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 11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 14  * accompanied this code).
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 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 void ShenandoahHeap::increase_object_age(oop obj, uint additional_age) {
301   // This operates on new copy of an object. This means that the object's mark-word
302   // is thread-local and therefore safe to access. However, when the mark is
303   // displaced (i.e. stack-locked or monitor-locked), then it must be considered
304   // a shared memory location. It can be accessed by other threads.
305   // In particular, a competing evacuating thread can succeed to install its copy
306   // as the forwardee and continue to unlock the object, at which point 'our'
307   // write to the foreign stack-location would potentially over-write random
308   // information on that stack. Writing to a monitor is less problematic,
309   // but still not safe: while the ObjectMonitor would not randomly disappear,
310   // the other thread would also write to the same displaced header location,
311   // possibly leading to increase the age twice.
312   // For all these reasons, we take the conservative approach and not attempt
313   // to increase the age when the header is displaced.
314   markWord w = obj->mark();
315   // The mark-word has been copied from the original object. It can not be
316   // inflating, because inflation can not be interrupted by a safepoint,
317   // and after a safepoint, a Java thread would first have to successfully
318   // evacuate the object before it could inflate the monitor.
319   assert(!w.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT, "must not inflate monitor before evacuation of object succeeds");
320   // It is possible that we have copied the object after another thread has
321   // already successfully completed evacuation. While harmless (we would never
322   // publish our copy), don't even attempt to modify the age when that
323   // happens.
324   if (!w.has_displaced_mark_helper() && !w.is_marked()) {
325     w = w.set_age(MIN2(markWord::max_age, w.age() + additional_age));
326     obj->set_mark(w);
327   }
328 }
329 
330 // Return the object's age, or a sentinel value when the age can't
331 // necessarily be determined because of concurrent locking by the
332 // mutator
333 uint ShenandoahHeap::get_object_age(oop obj) {
334   // This is impossible to do unless we "freeze" ABA-type oscillations
335   // With Lilliput, we can do this more easily.
336   markWord w = obj->mark();
337   assert(!w.is_marked(), "must not be forwarded");
338   if (w.has_monitor()) {
339     w = w.monitor()->header();
340   } else if (w.is_being_inflated() || w.has_displaced_mark_helper()) {
341     // Informs caller that we aren't able to determine the age
342     return markWord::max_age + 1; // sentinel
343   }
344   assert(w.age() <= markWord::max_age, "Impossible!");
345   return w.age();
346 }
347 
348 inline bool ShenandoahHeap::is_in_active_generation(oop obj) const {
349   if (!mode()->is_generational()) {
350     // everything is the same single generation
351     assert(is_in_reserved(obj), "Otherwise shouldn't return true below");
352     return true;
353   }
354 
355   ShenandoahGeneration* const gen = active_generation();
356 
357   if (gen == nullptr) {
358     // no collection is happening: only expect this to be called
359     // when concurrent processing is active, but that could change
360     return false;
361   }
362 
363   assert(is_in_reserved(obj), "only check if is in active generation for objects (" PTR_FORMAT ") in heap", p2i(obj));
364   assert(gen->is_old() || gen->is_young() || gen->is_global(),
365          "Active generation must be old, young, or global");
366 
367   size_t index = heap_region_containing(obj)->index();
368 
369   // No flickering!
370   assert(gen == active_generation(), "Race?");
371 
372   switch (_affiliations[index]) {
373   case ShenandoahAffiliation::FREE:
374     // Free regions are in Old, Young, Global
375     return true;
376   case ShenandoahAffiliation::YOUNG_GENERATION:
377     // Young regions are in young_generation and global_generation, not in old_generation
378     return gen != (ShenandoahGeneration*)old_generation();
379   case ShenandoahAffiliation::OLD_GENERATION:
380     // Old regions are in old_generation and global_generation, not in young_generation
381     return gen != (ShenandoahGeneration*)young_generation();
382   default:
383     assert(false, "Bad affiliation (%d) for region " SIZE_FORMAT, _affiliations[index], index);
384     return false;
385   }
386 }
387 
388 inline bool ShenandoahHeap::is_in_young(const void* p) const {
389   return is_in_reserved(p) && (_affiliations[heap_region_index_containing(p)] == ShenandoahAffiliation::YOUNG_GENERATION);
390 }
391 
392 inline bool ShenandoahHeap::is_in_old(const void* p) const {
393   return is_in_reserved(p) && (_affiliations[heap_region_index_containing(p)] == ShenandoahAffiliation::OLD_GENERATION);
394 }
395 
396 inline bool ShenandoahHeap::is_old(oop obj) const {
397   return active_generation()->is_young() && is_in_old(obj);
398 }
399 
400 inline ShenandoahAffiliation ShenandoahHeap::region_affiliation(const ShenandoahHeapRegion *r) {
401   return (ShenandoahAffiliation) _affiliations[r->index()];
402 }
403 
404 inline void ShenandoahHeap::assert_lock_for_affiliation(ShenandoahAffiliation orig_affiliation,
405                                                         ShenandoahAffiliation new_affiliation) {
406   // A lock is required when changing from FREE to NON-FREE.  Though it may be possible to elide the lock when
407   // transitioning from in-use to FREE, the current implementation uses a lock for this transition.  A lock is
408   // not required to change from YOUNG to OLD (i.e. when promoting humongous region).
409   //
410   //         new_affiliation is:     FREE   YOUNG   OLD
411   //  orig_affiliation is:  FREE      X       L      L
412   //                       YOUNG      L       X
413   //                         OLD      L       X      X
414   //  X means state transition won't happen (so don't care)
415   //  L means lock should be held
416   //  Blank means no lock required because affiliation visibility will not be required until subsequent safepoint
417   //
418   // Note: during full GC, all transitions between states are possible.  During Full GC, we should be in a safepoint.
419 
420   if ((orig_affiliation == ShenandoahAffiliation::FREE) || (new_affiliation == ShenandoahAffiliation::FREE)) {
421     shenandoah_assert_heaplocked_or_safepoint();
422   }
423 }
424 
425 inline void ShenandoahHeap::set_affiliation(ShenandoahHeapRegion* r, ShenandoahAffiliation new_affiliation) {
426 #ifdef ASSERT
427   assert_lock_for_affiliation(region_affiliation(r), new_affiliation);
428 #endif
429   _affiliations[r->index()] = (uint8_t) new_affiliation;
430 }
431 
432 inline ShenandoahAffiliation ShenandoahHeap::region_affiliation(size_t index) {
433   return (ShenandoahAffiliation) _affiliations[index];
434 }
435 
436 inline bool ShenandoahHeap::requires_marking(const void* entry) const {
437   oop obj = cast_to_oop(entry);
438   return !_marking_context->is_marked_strong(obj);
439 }
440 
441 inline bool ShenandoahHeap::in_collection_set(oop p) const {
442   assert(collection_set() != nullptr, "Sanity");
443   return collection_set()->is_in(p);
444 }
445 
446 inline bool ShenandoahHeap::in_collection_set_loc(void* p) const {
447   assert(collection_set() != nullptr, "Sanity");
448   return collection_set()->is_in_loc(p);
449 }
450 
451 inline bool ShenandoahHeap::is_stable() const {
452   return _gc_state.is_clear();
453 }
454 
455 inline bool ShenandoahHeap::is_idle() const {
456   return _gc_state.is_unset(MARKING | EVACUATION | UPDATEREFS);
457 }
458 
459 inline bool ShenandoahHeap::is_concurrent_mark_in_progress() const {
460   return _gc_state.is_set(MARKING);
461 }
462 
463 inline bool ShenandoahHeap::is_concurrent_young_mark_in_progress() const {
464   return _gc_state.is_set(YOUNG_MARKING);
465 }
466 
467 inline bool ShenandoahHeap::is_concurrent_old_mark_in_progress() const {
468   return _gc_state.is_set(OLD_MARKING);
469 }
470 
471 inline bool ShenandoahHeap::is_evacuation_in_progress() const {
472   return _gc_state.is_set(EVACUATION);
473 }
474 
475 inline bool ShenandoahHeap::is_degenerated_gc_in_progress() const {
476   return _degenerated_gc_in_progress.is_set();
477 }
478 
479 inline bool ShenandoahHeap::is_full_gc_in_progress() const {
480   return _full_gc_in_progress.is_set();
481 }
482 
483 inline bool ShenandoahHeap::is_full_gc_move_in_progress() const {
484   return _full_gc_move_in_progress.is_set();
485 }
486 
487 inline bool ShenandoahHeap::is_update_refs_in_progress() const {
488   return _gc_state.is_set(UPDATEREFS);
489 }
490 
491 inline bool ShenandoahHeap::is_stw_gc_in_progress() const {
492   return is_full_gc_in_progress() || is_degenerated_gc_in_progress();
493 }
494 
495 inline bool ShenandoahHeap::is_concurrent_strong_root_in_progress() const {
496   return _concurrent_strong_root_in_progress.is_set();
497 }
498 
499 inline bool ShenandoahHeap::is_concurrent_weak_root_in_progress() const {
500   return _gc_state.is_set(WEAK_ROOTS);
501 }
502 
503 template<class T>
504 inline void ShenandoahHeap::marked_object_iterate(ShenandoahHeapRegion* region, T* cl) {
505   marked_object_iterate(region, cl, region->top());
506 }
507 
508 template<class T>
509 inline void ShenandoahHeap::marked_object_iterate(ShenandoahHeapRegion* region, T* cl, HeapWord* limit) {
510   assert(! region->is_humongous_continuation(), "no humongous continuation regions here");
511 
512   ShenandoahMarkingContext* const ctx = marking_context();
513 
514   HeapWord* tams = ctx->top_at_mark_start(region);
515 
516   size_t skip_bitmap_delta = 1;
517   HeapWord* start = region->bottom();
518   HeapWord* end = MIN2(tams, region->end());
519 
520   // Step 1. Scan below the TAMS based on bitmap data.
521   HeapWord* limit_bitmap = MIN2(limit, tams);
522 
523   // Try to scan the initial candidate. If the candidate is above the TAMS, it would
524   // fail the subsequent "< limit_bitmap" checks, and fall through to Step 2.
525   HeapWord* cb = ctx->get_next_marked_addr(start, end);
526 
527   intx dist = ShenandoahMarkScanPrefetch;
528   if (dist > 0) {
529     // Batched scan that prefetches the oop data, anticipating the access to
530     // either header, oop field, or forwarding pointer. Not that we cannot
531     // touch anything in oop, while it still being prefetched to get enough
532     // time for prefetch to work. This is why we try to scan the bitmap linearly,
533     // disregarding the object size. However, since we know forwarding pointer
534     // precedes the object, we can skip over it. Once we cannot trust the bitmap,
535     // there is no point for prefetching the oop contents, as oop->size() will
536     // touch it prematurely.
537 
538     // No variable-length arrays in standard C++, have enough slots to fit
539     // the prefetch distance.
540     static const int SLOT_COUNT = 256;
541     guarantee(dist <= SLOT_COUNT, "adjust slot count");
542     HeapWord* slots[SLOT_COUNT];
543 
544     int avail;
545     do {
546       avail = 0;
547       for (int c = 0; (c < dist) && (cb < limit_bitmap); c++) {
548         Prefetch::read(cb, oopDesc::mark_offset_in_bytes());
549         slots[avail++] = cb;
550         cb += skip_bitmap_delta;
551         if (cb < limit_bitmap) {
552           cb = ctx->get_next_marked_addr(cb, limit_bitmap);
553         }
554       }
555 
556       for (int c = 0; c < avail; c++) {
557         assert (slots[c] < tams,  "only objects below TAMS here: "  PTR_FORMAT " (" PTR_FORMAT ")", p2i(slots[c]), p2i(tams));
558         assert (slots[c] < limit, "only objects below limit here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(slots[c]), p2i(limit));
559         oop obj = cast_to_oop(slots[c]);
560         assert(oopDesc::is_oop(obj), "sanity");
561         assert(ctx->is_marked(obj), "object expected to be marked");
562         cl->do_object(obj);
563       }
564     } while (avail > 0);
565   } else {
566     while (cb < limit_bitmap) {
567       assert (cb < tams,  "only objects below TAMS here: "  PTR_FORMAT " (" PTR_FORMAT ")", p2i(cb), p2i(tams));
568       assert (cb < limit, "only objects below limit here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(cb), p2i(limit));
569       oop obj = cast_to_oop(cb);
570       assert(oopDesc::is_oop(obj), "sanity");
571       assert(ctx->is_marked(obj), "object expected to be marked");
572       cl->do_object(obj);
573       cb += skip_bitmap_delta;
574       if (cb < limit_bitmap) {
575         cb = ctx->get_next_marked_addr(cb, limit_bitmap);
576       }
577     }
578   }
579 
580   // Step 2. Accurate size-based traversal, happens past the TAMS.
581   // This restarts the scan at TAMS, which makes sure we traverse all objects,
582   // regardless of what happened at Step 1.
583   HeapWord* cs = tams;
584   while (cs < limit) {
585     assert (cs >= tams, "only objects past TAMS here: "   PTR_FORMAT " (" PTR_FORMAT ")", p2i(cs), p2i(tams));
586     assert (cs < limit, "only objects below limit here: " PTR_FORMAT " (" PTR_FORMAT ")", p2i(cs), p2i(limit));
587     oop obj = cast_to_oop(cs);
588     assert(oopDesc::is_oop(obj), "sanity");
589     assert(ctx->is_marked(obj), "object expected to be marked");
590     size_t size = obj->size();
591     cl->do_object(obj);
592     cs += size;
593   }
594 }
595 
596 template <class T>
597 class ShenandoahObjectToOopClosure : public ObjectClosure {
598   T* _cl;
599 public:
600   ShenandoahObjectToOopClosure(T* cl) : _cl(cl) {}
601 
602   void do_object(oop obj) {
603     obj->oop_iterate(_cl);
604   }
605 };
606 
607 template <class T>
608 class ShenandoahObjectToOopBoundedClosure : public ObjectClosure {
609   T* _cl;
610   MemRegion _bounds;
611 public:
612   ShenandoahObjectToOopBoundedClosure(T* cl, HeapWord* bottom, HeapWord* top) :
613     _cl(cl), _bounds(bottom, top) {}
614 
615   void do_object(oop obj) {
616     obj->oop_iterate(_cl, _bounds);
617   }
618 };
619 
620 template<class T>
621 inline void ShenandoahHeap::marked_object_oop_iterate(ShenandoahHeapRegion* region, T* cl, HeapWord* top) {
622   if (region->is_humongous()) {
623     HeapWord* bottom = region->bottom();
624     if (top > bottom) {
625       region = region->humongous_start_region();
626       ShenandoahObjectToOopBoundedClosure<T> objs(cl, bottom, top);
627       marked_object_iterate(region, &objs);
628     }
629   } else {
630     ShenandoahObjectToOopClosure<T> objs(cl);
631     marked_object_iterate(region, &objs, top);
632   }
633 }
634 
635 inline ShenandoahHeapRegion* ShenandoahHeap::get_region(size_t region_idx) const {
636   if (region_idx < _num_regions) {
637     return _regions[region_idx];
638   } else {
639     return nullptr;
640   }
641 }
642 
643 inline ShenandoahMarkingContext* ShenandoahHeap::complete_marking_context() const {
644   assert (_marking_context->is_complete()," sanity");
645   return _marking_context;
646 }
647 
648 inline ShenandoahMarkingContext* ShenandoahHeap::marking_context() const {
649   return _marking_context;
650 }
651 
652 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHHEAP_INLINE_HPP