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8031401: Remove unused code in the reference processor

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Assume pending_list uses discovered field and remove resulting dead code.

Reviewed-by: brutisso, pliden
This commit is contained in:
Kim Barrett 2015-04-23 11:26:32 -04:00
parent 7d01ef4a6e
commit 878cf5e641
8 changed files with 78 additions and 204 deletions
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104
hotspot/src/share/vm/memory/referenceProcessor.cpp
View file

@ -37,7 +37,6 @@
ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
bool ReferenceProcessor::_pending_list_uses_discovered_field = false;
jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
void referenceProcessor_init() {
@ -63,7 +62,6 @@ void ReferenceProcessor::init_statics() {
guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
RefDiscoveryPolicy == ReferentBasedDiscovery,
"Unrecognized RefDiscoveryPolicy");
_pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field();
}
void ReferenceProcessor::enable_discovery(bool check_no_refs) {
@ -353,10 +351,6 @@ void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
// 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, p2i(refs_list.head()));
@ -364,64 +358,30 @@ void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
oop obj = NULL;
oop next_d = refs_list.head();
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");
next_d = java_lang_ref_Reference::discovered(obj);
if (TraceReferenceGC && PrintGCDetails) {
gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
p2i(obj), p2i(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.
java_lang_ref_Reference::set_next_raw(obj, obj);
if (next_d != obj) {
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. See enqueue_discovered_ref_helper() above.
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);
}
// 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");
next_d = java_lang_ref_Reference::discovered(obj);
if (TraceReferenceGC && PrintGCDetails) {
gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
p2i(obj), p2i(next_d));
}
} else { // Old behavior
// Walk down the list, copying the discovered field into
// the next field and clearing the discovered field.
while (obj != next_d) {
obj = next_d;
assert(obj->is_instanceRef(), "should be reference object");
next_d = java_lang_ref_Reference::discovered(obj);
if (TraceReferenceGC && PrintGCDetails) {
gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
p2i(obj), p2i(next_d));
}
assert(java_lang_ref_Reference::next(obj) == NULL,
"The reference should not be enqueued");
if (next_d == obj) { // obj is last
// Swap refs_list into pending_list_addr and
// set obj's next to what we read from pending_list_addr.
oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
// Need oop_check on pending_list_addr above;
// see special oop-check code at the end of
// enqueue_discovered_reflists() further below.
if (old == NULL) {
// obj should be made to point to itself, since
// pending list was empty.
java_lang_ref_Reference::set_next(obj, obj);
} else {
java_lang_ref_Reference::set_next(obj, old);
}
} else {
java_lang_ref_Reference::set_next(obj, next_d);
}
java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
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.
java_lang_ref_Reference::set_next_raw(obj, obj);
if (next_d != obj) {
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. See enqueue_discovered_ref_helper() above.
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);
}
}
}
@ -515,22 +475,6 @@ void DiscoveredListIterator::remove() {
_refs_list.dec_length(1);
}
// Make the Reference object active again.
void DiscoveredListIterator::make_active() {
// The pre barrier for G1 is probably just needed for the old
// reference processing behavior. Should we guard this with
// ReferenceProcessor::pending_list_uses_discovered_field() ?
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);
}
void DiscoveredListIterator::clear_referent() {
oop_store_raw(_referent_addr, NULL);
}
@ -567,8 +511,6 @@ ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
}
// Remove Reference object from list
iter.remove();
// Make the Reference object active again
iter.make_active();
// keep the referent around
iter.make_referent_alive();
iter.move_to_next();