Called explicitly from a mutator thread to let the collector know
* it (may) block for an unknown period of time.
*
* The current continuation is required so that we can trace over it
* in case the collector has to cooperate for the mutator.
*/
void gc_mutator_thread_blocked(gc_thread_data *thd, object cont)
{
if(!ck_pr_cas_int((int *)&(thd->thread_state),
CYC_THREAD_STATE_RUNNABLE,
CYC_THREAD_STATE_BLOCKED)){
fprintf(stderr, "Unable to change thread from runnable to blocked. status = %d\n", thd->thread_state);
exit(1);
}
thd->gc_cont = cont;
thd->gc_num_args = 0; // Will be set later, after collection
}
/**
* Called explicitly from a mutator thread to let the collector know
* that it has finished blocking. In addition, if the collector
* cooperated on behalf of the mutator while it was blocking, the mutator
* will move any remaining stack objects to the heap and longjmp.
*/
void gc_mutator_thread_runnable(gc_thread_data *thd, object result)
{
char stack_limit;
// Transition from blocked back to runnable using CAS.
// If we are unable to transition back, assume collector
// has cooperated on behalf of this mutator thread.
if (!ck_pr_cas_int((int *)&(thd->thread_state),
CYC_THREAD_STATE_BLOCKED,
CYC_THREAD_STATE_RUNNABLE)){
//printf("DEBUG - Collector cooperated, wait for it to finish. status is %d\n", thd->thread_state);
// wait for the collector to finish
pthread_mutex_lock(&(thd->lock));
pthread_mutex_unlock(&(thd->lock));
// update thread status
while(!ck_pr_cas_int((int *)&(thd->thread_state),
CYC_THREAD_STATE_BLOCKED_COOPERATING,
CYC_THREAD_STATE_RUNNABLE)){}
// Setup value to send to continuation
thd->gc_args[0] = result;
thd->gc_num_args = 1;
// Move any remaining stack objects (should only be the result?) to heap
gc_minor(thd, &stack_limit, thd->stack_start, thd->gc_cont, thd->gc_args, thd->gc_num_args);
//printf("DEBUG - Call into gc_cont after collector coop\n");
// Whoa.
longjmp(*(thd->jmp_start), 1);
} else {
// Collector didn't do anything; make a normal continuation call
(((closure)(thd->gc_cont))->fn)(thd, 1, thd->gc_cont, result);
}
}
//// Unit testing:
//int main(int argc, char **argv) {
// int a = 1, b = 2, c = 3, i;
// void **buf = NULL;
// int size = 1;
//
// buf = vpbuffer_realloc(buf, &size);
// printf("buf = %p, size = %d\n", buf, size);
// buf = vpbuffer_add(buf, &size, 0, &a);
// printf("buf = %p, size = %d\n", buf, size);
// buf = vpbuffer_add(buf, &size, 1, &b);
// printf("buf = %p, size = %d\n", buf, size);
// buf = vpbuffer_add(buf, &size, 2, &c);
// printf("buf = %p, size = %d\n", buf, size);
// buf = vpbuffer_add(buf, &size, 3, &a);
// printf("buf = %p, size = %d\n", buf, size);
// buf = vpbuffer_add(buf, &size, 4, &b);
// printf("buf = %p, size = %d\n", buf, size);
// for (i = 5; i < 20; i++) {
// buf = vpbuffer_add(buf, &size, i, &c);
// }
//
// for (i = 0; i < 20; i++){
// printf("%d\n", *((int *) buf[i]));
// }
// vpbuffer_free(buf);
// printf("buf = %p, size = %d\n", buf, size);
// return 0;
//}
//
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