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