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; 104 105 unsigned int _total_collections; // ... started 106 unsigned int _total_full_collections; // ... started 107 NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;) 108 NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;) 109 110 // Reason for current garbage collection. Should be set to 111 // a value reflecting no collection between collections. 112 GCCause::Cause _gc_cause; 113 GCCause::Cause _gc_lastcause; 114 PerfStringVariable* _perf_gc_cause; 115 PerfStringVariable* _perf_gc_lastcause; 116 117 // Constructor 118 CollectedHeap(); 119 120 // Do common initializations that must follow instance construction, 121 // for example, those needing virtual calls. 122 // This code could perhaps be moved into initialize() but would 123 // be slightly more awkward because we want the latter to be a 124 // pure virtual. 125 void pre_initialize(); 126 127 // Create a new tlab. All TLAB allocations must go through this. 128 virtual HeapWord* allocate_new_tlab(size_t size); 129 130 // Accumulate statistics on all tlabs. 131 virtual void accumulate_statistics_all_tlabs(); 132 133 // Reinitialize tlabs before resuming mutators. 134 virtual void resize_all_tlabs(); 135 136 // Allocate from the current thread's TLAB, with broken-out slow path. 137 inline static HeapWord* allocate_from_tlab(KlassHandle klass, Thread* thread, size_t size); 138 static HeapWord* allocate_from_tlab_slow(KlassHandle klass, Thread* thread, size_t size); 139 140 // Allocate an uninitialized block of the given size, or returns NULL if 141 // this is impossible. 142 inline static HeapWord* common_mem_allocate_noinit(KlassHandle klass, size_t size, TRAPS); 143 144 // Like allocate_init, but the block returned by a successful allocation 145 // is guaranteed initialized to zeros. 146 inline static HeapWord* common_mem_allocate_init(KlassHandle klass, size_t size, TRAPS); 147 148 // Helper functions for (VM) allocation. 149 inline static void post_allocation_setup_common(KlassHandle klass, HeapWord* obj); 150 inline static void post_allocation_setup_no_klass_install(KlassHandle klass, 151 HeapWord* objPtr); 152 153 inline static void post_allocation_setup_obj(KlassHandle klass, HeapWord* obj, int size); 154 155 inline static void post_allocation_setup_array(KlassHandle klass, 156 HeapWord* obj, int length); 157 158 // Clears an allocated object. 159 inline static void init_obj(HeapWord* obj, size_t size); 160 161 // Filler object utilities. 162 static inline size_t filler_array_hdr_size(); 163 static inline size_t filler_array_min_size(); 164 165 DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);) 166 DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);) 167 168 // Fill with a single array; caller must ensure filler_array_min_size() <= 169 // words <= filler_array_max_size(). 170 static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true); 171 172 // Fill with a single object (either an int array or a java.lang.Object). 173 static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true); 174 175 virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer); 176 177 // Verification functions 178 virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size) 179 PRODUCT_RETURN; 180 virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size) 181 PRODUCT_RETURN; 182 debug_only(static void check_for_valid_allocation_state();) 183 184 public: 185 enum Name { 186 GenCollectedHeap, 187 ParallelScavengeHeap, 188 G1CollectedHeap 189 }; 190 191 static inline size_t filler_array_max_size() { 192 return _filler_array_max_size; 193 } 194 195 virtual Name kind() const = 0; 196 197 /** 198 * Returns JNI error code JNI_ENOMEM if memory could not be allocated, 199 * and JNI_OK on success. 200 */ 201 virtual jint initialize() = 0; 202 203 // In many heaps, there will be a need to perform some initialization activities 204 // after the Universe is fully formed, but before general heap allocation is allowed. 205 // This is the correct place to place such initialization methods. 206 virtual void post_initialize(); 207 208 // Stop any onging concurrent work and prepare for exit. 209 virtual void stop() {} 210 211 void initialize_reserved_region(HeapWord *start, HeapWord *end); 212 MemRegion reserved_region() const { return _reserved; } 213 address base() const { return (address)reserved_region().start(); } 214 215 virtual size_t capacity() const = 0; 216 virtual size_t used() const = 0; 217 218 // Return "true" if the part of the heap that allocates Java 219 // objects has reached the maximal committed limit that it can 220 // reach, without a garbage collection. 221 virtual bool is_maximal_no_gc() const = 0; 222 223 // Support for java.lang.Runtime.maxMemory(): return the maximum amount of 224 // memory that the vm could make available for storing 'normal' java objects. 225 // This is based on the reserved address space, but should not include space 226 // that the vm uses internally for bookkeeping or temporary storage 227 // (e.g., in the case of the young gen, one of the survivor 228 // spaces). 229 virtual size_t max_capacity() const = 0; 230 231 // Returns "TRUE" if "p" points into the reserved area of the heap. 232 bool is_in_reserved(const void* p) const { 233 return _reserved.contains(p); 234 } 235 236 bool is_in_reserved_or_null(const void* p) const { 237 return p == NULL || is_in_reserved(p); 238 } 239 240 // Returns "TRUE" iff "p" points into the committed areas of the heap. 241 // This method can be expensive so avoid using it in performance critical 242 // code. 243 virtual bool is_in(const void* p) const = 0; 244 245 DEBUG_ONLY(bool is_in_or_null(const void* p) const { return p == NULL || is_in(p); }) 246 247 // Let's define some terms: a "closed" subset of a heap is one that 248 // 249 // 1) contains all currently-allocated objects, and 250 // 251 // 2) is closed under reference: no object in the closed subset 252 // references one outside the closed subset. 253 // 254 // Membership in a heap's closed subset is useful for assertions. 255 // Clearly, the entire heap is a closed subset, so the default 256 // implementation is to use "is_in_reserved". But this may not be too 257 // liberal to perform useful checking. Also, the "is_in" predicate 258 // defines a closed subset, but may be too expensive, since "is_in" 259 // verifies that its argument points to an object head. The 260 // "closed_subset" method allows a heap to define an intermediate 261 // predicate, allowing more precise checking than "is_in_reserved" at 262 // lower cost than "is_in." 263 264 // One important case is a heap composed of disjoint contiguous spaces, 265 // such as the Garbage-First collector. Such heaps have a convenient 266 // closed subset consisting of the allocated portions of those 267 // contiguous spaces. 268 269 // Return "TRUE" iff the given pointer points into the heap's defined 270 // closed subset (which defaults to the entire heap). 271 virtual bool is_in_closed_subset(const void* p) const { 272 return is_in_reserved(p); 273 } 274 275 bool is_in_closed_subset_or_null(const void* p) const { 276 return p == NULL || is_in_closed_subset(p); 277 } 278 279 // An object is scavengable if its location may move during a scavenge. 280 // (A scavenge is a GC which is not a full GC.) 281 virtual bool is_scavengable(const void *p) = 0; 282 283 void set_gc_cause(GCCause::Cause v) { 284 if (UsePerfData) { 285 _gc_lastcause = _gc_cause; 286 _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause)); 287 _perf_gc_cause->set_value(GCCause::to_string(v)); 288 } 289 _gc_cause = v; 290 } 291 GCCause::Cause gc_cause() { return _gc_cause; } 292 293 // May be overridden to set additional parallelism. 294 virtual void set_par_threads(uint t) { (void)t; }; 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 void pre_full_gc_dump(GCTimer* timer); 525 void post_full_gc_dump(GCTimer* timer); 526 527 VirtualSpaceSummary create_heap_space_summary(); 528 GCHeapSummary create_heap_summary(); 529 530 MetaspaceSummary create_metaspace_summary(); 531 532 // Print heap information on the given outputStream. 533 virtual void print_on(outputStream* st) const = 0; 534 // The default behavior is to call print_on() on tty. 535 virtual void print() const { 536 print_on(tty); 537 } 538 // Print more detailed heap information on the given 539 // outputStream. The default behavior is to call print_on(). It is 540 // up to each subclass to override it and add any additional output 541 // it needs. 542 virtual void print_extended_on(outputStream* st) const { 543 print_on(st); 544 } 545 546 virtual void print_on_error(outputStream* st) const; 547 548 // Print all GC threads (other than the VM thread) 549 // used by this heap. 550 virtual void print_gc_threads_on(outputStream* st) const = 0; 551 // The default behavior is to call print_gc_threads_on() on tty. 552 void print_gc_threads() { 553 print_gc_threads_on(tty); 554 } 555 // Iterator for all GC threads (other than VM thread) 556 virtual void gc_threads_do(ThreadClosure* tc) const = 0; 557 558 // Print any relevant tracing info that flags imply. 559 // Default implementation does nothing. 560 virtual void print_tracing_info() const = 0; 561 562 void print_heap_before_gc(); 563 void print_heap_after_gc(); 564 565 // Registering and unregistering an nmethod (compiled code) with the heap. 566 // Override with specific mechanism for each specialized heap type. 567 virtual void register_nmethod(nmethod* nm); 568 virtual void unregister_nmethod(nmethod* nm); 569 570 void trace_heap_before_gc(const GCTracer* gc_tracer); 571 void trace_heap_after_gc(const GCTracer* gc_tracer); 572 573 // Heap verification 574 virtual void verify(bool silent, VerifyOption option) = 0; 575 576 // Non product verification and debugging. 577 #ifndef PRODUCT 578 // Support for PromotionFailureALot. Return true if it's time to cause a 579 // promotion failure. The no-argument version uses 580 // this->_promotion_failure_alot_count as the counter. 581 inline bool promotion_should_fail(volatile size_t* count); 582 inline bool promotion_should_fail(); 583 584 // Reset the PromotionFailureALot counters. Should be called at the end of a 585 // GC in which promotion failure occurred. 586 inline void reset_promotion_should_fail(volatile size_t* count); 587 inline void reset_promotion_should_fail(); 588 #endif // #ifndef PRODUCT 589 590 #ifdef ASSERT 591 static int fired_fake_oom() { 592 return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt); 593 } 594 #endif 595 596 public: 597 // Copy the current allocation context statistics for the specified contexts. 598 // For each context in contexts, set the corresponding entries in the totals 599 // and accuracy arrays to the current values held by the statistics. Each 600 // array should be of length len. 601 // Returns true if there are more stats available. 602 virtual bool copy_allocation_context_stats(const jint* contexts, 603 jlong* totals, 604 jbyte* accuracy, 605 jint len) { 606 return false; 607 } 608 609 /////////////// Unit tests /////////////// 610 611 NOT_PRODUCT(static void test_is_in();) 612 }; 613 614 // Class to set and reset the GC cause for a CollectedHeap. 615 616 class GCCauseSetter : StackObj { 617 CollectedHeap* _heap; 618 GCCause::Cause _previous_cause; 619 public: 620 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) { 621 assert(SafepointSynchronize::is_at_safepoint(), 622 "This method manipulates heap state without locking"); 623 _heap = heap; 624 _previous_cause = _heap->gc_cause(); 625 _heap->set_gc_cause(cause); 626 } 627 628 ~GCCauseSetter() { 629 assert(SafepointSynchronize::is_at_safepoint(), 630 "This method manipulates heap state without locking"); 631 _heap->set_gc_cause(_previous_cause); 632 } 633 }; 634 635 #endif // SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP