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avoid races in marking shared-space objects

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Although the race condition for setting mark bits
shouldn't matter, reasoning about the race is
difficult and asking for trouble, so don't do it.
This commit is contained in:
Matthew Flatt 2015-08-28 15:32:53 -06:00
parent 460743021d
commit 2773737c9c
2 changed files with 31 additions and 6 deletions
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34
racket/src/racket/gc2/newgc.c
View File

@ -2952,7 +2952,7 @@ static void sync_master_progress(NewGC *gc, int done, Log_Master_Info *lmi) {
} else {
int i = 0;
int alive = MASTERGCINFO->alive;
/* wake everyone back up, except MASTERGC and ourself */
/* wake everyone back up, except MASTERGC and ourself */
for (i = 2; i < alive; i++) {
mzrt_sema_post(MASTERGCINFO->wait_go_sema);
}
@ -3369,11 +3369,11 @@ static void promote_marked_gen0_big_page(NewGC *gc, mpage *page) {
#endif
}
static void mark_recur_or_push_ptr(struct NewGC *gc, void *p)
static void mark_recur_or_push_ptr(struct NewGC *gc, void *p, int is_a_master_page)
{
objhead *ohead = OBJPTR_TO_OBJHEAD(p);
if (gc->mark_depth < MAX_RECUR_MARK_DEPTH) {
if ((gc->mark_depth < MAX_RECUR_MARK_DEPTH) && !is_a_master_page) {
switch (ohead->type) {
case PAGE_TAGGED:
{
@ -3406,6 +3406,20 @@ static void mark_recur_or_push_ptr(struct NewGC *gc, void *p)
push_ptr(gc, p);
}
#ifdef MZ_USE_PLACES
static void adjust_page_lock(int is_a_master_page, mpage *page, intptr_t prev, intptr_t next)
{
if (is_a_master_page) {
while (!mzrt_cas(&page->page_lock, prev, next)) { /* spin! */ }
}
}
# define TAKE_PAGE_LOCK(is_a_master_page, page) adjust_page_lock(is_a_master_page, page, 0, 1);
# define RELEASE_PAGE_LOCK(is_a_master_page, page) adjust_page_lock(is_a_master_page, page, 1, 0);
#else
# define TAKE_PAGE_LOCK(is_a_master_page, page) /* empty */
# define RELEASE_PAGE_LOCK(is_a_master_page, page) /* empty */
#endif
/* This is the first mark routine. It's a bit complicated. */
void GC_mark2(const void *const_p, struct NewGC *gc)
{
@ -3433,10 +3447,13 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
}
}
TAKE_PAGE_LOCK(is_a_master_page, page);
#ifdef NEWGC_BTC_ACCOUNT
/* toss this over to the BTC mark routine if we're doing accounting */
if(gc->doing_memory_accounting) {
BTC_memory_account_mark(gc, page, p, is_a_master_page);
RELEASE_PAGE_LOCK(is_a_master_page, page);
return;
}
#endif
@ -3449,6 +3466,7 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
previously */
if (page->size_class != 2) {
GCDEBUG((DEBUGOUTF, "Not marking %p on big %p (already marked)\n", p, page));
RELEASE_PAGE_LOCK(is_a_master_page, page);
return;
}
/* in this case, it has not. So we want to mark it, first off. */
@ -3469,6 +3487,7 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
objhead *info = MED_OBJHEAD(p, page->size);
if (info->mark) {
GCDEBUG((DEBUGOUTF,"Not marking %p (already marked)\n", p));
RELEASE_PAGE_LOCK(is_a_master_page, page);
return;
}
info->mark = 1;
@ -3476,7 +3495,7 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
p = OBJHEAD_TO_OBJPTR(info);
backtrace_new_page_if_needed(gc, page);
record_backtrace(gc, page, p);
mark_recur_or_push_ptr(gc, p);
mark_recur_or_push_ptr(gc, p, is_a_master_page);
}
}
/* SMALL_PAGE from gen0 or gen1 */
@ -3485,6 +3504,7 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
if(ohead->mark) {
GCDEBUG((DEBUGOUTF,"Not marking %p (already marked)\n", p));
RELEASE_PAGE_LOCK(is_a_master_page, page);
return;
}
@ -3503,7 +3523,7 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
page->previous_size = PREFIX_SIZE;
page->live_size += ohead->size;
record_backtrace(gc, page, p);
mark_recur_or_push_ptr(gc, p);
mark_recur_or_push_ptr(gc, p, is_a_master_page);
} else {
GCDEBUG((DEBUGOUTF, "Not marking %p (it's old; %p / %i)\n", p, page, page->previous_size));
}
@ -3608,10 +3628,12 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
/* set forwarding pointer */
GCDEBUG((DEBUGOUTF,"Marking %p (moved to %p on page %p)\n", p, newp, work));
*(void**)p = newp;
mark_recur_or_push_ptr(gc, newp);
mark_recur_or_push_ptr(gc, newp, is_a_master_page);
}
}
}
RELEASE_PAGE_LOCK(is_a_master_page, page);
}
void GC_mark(const void *const_p)

3
racket/src/racket/gc2/newgc.h
View File

@ -29,6 +29,9 @@ typedef struct mpage {
void *backtrace_page_src;
#endif
void *mmu_src_block;
#ifdef MZ_USE_PLACES
uintptr_t page_lock; /* for master GC pages during marking */
#endif
} mpage;
typedef struct Gen0 {