Author: Armin Rigo <[email protected]>
Branch:
Changeset: r16:8cfb3a9e834d
Date: 2013-05-26 15:01 +0200
http://bitbucket.org/pypy/stmgc/changeset/8cfb3a9e834d/
Log: Fix stmgc_nursery_hiding(): use a real refcount and locking policy
now, which avoids races when stealing.
diff --git a/c3/nursery.c b/c3/nursery.c
--- a/c3/nursery.c
+++ b/c3/nursery.c
@@ -217,10 +217,6 @@
void stmgc_abort_transaction(struct tx_descriptor *d)
{
- /* cancel the change to the h_revision done in LocalizeProtected() */
- long i, size = d->protected_with_private_copy.size;
- gcptr *items = d->protected_with_private_copy.items;
-
/* Note that the thrown-away private objects are kept around. It
may possibly be a small optimization to reuse the part of the
nursery that contains them. To be on the safe "future-proof"
@@ -231,6 +227,10 @@
if (d->collection_lock != 'C')
spinlock_acquire(d->collection_lock);
+ /* cancel the change to the h_revision done in LocalizeProtected() */
+ long i, size = d->protected_with_private_copy.size;
+ gcptr *items = d->protected_with_private_copy.items;
+
for (i = 0; i < size; i++) {
gcptr R = items[i];
assert(dclassify(R) == K_PROTECTED);
@@ -805,30 +805,51 @@
{
#ifdef _GC_DEBUG
struct tx_descriptor *d = thread_descriptor;
+ wlog_t *item;
+ revision_t count;
+
+ /* 'd->debug_nursery_access' works like a refcount: when it is 0,
+ no-one should be accessing young objects of 'd'. We ensure that
+ it is the case using mprotect. */
+ while (1) {
+ count = ACCESS_ONCE(d->debug_nursery_access);
+ if (count == (revision_t)-1) {
+ spinloop();
+ continue;
+ }
+ if (bool_cas(&d->debug_nursery_access, count, (revision_t)-1))
+ break;
+ }
+
if (hide) {
- stm_dbgmem_not_used(d->nursery, GC_NURSERY, 1);
+ /* decrement the "refcount" */
+ assert(count > 0);
+ count--;
+ if (count == 0) {
+ stm_dbgmem_not_used(d->nursery, GC_NURSERY, 1);
+
+ G2L_LOOP_FORWARD(d->young_objects_outside_nursery, item) {
+ gcptr obj = item->addr;
+ size_t size = stmcb_size(obj);
+ stm_dbgmem_not_used(obj, size, 0);
+ } G2L_LOOP_END;
+ }
}
else {
- stm_dbgmem_used_again(d->nursery,
- d->nursery_current - d->nursery, 1);
+ if (count == 0) {
+ stm_dbgmem_used_again(d->nursery,
+ d->nursery_current - d->nursery, 1);
+ G2L_LOOP_FORWARD(d->young_objects_outside_nursery, item) {
+ gcptr obj = item->addr;
+ stm_dbgmem_used_again(obj, sizeof(*obj), 0);
+ size_t size = stmcb_size(obj);
+ stm_dbgmem_used_again(obj, size, 0);
+ } G2L_LOOP_END;
+ }
+ count++;
}
-
- wlog_t *item;
-
- G2L_LOOP_FORWARD(d->young_objects_outside_nursery, item) {
-
- gcptr obj = item->addr;
- if (hide) {
- size_t size = stmcb_size(obj);
- stm_dbgmem_not_used(obj, size, 0);
- }
- else {
- stm_dbgmem_used_again(obj, sizeof(gcptr *), 0);
- size_t size = stmcb_size(obj);
- stm_dbgmem_used_again(obj, size, 0);
- }
-
- } G2L_LOOP_END;
+ smp_wmb();
+ ACCESS_ONCE(d->debug_nursery_access) = count;
#endif
return 1;
}
@@ -924,9 +945,10 @@
thread_descriptor = source_d;
stm_local_revision = *source_d->local_revision_ref;
+ fprintf(stderr, "STEALING: %p->h_revision points to %p\n", P, R);
+
/* debugging support: "activate" the foreign nursery */
- int was_active = stm_dbgmem_is_active(source_d->nursery, 0);
- if (!was_active) assert(stmgc_nursery_hiding(0));
+ assert(stmgc_nursery_hiding(0));
/* copy the protected source object */
gcptr N = extract_from_foreign_nursery(R);
@@ -941,7 +963,7 @@
P, R, N);
/* debugging support: "deactivate" the foreign nursery again */
- if (!was_active) assert(stmgc_nursery_hiding(1));
+ assert(stmgc_nursery_hiding(1));
/* restore my own identity */
stm_local_revision = my_local_rev;
diff --git a/c3/nursery.h b/c3/nursery.h
--- a/c3/nursery.h
+++ b/c3/nursery.h
@@ -14,7 +14,7 @@
gcptr **shadowstack_end_ref; \
gcptr *thread_local_obj_ref; \
\
- revision_t collection_lock; \
+ revision_t collection_lock, debug_nursery_access; \
struct G2L young_objects_outside_nursery; \
struct GcPtrList old_objects_to_trace; \
long num_read_objects_known_old; \
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