truffle: src/share/vm/memory/referenceProcessor.cpp comparison

comparison src/share/vm/memory/referenceProcessor.cpp @ 17976:8e20ef014b08

8043239: G1: Missing post barrier in processing of j.l.ref.Reference objects Summary: Removed all write barriers during reference processing and added explicit write barriers when iterating through the discovered list. Reviewed-by: pliden, jmasa, tschatzl

author	brutisso
date	Wed, 11 Jun 2014 10:46:47 +0200
parents	78bbf4d43a14
children	52b4284cb496 0982ec23da03 01dcaba9b3f3

comparison

equal deleted inserted replaced

-:bd4d69d9cb7d
+:8e20ef014b08
 bool      mt_processing,
 uint      mt_processing_degree,
 bool      mt_discovery,
 uint      mt_discovery_degree,
 bool      atomic_discovery,
-BoolObjectClosure* is_alive_non_header,
+BoolObjectClosure* is_alive_non_header)  :
-bool      discovered_list_needs_post_barrier)  :
 _discovering_refs(false),
 _enqueuing_is_done(false),
 _is_alive_non_header(is_alive_non_header),
-_discovered_list_needs_post_barrier(discovered_list_needs_post_barrier),
 _processing_is_mt(mt_processing),
 _next_id(0)
 {
 _span = span;
 _discovery_is_atomic = atomic_discovery;
 HeapWord* pending_list_addr) {
 // Given a list of refs linked through the "discovered" field
 // (java.lang.ref.Reference.discovered), self-loop their "next" field
 // thus distinguishing them from active References, then
 // prepend them to the pending list.
+//
+// The Java threads will see the Reference objects linked together through
+// the discovered field. Instead of trying to do the write barrier updates
+// in all places in the reference processor where we manipulate the discovered
+// field we make sure to do the barrier here where we anyway iterate through
+// all linked Reference objects. Note that it is important to not dirty any
+// cards during reference processing since this will cause card table
+// verification to fail for G1.
+//
 // BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777),
 // the "next" field is used to chain the pending list, not the discovered
 // field.
 if (TraceReferenceGC && PrintGCDetails) {
 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
 INTPTR_FORMAT, (address)refs_list.head());
 }
 oop obj = NULL;
 oop next_d = refs_list.head();
-if (pending_list_uses_discovered_field()) { // New behaviour
+if (pending_list_uses_discovered_field()) { // New behavior
 // Walk down the list, self-looping the next field
 // so that the References are not considered active.
 while (obj != next_d) {
 obj = next_d;
 assert(obj->is_instanceRef(), "should be reference object");
 (void *)obj, (void *)next_d);
 }
 assert(java_lang_ref_Reference::next(obj) == NULL,
 "Reference not active; should not be discovered");
 // Self-loop next, so as to make Ref not active.
-// Post-barrier not needed when looping to self.
 java_lang_ref_Reference::set_next_raw(obj, obj);
-if (next_d == obj) {  // obj is last
+if (next_d != obj) {
-// Swap refs_list into pendling_list_addr and
+oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
+} else {
+// This is the last object.
+// Swap refs_list into pending_list_addr and
 // set obj's discovered to what we read from pending_list_addr.
 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
-// Need post-barrier on pending_list_addr above;
+// Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
-// see special post-barrier code at the end of
-// enqueue_discovered_reflists() further below.
 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
 }
 }
 } else { // Old behaviour
 }
 // Remove Reference object from discovered list. Note that G1 does not need a
 // pre-barrier here because we know the Reference has already been found/marked,
 // that's how it ended up in the discovered list in the first place.
 oop_store_raw(_prev_next, new_next);
-if (_discovered_list_needs_post_barrier && _prev_next != _refs_list.adr_head()) {
-// Needs post-barrier and this is not the list head (which is not on the heap)
-oopDesc::bs()->write_ref_field(_prev_next, new_next);
-}
 NOT_PRODUCT(_removed++);
 _refs_list.dec_length(1);
 }
 // Make the Reference object active again.
 void DiscoveredListIterator::make_active() {
-// For G1 we don't want to use set_next - it
+// The pre barrier for G1 is probably just needed for the old
-// will dirty the card for the next field of
+// reference processing behavior. Should we guard this with
-// the reference object and will fail
+// ReferenceProcessor::pending_list_uses_discovered_field() ?
-// CT verification.
 if (UseG1GC) {
 HeapWord* next_addr = java_lang_ref_Reference::next_addr(_ref);
 if (UseCompressedOops) {
 oopDesc::bs()->write_ref_field_pre((narrowOop*)next_addr, NULL);
 } else {
 oopDesc::bs()->write_ref_field_pre((oop*)next_addr, NULL);
 }
-java_lang_ref_Reference::set_next_raw(_ref, NULL);
+}
-} else {
+java_lang_ref_Reference::set_next_raw(_ref, NULL);
-java_lang_ref_Reference::set_next(_ref, NULL);
-}
 }
 void DiscoveredListIterator::clear_referent() {
 oop_store_raw(_referent_addr, NULL);
 }
 ReferencePolicy*   policy,
 BoolObjectClosure* is_alive,
 OopClosure*        keep_alive,
 VoidClosure*       complete_gc) {
 assert(policy != NULL, "Must have a non-NULL policy");
-DiscoveredListIterator iter(refs_list, keep_alive, is_alive, _discovered_list_needs_post_barrier);
+DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
 // Decide which softly reachable refs should be kept alive.
 while (iter.has_next()) {
 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
 if (referent_is_dead &&
 void
 ReferenceProcessor::pp2_work(DiscoveredList&    refs_list,
 BoolObjectClosure* is_alive,
 OopClosure*        keep_alive) {
 assert(discovery_is_atomic(), "Error");
-DiscoveredListIterator iter(refs_list, keep_alive, is_alive, _discovered_list_needs_post_barrier);
+DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
 while (iter.has_next()) {
 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
 assert(next == NULL, "Should not discover inactive Reference");
 if (iter.is_referent_alive()) {
 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList&    refs_list,
 BoolObjectClosure* is_alive,
 OopClosure*        keep_alive,
 VoidClosure*       complete_gc) {
 assert(!discovery_is_atomic(), "Error");
-DiscoveredListIterator iter(refs_list, keep_alive, is_alive, _discovered_list_needs_post_barrier);
+DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
 while (iter.has_next()) {
 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
 oop next = java_lang_ref_Reference::next(iter.obj());
 if ((iter.referent() == NULL || iter.is_referent_alive() ||
 bool               clear_referent,
 BoolObjectClosure* is_alive,
 OopClosure*        keep_alive,
 VoidClosure*       complete_gc) {
 ResourceMark rm;
-DiscoveredListIterator iter(refs_list, keep_alive, is_alive, _discovered_list_needs_post_barrier);
+DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
 while (iter.has_next()) {
 iter.update_discovered();
 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
 if (clear_referent) {
 // NULL out referent pointer
 }
 private:
 bool _clear_referent;
 };
-void ReferenceProcessor::set_discovered(oop ref, oop value) {
-java_lang_ref_Reference::set_discovered_raw(ref, value);
-if (_discovered_list_needs_post_barrier) {
-oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(ref), value);
-}
-}
 // Balances reference queues.
 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
 // queues[0, 1, ..., _num_q-1] because only the first _num_q
 // corresponding to the active workers will be processed.
 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
 }
 // Add the chain to the to list.
 if (ref_lists[to_idx].head() == NULL) {
 // to list is empty. Make a loop at the end.
-set_discovered(move_tail, move_tail);
+java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
 } else {
-set_discovered(move_tail, ref_lists[to_idx].head());
+java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
 }
 ref_lists[to_idx].set_head(move_head);
 ref_lists[to_idx].inc_length(refs_to_move);
 // Remove the chain from the from list.
 }
 }
 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) {
 assert(!discovery_is_atomic(), "Else why call this method?");
-DiscoveredListIterator iter(refs_list, NULL, NULL, _discovered_list_needs_post_barrier);
+DiscoveredListIterator iter(refs_list, NULL, NULL);
 while (iter.has_next()) {
 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
 oop next = java_lang_ref_Reference::next(iter.obj());
 assert(next->is_oop_or_null(), "bad next field");
 // If referent has been cleared or Reference is not active,
 // discovered_addr.
 oop current_head = refs_list.head();
 // The last ref must have its discovered field pointing to itself.
 oop next_discovered = (current_head != NULL) ? current_head : obj;
-// Note: In the case of G1, this specific pre-barrier is strictly
-// not necessary because the only case we are interested in
-// here is when *discovered_addr is NULL (see the CAS further below),
-// so this will expand to nothing. As a result, we have manually
-// elided this out for G1, but left in the test for some future
-// collector that might have need for a pre-barrier here, e.g.:-
-// oopDesc::bs()->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered);
-assert(!_discovered_list_needs_post_barrier || UseG1GC,
-"Need to check non-G1 collector: "
-"may need a pre-write-barrier for CAS from NULL below");
 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
 NULL);
 if (retest == NULL) {
 // This thread just won the right to enqueue the object.
 // We have separate lists for enqueueing, so no synchronization
 // is necessary.
 refs_list.set_head(obj);
 refs_list.inc_length(1);
-if (_discovered_list_needs_post_barrier) {
-oopDesc::bs()->write_ref_field((void*)discovered_addr, next_discovered);
-}
 if (TraceReferenceGC) {
 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
 (void *)obj, obj->klass()->internal_name());
 }
 }
 if (_discovery_is_mt) {
 add_to_discovered_list_mt(*list, obj, discovered_addr);
 } else {
-// If "_discovered_list_needs_post_barrier", we do write barriers when
+// We do a raw store here: the field will be visited later when processing
-// updating the discovered reference list.  Otherwise, we do a raw store
+// the discovered references.
-// here: the field will be visited later when processing the discovered
-// references.
 oop current_head = list->head();
 // The last ref must have its discovered field pointing to itself.
 oop next_discovered = (current_head != NULL) ? current_head : obj;
-// As in the case further above, since we are over-writing a NULL
-// pre-value, we can safely elide the pre-barrier here for the case of G1.
-// e.g.:- oopDesc::bs()->write_ref_field_pre((oop* or narrowOop*)discovered_addr, next_discovered);
 assert(discovered == NULL, "control point invariant");
-assert(!_discovered_list_needs_post_barrier || UseG1GC,
-"For non-G1 collector, may need a pre-write-barrier for CAS from NULL below");
 oop_store_raw(discovered_addr, next_discovered);
-if (_discovered_list_needs_post_barrier) {
-oopDesc::bs()->write_ref_field((void*)discovered_addr, next_discovered);
-}
 list->set_head(obj);
 list->inc_length(1);
 if (TraceReferenceGC) {
 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)",
 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList&    refs_list,
 BoolObjectClosure* is_alive,
 OopClosure*        keep_alive,
 VoidClosure*       complete_gc,
 YieldClosure*      yield) {
-DiscoveredListIterator iter(refs_list, keep_alive, is_alive, _discovered_list_needs_post_barrier);
+DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
 while (iter.has_next()) {
 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
 oop obj = iter.obj();
 oop next = java_lang_ref_Reference::next(obj);
 if (iter.referent() == NULL || iter.is_referent_alive() ||

Mercurial > hg > truffle

comparison src/share/vm/memory/referenceProcessor.cpp @ 17976:8e20ef014b08