1 /* 2 * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP 26 #define SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP 27 28 #include "gc/shared/gcCause.hpp" 29 #include "gc/shared/gcWhen.hpp" 30 #include "memory/allocation.hpp" 31 #include "runtime/handles.hpp" 32 #include "runtime/perfData.hpp" 33 #include "runtime/safepoint.hpp" 34 #include "utilities/debug.hpp" 35 #include "utilities/events.hpp" 36 #include "utilities/formatBuffer.hpp" 37 #include "utilities/growableArray.hpp" 38 39 // A "CollectedHeap" is an implementation of a java heap for HotSpot. This 40 // is an abstract class: there may be many different kinds of heaps. This 41 // class defines the functions that a heap must implement, and contains 42 // infrastructure common to all heaps. 43 44 class AdaptiveSizePolicy; 45 class BarrierSet; 46 class CollectorPolicy; 47 class GCHeapSummary; 48 class GCTimer; 49 class GCTracer; 50 class GCMemoryManager; 51 class MemoryPool; 52 class MetaspaceSummary; 53 class SoftRefPolicy; 54 class Thread; 55 class ThreadClosure; 56 class VirtualSpaceSummary; 57 class WorkGang; 58 class nmethod; 59 60 class GCMessage : public FormatBuffer<1024> { 61 public: 62 bool is_before; 63 64 public: 65 GCMessage() {} 66 }; 67 68 class CollectedHeap; 69 70 class GCHeapLog : public EventLogBase<GCMessage> { 71 private: 72 void log_heap(CollectedHeap* heap, bool before); 73 74 public: 75 GCHeapLog() : EventLogBase<GCMessage>("GC Heap History") {} 76 77 void log_heap_before(CollectedHeap* heap) { 78 log_heap(heap, true); 79 } 80 void log_heap_after(CollectedHeap* heap) { 81 log_heap(heap, false); 82 } 83 }; 84 85 // 86 // CollectedHeap 87 // GenCollectedHeap 88 // SerialHeap 89 // CMSHeap 90 // G1CollectedHeap 91 // ParallelScavengeHeap 92 // 93 class CollectedHeap : public CHeapObj<mtInternal> { 94 friend class VMStructs; 95 friend class JVMCIVMStructs; 96 friend class IsGCActiveMark; // Block structured external access to _is_gc_active 97 98 private: 99 #ifdef ASSERT 100 static int _fire_out_of_memory_count; 101 #endif 102 103 GCHeapLog* _gc_heap_log; 104 105 MemRegion _reserved; 106 107 protected: 108 BarrierSet* _barrier_set; 109 bool _is_gc_active; 110 111 // Used for filler objects (static, but initialized in ctor). 112 static size_t _filler_array_max_size; 113 114 unsigned int _total_collections; // ... started 115 unsigned int _total_full_collections; // ... started 116 NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;) 117 NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;) 118 119 // Reason for current garbage collection. Should be set to 120 // a value reflecting no collection between collections. 121 GCCause::Cause _gc_cause; 122 GCCause::Cause _gc_lastcause; 123 PerfStringVariable* _perf_gc_cause; 124 PerfStringVariable* _perf_gc_lastcause; 125 126 // Constructor 127 CollectedHeap(); 128 129 // Create a new tlab. All TLAB allocations must go through this. 130 virtual HeapWord* allocate_new_tlab(size_t size); 131 132 // Accumulate statistics on all tlabs. 133 virtual void accumulate_statistics_all_tlabs(); 134 135 // Reinitialize tlabs before resuming mutators. 136 virtual void resize_all_tlabs(); 137 138 // Allocate from the current thread's TLAB, with broken-out slow path. 139 inline static HeapWord* allocate_from_tlab(Klass* klass, Thread* thread, size_t size); 140 static HeapWord* allocate_from_tlab_slow(Klass* klass, Thread* thread, size_t size); 141 142 // Allocate an uninitialized block of the given size, or returns NULL if 143 // this is impossible. 144 inline static HeapWord* common_mem_allocate_noinit(Klass* klass, size_t size, TRAPS); 145 146 // Like allocate_init, but the block returned by a successful allocation 147 // is guaranteed initialized to zeros. 148 inline static HeapWord* common_mem_allocate_init(Klass* klass, size_t size, TRAPS); 149 150 151 // Helper functions for (VM) allocation. 152 inline static void post_allocation_setup_common(Klass* klass, HeapWord* obj); 153 inline static void post_allocation_setup_no_klass_install(Klass* klass, 154 HeapWord* objPtr); 155 156 inline static void post_allocation_setup_obj(Klass* klass, HeapWord* obj, int size); 157 158 inline static void post_allocation_setup_array(Klass* klass, 159 HeapWord* obj, int length); 160 161 inline static void post_allocation_setup_class(Klass* klass, HeapWord* obj, int size); 162 163 // Clears an allocated object. 164 inline static void init_obj(HeapWord* obj, size_t size); 165 166 // Filler object utilities. 167 static inline size_t filler_array_hdr_size(); 168 static inline size_t filler_array_min_size(); 169 170 DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);) 171 DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);) 172 173 // Fill with a single array; caller must ensure filler_array_min_size() <= 174 // words <= filler_array_max_size(). 175 static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true); 176 177 // Fill with a single object (either an int array or a java.lang.Object). 178 static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true); 179 180 virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer); 181 182 // Verification functions 183 virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size) 184 PRODUCT_RETURN; 185 virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size) 186 PRODUCT_RETURN; 187 debug_only(static void check_for_valid_allocation_state();) 188 189 public: 190 enum Name { 191 SerialHeap, 192 ParallelScavengeHeap, 193 G1CollectedHeap, 194 CMSHeap 195 }; 196 197 static inline size_t filler_array_max_size() { 198 return _filler_array_max_size; 199 } 200 201 virtual Name kind() const = 0; 202 203 virtual const char* name() const = 0; 204 205 /** 206 * Returns JNI error code JNI_ENOMEM if memory could not be allocated, 207 * and JNI_OK on success. 208 */ 209 virtual jint initialize() = 0; 210 211 // In many heaps, there will be a need to perform some initialization activities 212 // after the Universe is fully formed, but before general heap allocation is allowed. 213 // This is the correct place to place such initialization methods. 214 virtual void post_initialize(); 215 216 // Stop any onging concurrent work and prepare for exit. 217 virtual void stop() {} 218 219 // Stop and resume concurrent GC threads interfering with safepoint operations 220 virtual void safepoint_synchronize_begin() {} 221 virtual void safepoint_synchronize_end() {} 222 223 void initialize_reserved_region(HeapWord *start, HeapWord *end); 224 MemRegion reserved_region() const { return _reserved; } 225 address base() const { return (address)reserved_region().start(); } 226 227 virtual size_t capacity() const = 0; 228 virtual size_t used() const = 0; 229 230 // Return "true" if the part of the heap that allocates Java 231 // objects has reached the maximal committed limit that it can 232 // reach, without a garbage collection. 233 virtual bool is_maximal_no_gc() const = 0; 234 235 // Support for java.lang.Runtime.maxMemory(): return the maximum amount of 236 // memory that the vm could make available for storing 'normal' java objects. 237 // This is based on the reserved address space, but should not include space 238 // that the vm uses internally for bookkeeping or temporary storage 239 // (e.g., in the case of the young gen, one of the survivor 240 // spaces). 241 virtual size_t max_capacity() const = 0; 242 243 // Returns "TRUE" if "p" points into the reserved area of the heap. 244 bool is_in_reserved(const void* p) const { 245 return _reserved.contains(p); 246 } 247 248 bool is_in_reserved_or_null(const void* p) const { 249 return p == NULL || is_in_reserved(p); 250 } 251 252 // Returns "TRUE" iff "p" points into the committed areas of the heap. 253 // This method can be expensive so avoid using it in performance critical 254 // code. 255 virtual bool is_in(const void* p) const = 0; 256 257 DEBUG_ONLY(bool is_in_or_null(const void* p) const { return p == NULL || is_in(p); }) 258 259 // Let's define some terms: a "closed" subset of a heap is one that 260 // 261 // 1) contains all currently-allocated objects, and 262 // 263 // 2) is closed under reference: no object in the closed subset 264 // references one outside the closed subset. 265 // 266 // Membership in a heap's closed subset is useful for assertions. 267 // Clearly, the entire heap is a closed subset, so the default 268 // implementation is to use "is_in_reserved". But this may not be too 269 // liberal to perform useful checking. Also, the "is_in" predicate 270 // defines a closed subset, but may be too expensive, since "is_in" 271 // verifies that its argument points to an object head. The 272 // "closed_subset" method allows a heap to define an intermediate 273 // predicate, allowing more precise checking than "is_in_reserved" at 274 // lower cost than "is_in." 275 276 // One important case is a heap composed of disjoint contiguous spaces, 277 // such as the Garbage-First collector. Such heaps have a convenient 278 // closed subset consisting of the allocated portions of those 279 // contiguous spaces. 280 281 // Return "TRUE" iff the given pointer points into the heap's defined 282 // closed subset (which defaults to the entire heap). 283 virtual bool is_in_closed_subset(const void* p) const { 284 return is_in_reserved(p); 285 } 286 287 bool is_in_closed_subset_or_null(const void* p) const { 288 return p == NULL || is_in_closed_subset(p); 289 } 290 291 void set_gc_cause(GCCause::Cause v) { 292 if (UsePerfData) { 293 _gc_lastcause = _gc_cause; 294 _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause)); 295 _perf_gc_cause->set_value(GCCause::to_string(v)); 296 } 297 _gc_cause = v; 298 } 299 GCCause::Cause gc_cause() { return _gc_cause; } 300 301 // General obj/array allocation facilities. 302 inline static oop obj_allocate(Klass* klass, int size, TRAPS); 303 inline static oop array_allocate(Klass* klass, int size, int length, TRAPS); 304 inline static oop array_allocate_nozero(Klass* klass, int size, int length, TRAPS); 305 inline static oop class_allocate(Klass* klass, int size, TRAPS); 306 307 // Raw memory allocation facilities 308 // The obj and array allocate methods are covers for these methods. 309 // mem_allocate() should never be 310 // called to allocate TLABs, only individual objects. 311 virtual HeapWord* mem_allocate(size_t size, 312 bool* gc_overhead_limit_was_exceeded) = 0; 313 314 // Utilities for turning raw memory into filler objects. 315 // 316 // min_fill_size() is the smallest region that can be filled. 317 // fill_with_objects() can fill arbitrary-sized regions of the heap using 318 // multiple objects. fill_with_object() is for regions known to be smaller 319 // than the largest array of integers; it uses a single object to fill the 320 // region and has slightly less overhead. 321 static size_t min_fill_size() { 322 return size_t(align_object_size(oopDesc::header_size())); 323 } 324 325 static void fill_with_objects(HeapWord* start, size_t words, bool zap = true); 326 327 static void fill_with_object(HeapWord* start, size_t words, bool zap = true); 328 static void fill_with_object(MemRegion region, bool zap = true) { 329 fill_with_object(region.start(), region.word_size(), zap); 330 } 331 static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) { 332 fill_with_object(start, pointer_delta(end, start), zap); 333 } 334 335 // Return the address "addr" aligned by "alignment_in_bytes" if such 336 // an address is below "end". Return NULL otherwise. 337 inline static HeapWord* align_allocation_or_fail(HeapWord* addr, 338 HeapWord* end, 339 unsigned short alignment_in_bytes); 340 341 // Some heaps may offer a contiguous region for shared non-blocking 342 // allocation, via inlined code (by exporting the address of the top and 343 // end fields defining the extent of the contiguous allocation region.) 344 345 // This function returns "true" iff the heap supports this kind of 346 // allocation. (Default is "no".) 347 virtual bool supports_inline_contig_alloc() const { 348 return false; 349 } 350 // These functions return the addresses of the fields that define the 351 // boundaries of the contiguous allocation area. (These fields should be 352 // physically near to one another.) 353 virtual HeapWord* volatile* top_addr() const { 354 guarantee(false, "inline contiguous allocation not supported"); 355 return NULL; 356 } 357 virtual HeapWord** end_addr() const { 358 guarantee(false, "inline contiguous allocation not supported"); 359 return NULL; 360 } 361 362 // Some heaps may be in an unparseable state at certain times between 363 // collections. This may be necessary for efficient implementation of 364 // certain allocation-related activities. Calling this function before 365 // attempting to parse a heap ensures that the heap is in a parsable 366 // state (provided other concurrent activity does not introduce 367 // unparsability). It is normally expected, therefore, that this 368 // method is invoked with the world stopped. 369 // NOTE: if you override this method, make sure you call 370 // super::ensure_parsability so that the non-generational 371 // part of the work gets done. See implementation of 372 // CollectedHeap::ensure_parsability and, for instance, 373 // that of GenCollectedHeap::ensure_parsability(). 374 // The argument "retire_tlabs" controls whether existing TLABs 375 // are merely filled or also retired, thus preventing further 376 // allocation from them and necessitating allocation of new TLABs. 377 virtual void ensure_parsability(bool retire_tlabs); 378 379 // Section on thread-local allocation buffers (TLABs) 380 // If the heap supports thread-local allocation buffers, it should override 381 // the following methods: 382 // Returns "true" iff the heap supports thread-local allocation buffers. 383 // The default is "no". 384 virtual bool supports_tlab_allocation() const = 0; 385 386 // The amount of space available for thread-local allocation buffers. 387 virtual size_t tlab_capacity(Thread *thr) const = 0; 388 389 // The amount of used space for thread-local allocation buffers for the given thread. 390 virtual size_t tlab_used(Thread *thr) const = 0; 391 392 virtual size_t max_tlab_size() const; 393 394 // An estimate of the maximum allocation that could be performed 395 // for thread-local allocation buffers without triggering any 396 // collection or expansion activity. 397 virtual size_t unsafe_max_tlab_alloc(Thread *thr) const { 398 guarantee(false, "thread-local allocation buffers not supported"); 399 return 0; 400 } 401 402 // Perform a collection of the heap; intended for use in implementing 403 // "System.gc". This probably implies as full a collection as the 404 // "CollectedHeap" supports. 405 virtual void collect(GCCause::Cause cause) = 0; 406 407 // Perform a full collection 408 virtual void do_full_collection(bool clear_all_soft_refs) = 0; 409 410 // This interface assumes that it's being called by the 411 // vm thread. It collects the heap assuming that the 412 // heap lock is already held and that we are executing in 413 // the context of the vm thread. 414 virtual void collect_as_vm_thread(GCCause::Cause cause); 415 416 virtual MetaWord* satisfy_failed_metadata_allocation(ClassLoaderData* loader_data, 417 size_t size, 418 Metaspace::MetadataType mdtype); 419 420 // Returns the barrier set for this heap 421 BarrierSet* barrier_set() { return _barrier_set; } 422 void set_barrier_set(BarrierSet* barrier_set); 423 424 // Returns "true" iff there is a stop-world GC in progress. (I assume 425 // that it should answer "false" for the concurrent part of a concurrent 426 // collector -- dld). 427 bool is_gc_active() const { return _is_gc_active; } 428 429 // Total number of GC collections (started) 430 unsigned int total_collections() const { return _total_collections; } 431 unsigned int total_full_collections() const { return _total_full_collections;} 432 433 // Increment total number of GC collections (started) 434 // Should be protected but used by PSMarkSweep - cleanup for 1.4.2 435 void increment_total_collections(bool full = false) { 436 _total_collections++; 437 if (full) { 438 increment_total_full_collections(); 439 } 440 } 441 442 void increment_total_full_collections() { _total_full_collections++; } 443 444 // Return the CollectorPolicy for the heap 445 virtual CollectorPolicy* collector_policy() const = 0; 446 447 // Return the SoftRefPolicy for the heap; 448 virtual SoftRefPolicy* soft_ref_policy() = 0; 449 450 virtual GrowableArray<GCMemoryManager*> memory_managers() = 0; 451 virtual GrowableArray<MemoryPool*> memory_pools() = 0; 452 453 // Iterate over all objects, calling "cl.do_object" on each. 454 virtual void object_iterate(ObjectClosure* cl) = 0; 455 456 // Similar to object_iterate() except iterates only 457 // over live objects. 458 virtual void safe_object_iterate(ObjectClosure* cl) = 0; 459 460 // NOTE! There is no requirement that a collector implement these 461 // functions. 462 // 463 // A CollectedHeap is divided into a dense sequence of "blocks"; that is, 464 // each address in the (reserved) heap is a member of exactly 465 // one block. The defining characteristic of a block is that it is 466 // possible to find its size, and thus to progress forward to the next 467 // block. (Blocks may be of different sizes.) Thus, blocks may 468 // represent Java objects, or they might be free blocks in a 469 // free-list-based heap (or subheap), as long as the two kinds are 470 // distinguishable and the size of each is determinable. 471 472 // Returns the address of the start of the "block" that contains the 473 // address "addr". We say "blocks" instead of "object" since some heaps 474 // may not pack objects densely; a chunk may either be an object or a 475 // non-object. 476 virtual HeapWord* block_start(const void* addr) const = 0; 477 478 // Requires "addr" to be the start of a chunk, and returns its size. 479 // "addr + size" is required to be the start of a new chunk, or the end 480 // of the active area of the heap. 481 virtual size_t block_size(const HeapWord* addr) const = 0; 482 483 // Requires "addr" to be the start of a block, and returns "TRUE" iff 484 // the block is an object. 485 virtual bool block_is_obj(const HeapWord* addr) const = 0; 486 487 // Returns the longest time (in ms) that has elapsed since the last 488 // time that any part of the heap was examined by a garbage collection. 489 virtual jlong millis_since_last_gc() = 0; 490 491 // Perform any cleanup actions necessary before allowing a verification. 492 virtual void prepare_for_verify() = 0; 493 494 // Generate any dumps preceding or following a full gc 495 private: 496 void full_gc_dump(GCTimer* timer, bool before); 497 498 virtual void initialize_serviceability() = 0; 499 500 public: 501 void pre_full_gc_dump(GCTimer* timer); 502 void post_full_gc_dump(GCTimer* timer); 503 504 virtual VirtualSpaceSummary create_heap_space_summary(); 505 GCHeapSummary create_heap_summary(); 506 507 MetaspaceSummary create_metaspace_summary(); 508 509 // Print heap information on the given outputStream. 510 virtual void print_on(outputStream* st) const = 0; 511 // The default behavior is to call print_on() on tty. 512 virtual void print() const { 513 print_on(tty); 514 } 515 // Print more detailed heap information on the given 516 // outputStream. The default behavior is to call print_on(). It is 517 // up to each subclass to override it and add any additional output 518 // it needs. 519 virtual void print_extended_on(outputStream* st) const { 520 print_on(st); 521 } 522 523 virtual void print_on_error(outputStream* st) const; 524 525 // Print all GC threads (other than the VM thread) 526 // used by this heap. 527 virtual void print_gc_threads_on(outputStream* st) const = 0; 528 // The default behavior is to call print_gc_threads_on() on tty. 529 void print_gc_threads() { 530 print_gc_threads_on(tty); 531 } 532 // Iterator for all GC threads (other than VM thread) 533 virtual void gc_threads_do(ThreadClosure* tc) const = 0; 534 535 // Print any relevant tracing info that flags imply. 536 // Default implementation does nothing. 537 virtual void print_tracing_info() const = 0; 538 539 void print_heap_before_gc(); 540 void print_heap_after_gc(); 541 542 // An object is scavengable if its location may move during a scavenge. 543 // (A scavenge is a GC which is not a full GC.) 544 virtual bool is_scavengable(oop obj) = 0; 545 // Registering and unregistering an nmethod (compiled code) with the heap. 546 // Override with specific mechanism for each specialized heap type. 547 virtual void register_nmethod(nmethod* nm) {} 548 virtual void unregister_nmethod(nmethod* nm) {} 549 virtual void verify_nmethod(nmethod* nmethod) {} 550 551 void trace_heap_before_gc(const GCTracer* gc_tracer); 552 void trace_heap_after_gc(const GCTracer* gc_tracer); 553 554 // Heap verification 555 virtual void verify(VerifyOption option) = 0; 556 557 // Return true if concurrent phase control (via 558 // request_concurrent_phase_control) is supported by this collector. 559 // The default implementation returns false. 560 virtual bool supports_concurrent_phase_control() const; 561 562 // Return a NULL terminated array of concurrent phase names provided 563 // by this collector. Supports Whitebox testing. These are the 564 // names recognized by request_concurrent_phase(). The default 565 // implementation returns an array of one NULL element. 566 virtual const char* const* concurrent_phases() const; 567 568 // Request the collector enter the indicated concurrent phase, and 569 // wait until it does so. Supports WhiteBox testing. Only one 570 // request may be active at a time. Phases are designated by name; 571 // the set of names and their meaning is GC-specific. Once the 572 // requested phase has been reached, the collector will attempt to 573 // avoid transitioning to a new phase until a new request is made. 574 // [Note: A collector might not be able to remain in a given phase. 575 // For example, a full collection might cancel an in-progress 576 // concurrent collection.] 577 // 578 // Returns true when the phase is reached. Returns false for an 579 // unknown phase. The default implementation returns false. 580 virtual bool request_concurrent_phase(const char* phase); 581 582 // Provides a thread pool to SafepointSynchronize to use 583 // for parallel safepoint cleanup. 584 // GCs that use a GC worker thread pool may want to share 585 // it for use during safepoint cleanup. This is only possible 586 // if the GC can pause and resume concurrent work (e.g. G1 587 // concurrent marking) for an intermittent non-GC safepoint. 588 // If this method returns NULL, SafepointSynchronize will 589 // perform cleanup tasks serially in the VMThread. 590 virtual WorkGang* get_safepoint_workers() { return NULL; } 591 592 // Non product verification and debugging. 593 #ifndef PRODUCT 594 // Support for PromotionFailureALot. Return true if it's time to cause a 595 // promotion failure. The no-argument version uses 596 // this->_promotion_failure_alot_count as the counter. 597 inline bool promotion_should_fail(volatile size_t* count); 598 inline bool promotion_should_fail(); 599 600 // Reset the PromotionFailureALot counters. Should be called at the end of a 601 // GC in which promotion failure occurred. 602 inline void reset_promotion_should_fail(volatile size_t* count); 603 inline void reset_promotion_should_fail(); 604 #endif // #ifndef PRODUCT 605 606 #ifdef ASSERT 607 static int fired_fake_oom() { 608 return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt); 609 } 610 #endif 611 612 public: 613 // Copy the current allocation context statistics for the specified contexts. 614 // For each context in contexts, set the corresponding entries in the totals 615 // and accuracy arrays to the current values held by the statistics. Each 616 // array should be of length len. 617 // Returns true if there are more stats available. 618 virtual bool copy_allocation_context_stats(const jint* contexts, 619 jlong* totals, 620 jbyte* accuracy, 621 jint len) { 622 return false; 623 } 624 625 }; 626 627 // Class to set and reset the GC cause for a CollectedHeap. 628 629 class GCCauseSetter : StackObj { 630 CollectedHeap* _heap; 631 GCCause::Cause _previous_cause; 632 public: 633 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) { 634 _heap = heap; 635 _previous_cause = _heap->gc_cause(); 636 _heap->set_gc_cause(cause); 637 } 638 639 ~GCCauseSetter() { 640 _heap->set_gc_cause(_previous_cause); 641 } 642 }; 643 644 #endif // SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP