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/*
* Copyright (c) 2015, 2023, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2020, 2021, Red Hat, Inc. and/or its affiliates.
+ * Copyright Amazon.com Inc. or its affiliates. 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.
*/
#include "precompiled.hpp"
#include "classfile/javaClasses.hpp"
#include "gc/shared/workerThread.hpp"
+ #include "gc/shenandoah/shenandoahGeneration.hpp"
#include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
#include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
#include "gc/shenandoah/shenandoahThreadLocalData.hpp"
#include "gc/shenandoah/shenandoahUtils.hpp"
#include "runtime/atomic.hpp"
ShouldNotReachHere();
return nullptr;
}
}
+ template <typename T>
+ static void card_mark_barrier(T* field, oop value) {
+ ShenandoahHeap* heap = ShenandoahHeap::heap();
+ assert(heap->is_in_or_null(value), "Should be in heap");
+ assert(ShenandoahCardBarrier, "Card-mark barrier should be on");
+ if (heap->is_in_old(field) && heap->is_in_young(value)) {
+ // For Shenandoah, each generation collects all the _referents_ that belong to the
+ // collected generation. We can end up with discovered lists that contain a mixture
+ // of old and young _references_. These references are linked together through the
+ // discovered field in java.lang.Reference. In some cases, creating or editing this
+ // list may result in the creation of _new_ old-to-young pointers which must dirty
+ // the corresponding card. Failing to do this may cause heap verification errors and
+ // lead to incorrect GC behavior.
+ heap->card_scan()->mark_card_as_dirty(reinterpret_cast<HeapWord*>(field));
+ }
+ }
+
template <typename T>
static void set_oop_field(T* field, oop value);
template <>
void set_oop_field<oop>(oop* field, oop value) {
*field = value;
+ if (ShenandoahCardBarrier) {
+ card_mark_barrier(field, value);
+ }
}
template <>
void set_oop_field<narrowOop>(narrowOop* field, oop value) {
*field = CompressedOops::encode(value);
+ if (ShenandoahCardBarrier) {
+ card_mark_barrier(field, value);
+ }
}
static oop lrb(oop obj) {
if (obj != nullptr && ShenandoahHeap::heap()->marking_context()->is_marked(obj)) {
return ShenandoahBarrierSet::barrier_set()->load_reference_barrier(obj);
template <typename T>
bool ShenandoahReferenceProcessor::should_discover(oop reference, ReferenceType type) const {
T* referent_addr = (T*) java_lang_ref_Reference::referent_addr_raw(reference);
T heap_oop = RawAccess<>::oop_load(referent_addr);
oop referent = CompressedOops::decode(heap_oop);
+ ShenandoahHeap* heap = ShenandoahHeap::heap();
if (is_inactive<T>(reference, referent, type)) {
log_trace(gc,ref)("Reference inactive: " PTR_FORMAT, p2i(reference));
return false;
}
if (is_softly_live(reference, type)) {
log_trace(gc,ref)("Reference softly live: " PTR_FORMAT, p2i(reference));
return false;
}
+ if (!heap->is_in_active_generation(referent)) {
+ log_trace(gc,ref)("Referent outside of active generation: " PTR_FORMAT, p2i(referent));
+ return false;
+ }
+
return true;
}
template <typename T>
bool ShenandoahReferenceProcessor::should_drop(oop reference, ReferenceType type) const {
}
cl->set_weak(weak);
}
// Add reference to discovered list
+ // Each worker thread has a private copy of refproc_data, which includes a private discovered list. This means
+ // there's no risk that a different worker thread will try to manipulate my discovered list head while I'm making
+ // reference the head of my discovered list.
ShenandoahRefProcThreadLocal& refproc_data = _ref_proc_thread_locals[worker_id];
oop discovered_head = refproc_data.discovered_list_head<T>();
if (discovered_head == nullptr) {
// Self-loop tail of list. We distinguish discovered from not-discovered references by looking at their
// discovered field: if it is null, then it is not-yet discovered, otherwise it is discovered
discovered_head = reference;
}
if (reference_cas_discovered<T>(reference, discovered_head)) {
+ // We successfully set this reference object's next pointer to discovered_head. This marks reference as discovered.
+ // If reference_cas_discovered fails, that means some other worker thread took credit for discovery of this reference,
+ // and that other thread will place reference on its discovered list, so I can ignore reference.
+
+ // In case we have created an interesting pointer, mark the remembered set card as dirty.
+ ShenandoahHeap* heap = ShenandoahHeap::heap();
+ if (ShenandoahCardBarrier) {
+ T* addr = reinterpret_cast<T*>(java_lang_ref_Reference::discovered_addr_raw(reference));
+ card_mark_barrier(addr, discovered_head);
+ }
+
+ // Make the discovered_list_head point to reference.
refproc_data.set_discovered_list_head<T>(reference);
assert(refproc_data.discovered_list_head<T>() == reference, "reference must be new discovered head");
log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
_ref_proc_thread_locals[worker_id].inc_discovered(type);
}
if (!RegisterReferences) {
// Reference processing disabled
return false;
}
- log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
+ log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s, %s)",
+ p2i(reference), reference_type_name(type), ShenandoahHeap::heap()->heap_region_containing(reference)->affiliation_name());
uint worker_id = WorkerThread::worker_id();
_ref_proc_thread_locals->inc_encountered(type);
if (UseCompressedOops) {
return discover<narrowOop>(reference, type, worker_id);
template <typename T>
oop ShenandoahReferenceProcessor::drop(oop reference, ReferenceType type) {
log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
- #ifdef ASSERT
+ ShenandoahHeap* heap = ShenandoahHeap::heap();
oop referent = reference_referent<T>(reference);
- assert(referent == nullptr || ShenandoahHeap::heap()->marking_context()->is_marked(referent),
- "only drop references with alive referents");
- #endif
+ assert(referent == nullptr || heap->marking_context()->is_marked(referent), "only drop references with alive referents");
// Unlink and return next in list
oop next = reference_discovered<T>(reference);
reference_set_discovered<T>(reference, nullptr);
+ // When this reference was discovered, it would not have been marked. If it ends up surviving
+ // the cycle, we need to dirty the card if the reference is old and the referent is young. Note
+ // that if the reference is not dropped, then its pointer to the referent will be nulled before
+ // evacuation begins so card does not need to be dirtied.
+ if (heap->mode()->is_generational() && heap->is_in_old(reference) && heap->is_in_young(referent)) {
+ // Note: would be sufficient to mark only the card that holds the start of this Reference object.
+ heap->card_scan()->mark_range_as_dirty(cast_from_oop<HeapWord*>(reference), reference->size());
+ }
return next;
}
template <typename T>
T* ShenandoahReferenceProcessor::keep(oop reference, ReferenceType type, uint worker_id) {
break;
}
}
// Prepend discovered references to internal pending list
+ // set_oop_field maintains the card mark barrier as this list is constructed.
if (!CompressedOops::is_null(*list)) {
oop head = lrb(CompressedOops::decode_not_null(*list));
shenandoah_assert_not_in_cset_except(&head, head, ShenandoahHeap::heap()->cancelled_gc() || !ShenandoahLoadRefBarrier);
oop prev = Atomic::xchg(&_pending_list, head);
- RawAccess<>::oop_store(p, prev);
+ set_oop_field(p, prev);
if (prev == nullptr) {
// First to prepend to list, record tail
_pending_list_tail = reinterpret_cast<void*>(p);
}
}
void ShenandoahReferenceProcessor::enqueue_references_locked() {
// Prepend internal pending list to external pending list
shenandoah_assert_not_in_cset_except(&_pending_list, _pending_list, ShenandoahHeap::heap()->cancelled_gc() || !ShenandoahLoadRefBarrier);
+
+ // During reference processing, we maintain a local list of references that are identified by
+ // _pending_list and _pending_list_tail. _pending_list_tail points to the next field of the last Reference object on
+ // the local list.
+ //
+ // There is also a global list of reference identified by Universe::_reference_pending_list
+
+ // The following code has the effect of:
+ // 1. Making the global Universe::_reference_pending_list point to my local list
+ // 2. Overwriting the next field of the last Reference on my local list to point at the previous head of the
+ // global Universe::_reference_pending_list
+
+ oop former_head_of_global_list = Universe::swap_reference_pending_list(_pending_list);
if (UseCompressedOops) {
- *reinterpret_cast<narrowOop*>(_pending_list_tail) = CompressedOops::encode(Universe::swap_reference_pending_list(_pending_list));
+ set_oop_field<narrowOop>(reinterpret_cast<narrowOop*>(_pending_list_tail), former_head_of_global_list);
} else {
- *reinterpret_cast<oop*>(_pending_list_tail) = Universe::swap_reference_pending_list(_pending_list);
+ set_oop_field<oop>(reinterpret_cast<oop*>(_pending_list_tail), former_head_of_global_list);
}
}
void ShenandoahReferenceProcessor::enqueue_references(bool concurrent) {
if (_pending_list == nullptr) {
// Nothing to enqueue
return;
}
-
if (!concurrent) {
// When called from mark-compact or degen-GC, the locking is done by the VMOperation,
enqueue_references_locked();
} else {
// Heap_lock protects external pending list
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