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 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