1 /*
2 * Copyright (c) 2015, 2020, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHHEAP_INLINE_HPP
27 #define SHARE_GC_SHENANDOAH_SHENANDOAHHEAP_INLINE_HPP
28
29 #include "gc/shenandoah/shenandoahHeap.hpp"
30
31 #include "classfile/javaClasses.inline.hpp"
32 #include "gc/shared/markBitMap.inline.hpp"
33 #include "gc/shared/threadLocalAllocBuffer.inline.hpp"
34 #include "gc/shared/continuationGCSupport.inline.hpp"
35 #include "gc/shared/suspendibleThreadSet.hpp"
36 #include "gc/shared/tlab_globals.hpp"
37 #include "gc/shenandoah/shenandoahAsserts.hpp"
38 #include "gc/shenandoah/shenandoahBarrierSet.inline.hpp"
39 #include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"
40 #include "gc/shenandoah/shenandoahForwarding.inline.hpp"
41 #include "gc/shenandoah/shenandoahWorkGroup.hpp"
42 #include "gc/shenandoah/shenandoahHeapRegionSet.inline.hpp"
43 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
44 #include "gc/shenandoah/shenandoahGeneration.hpp"
45 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
46 #include "gc/shenandoah/shenandoahThreadLocalData.hpp"
47 #include "gc/shenandoah/mode/shenandoahMode.hpp"
48 #include "oops/compressedOops.inline.hpp"
49 #include "oops/oop.inline.hpp"
50 #include "runtime/atomic.hpp"
51 #include "runtime/javaThread.hpp"
52 #include "runtime/prefetch.inline.hpp"
53 #include "runtime/objectMonitor.inline.hpp"
54 #include "utilities/copy.hpp"
55 #include "utilities/globalDefinitions.hpp"
56
57 inline ShenandoahHeap* ShenandoahHeap::heap() {
58 return named_heap<ShenandoahHeap>(CollectedHeap::Shenandoah);
59 }
60
61 inline ShenandoahHeapRegion* ShenandoahRegionIterator::next() {
62 size_t new_index = Atomic::add(&_index, (size_t) 1, memory_order_relaxed);
63 // get_region() provides the bounds-check and returns null on OOB.
64 return _heap->get_region(new_index - 1);
65 }
66
67 inline bool ShenandoahHeap::has_forwarded_objects() const {
68 return _gc_state.is_set(HAS_FORWARDED);
69 }
70
71 inline WorkerThreads* ShenandoahHeap::workers() const {
72 return _workers;
73 }
74
75 inline WorkerThreads* ShenandoahHeap::safepoint_workers() {
76 return _safepoint_workers;
77 }
78
79 inline void ShenandoahHeap::notify_gc_progress() {
80 Atomic::store(&_gc_no_progress_count, (size_t) 0);
81
82 }
83 inline void ShenandoahHeap::notify_gc_no_progress() {
84 Atomic::inc(&_gc_no_progress_count);
85 }
86
87 inline size_t ShenandoahHeap::get_gc_no_progress_count() const {
88 return Atomic::load(&_gc_no_progress_count);
89 }
90
91 inline size_t ShenandoahHeap::heap_region_index_containing(const void* addr) const {
92 uintptr_t region_start = ((uintptr_t) addr);
93 uintptr_t index = (region_start - (uintptr_t) base()) >> ShenandoahHeapRegion::region_size_bytes_shift();
94 assert(index < num_regions(), "Region index is in bounds: " PTR_FORMAT, p2i(addr));
95 return index;
96 }
97
98 inline ShenandoahHeapRegion* ShenandoahHeap::heap_region_containing(const void* addr) const {
99 size_t index = heap_region_index_containing(addr);
100 ShenandoahHeapRegion* const result = get_region(index);
101 assert(addr >= result->bottom() && addr < result->end(), "Heap region contains the address: " PTR_FORMAT, p2i(addr));
102 return result;
103 }
104
105 inline void ShenandoahHeap::enter_evacuation(Thread* t) {
106 _oom_evac_handler.enter_evacuation(t);
107 }
108
109 inline void ShenandoahHeap::leave_evacuation(Thread* t) {
110 _oom_evac_handler.leave_evacuation(t);
111 }
112
113 template <class T>
114 inline void ShenandoahHeap::update_with_forwarded(T* p) {
115 T o = RawAccess<>::oop_load(p);
116 if (!CompressedOops::is_null(o)) {
117 oop obj = CompressedOops::decode_not_null(o);
118 if (in_collection_set(obj)) {
119 // Corner case: when evacuation fails, there are objects in collection
120 // set that are not really forwarded. We can still go and try and update them
121 // (uselessly) to simplify the common path.
122 shenandoah_assert_forwarded_except(p, obj, cancelled_gc());
123 oop fwd = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
124 shenandoah_assert_not_in_cset_except(p, fwd, cancelled_gc());
125
126 // Unconditionally store the update: no concurrent updates expected.
127 RawAccess<IS_NOT_NULL>::oop_store(p, fwd);
128 }
129 }
130 }
131
132 template <class T>
133 inline void ShenandoahHeap::conc_update_with_forwarded(T* p) {
134 T o = RawAccess<>::oop_load(p);
135 if (!CompressedOops::is_null(o)) {
136 oop obj = CompressedOops::decode_not_null(o);
137 if (in_collection_set(obj)) {
138 // Corner case: when evacuation fails, there are objects in collection
139 // set that are not really forwarded. We can still go and try CAS-update them
140 // (uselessly) to simplify the common path.
141 shenandoah_assert_forwarded_except(p, obj, cancelled_gc());
142 oop fwd = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
143 shenandoah_assert_not_in_cset_except(p, fwd, cancelled_gc());
144
145 // Sanity check: we should not be updating the cset regions themselves,
146 // unless we are recovering from the evacuation failure.
147 shenandoah_assert_not_in_cset_loc_except(p, !is_in(p) || cancelled_gc());
148
149 // Either we succeed in updating the reference, or something else gets in our way.
150 // We don't care if that is another concurrent GC update, or another mutator update.
151 atomic_update_oop(fwd, p, obj);
152 }
153 }
154 }
155
156 // Atomic updates of heap location. This is only expected to work with updating the same
157 // logical object with its forwardee. The reason why we need stronger-than-relaxed memory
158 // ordering has to do with coordination with GC barriers and mutator accesses.
159 //
160 // In essence, stronger CAS access is required to maintain the transitive chains that mutator
161 // accesses build by themselves. To illustrate this point, consider the following example.
162 //
163 // Suppose "o" is the object that has a field "x" and the reference to "o" is stored
164 // to field at "addr", which happens to be Java volatile field. Normally, the accesses to volatile
165 // field at "addr" would be matched with release/acquire barriers. This changes when GC moves
166 // the object under mutator feet.
167 //
168 // Thread 1 (Java)
169 // // --- previous access starts here
170 // ...
171 // T1.1: store(&o.x, 1, mo_relaxed)
172 // T1.2: store(&addr, o, mo_release) // volatile store
173 //
174 // // --- new access starts here
175 // // LRB: copy and install the new copy to fwdptr
176 // T1.3: var copy = copy(o)
177 // T1.4: cas(&fwd, t, copy, mo_release) // pointer-mediated publication
178 // <access continues>
179 //
180 // Thread 2 (GC updater)
181 // T2.1: var f = load(&fwd, mo_{consume|acquire}) // pointer-mediated acquisition
182 // T2.2: cas(&addr, o, f, mo_release) // this method
183 //
184 // Thread 3 (Java)
185 // T3.1: var o = load(&addr, mo_acquire) // volatile read
186 // T3.2: if (o != null)
187 // T3.3: var r = load(&o.x, mo_relaxed)
188 //
189 // r is guaranteed to contain "1".
190 //
191 // Without GC involvement, there is synchronizes-with edge from T1.2 to T3.1,
192 // which guarantees this. With GC involvement, when LRB copies the object and
193 // another thread updates the reference to it, we need to have the transitive edge
194 // from T1.4 to T2.1 (that one is guaranteed by forwarding accesses), plus the edge
195 // from T2.2 to T3.1 (which is brought by this CAS).
196 //
197 // Note that we do not need to "acquire" in these methods, because we do not read the
198 // failure witnesses contents on any path, and "release" is enough.
199 //
200
201 inline void ShenandoahHeap::atomic_update_oop(oop update, oop* addr, oop compare) {
202 assert(is_aligned(addr, HeapWordSize), "Address should be aligned: " PTR_FORMAT, p2i(addr));
203 Atomic::cmpxchg(addr, compare, update, memory_order_release);
204 }
205
206 inline void ShenandoahHeap::atomic_update_oop(oop update, narrowOop* addr, narrowOop compare) {
207 assert(is_aligned(addr, sizeof(narrowOop)), "Address should be aligned: " PTR_FORMAT, p2i(addr));
208 narrowOop u = CompressedOops::encode(update);
209 Atomic::cmpxchg(addr, compare, u, memory_order_release);
210 }
211
212 inline void ShenandoahHeap::atomic_update_oop(oop update, narrowOop* addr, oop compare) {
213 assert(is_aligned(addr, sizeof(narrowOop)), "Address should be aligned: " PTR_FORMAT, p2i(addr));
214 narrowOop c = CompressedOops::encode(compare);
215 narrowOop u = CompressedOops::encode(update);
216 Atomic::cmpxchg(addr, c, u, memory_order_release);
217 }
218
219 inline bool ShenandoahHeap::atomic_update_oop_check(oop update, oop* addr, oop compare) {
220 assert(is_aligned(addr, HeapWordSize), "Address should be aligned: " PTR_FORMAT, p2i(addr));
221 return (oop) Atomic::cmpxchg(addr, compare, update, memory_order_release) == compare;
222 }
223
224 inline bool ShenandoahHeap::atomic_update_oop_check(oop update, narrowOop* addr, narrowOop compare) {
225 assert(is_aligned(addr, sizeof(narrowOop)), "Address should be aligned: " PTR_FORMAT, p2i(addr));
226 narrowOop u = CompressedOops::encode(update);
227 return (narrowOop) Atomic::cmpxchg(addr, compare, u, memory_order_release) == compare;
228 }
229
230 inline bool ShenandoahHeap::atomic_update_oop_check(oop update, narrowOop* addr, oop compare) {
231 assert(is_aligned(addr, sizeof(narrowOop)), "Address should be aligned: " PTR_FORMAT, p2i(addr));
232 narrowOop c = CompressedOops::encode(compare);
233 narrowOop u = CompressedOops::encode(update);
234 return CompressedOops::decode(Atomic::cmpxchg(addr, c, u, memory_order_release)) == compare;
235 }
236
237 // The memory ordering discussion above does not apply for methods that store nulls:
238 // then, there is no transitive reads in mutator (as we see nulls), and we can do
239 // relaxed memory ordering there.
240
241 inline void ShenandoahHeap::atomic_clear_oop(oop* addr, oop compare) {
242 assert(is_aligned(addr, HeapWordSize), "Address should be aligned: " PTR_FORMAT, p2i(addr));
243 Atomic::cmpxchg(addr, compare, oop(), memory_order_relaxed);
244 }
245
246 inline void ShenandoahHeap::atomic_clear_oop(narrowOop* addr, oop compare) {
247 assert(is_aligned(addr, sizeof(narrowOop)), "Address should be aligned: " PTR_FORMAT, p2i(addr));
248 narrowOop cmp = CompressedOops::encode(compare);
249 Atomic::cmpxchg(addr, cmp, narrowOop(), memory_order_relaxed);
250 }
251
252 inline void ShenandoahHeap::atomic_clear_oop(narrowOop* addr, narrowOop compare) {
253 assert(is_aligned(addr, sizeof(narrowOop)), "Address should be aligned: " PTR_FORMAT, p2i(addr));
254 Atomic::cmpxchg(addr, compare, narrowOop(), memory_order_relaxed);
255 }
256
257 inline bool ShenandoahHeap::cancelled_gc() const {
258 return _cancelled_gc.get() == CANCELLED;
259 }
260
261 inline bool ShenandoahHeap::check_cancelled_gc_and_yield(bool sts_active) {
262 if (sts_active && !cancelled_gc()) {
263 if (SuspendibleThreadSet::should_yield()) {
264 SuspendibleThreadSet::yield();
265 }
266 }
267 return cancelled_gc();
268 }
269
270 inline void ShenandoahHeap::clear_cancelled_gc(bool clear_oom_handler) {
271 _cancelled_gc.set(CANCELLABLE);
272 if (_cancel_requested_time > 0) {
273 double cancel_time = os::elapsedTime() - _cancel_requested_time;
274 log_info(gc)("GC cancellation took %.3fs", cancel_time);
275 _cancel_requested_time = 0;
276 }
277
278 if (clear_oom_handler) {
279 _oom_evac_handler.clear();
280 }
281 }
282
283 inline HeapWord* ShenandoahHeap::allocate_from_gclab(Thread* thread, size_t size) {
284 assert(UseTLAB, "TLABs should be enabled");
285
286 PLAB* gclab = ShenandoahThreadLocalData::gclab(thread);
287 if (gclab == nullptr) {
288 assert(!thread->is_Java_thread() && !thread->is_Worker_thread(),
289 "Performance: thread should have GCLAB: %s", thread->name());
290 // No GCLABs in this thread, fallback to shared allocation
291 return nullptr;
292 }
293 HeapWord* obj = gclab->allocate(size);
294 if (obj != nullptr) {
295 return obj;
296 }
297 return allocate_from_gclab_slow(thread, size);
298 }
299
300 inline ShenandoahAgeCensus* ShenandoahHeap::age_census() const {
301 assert(mode()->is_generational(), "Only in generational mode");
302 assert(_age_census != nullptr, "Error: not initialized");
303 return _age_census;
304 }
305
306 void ShenandoahHeap::increase_object_age(oop obj, uint additional_age) {
307 // This operates on new copy of an object. This means that the object's mark-word
308 // is thread-local and therefore safe to access. However, when the mark is
309 // displaced (i.e. stack-locked or monitor-locked), then it must be considered
310 // a shared memory location. It can be accessed by other threads.
311 // In particular, a competing evacuating thread can succeed to install its copy
312 // as the forwardee and continue to unlock the object, at which point 'our'
313 // write to the foreign stack-location would potentially over-write random
314 // information on that stack. Writing to a monitor is less problematic,
315 // but still not safe: while the ObjectMonitor would not randomly disappear,
316 // the other thread would also write to the same displaced header location,
317 // possibly leading to increase the age twice.
318 // For all these reasons, we take the conservative approach and not attempt
319 // to increase the age when the header is displaced.
320 markWord w = obj->mark();
321 // The mark-word has been copied from the original object. It can not be
322 // inflating, because inflation can not be interrupted by a safepoint,
323 // and after a safepoint, a Java thread would first have to successfully
324 // evacuate the object before it could inflate the monitor.
325 assert(!w.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT, "must not inflate monitor before evacuation of object succeeds");
326 // It is possible that we have copied the object after another thread has
327 // already successfully completed evacuation. While harmless (we would never
328 // publish our copy), don't even attempt to modify the age when that
329 // happens.
330 if (!w.has_displaced_mark_helper() && !w.is_marked()) {
331 w = w.set_age(MIN2(markWord::max_age, w.age() + additional_age));
332 obj->set_mark(w);
333 }
334 }
335
336 // Return the object's age, or a sentinel value when the age can't
337 // necessarily be determined because of concurrent locking by the
338 // mutator
339 uint ShenandoahHeap::get_object_age(oop obj) {
340 // This is impossible to do unless we "freeze" ABA-type oscillations
341 // With Lilliput, we can do this more easily.
342 markWord w = obj->mark();
343 assert(!w.is_marked(), "must not be forwarded");
344 if (w.has_monitor()) {
345 w = w.monitor()->header();
346 } else if (w.is_being_inflated() || w.has_displaced_mark_helper()) {
347 // Informs caller that we aren't able to determine the age
348 return markWord::max_age + 1; // sentinel
349 }
350 assert(w.age() <= markWord::max_age, "Impossible!");
351 return w.age();
352 }
353
354 bool ShenandoahHeap::is_in(const void* p) const {
355 HeapWord* heap_base = (HeapWord*) base();
356 HeapWord* last_region_end = heap_base + ShenandoahHeapRegion::region_size_words() * num_regions();
357 return p >= heap_base && p < last_region_end;
358 }
359
360 inline bool ShenandoahHeap::is_in_active_generation(oop obj) const {
361 if (!mode()->is_generational()) {
362 // everything is the same single generation
363 return true;
364 }
365
366 if (active_generation() == nullptr) {
367 // no collection is happening, only expect this to be called
368 // when concurrent processing is active, but that could change
369 return false;
370 }
371
372 assert(is_in(obj), "only check if is in active generation for objects (" PTR_FORMAT ") in heap", p2i(obj));
373 assert((active_generation() == (ShenandoahGeneration*) old_generation()) ||
374 (active_generation() == (ShenandoahGeneration*) young_generation()) ||
375 (active_generation() == global_generation()), "Active generation must be old, young, or global");
376
377 size_t index = heap_region_containing(obj)->index();
378 switch (_affiliations[index]) {
379 case ShenandoahAffiliation::FREE:
380 // Free regions are in Old, Young, Global
381 return true;
382 case ShenandoahAffiliation::YOUNG_GENERATION:
383 // Young regions are in young_generation and global_generation, not in old_generation
384 return (active_generation() != (ShenandoahGeneration*) old_generation());
385 case ShenandoahAffiliation::OLD_GENERATION:
386 // Old regions are in old_generation and global_generation, not in young_generation
387 return (active_generation() != (ShenandoahGeneration*) young_generation());
388 default:
389 assert(false, "Bad affiliation (%d) for region " SIZE_FORMAT, _affiliations[index], index);
390 return false;
391 }
392 }
393
394 inline bool ShenandoahHeap::is_in_young(const void* p) const {
395 return is_in(p) && (_affiliations[heap_region_index_containing(p)] == ShenandoahAffiliation::YOUNG_GENERATION);
396 }
397
398 inline bool ShenandoahHeap::is_in_old(const void* p) const {
399 return is_in(p) && (_affiliations[heap_region_index_containing(p)] == ShenandoahAffiliation::OLD_GENERATION);
400 }
401
402 inline bool ShenandoahHeap::is_old(oop obj) const {
403 return active_generation()->is_young() && is_in_old(obj);
404 }
405
406 inline ShenandoahAffiliation ShenandoahHeap::region_affiliation(const ShenandoahHeapRegion *r) {
407 return (ShenandoahAffiliation) _affiliations[r->index()];
408 }
409
410 inline void ShenandoahHeap::assert_lock_for_affiliation(ShenandoahAffiliation orig_affiliation,
411 ShenandoahAffiliation new_affiliation) {
412 // A lock is required when changing from FREE to NON-FREE. Though it may be possible to elide the lock when
413 // transitioning from in-use to FREE, the current implementation uses a lock for this transition. A lock is
414 // not required to change from YOUNG to OLD (i.e. when promoting humongous region).
415 //
416 // new_affiliation is: FREE YOUNG OLD
417 // orig_affiliation is: FREE X L L
418 // YOUNG L X
419 // OLD L X X
420 // X means state transition won't happen (so don't care)
421 // L means lock should be held
422 // Blank means no lock required because affiliation visibility will not be required until subsequent safepoint
423 //
424 // Note: during full GC, all transitions between states are possible. During Full GC, we should be in a safepoint.
425
426 if ((orig_affiliation == ShenandoahAffiliation::FREE) || (new_affiliation == ShenandoahAffiliation::FREE)) {
427 shenandoah_assert_heaplocked_or_fullgc_safepoint();
428 }
429 }
430
431 inline void ShenandoahHeap::set_affiliation(ShenandoahHeapRegion* r, ShenandoahAffiliation new_affiliation) {
432 #ifdef ASSERT
433 assert_lock_for_affiliation(region_affiliation(r), new_affiliation);
434 #endif
435 _affiliations[r->index()] = (uint8_t) new_affiliation;
436 }
437
438 inline ShenandoahAffiliation ShenandoahHeap::region_affiliation(size_t index) {
439 return (ShenandoahAffiliation) _affiliations[index];
440 }
441
442 inline bool ShenandoahHeap::requires_marking(const void* entry) const {
443 oop obj = cast_to_oop(entry);
444 return !_marking_context->is_marked_strong(obj);
445 }
446
447 inline bool ShenandoahHeap::in_collection_set(oop p) const {
448 assert(collection_set() != nullptr, "Sanity");
449 return collection_set()->is_in(p);
450 }
451
452 inline bool ShenandoahHeap::in_collection_set_loc(void* p) const {
453 assert(collection_set() != nullptr, "Sanity");
454 return collection_set()->is_in_loc(p);
455 }
456
457
458 inline bool ShenandoahHeap::is_stable() const {
459 return _gc_state.is_clear();
460 }
461
462 inline bool ShenandoahHeap::is_idle() const {
463 return _gc_state.is_unset(MARKING | EVACUATION | UPDATEREFS);
464 }
465
466 inline bool ShenandoahHeap::is_concurrent_mark_in_progress() const {
467 return _gc_state.is_set(MARKING);
468 }
469
470 inline bool ShenandoahHeap::is_concurrent_young_mark_in_progress() const {
471 return _gc_state.is_set(YOUNG_MARKING);
472 }
473
474 inline bool ShenandoahHeap::is_concurrent_old_mark_in_progress() const {
475 return _gc_state.is_set(OLD_MARKING);
476 }
477
478 inline bool ShenandoahHeap::is_evacuation_in_progress() const {
479 return _gc_state.is_set(EVACUATION);
480 }
481
482 inline bool ShenandoahHeap::is_degenerated_gc_in_progress() const {
483 return _degenerated_gc_in_progress.is_set();
484 }
485
486 inline bool ShenandoahHeap::is_full_gc_in_progress() const {
487 return _full_gc_in_progress.is_set();
488 }
489
490 inline bool ShenandoahHeap::is_full_gc_move_in_progress() const {
491 return _full_gc_move_in_progress.is_set();
492 }
493
494 inline bool ShenandoahHeap::is_update_refs_in_progress() const {
495 return _gc_state.is_set(UPDATEREFS);
496 }
497
498 inline bool ShenandoahHeap::is_stw_gc_in_progress() const {
499 return is_full_gc_in_progress() || is_degenerated_gc_in_progress();
500 }
501
502 inline bool ShenandoahHeap::is_concurrent_strong_root_in_progress() const {
503 return _concurrent_strong_root_in_progress.is_set();
504 }
505
506 inline bool ShenandoahHeap::is_concurrent_weak_root_in_progress() const {
507 return _gc_state.is_set(WEAK_ROOTS);
508 }
509
510 inline bool ShenandoahHeap::is_aging_cycle() const {
511 return _is_aging_cycle.is_set();
512 }
513
514 template<class T>
515 inline void ShenandoahHeap::marked_object_iterate(ShenandoahHeapRegion* region, T* cl) {
516 marked_object_iterate(region, cl, region->top());
517 }
518
519 template<class T>
520 inline void ShenandoahHeap::marked_object_iterate(ShenandoahHeapRegion* region, T* cl, HeapWord* limit) {
521 assert(! region->is_humongous_continuation(), "no humongous continuation regions here");
522
523 ShenandoahMarkingContext* const ctx = marking_context();
524
525 HeapWord* tams = ctx->top_at_mark_start(region);
526
527 size_t skip_bitmap_delta = 1;
528 HeapWord* start = region->bottom();
529 HeapWord* end = MIN2(tams, region->end());
530
531 // Step 1. Scan below the TAMS based on bitmap data.
532 HeapWord* limit_bitmap = MIN2(limit, tams);
533
534 // Try to scan the initial candidate. If the candidate is above the TAMS, it would
535 // fail the subsequent "< limit_bitmap" checks, and fall through to Step 2.
536 HeapWord* cb = ctx->get_next_marked_addr(start, end);
537
538 intx dist = ShenandoahMarkScanPrefetch;
539 if (dist > 0) {
540 // Batched scan that prefetches the oop data, anticipating the access to
541 // either header, oop field, or forwarding pointer. Not that we cannot
542 // touch anything in oop, while it still being prefetched to get enough
543 // time for prefetch to work. This is why we try to scan the bitmap linearly,
544 // disregarding the object size. However, since we know forwarding pointer
545 // precedes the object, we can skip over it. Once we cannot trust the bitmap,
546 // there is no point for prefetching the oop contents, as oop->size() will
547 // touch it prematurely.
548
549 // No variable-length arrays in standard C++, have enough slots to fit
550 // the prefetch distance.
551 static const int SLOT_COUNT = 256;
552 guarantee(dist <= SLOT_COUNT, "adjust slot count");
553 HeapWord* slots[SLOT_COUNT];
554
555 int avail;
556 do {
557 avail = 0;
558 for (int c = 0; (c < dist) && (cb < limit_bitmap); c++) {
559 Prefetch::read(cb, oopDesc::mark_offset_in_bytes());
560 slots[avail++] = cb;
561 cb += skip_bitmap_delta;
562 if (cb < limit_bitmap) {
563 cb = ctx->get_next_marked_addr(cb, limit_bitmap);
564 }
565 }
566
567 for (int c = 0; c < avail; c++) {
568 assert (slots[c] < tams, "only objects below TAMS here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(slots[c]), p2i(tams));
569 assert (slots[c] < limit, "only objects below limit here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(slots[c]), p2i(limit));
570 oop obj = cast_to_oop(slots[c]);
571 assert(oopDesc::is_oop(obj), "sanity");
572 assert(ctx->is_marked(obj), "object expected to be marked");
573 cl->do_object(obj);
574 }
575 } while (avail > 0);
576 } else {
577 while (cb < limit_bitmap) {
578 assert (cb < tams, "only objects below TAMS here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(cb), p2i(tams));
579 assert (cb < limit, "only objects below limit here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(cb), p2i(limit));
580 oop obj = cast_to_oop(cb);
581 assert(oopDesc::is_oop(obj), "sanity");
582 assert(ctx->is_marked(obj), "object expected to be marked");
583 cl->do_object(obj);
584 cb += skip_bitmap_delta;
585 if (cb < limit_bitmap) {
586 cb = ctx->get_next_marked_addr(cb, limit_bitmap);
587 }
588 }
589 }
590
591 // Step 2. Accurate size-based traversal, happens past the TAMS.
592 // This restarts the scan at TAMS, which makes sure we traverse all objects,
593 // regardless of what happened at Step 1.
594 HeapWord* cs = tams;
595 while (cs < limit) {
596 assert (cs >= tams, "only objects past TAMS here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(cs), p2i(tams));
597 assert (cs < limit, "only objects below limit here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(cs), p2i(limit));
598 oop obj = cast_to_oop(cs);
599 assert(oopDesc::is_oop(obj), "sanity");
600 assert(ctx->is_marked(obj), "object expected to be marked");
601 size_t size = obj->size();
602 cl->do_object(obj);
603 cs += size;
604 }
605 }
606
607 template <class T>
608 class ShenandoahObjectToOopClosure : public ObjectClosure {
609 T* _cl;
610 public:
611 ShenandoahObjectToOopClosure(T* cl) : _cl(cl) {}
612
613 void do_object(oop obj) {
614 obj->oop_iterate(_cl);
615 }
616 };
617
618 template <class T>
619 class ShenandoahObjectToOopBoundedClosure : public ObjectClosure {
620 T* _cl;
621 MemRegion _bounds;
622 public:
623 ShenandoahObjectToOopBoundedClosure(T* cl, HeapWord* bottom, HeapWord* top) :
624 _cl(cl), _bounds(bottom, top) {}
625
626 void do_object(oop obj) {
627 obj->oop_iterate(_cl, _bounds);
628 }
629 };
630
631 template<class T>
632 inline void ShenandoahHeap::marked_object_oop_iterate(ShenandoahHeapRegion* region, T* cl, HeapWord* top) {
633 if (region->is_humongous()) {
634 HeapWord* bottom = region->bottom();
635 if (top > bottom) {
636 region = region->humongous_start_region();
637 ShenandoahObjectToOopBoundedClosure<T> objs(cl, bottom, top);
638 marked_object_iterate(region, &objs);
639 }
640 } else {
641 ShenandoahObjectToOopClosure<T> objs(cl);
642 marked_object_iterate(region, &objs, top);
643 }
644 }
645
646 inline ShenandoahHeapRegion* ShenandoahHeap::get_region(size_t region_idx) const {
647 if (region_idx < _num_regions) {
648 return _regions[region_idx];
649 } else {
650 return nullptr;
651 }
652 }
653
654 inline ShenandoahMarkingContext* ShenandoahHeap::complete_marking_context() const {
655 assert (_marking_context->is_complete()," sanity");
656 return _marking_context;
657 }
658
659 inline ShenandoahMarkingContext* ShenandoahHeap::marking_context() const {
660 return _marking_context;
661 }
662
663 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHHEAP_INLINE_HPP