1 /* 2 * Copyright (c) 2001, 2015, 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/events.hpp" 35 36 // A "CollectedHeap" is an implementation of a java heap for HotSpot. This 37 // is an abstract class: there may be many different kinds of heaps. This 38 // class defines the functions that a heap must implement, and contains 39 // infrastructure common to all heaps. 40 41 class AdaptiveSizePolicy; 42 class BarrierSet; 43 class CollectorPolicy; 44 class GCHeapSummary; 45 class GCTimer; 46 class GCTracer; 47 class MetaspaceSummary; 48 class Thread; 49 class ThreadClosure; 50 class VirtualSpaceSummary; 51 class nmethod; 52 53 class GCMessage : public FormatBuffer<1024> { 54 public: 55 bool is_before; 56 57 public: 58 GCMessage() {} 59 }; 60 61 class GCHeapLog : public EventLogBase<GCMessage> { 62 private: 63 void log_heap(bool before); 64 65 public: 66 GCHeapLog() : EventLogBase<GCMessage>("GC Heap History") {} 67 68 void log_heap_before() { 69 log_heap(true); 70 } 71 void log_heap_after() { 72 log_heap(false); 73 } 74 }; 75 76 // 77 // CollectedHeap 78 // GenCollectedHeap 79 // G1CollectedHeap 80 // ParallelScavengeHeap 81 // 82 class CollectedHeap : public CHeapObj<mtInternal> { 83 friend class VMStructs; 84 friend class IsGCActiveMark; // Block structured external access to _is_gc_active 85 86 private: 87 #ifdef ASSERT 88 static int _fire_out_of_memory_count; 89 #endif 90 91 // Used for filler objects (static, but initialized in ctor). 92 static size_t _filler_array_max_size; 93 94 GCHeapLog* _gc_heap_log; 95 96 // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2 is being used 97 bool _defer_initial_card_mark; 98 99 MemRegion _reserved; 100 101 protected: 102 BarrierSet* _barrier_set; 103 bool _is_gc_active; 104 uint _n_par_threads; 105 106 unsigned int _total_collections; // ... started 107 unsigned int _total_full_collections; // ... started 108 NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;) 109 NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;) 110 111 // Reason for current garbage collection. Should be set to 112 // a value reflecting no collection between collections. 113 GCCause::Cause _gc_cause; 114 GCCause::Cause _gc_lastcause; 115 PerfStringVariable* _perf_gc_cause; 116 PerfStringVariable* _perf_gc_lastcause; 117 118 // Constructor 119 CollectedHeap(); 120 121 // Do common initializations that must follow instance construction, 122 // for example, those needing virtual calls. 123 // This code could perhaps be moved into initialize() but would 124 // be slightly more awkward because we want the latter to be a 125 // pure virtual. 126 void pre_initialize(); 127 128 // Create a new tlab. All TLAB allocations must go through this. 129 virtual HeapWord* allocate_new_tlab(size_t size); 130 131 // Accumulate statistics on all tlabs. 132 virtual void accumulate_statistics_all_tlabs(); 133 134 // Reinitialize tlabs before resuming mutators. 135 virtual void resize_all_tlabs(); 136 137 // Allocate from the current thread's TLAB, with broken-out slow path. 138 inline static HeapWord* allocate_from_tlab(KlassHandle klass, Thread* thread, size_t size); 139 static HeapWord* allocate_from_tlab_slow(KlassHandle klass, Thread* thread, size_t size); 140 141 // Allocate an uninitialized block of the given size, or returns NULL if 142 // this is impossible. 143 inline static HeapWord* common_mem_allocate_noinit(KlassHandle klass, size_t size, TRAPS); 144 145 // Like allocate_init, but the block returned by a successful allocation 146 // is guaranteed initialized to zeros. 147 inline static HeapWord* common_mem_allocate_init(KlassHandle klass, size_t size, TRAPS); 148 149 // Helper functions for (VM) allocation. 150 inline static void post_allocation_setup_common(KlassHandle klass, HeapWord* obj); 151 inline static void post_allocation_setup_no_klass_install(KlassHandle klass, 152 HeapWord* objPtr); 153 154 inline static void post_allocation_setup_obj(KlassHandle klass, HeapWord* obj, int size); 155 156 inline static void post_allocation_setup_array(KlassHandle klass, 157 HeapWord* obj, int length); 158 159 // Clears an allocated object. 160 inline static void init_obj(HeapWord* obj, size_t size); 161 162 // Filler object utilities. 163 static inline size_t filler_array_hdr_size(); 164 static inline size_t filler_array_min_size(); 165 166 DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);) 167 DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);) 168 169 // Fill with a single array; caller must ensure filler_array_min_size() <= 170 // words <= filler_array_max_size(). 171 static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true); 172 173 // Fill with a single object (either an int array or a java.lang.Object). 174 static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true); 175 176 virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer); 177 178 // Verification functions 179 virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size) 180 PRODUCT_RETURN; 181 virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size) 182 PRODUCT_RETURN; 183 debug_only(static void check_for_valid_allocation_state();) 184 185 public: 186 enum Name { 187 GenCollectedHeap, 188 ParallelScavengeHeap, 189 G1CollectedHeap 190 }; 191 192 static inline size_t filler_array_max_size() { 193 return _filler_array_max_size; 194 } 195 196 virtual Name kind() const = 0; 197 198 /** 199 * Returns JNI error code JNI_ENOMEM if memory could not be allocated, 200 * and JNI_OK on success. 201 */ 202 virtual jint initialize() = 0; 203 204 // In many heaps, there will be a need to perform some initialization activities 205 // after the Universe is fully formed, but before general heap allocation is allowed. 206 // This is the correct place to place such initialization methods. 207 virtual void post_initialize(); 208 209 // Stop any onging concurrent work and prepare for exit. 210 virtual void stop() {} 211 212 void initialize_reserved_region(HeapWord *start, HeapWord *end); 213 MemRegion reserved_region() const { return _reserved; } 214 address base() const { return (address)reserved_region().start(); } 215 216 virtual size_t capacity() const = 0; 217 virtual size_t used() const = 0; 218 219 // Return "true" if the part of the heap that allocates Java 220 // objects has reached the maximal committed limit that it can 221 // reach, without a garbage collection. 222 virtual bool is_maximal_no_gc() const = 0; 223 224 // Support for java.lang.Runtime.maxMemory(): return the maximum amount of 225 // memory that the vm could make available for storing 'normal' java objects. 226 // This is based on the reserved address space, but should not include space 227 // that the vm uses internally for bookkeeping or temporary storage 228 // (e.g., in the case of the young gen, one of the survivor 229 // spaces). 230 virtual size_t max_capacity() const = 0; 231 232 // Returns "TRUE" if "p" points into the reserved area of the heap. 233 bool is_in_reserved(const void* p) const { 234 return _reserved.contains(p); 235 } 236 237 bool is_in_reserved_or_null(const void* p) const { 238 return p == NULL || is_in_reserved(p); 239 } 240 241 // Returns "TRUE" iff "p" points into the committed areas of the heap. 242 // This method can be expensive so avoid using it in performance critical 243 // code. 244 virtual bool is_in(const void* p) const = 0; 245 246 DEBUG_ONLY(bool is_in_or_null(const void* p) const { return p == NULL || is_in(p); }) 247 248 // Let's define some terms: a "closed" subset of a heap is one that 249 // 250 // 1) contains all currently-allocated objects, and 251 // 252 // 2) is closed under reference: no object in the closed subset 253 // references one outside the closed subset. 254 // 255 // Membership in a heap's closed subset is useful for assertions. 256 // Clearly, the entire heap is a closed subset, so the default 257 // implementation is to use "is_in_reserved". But this may not be too 258 // liberal to perform useful checking. Also, the "is_in" predicate 259 // defines a closed subset, but may be too expensive, since "is_in" 260 // verifies that its argument points to an object head. The 261 // "closed_subset" method allows a heap to define an intermediate 262 // predicate, allowing more precise checking than "is_in_reserved" at 263 // lower cost than "is_in." 264 265 // One important case is a heap composed of disjoint contiguous spaces, 266 // such as the Garbage-First collector. Such heaps have a convenient 267 // closed subset consisting of the allocated portions of those 268 // contiguous spaces. 269 270 // Return "TRUE" iff the given pointer points into the heap's defined 271 // closed subset (which defaults to the entire heap). 272 virtual bool is_in_closed_subset(const void* p) const { 273 return is_in_reserved(p); 274 } 275 276 bool is_in_closed_subset_or_null(const void* p) const { 277 return p == NULL || is_in_closed_subset(p); 278 } 279 280 // An object is scavengable if its location may move during a scavenge. 281 // (A scavenge is a GC which is not a full GC.) 282 virtual bool is_scavengable(const void *p) = 0; 283 284 void set_gc_cause(GCCause::Cause v) { 285 if (UsePerfData) { 286 _gc_lastcause = _gc_cause; 287 _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause)); 288 _perf_gc_cause->set_value(GCCause::to_string(v)); 289 } 290 _gc_cause = v; 291 } 292 GCCause::Cause gc_cause() { return _gc_cause; } 293 294 // Number of threads currently working on GC tasks. 295 uint n_par_threads() { return _n_par_threads; } 296 297 // May be overridden to set additional parallelism. 298 virtual void set_par_threads(uint t) { _n_par_threads = t; }; 299 300 // General obj/array allocation facilities. 301 inline static oop obj_allocate(KlassHandle klass, int size, TRAPS); 302 inline static oop array_allocate(KlassHandle klass, int size, int length, TRAPS); 303 inline static oop array_allocate_nozero(KlassHandle klass, int size, int length, TRAPS); 304 305 inline static void post_allocation_install_obj_klass(KlassHandle klass, 306 oop obj); 307 308 // Raw memory allocation facilities 309 // The obj and array allocate methods are covers for these methods. 310 // mem_allocate() should never be 311 // called to allocate TLABs, only individual objects. 312 virtual HeapWord* mem_allocate(size_t size, 313 bool* gc_overhead_limit_was_exceeded) = 0; 314 315 // Utilities for turning raw memory into filler objects. 316 // 317 // min_fill_size() is the smallest region that can be filled. 318 // fill_with_objects() can fill arbitrary-sized regions of the heap using 319 // multiple objects. fill_with_object() is for regions known to be smaller 320 // than the largest array of integers; it uses a single object to fill the 321 // region and has slightly less overhead. 322 static size_t min_fill_size() { 323 return size_t(align_object_size(oopDesc::header_size())); 324 } 325 326 static void fill_with_objects(HeapWord* start, size_t words, bool zap = true); 327 328 static void fill_with_object(HeapWord* start, size_t words, bool zap = true); 329 static void fill_with_object(MemRegion region, bool zap = true) { 330 fill_with_object(region.start(), region.word_size(), zap); 331 } 332 static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) { 333 fill_with_object(start, pointer_delta(end, start), zap); 334 } 335 336 // Return the address "addr" aligned by "alignment_in_bytes" if such 337 // an address is below "end". Return NULL otherwise. 338 inline static HeapWord* align_allocation_or_fail(HeapWord* addr, 339 HeapWord* end, 340 unsigned short alignment_in_bytes); 341 342 // Some heaps may offer a contiguous region for shared non-blocking 343 // allocation, via inlined code (by exporting the address of the top and 344 // end fields defining the extent of the contiguous allocation region.) 345 346 // This function returns "true" iff the heap supports this kind of 347 // allocation. (Default is "no".) 348 virtual bool supports_inline_contig_alloc() const { 349 return false; 350 } 351 // These functions return the addresses of the fields that define the 352 // boundaries of the contiguous allocation area. (These fields should be 353 // physically near to one another.) 354 virtual HeapWord** top_addr() const { 355 guarantee(false, "inline contiguous allocation not supported"); 356 return NULL; 357 } 358 virtual HeapWord** end_addr() const { 359 guarantee(false, "inline contiguous allocation not supported"); 360 return NULL; 361 } 362 363 // Some heaps may be in an unparseable state at certain times between 364 // collections. This may be necessary for efficient implementation of 365 // certain allocation-related activities. Calling this function before 366 // attempting to parse a heap ensures that the heap is in a parsable 367 // state (provided other concurrent activity does not introduce 368 // unparsability). It is normally expected, therefore, that this 369 // method is invoked with the world stopped. 370 // NOTE: if you override this method, make sure you call 371 // super::ensure_parsability so that the non-generational 372 // part of the work gets done. See implementation of 373 // CollectedHeap::ensure_parsability and, for instance, 374 // that of GenCollectedHeap::ensure_parsability(). 375 // The argument "retire_tlabs" controls whether existing TLABs 376 // are merely filled or also retired, thus preventing further 377 // allocation from them and necessitating allocation of new TLABs. 378 virtual void ensure_parsability(bool retire_tlabs); 379 380 // Section on thread-local allocation buffers (TLABs) 381 // If the heap supports thread-local allocation buffers, it should override 382 // the following methods: 383 // Returns "true" iff the heap supports thread-local allocation buffers. 384 // The default is "no". 385 virtual bool supports_tlab_allocation() const = 0; 386 387 // The amount of space available for thread-local allocation buffers. 388 virtual size_t tlab_capacity(Thread *thr) const = 0; 389 390 // The amount of used space for thread-local allocation buffers for the given thread. 391 virtual size_t tlab_used(Thread *thr) const = 0; 392 393 virtual size_t max_tlab_size() const; 394 395 // An estimate of the maximum allocation that could be performed 396 // for thread-local allocation buffers without triggering any 397 // collection or expansion activity. 398 virtual size_t unsafe_max_tlab_alloc(Thread *thr) const { 399 guarantee(false, "thread-local allocation buffers not supported"); 400 return 0; 401 } 402 403 // Can a compiler initialize a new object without store barriers? 404 // This permission only extends from the creation of a new object 405 // via a TLAB up to the first subsequent safepoint. If such permission 406 // is granted for this heap type, the compiler promises to call 407 // defer_store_barrier() below on any slow path allocation of 408 // a new object for which such initializing store barriers will 409 // have been elided. 410 virtual bool can_elide_tlab_store_barriers() const = 0; 411 412 // If a compiler is eliding store barriers for TLAB-allocated objects, 413 // there is probably a corresponding slow path which can produce 414 // an object allocated anywhere. The compiler's runtime support 415 // promises to call this function on such a slow-path-allocated 416 // object before performing initializations that have elided 417 // store barriers. Returns new_obj, or maybe a safer copy thereof. 418 virtual oop new_store_pre_barrier(JavaThread* thread, oop new_obj); 419 420 // Answers whether an initializing store to a new object currently 421 // allocated at the given address doesn't need a store 422 // barrier. Returns "true" if it doesn't need an initializing 423 // store barrier; answers "false" if it does. 424 virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0; 425 426 // If a compiler is eliding store barriers for TLAB-allocated objects, 427 // we will be informed of a slow-path allocation by a call 428 // to new_store_pre_barrier() above. Such a call precedes the 429 // initialization of the object itself, and no post-store-barriers will 430 // be issued. Some heap types require that the barrier strictly follows 431 // the initializing stores. (This is currently implemented by deferring the 432 // barrier until the next slow-path allocation or gc-related safepoint.) 433 // This interface answers whether a particular heap type needs the card 434 // mark to be thus strictly sequenced after the stores. 435 virtual bool card_mark_must_follow_store() const = 0; 436 437 // If the CollectedHeap was asked to defer a store barrier above, 438 // this informs it to flush such a deferred store barrier to the 439 // remembered set. 440 virtual void flush_deferred_store_barrier(JavaThread* thread); 441 442 // Perform a collection of the heap; intended for use in implementing 443 // "System.gc". This probably implies as full a collection as the 444 // "CollectedHeap" supports. 445 virtual void collect(GCCause::Cause cause) = 0; 446 447 // Perform a full collection 448 virtual void do_full_collection(bool clear_all_soft_refs) = 0; 449 450 // This interface assumes that it's being called by the 451 // vm thread. It collects the heap assuming that the 452 // heap lock is already held and that we are executing in 453 // the context of the vm thread. 454 virtual void collect_as_vm_thread(GCCause::Cause cause); 455 456 // Returns the barrier set for this heap 457 BarrierSet* barrier_set() { return _barrier_set; } 458 void set_barrier_set(BarrierSet* barrier_set); 459 460 // Returns "true" iff there is a stop-world GC in progress. (I assume 461 // that it should answer "false" for the concurrent part of a concurrent 462 // collector -- dld). 463 bool is_gc_active() const { return _is_gc_active; } 464 465 // Total number of GC collections (started) 466 unsigned int total_collections() const { return _total_collections; } 467 unsigned int total_full_collections() const { return _total_full_collections;} 468 469 // Increment total number of GC collections (started) 470 // Should be protected but used by PSMarkSweep - cleanup for 1.4.2 471 void increment_total_collections(bool full = false) { 472 _total_collections++; 473 if (full) { 474 increment_total_full_collections(); 475 } 476 } 477 478 void increment_total_full_collections() { _total_full_collections++; } 479 480 // Return the AdaptiveSizePolicy for the heap. 481 virtual AdaptiveSizePolicy* size_policy() = 0; 482 483 // Return the CollectorPolicy for the heap 484 virtual CollectorPolicy* collector_policy() const = 0; 485 486 // Iterate over all objects, calling "cl.do_object" on each. 487 virtual void object_iterate(ObjectClosure* cl) = 0; 488 489 // Similar to object_iterate() except iterates only 490 // over live objects. 491 virtual void safe_object_iterate(ObjectClosure* cl) = 0; 492 493 // NOTE! There is no requirement that a collector implement these 494 // functions. 495 // 496 // A CollectedHeap is divided into a dense sequence of "blocks"; that is, 497 // each address in the (reserved) heap is a member of exactly 498 // one block. The defining characteristic of a block is that it is 499 // possible to find its size, and thus to progress forward to the next 500 // block. (Blocks may be of different sizes.) Thus, blocks may 501 // represent Java objects, or they might be free blocks in a 502 // free-list-based heap (or subheap), as long as the two kinds are 503 // distinguishable and the size of each is determinable. 504 505 // Returns the address of the start of the "block" that contains the 506 // address "addr". We say "blocks" instead of "object" since some heaps 507 // may not pack objects densely; a chunk may either be an object or a 508 // non-object. 509 virtual HeapWord* block_start(const void* addr) const = 0; 510 511 // Requires "addr" to be the start of a chunk, and returns its size. 512 // "addr + size" is required to be the start of a new chunk, or the end 513 // of the active area of the heap. 514 virtual size_t block_size(const HeapWord* addr) const = 0; 515 516 // Requires "addr" to be the start of a block, and returns "TRUE" iff 517 // the block is an object. 518 virtual bool block_is_obj(const HeapWord* addr) const = 0; 519 520 // Returns the longest time (in ms) that has elapsed since the last 521 // time that any part of the heap was examined by a garbage collection. 522 virtual jlong millis_since_last_gc() = 0; 523 524 // Perform any cleanup actions necessary before allowing a verification. 525 virtual void prepare_for_verify() = 0; 526 527 // Generate any dumps preceding or following a full gc 528 void pre_full_gc_dump(GCTimer* timer); 529 void post_full_gc_dump(GCTimer* timer); 530 531 VirtualSpaceSummary create_heap_space_summary(); 532 GCHeapSummary create_heap_summary(); 533 534 MetaspaceSummary create_metaspace_summary(); 535 536 // Print heap information on the given outputStream. 537 virtual void print_on(outputStream* st) const = 0; 538 // The default behavior is to call print_on() on tty. 539 virtual void print() const { 540 print_on(tty); 541 } 542 // Print more detailed heap information on the given 543 // outputStream. The default behavior is to call print_on(). It is 544 // up to each subclass to override it and add any additional output 545 // it needs. 546 virtual void print_extended_on(outputStream* st) const { 547 print_on(st); 548 } 549 550 virtual void print_on_error(outputStream* st) const; 551 552 // Print all GC threads (other than the VM thread) 553 // used by this heap. 554 virtual void print_gc_threads_on(outputStream* st) const = 0; 555 // The default behavior is to call print_gc_threads_on() on tty. 556 void print_gc_threads() { 557 print_gc_threads_on(tty); 558 } 559 // Iterator for all GC threads (other than VM thread) 560 virtual void gc_threads_do(ThreadClosure* tc) const = 0; 561 562 // Print any relevant tracing info that flags imply. 563 // Default implementation does nothing. 564 virtual void print_tracing_info() const = 0; 565 566 void print_heap_before_gc(); 567 void print_heap_after_gc(); 568 569 // Registering and unregistering an nmethod (compiled code) with the heap. 570 // Override with specific mechanism for each specialized heap type. 571 virtual void register_nmethod(nmethod* nm); 572 virtual void unregister_nmethod(nmethod* nm); 573 574 void trace_heap_before_gc(const GCTracer* gc_tracer); 575 void trace_heap_after_gc(const GCTracer* gc_tracer); 576 577 // Heap verification 578 virtual void verify(bool silent, VerifyOption option) = 0; 579 580 // Non product verification and debugging. 581 #ifndef PRODUCT 582 // Support for PromotionFailureALot. Return true if it's time to cause a 583 // promotion failure. The no-argument version uses 584 // this->_promotion_failure_alot_count as the counter. 585 inline bool promotion_should_fail(volatile size_t* count); 586 inline bool promotion_should_fail(); 587 588 // Reset the PromotionFailureALot counters. Should be called at the end of a 589 // GC in which promotion failure occurred. 590 inline void reset_promotion_should_fail(volatile size_t* count); 591 inline void reset_promotion_should_fail(); 592 #endif // #ifndef PRODUCT 593 594 #ifdef ASSERT 595 static int fired_fake_oom() { 596 return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt); 597 } 598 #endif 599 600 public: 601 // Copy the current allocation context statistics for the specified contexts. 602 // For each context in contexts, set the corresponding entries in the totals 603 // and accuracy arrays to the current values held by the statistics. Each 604 // array should be of length len. 605 // Returns true if there are more stats available. 606 virtual bool copy_allocation_context_stats(const jint* contexts, 607 jlong* totals, 608 jbyte* accuracy, 609 jint len) { 610 return false; 611 } 612 613 /////////////// Unit tests /////////////// 614 615 NOT_PRODUCT(static void test_is_in();) 616 }; 617 618 // Class to set and reset the GC cause for a CollectedHeap. 619 620 class GCCauseSetter : StackObj { 621 CollectedHeap* _heap; 622 GCCause::Cause _previous_cause; 623 public: 624 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) { 625 assert(SafepointSynchronize::is_at_safepoint(), 626 "This method manipulates heap state without locking"); 627 _heap = heap; 628 _previous_cause = _heap->gc_cause(); 629 _heap->set_gc_cause(cause); 630 } 631 632 ~GCCauseSetter() { 633 assert(SafepointSynchronize::is_at_safepoint(), 634 "This method manipulates heap state without locking"); 635 _heap->set_gc_cause(_previous_cause); 636 } 637 }; 638 639 #endif // SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP