6843629: Make current hotspot build part of jdk5 control build
Summary: Source changes for older compilers plus makefile changes.
Reviewed-by: xlu
/*
* Copyright 2001-2009 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*
*/
# include "incls/_precompiled.incl"
# include "incls/_referenceProcessor.cpp.incl"
ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
oop ReferenceProcessor::_sentinelRef = NULL;
const int subclasses_of_ref = REF_PHANTOM - REF_OTHER;
// List of discovered references.
class DiscoveredList {
public:
DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
oop head() const {
return UseCompressedOops ? oopDesc::decode_heap_oop_not_null(_compressed_head) :
_oop_head;
}
HeapWord* adr_head() {
return UseCompressedOops ? (HeapWord*)&_compressed_head :
(HeapWord*)&_oop_head;
}
void set_head(oop o) {
if (UseCompressedOops) {
// Must compress the head ptr.
_compressed_head = oopDesc::encode_heap_oop_not_null(o);
} else {
_oop_head = o;
}
}
bool empty() const { return head() == ReferenceProcessor::sentinel_ref(); }
size_t length() { return _len; }
void set_length(size_t len) { _len = len; }
void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
void dec_length(size_t dec) { _len -= dec; }
private:
// Set value depending on UseCompressedOops. This could be a template class
// but then we have to fix all the instantiations and declarations that use this class.
oop _oop_head;
narrowOop _compressed_head;
size_t _len;
};
void referenceProcessor_init() {
ReferenceProcessor::init_statics();
}
void ReferenceProcessor::init_statics() {
assert(_sentinelRef == NULL, "should be initialized precisely once");
EXCEPTION_MARK;
_sentinelRef = instanceKlass::cast(
SystemDictionary::reference_klass())->
allocate_permanent_instance(THREAD);
// Initialize the master soft ref clock.
java_lang_ref_SoftReference::set_clock(os::javaTimeMillis());
if (HAS_PENDING_EXCEPTION) {
Handle ex(THREAD, PENDING_EXCEPTION);
vm_exit_during_initialization(ex);
}
assert(_sentinelRef != NULL && _sentinelRef->is_oop(),
"Just constructed it!");
_always_clear_soft_ref_policy = new AlwaysClearPolicy();
_default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
NOT_COMPILER2(LRUCurrentHeapPolicy());
if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
vm_exit_during_initialization("Could not allocate reference policy object");
}
guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
RefDiscoveryPolicy == ReferentBasedDiscovery,
"Unrecongnized RefDiscoveryPolicy");
}
ReferenceProcessor*
ReferenceProcessor::create_ref_processor(MemRegion span,
bool atomic_discovery,
bool mt_discovery,
BoolObjectClosure* is_alive_non_header,
int parallel_gc_threads,
bool mt_processing,
bool dl_needs_barrier) {
int mt_degree = 1;
if (parallel_gc_threads > 1) {
mt_degree = parallel_gc_threads;
}
ReferenceProcessor* rp =
new ReferenceProcessor(span, atomic_discovery,
mt_discovery, mt_degree,
mt_processing && (parallel_gc_threads > 0),
dl_needs_barrier);
if (rp == NULL) {
vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
}
rp->set_is_alive_non_header(is_alive_non_header);
rp->setup_policy(false /* default soft ref policy */);
return rp;
}
ReferenceProcessor::ReferenceProcessor(MemRegion span,
bool atomic_discovery,
bool mt_discovery,
int mt_degree,
bool mt_processing,
bool discovered_list_needs_barrier) :
_discovering_refs(false),
_enqueuing_is_done(false),
_is_alive_non_header(NULL),
_discovered_list_needs_barrier(discovered_list_needs_barrier),
_bs(NULL),
_processing_is_mt(mt_processing),
_next_id(0)
{
_span = span;
_discovery_is_atomic = atomic_discovery;
_discovery_is_mt = mt_discovery;
_num_q = mt_degree;
_discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _num_q * subclasses_of_ref);
if (_discoveredSoftRefs == NULL) {
vm_exit_during_initialization("Could not allocated RefProc Array");
}
_discoveredWeakRefs = &_discoveredSoftRefs[_num_q];
_discoveredFinalRefs = &_discoveredWeakRefs[_num_q];
_discoveredPhantomRefs = &_discoveredFinalRefs[_num_q];
assert(sentinel_ref() != NULL, "_sentinelRef is NULL");
// Initialized all entries to _sentinelRef
for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
_discoveredSoftRefs[i].set_head(sentinel_ref());
_discoveredSoftRefs[i].set_length(0);
}
// If we do barreirs, cache a copy of the barrier set.
if (discovered_list_needs_barrier) {
_bs = Universe::heap()->barrier_set();
}
}
#ifndef PRODUCT
void ReferenceProcessor::verify_no_references_recorded() {
guarantee(!_discovering_refs, "Discovering refs?");
for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
guarantee(_discoveredSoftRefs[i].empty(),
"Found non-empty discovered list");
}
}
#endif
void ReferenceProcessor::weak_oops_do(OopClosure* f) {
for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
if (UseCompressedOops) {
f->do_oop((narrowOop*)_discoveredSoftRefs[i].adr_head());
} else {
f->do_oop((oop*)_discoveredSoftRefs[i].adr_head());
}
}
}
void ReferenceProcessor::oops_do(OopClosure* f) {
f->do_oop(adr_sentinel_ref());
}
void ReferenceProcessor::update_soft_ref_master_clock() {
// Update (advance) the soft ref master clock field. This must be done
// after processing the soft ref list.
jlong now = os::javaTimeMillis();
jlong clock = java_lang_ref_SoftReference::clock();
NOT_PRODUCT(
if (now < clock) {
warning("time warp: %d to %d", clock, now);
}
)
// In product mode, protect ourselves from system time being adjusted
// externally and going backward; see note in the implementation of
// GenCollectedHeap::time_since_last_gc() for the right way to fix
// this uniformly throughout the VM; see bug-id 4741166. XXX
if (now > clock) {
java_lang_ref_SoftReference::set_clock(now);
}
// Else leave clock stalled at its old value until time progresses
// past clock value.
}
void ReferenceProcessor::process_discovered_references(
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc,
AbstractRefProcTaskExecutor* task_executor) {
NOT_PRODUCT(verify_ok_to_handle_reflists());
assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
// Stop treating discovered references specially.
disable_discovery();
bool trace_time = PrintGCDetails && PrintReferenceGC;
// Soft references
{
TraceTime tt("SoftReference", trace_time, false, gclog_or_tty);
process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
is_alive, keep_alive, complete_gc, task_executor);
}
update_soft_ref_master_clock();
// Weak references
{
TraceTime tt("WeakReference", trace_time, false, gclog_or_tty);
process_discovered_reflist(_discoveredWeakRefs, NULL, true,
is_alive, keep_alive, complete_gc, task_executor);
}
// Final references
{
TraceTime tt("FinalReference", trace_time, false, gclog_or_tty);
process_discovered_reflist(_discoveredFinalRefs, NULL, false,
is_alive, keep_alive, complete_gc, task_executor);
}
// Phantom references
{
TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty);
process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
is_alive, keep_alive, complete_gc, task_executor);
}
// Weak global JNI references. It would make more sense (semantically) to
// traverse these simultaneously with the regular weak references above, but
// that is not how the JDK1.2 specification is. See #4126360. Native code can
// thus use JNI weak references to circumvent the phantom references and
// resurrect a "post-mortem" object.
{
TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty);
if (task_executor != NULL) {
task_executor->set_single_threaded_mode();
}
process_phaseJNI(is_alive, keep_alive, complete_gc);
}
}
#ifndef PRODUCT
// Calculate the number of jni handles.
uint ReferenceProcessor::count_jni_refs() {
class AlwaysAliveClosure: public BoolObjectClosure {
public:
virtual bool do_object_b(oop obj) { return true; }
virtual void do_object(oop obj) { assert(false, "Don't call"); }
};
class CountHandleClosure: public OopClosure {
private:
int _count;
public:
CountHandleClosure(): _count(0) {}
void do_oop(oop* unused) { _count++; }
void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
int count() { return _count; }
};
CountHandleClosure global_handle_count;
AlwaysAliveClosure always_alive;
JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
return global_handle_count.count();
}
#endif
void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc) {
#ifndef PRODUCT
if (PrintGCDetails && PrintReferenceGC) {
unsigned int count = count_jni_refs();
gclog_or_tty->print(", %u refs", count);
}
#endif
JNIHandles::weak_oops_do(is_alive, keep_alive);
// Finally remember to keep sentinel around
keep_alive->do_oop(adr_sentinel_ref());
complete_gc->do_void();
}
template <class T>
bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
AbstractRefProcTaskExecutor* task_executor) {
// Remember old value of pending references list
T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
T old_pending_list_value = *pending_list_addr;
// Enqueue references that are not made active again, and
// clear the decks for the next collection (cycle).
ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
// Do the oop-check on pending_list_addr missed in
// enqueue_discovered_reflist. We should probably
// do a raw oop_check so that future such idempotent
// oop_stores relying on the oop-check side-effect
// may be elided automatically and safely without
// affecting correctness.
oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
// Stop treating discovered references specially.
ref->disable_discovery();
// Return true if new pending references were added
return old_pending_list_value != *pending_list_addr;
}
bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
NOT_PRODUCT(verify_ok_to_handle_reflists());
if (UseCompressedOops) {
return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
} else {
return enqueue_discovered_ref_helper<oop>(this, task_executor);
}
}
void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
HeapWord* pending_list_addr) {
// Given a list of refs linked through the "discovered" field
// (java.lang.ref.Reference.discovered) chain them through the
// "next" field (java.lang.ref.Reference.next) and prepend
// to the pending list.
if (TraceReferenceGC && PrintGCDetails) {
gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
INTPTR_FORMAT, (address)refs_list.head());
}
oop obj = refs_list.head();
// Walk down the list, copying the discovered field into
// the next field and clearing it (except for the last
// non-sentinel object which is treated specially to avoid
// confusion with an active reference).
while (obj != sentinel_ref()) {
assert(obj->is_instanceRef(), "should be reference object");
oop next = java_lang_ref_Reference::discovered(obj);
if (TraceReferenceGC && PrintGCDetails) {
gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT,
obj, next);
}
assert(java_lang_ref_Reference::next(obj) == NULL,
"The reference should not be enqueued");
if (next == sentinel_ref()) { // obj is last
// Swap refs_list into pendling_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);
}
java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
obj = next;
}
}
// Parallel enqueue task
class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
public:
RefProcEnqueueTask(ReferenceProcessor& ref_processor,
DiscoveredList discovered_refs[],
HeapWord* pending_list_addr,
oop sentinel_ref,
int n_queues)
: EnqueueTask(ref_processor, discovered_refs,
pending_list_addr, sentinel_ref, n_queues)
{ }
virtual void work(unsigned int work_id) {
assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds");
// Simplest first cut: static partitioning.
int index = work_id;
for (int j = 0; j < subclasses_of_ref; j++, index += _n_queues) {
_ref_processor.enqueue_discovered_reflist(
_refs_lists[index], _pending_list_addr);
_refs_lists[index].set_head(_sentinel_ref);
_refs_lists[index].set_length(0);
}
}
};
// Enqueue references that are not made active again
void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
AbstractRefProcTaskExecutor* task_executor) {
if (_processing_is_mt && task_executor != NULL) {
// Parallel code
RefProcEnqueueTask tsk(*this, _discoveredSoftRefs,
pending_list_addr, sentinel_ref(), _num_q);
task_executor->execute(tsk);
} else {
// Serial code: call the parent class's implementation
for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr);
_discoveredSoftRefs[i].set_head(sentinel_ref());
_discoveredSoftRefs[i].set_length(0);
}
}
}
// Iterator for the list of discovered references.
class DiscoveredListIterator {
public:
inline DiscoveredListIterator(DiscoveredList& refs_list,
OopClosure* keep_alive,
BoolObjectClosure* is_alive);
// End Of List.
inline bool has_next() const { return _next != ReferenceProcessor::sentinel_ref(); }
// Get oop to the Reference object.
inline oop obj() const { return _ref; }
// Get oop to the referent object.
inline oop referent() const { return _referent; }
// Returns true if referent is alive.
inline bool is_referent_alive() const;
// Loads data for the current reference.
// The "allow_null_referent" argument tells us to allow for the possibility
// of a NULL referent in the discovered Reference object. This typically
// happens in the case of concurrent collectors that may have done the
// discovery concurrently, or interleaved, with mutator execution.
inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
// Move to the next discovered reference.
inline void next();
// Remove the current reference from the list
inline void remove();
// Make the Reference object active again.
inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); }
// Make the referent alive.
inline void make_referent_alive() {
if (UseCompressedOops) {
_keep_alive->do_oop((narrowOop*)_referent_addr);
} else {
_keep_alive->do_oop((oop*)_referent_addr);
}
}
// Update the discovered field.
inline void update_discovered() {
// First _prev_next ref actually points into DiscoveredList (gross).
if (UseCompressedOops) {
_keep_alive->do_oop((narrowOop*)_prev_next);
} else {
_keep_alive->do_oop((oop*)_prev_next);
}
}
// NULL out referent pointer.
inline void clear_referent() { oop_store_raw(_referent_addr, NULL); }
// Statistics
NOT_PRODUCT(
inline size_t processed() const { return _processed; }
inline size_t removed() const { return _removed; }
)
inline void move_to_next();
private:
DiscoveredList& _refs_list;
HeapWord* _prev_next;
oop _ref;
HeapWord* _discovered_addr;
oop _next;
HeapWord* _referent_addr;
oop _referent;
OopClosure* _keep_alive;
BoolObjectClosure* _is_alive;
DEBUG_ONLY(
oop _first_seen; // cyclic linked list check
)
NOT_PRODUCT(
size_t _processed;
size_t _removed;
)
};
inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list,
OopClosure* keep_alive,
BoolObjectClosure* is_alive)
: _refs_list(refs_list),
_prev_next(refs_list.adr_head()),
_ref(refs_list.head()),
#ifdef ASSERT
_first_seen(refs_list.head()),
#endif
#ifndef PRODUCT
_processed(0),
_removed(0),
#endif
_next(refs_list.head()),
_keep_alive(keep_alive),
_is_alive(is_alive)
{ }
inline bool DiscoveredListIterator::is_referent_alive() const {
return _is_alive->do_object_b(_referent);
}
inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
_discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
oop discovered = java_lang_ref_Reference::discovered(_ref);
assert(_discovered_addr && discovered->is_oop_or_null(),
"discovered field is bad");
_next = discovered;
_referent_addr = java_lang_ref_Reference::referent_addr(_ref);
_referent = java_lang_ref_Reference::referent(_ref);
assert(Universe::heap()->is_in_reserved_or_null(_referent),
"Wrong oop found in java.lang.Reference object");
assert(allow_null_referent ?
_referent->is_oop_or_null()
: _referent->is_oop(),
"bad referent");
}
inline void DiscoveredListIterator::next() {
_prev_next = _discovered_addr;
move_to_next();
}
inline void DiscoveredListIterator::remove() {
assert(_ref->is_oop(), "Dropping a bad reference");
oop_store_raw(_discovered_addr, NULL);
// First _prev_next ref actually points into DiscoveredList (gross).
if (UseCompressedOops) {
// Remove Reference object from list.
oopDesc::encode_store_heap_oop_not_null((narrowOop*)_prev_next, _next);
} else {
// Remove Reference object from list.
oopDesc::store_heap_oop((oop*)_prev_next, _next);
}
NOT_PRODUCT(_removed++);
_refs_list.dec_length(1);
}
inline void DiscoveredListIterator::move_to_next() {
_ref = _next;
assert(_ref != _first_seen, "cyclic ref_list found");
NOT_PRODUCT(_processed++);
}
// NOTE: process_phase*() are largely similar, and at a high level
// merely iterate over the extant list applying a predicate to
// each of its elements and possibly removing that element from the
// list and applying some further closures to that element.
// We should consider the possibility of replacing these
// process_phase*() methods by abstracting them into
// a single general iterator invocation that receives appropriate
// closures that accomplish this work.
// (SoftReferences only) Traverse the list and remove any SoftReferences whose
// referents are not alive, but that should be kept alive for policy reasons.
// Keep alive the transitive closure of all such referents.
void
ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
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);
// 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 && !policy->should_clear_reference(iter.obj())) {
if (TraceReferenceGC) {
gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
iter.obj(), iter.obj()->blueprint()->internal_name());
}
// 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();
} else {
iter.next();
}
}
// Close the reachable set
complete_gc->do_void();
NOT_PRODUCT(
if (PrintGCDetails && TraceReferenceGC) {
gclog_or_tty->print(" Dropped %d dead Refs out of %d "
"discovered Refs by policy ", iter.removed(), iter.processed());
}
)
}
// Traverse the list and remove any Refs that are not active, or
// whose referents are either alive or NULL.
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);
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()) {
if (TraceReferenceGC) {
gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
iter.obj(), iter.obj()->blueprint()->internal_name());
}
// The referent is reachable after all.
// Remove Reference object from list.
iter.remove();
// Update the referent pointer as necessary: Note that this
// should not entail any recursive marking because the
// referent must already have been traversed.
iter.make_referent_alive();
iter.move_to_next();
} else {
iter.next();
}
}
NOT_PRODUCT(
if (PrintGCDetails && TraceReferenceGC) {
gclog_or_tty->print(" Dropped %d active Refs out of %d "
"Refs in discovered list ", iter.removed(), iter.processed());
}
)
}
void
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);
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() ||
next != NULL)) {
assert(next->is_oop_or_null(), "bad next field");
// Remove Reference object from list
iter.remove();
// Trace the cohorts
iter.make_referent_alive();
if (UseCompressedOops) {
keep_alive->do_oop((narrowOop*)next_addr);
} else {
keep_alive->do_oop((oop*)next_addr);
}
iter.move_to_next();
} else {
iter.next();
}
}
// Now close the newly reachable set
complete_gc->do_void();
NOT_PRODUCT(
if (PrintGCDetails && TraceReferenceGC) {
gclog_or_tty->print(" Dropped %d active Refs out of %d "
"Refs in discovered list ", iter.removed(), iter.processed());
}
)
}
// Traverse the list and process the referents, by either
// clearing them or keeping them (and their reachable
// closure) alive.
void
ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
bool clear_referent,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc) {
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
iter.clear_referent();
} else {
// keep the referent around
iter.make_referent_alive();
}
if (TraceReferenceGC) {
gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
clear_referent ? "cleared " : "",
iter.obj(), iter.obj()->blueprint()->internal_name());
}
assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
iter.next();
}
// Remember to keep sentinel pointer around
iter.update_discovered();
// Close the reachable set
complete_gc->do_void();
}
void
ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) {
oop obj = refs_list.head();
while (obj != sentinel_ref()) {
oop discovered = java_lang_ref_Reference::discovered(obj);
java_lang_ref_Reference::set_discovered_raw(obj, NULL);
obj = discovered;
}
refs_list.set_head(sentinel_ref());
refs_list.set_length(0);
}
void ReferenceProcessor::abandon_partial_discovery() {
// loop over the lists
for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) {
gclog_or_tty->print_cr(
"\nAbandoning %s discovered list",
list_name(i));
}
abandon_partial_discovered_list(_discoveredSoftRefs[i]);
}
}
class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
public:
RefProcPhase1Task(ReferenceProcessor& ref_processor,
DiscoveredList refs_lists[],
ReferencePolicy* policy,
bool marks_oops_alive)
: ProcessTask(ref_processor, refs_lists, marks_oops_alive),
_policy(policy)
{ }
virtual void work(unsigned int i, BoolObjectClosure& is_alive,
OopClosure& keep_alive,
VoidClosure& complete_gc)
{
_ref_processor.process_phase1(_refs_lists[i], _policy,
&is_alive, &keep_alive, &complete_gc);
}
private:
ReferencePolicy* _policy;
};
class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
public:
RefProcPhase2Task(ReferenceProcessor& ref_processor,
DiscoveredList refs_lists[],
bool marks_oops_alive)
: ProcessTask(ref_processor, refs_lists, marks_oops_alive)
{ }
virtual void work(unsigned int i, BoolObjectClosure& is_alive,
OopClosure& keep_alive,
VoidClosure& complete_gc)
{
_ref_processor.process_phase2(_refs_lists[i],
&is_alive, &keep_alive, &complete_gc);
}
};
class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
public:
RefProcPhase3Task(ReferenceProcessor& ref_processor,
DiscoveredList refs_lists[],
bool clear_referent,
bool marks_oops_alive)
: ProcessTask(ref_processor, refs_lists, marks_oops_alive),
_clear_referent(clear_referent)
{ }
virtual void work(unsigned int i, BoolObjectClosure& is_alive,
OopClosure& keep_alive,
VoidClosure& complete_gc)
{
_ref_processor.process_phase3(_refs_lists[i], _clear_referent,
&is_alive, &keep_alive, &complete_gc);
}
private:
bool _clear_referent;
};
// Balances reference queues.
void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
{
// calculate total length
size_t total_refs = 0;
for (int i = 0; i < _num_q; ++i) {
total_refs += ref_lists[i].length();
}
size_t avg_refs = total_refs / _num_q + 1;
int to_idx = 0;
for (int from_idx = 0; from_idx < _num_q; from_idx++) {
while (ref_lists[from_idx].length() > avg_refs) {
assert(to_idx < _num_q, "Sanity Check!");
if (ref_lists[to_idx].length() < avg_refs) {
// move superfluous refs
size_t refs_to_move =
MIN2(ref_lists[from_idx].length() - avg_refs,
avg_refs - ref_lists[to_idx].length());
oop move_head = ref_lists[from_idx].head();
oop move_tail = move_head;
oop new_head = move_head;
// find an element to split the list on
for (size_t j = 0; j < refs_to_move; ++j) {
move_tail = new_head;
new_head = java_lang_ref_Reference::discovered(new_head);
}
java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head());
ref_lists[to_idx].set_head(move_head);
ref_lists[to_idx].inc_length(refs_to_move);
ref_lists[from_idx].set_head(new_head);
ref_lists[from_idx].dec_length(refs_to_move);
} else {
++to_idx;
}
}
}
}
void
ReferenceProcessor::process_discovered_reflist(
DiscoveredList refs_lists[],
ReferencePolicy* policy,
bool clear_referent,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc,
AbstractRefProcTaskExecutor* task_executor)
{
bool mt = task_executor != NULL && _processing_is_mt;
if (mt && ParallelRefProcBalancingEnabled) {
balance_queues(refs_lists);
}
if (PrintReferenceGC && PrintGCDetails) {
size_t total = 0;
for (int i = 0; i < _num_q; ++i) {
total += refs_lists[i].length();
}
gclog_or_tty->print(", %u refs", total);
}
// Phase 1 (soft refs only):
// . Traverse the list and remove any SoftReferences whose
// referents are not alive, but that should be kept alive for
// policy reasons. Keep alive the transitive closure of all
// such referents.
if (policy != NULL) {
if (mt) {
RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
task_executor->execute(phase1);
} else {
for (int i = 0; i < _num_q; i++) {
process_phase1(refs_lists[i], policy,
is_alive, keep_alive, complete_gc);
}
}
} else { // policy == NULL
assert(refs_lists != _discoveredSoftRefs,
"Policy must be specified for soft references.");
}
// Phase 2:
// . Traverse the list and remove any refs whose referents are alive.
if (mt) {
RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
task_executor->execute(phase2);
} else {
for (int i = 0; i < _num_q; i++) {
process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
}
}
// Phase 3:
// . Traverse the list and process referents as appropriate.
if (mt) {
RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
task_executor->execute(phase3);
} else {
for (int i = 0; i < _num_q; i++) {
process_phase3(refs_lists[i], clear_referent,
is_alive, keep_alive, complete_gc);
}
}
}
void ReferenceProcessor::clean_up_discovered_references() {
// loop over the lists
for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) {
gclog_or_tty->print_cr(
"\nScrubbing %s discovered list of Null referents",
list_name(i));
}
clean_up_discovered_reflist(_discoveredSoftRefs[i]);
}
}
void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) {
assert(!discovery_is_atomic(), "Else why call this method?");
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,
// drop it.
if (iter.referent() == NULL || next != NULL) {
debug_only(
if (PrintGCDetails && TraceReferenceGC) {
gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: "
INTPTR_FORMAT " with next field: " INTPTR_FORMAT
" and referent: " INTPTR_FORMAT,
iter.obj(), next, iter.referent());
}
)
// Remove Reference object from list
iter.remove();
iter.move_to_next();
} else {
iter.next();
}
}
NOT_PRODUCT(
if (PrintGCDetails && TraceReferenceGC) {
gclog_or_tty->print(
" Removed %d Refs with NULL referents out of %d discovered Refs",
iter.removed(), iter.processed());
}
)
}
inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
int id = 0;
// Determine the queue index to use for this object.
if (_discovery_is_mt) {
// During a multi-threaded discovery phase,
// each thread saves to its "own" list.
Thread* thr = Thread::current();
assert(thr->is_GC_task_thread(),
"Dubious cast from Thread* to WorkerThread*?");
id = ((WorkerThread*)thr)->id();
} else {
// single-threaded discovery, we save in round-robin
// fashion to each of the lists.
if (_processing_is_mt) {
id = next_id();
}
}
assert(0 <= id && id < _num_q, "Id is out-of-bounds (call Freud?)");
// Get the discovered queue to which we will add
DiscoveredList* list = NULL;
switch (rt) {
case REF_OTHER:
// Unknown reference type, no special treatment
break;
case REF_SOFT:
list = &_discoveredSoftRefs[id];
break;
case REF_WEAK:
list = &_discoveredWeakRefs[id];
break;
case REF_FINAL:
list = &_discoveredFinalRefs[id];
break;
case REF_PHANTOM:
list = &_discoveredPhantomRefs[id];
break;
case REF_NONE:
// we should not reach here if we are an instanceRefKlass
default:
ShouldNotReachHere();
}
return list;
}
inline void
ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
oop obj,
HeapWord* discovered_addr) {
assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
// First we must make sure this object is only enqueued once. CAS in a non null
// discovered_addr.
oop current_head = refs_list.head();
// 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.
if (_discovered_list_needs_barrier && !UseG1GC) {
if (UseCompressedOops) {
_bs->write_ref_field_pre((narrowOop*)discovered_addr, current_head);
} else {
_bs->write_ref_field_pre((oop*)discovered_addr, current_head);
}
guarantee(false, "Need to check non-G1 collector");
}
oop retest = oopDesc::atomic_compare_exchange_oop(current_head, 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_barrier) {
_bs->write_ref_field((void*)discovered_addr, current_head);
}
} else {
// If retest was non NULL, another thread beat us to it:
// The reference has already been discovered...
if (TraceReferenceGC) {
gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
obj, obj->blueprint()->internal_name());
}
}
}
// We mention two of several possible choices here:
// #0: if the reference object is not in the "originating generation"
// (or part of the heap being collected, indicated by our "span"
// we don't treat it specially (i.e. we scan it as we would
// a normal oop, treating its references as strong references).
// This means that references can't be enqueued unless their
// referent is also in the same span. This is the simplest,
// most "local" and most conservative approach, albeit one
// that may cause weak references to be enqueued least promptly.
// We call this choice the "ReferenceBasedDiscovery" policy.
// #1: the reference object may be in any generation (span), but if
// the referent is in the generation (span) being currently collected
// then we can discover the reference object, provided
// the object has not already been discovered by
// a different concurrently running collector (as may be the
// case, for instance, if the reference object is in CMS and
// the referent in DefNewGeneration), and provided the processing
// of this reference object by the current collector will
// appear atomic to every other collector in the system.
// (Thus, for instance, a concurrent collector may not
// discover references in other generations even if the
// referent is in its own generation). This policy may,
// in certain cases, enqueue references somewhat sooner than
// might Policy #0 above, but at marginally increased cost
// and complexity in processing these references.
// We call this choice the "RefeferentBasedDiscovery" policy.
bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
// We enqueue references only if we are discovering refs
// (rather than processing discovered refs).
if (!_discovering_refs || !RegisterReferences) {
return false;
}
// We only enqueue active references.
oop next = java_lang_ref_Reference::next(obj);
if (next != NULL) {
return false;
}
HeapWord* obj_addr = (HeapWord*)obj;
if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
!_span.contains(obj_addr)) {
// Reference is not in the originating generation;
// don't treat it specially (i.e. we want to scan it as a normal
// object with strong references).
return false;
}
// We only enqueue references whose referents are not (yet) strongly
// reachable.
if (is_alive_non_header() != NULL) {
oop referent = java_lang_ref_Reference::referent(obj);
// In the case of non-concurrent discovery, the last
// disjunct below should hold. It may not hold in the
// case of concurrent discovery because mutators may
// concurrently clear() a Reference.
assert(UseConcMarkSweepGC || UseG1GC || referent != NULL,
"Refs with null referents already filtered");
if (is_alive_non_header()->do_object_b(referent)) {
return false; // referent is reachable
}
}
if (rt == REF_SOFT) {
// For soft refs we can decide now if these are not
// current candidates for clearing, in which case we
// can mark through them now, rather than delaying that
// to the reference-processing phase. Since all current
// time-stamp policies advance the soft-ref clock only
// at a major collection cycle, this is always currently
// accurate.
if (!_current_soft_ref_policy->should_clear_reference(obj)) {
return false;
}
}
HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
const oop discovered = java_lang_ref_Reference::discovered(obj);
assert(discovered->is_oop_or_null(), "bad discovered field");
if (discovered != NULL) {
// The reference has already been discovered...
if (TraceReferenceGC) {
gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
obj, obj->blueprint()->internal_name());
}
if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
// assumes that an object is not processed twice;
// if it's been already discovered it must be on another
// generation's discovered list; so we won't discover it.
return false;
} else {
assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
"Unrecognized policy");
// Check assumption that an object is not potentially
// discovered twice except by concurrent collectors that potentially
// trace the same Reference object twice.
assert(UseConcMarkSweepGC,
"Only possible with an incremental-update concurrent collector");
return true;
}
}
if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
oop referent = java_lang_ref_Reference::referent(obj);
assert(referent->is_oop(), "bad referent");
// enqueue if and only if either:
// reference is in our span or
// we are an atomic collector and referent is in our span
if (_span.contains(obj_addr) ||
(discovery_is_atomic() && _span.contains(referent))) {
// should_enqueue = true;
} else {
return false;
}
} else {
assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
_span.contains(obj_addr), "code inconsistency");
}
// Get the right type of discovered queue head.
DiscoveredList* list = get_discovered_list(rt);
if (list == NULL) {
return false; // nothing special needs to be done
}
if (_discovery_is_mt) {
add_to_discovered_list_mt(*list, obj, discovered_addr);
} else {
// If "_discovered_list_needs_barrier", we do write barriers when
// updating the discovered reference list. Otherwise, we do a raw store
// here: the field will be visited later when processing the discovered
// references.
oop current_head = list->head();
// 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.
assert(discovered == NULL, "control point invariant");
if (_discovered_list_needs_barrier && !UseG1GC) { // safe to elide for G1
if (UseCompressedOops) {
_bs->write_ref_field_pre((narrowOop*)discovered_addr, current_head);
} else {
_bs->write_ref_field_pre((oop*)discovered_addr, current_head);
}
guarantee(false, "Need to check non-G1 collector");
}
oop_store_raw(discovered_addr, current_head);
if (_discovered_list_needs_barrier) {
_bs->write_ref_field((void*)discovered_addr, current_head);
}
list->set_head(obj);
list->inc_length(1);
}
// In the MT discovery case, it is currently possible to see
// the following message multiple times if several threads
// discover a reference about the same time. Only one will
// however have actually added it to the disocvered queue.
// One could let add_to_discovered_list_mt() return an
// indication for success in queueing (by 1 thread) or
// failure (by all other threads), but I decided the extra
// code was not worth the effort for something that is
// only used for debugging support.
if (TraceReferenceGC) {
oop referent = java_lang_ref_Reference::referent(obj);
if (PrintGCDetails) {
gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)",
obj, obj->blueprint()->internal_name());
}
assert(referent->is_oop(), "Enqueued a bad referent");
}
assert(obj->is_oop(), "Enqueued a bad reference");
return true;
}
// Preclean the discovered references by removing those
// whose referents are alive, and by marking from those that
// are not active. These lists can be handled here
// in any order and, indeed, concurrently.
void ReferenceProcessor::preclean_discovered_references(
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc,
YieldClosure* yield) {
NOT_PRODUCT(verify_ok_to_handle_reflists());
#ifdef ASSERT
bool must_remember_klasses = ClassUnloading && !UseConcMarkSweepGC ||
CMSClassUnloadingEnabled && UseConcMarkSweepGC;
RememberKlassesChecker mx(must_remember_klasses);
#endif
// Soft references
{
TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
false, gclog_or_tty);
for (int i = 0; i < _num_q; i++) {
if (yield->should_return()) {
return;
}
preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
keep_alive, complete_gc, yield);
}
}
// Weak references
{
TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
false, gclog_or_tty);
for (int i = 0; i < _num_q; i++) {
if (yield->should_return()) {
return;
}
preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
keep_alive, complete_gc, yield);
}
}
// Final references
{
TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
false, gclog_or_tty);
for (int i = 0; i < _num_q; i++) {
if (yield->should_return()) {
return;
}
preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
keep_alive, complete_gc, yield);
}
}
// Phantom references
{
TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
false, gclog_or_tty);
for (int i = 0; i < _num_q; i++) {
if (yield->should_return()) {
return;
}
preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
keep_alive, complete_gc, yield);
}
}
}
// Walk the given discovered ref list, and remove all reference objects
// whose referents are still alive, whose referents are NULL or which
// are not active (have a non-NULL next field). NOTE: When we are
// thus precleaning the ref lists (which happens single-threaded today),
// we do not disable refs discovery to honour the correct semantics of
// java.lang.Reference. As a result, we need to be careful below
// that ref removal steps interleave safely with ref discovery steps
// (in this thread).
void
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);
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() ||
next != NULL) {
// The referent has been cleared, or is alive, or the Reference is not
// active; we need to trace and mark its cohort.
if (TraceReferenceGC) {
gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
iter.obj(), iter.obj()->blueprint()->internal_name());
}
// Remove Reference object from list
iter.remove();
// Keep alive its cohort.
iter.make_referent_alive();
if (UseCompressedOops) {
narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
keep_alive->do_oop(next_addr);
} else {
oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
keep_alive->do_oop(next_addr);
}
iter.move_to_next();
} else {
iter.next();
}
}
// Close the reachable set
complete_gc->do_void();
NOT_PRODUCT(
if (PrintGCDetails && PrintReferenceGC) {
gclog_or_tty->print(" Dropped %d Refs out of %d "
"Refs in discovered list ", iter.removed(), iter.processed());
}
)
}
const char* ReferenceProcessor::list_name(int i) {
assert(i >= 0 && i <= _num_q * subclasses_of_ref, "Out of bounds index");
int j = i / _num_q;
switch (j) {
case 0: return "SoftRef";
case 1: return "WeakRef";
case 2: return "FinalRef";
case 3: return "PhantomRef";
}
ShouldNotReachHere();
return NULL;
}
#ifndef PRODUCT
void ReferenceProcessor::verify_ok_to_handle_reflists() {
// empty for now
}
#endif
void ReferenceProcessor::verify() {
guarantee(sentinel_ref() != NULL && sentinel_ref()->is_oop(), "Lost _sentinelRef");
}
#ifndef PRODUCT
void ReferenceProcessor::clear_discovered_references() {
guarantee(!_discovering_refs, "Discovering refs?");
for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
oop obj = _discoveredSoftRefs[i].head();
while (obj != sentinel_ref()) {
oop next = java_lang_ref_Reference::discovered(obj);
java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
obj = next;
}
_discoveredSoftRefs[i].set_head(sentinel_ref());
_discoveredSoftRefs[i].set_length(0);
}
}
#endif // PRODUCT