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 GCHeapLog* _gc_heap_log; 92 93 // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2 is being used 94 bool _defer_initial_card_mark; 95 96 MemRegion _reserved; 97 98 protected: 99 BarrierSet* _barrier_set; 100 bool _is_gc_active; 101 102 // Used for filler objects (static, but initialized in ctor). 103 static size_t _filler_array_max_size; 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 // General obj/array allocation facilities. 294 inline static oop obj_allocate(KlassHandle klass, int size, TRAPS); 295 inline static oop array_allocate(KlassHandle klass, int size, int length, TRAPS); 296 inline static oop array_allocate_nozero(KlassHandle klass, int size, int length, TRAPS); 297 298 inline static void post_allocation_install_obj_klass(KlassHandle klass, 299 oop obj); 300 301 // Raw memory allocation facilities 302 // The obj and array allocate methods are covers for these methods. 303 // mem_allocate() should never be 304 // called to allocate TLABs, only individual objects. 305 virtual HeapWord* mem_allocate(size_t size, 306 bool* gc_overhead_limit_was_exceeded) = 0; 307 308 // Utilities for turning raw memory into filler objects. 309 // 310 // min_fill_size() is the smallest region that can be filled. 311 // fill_with_objects() can fill arbitrary-sized regions of the heap using 312 // multiple objects. fill_with_object() is for regions known to be smaller 313 // than the largest array of integers; it uses a single object to fill the 314 // region and has slightly less overhead. 315 static size_t min_fill_size() { 316 return size_t(align_object_size(oopDesc::header_size())); 317 } 318 319 static void fill_with_objects(HeapWord* start, size_t words, bool zap = true); 320 321 static void fill_with_object(HeapWord* start, size_t words, bool zap = true); 322 static void fill_with_object(MemRegion region, bool zap = true) { 323 fill_with_object(region.start(), region.word_size(), zap); 324 } 325 static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) { 326 fill_with_object(start, pointer_delta(end, start), zap); 327 } 328 329 // Return the address "addr" aligned by "alignment_in_bytes" if such 330 // an address is below "end". Return NULL otherwise. 331 inline static HeapWord* align_allocation_or_fail(HeapWord* addr, 332 HeapWord* end, 333 unsigned short alignment_in_bytes); 334 335 // Some heaps may offer a contiguous region for shared non-blocking 336 // allocation, via inlined code (by exporting the address of the top and 337 // end fields defining the extent of the contiguous allocation region.) 338 339 // This function returns "true" iff the heap supports this kind of 340 // allocation. (Default is "no".) 341 virtual bool supports_inline_contig_alloc() const { 342 return false; 343 } 344 // These functions return the addresses of the fields that define the 345 // boundaries of the contiguous allocation area. (These fields should be 346 // physically near to one another.) 347 virtual HeapWord** top_addr() const { 348 guarantee(false, "inline contiguous allocation not supported"); 349 return NULL; 350 } 351 virtual HeapWord** end_addr() const { 352 guarantee(false, "inline contiguous allocation not supported"); 353 return NULL; 354 } 355 356 // Some heaps may be in an unparseable state at certain times between 357 // collections. This may be necessary for efficient implementation of 358 // certain allocation-related activities. Calling this function before 359 // attempting to parse a heap ensures that the heap is in a parsable 360 // state (provided other concurrent activity does not introduce 361 // unparsability). It is normally expected, therefore, that this 362 // method is invoked with the world stopped. 363 // NOTE: if you override this method, make sure you call 364 // super::ensure_parsability so that the non-generational 365 // part of the work gets done. See implementation of 366 // CollectedHeap::ensure_parsability and, for instance, 367 // that of GenCollectedHeap::ensure_parsability(). 368 // The argument "retire_tlabs" controls whether existing TLABs 369 // are merely filled or also retired, thus preventing further 370 // allocation from them and necessitating allocation of new TLABs. 371 virtual void ensure_parsability(bool retire_tlabs); 372 373 // Section on thread-local allocation buffers (TLABs) 374 // If the heap supports thread-local allocation buffers, it should override 375 // the following methods: 376 // Returns "true" iff the heap supports thread-local allocation buffers. 377 // The default is "no". 378 virtual bool supports_tlab_allocation() const = 0; 379 380 // The amount of space available for thread-local allocation buffers. 381 virtual size_t tlab_capacity(Thread *thr) const = 0; 382 383 // The amount of used space for thread-local allocation buffers for the given thread. 384 virtual size_t tlab_used(Thread *thr) const = 0; 385 386 virtual size_t max_tlab_size() const; 387 388 // An estimate of the maximum allocation that could be performed 389 // for thread-local allocation buffers without triggering any 390 // collection or expansion activity. 391 virtual size_t unsafe_max_tlab_alloc(Thread *thr) const { 392 guarantee(false, "thread-local allocation buffers not supported"); 393 return 0; 394 } 395 396 // Can a compiler initialize a new object without store barriers? 397 // This permission only extends from the creation of a new object 398 // via a TLAB up to the first subsequent safepoint. If such permission 399 // is granted for this heap type, the compiler promises to call 400 // defer_store_barrier() below on any slow path allocation of 401 // a new object for which such initializing store barriers will 402 // have been elided. 403 virtual bool can_elide_tlab_store_barriers() const = 0; 404 405 // If a compiler is eliding store barriers for TLAB-allocated objects, 406 // there is probably a corresponding slow path which can produce 407 // an object allocated anywhere. The compiler's runtime support 408 // promises to call this function on such a slow-path-allocated 409 // object before performing initializations that have elided 410 // store barriers. Returns new_obj, or maybe a safer copy thereof. 411 virtual oop new_store_pre_barrier(JavaThread* thread, oop new_obj); 412 413 // Answers whether an initializing store to a new object currently 414 // allocated at the given address doesn't need a store 415 // barrier. Returns "true" if it doesn't need an initializing 416 // store barrier; answers "false" if it does. 417 virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0; 418 419 // If a compiler is eliding store barriers for TLAB-allocated objects, 420 // we will be informed of a slow-path allocation by a call 421 // to new_store_pre_barrier() above. Such a call precedes the 422 // initialization of the object itself, and no post-store-barriers will 423 // be issued. Some heap types require that the barrier strictly follows 424 // the initializing stores. (This is currently implemented by deferring the 425 // barrier until the next slow-path allocation or gc-related safepoint.) 426 // This interface answers whether a particular heap type needs the card 427 // mark to be thus strictly sequenced after the stores. 428 virtual bool card_mark_must_follow_store() const = 0; 429 430 // If the CollectedHeap was asked to defer a store barrier above, 431 // this informs it to flush such a deferred store barrier to the 432 // remembered set. 433 virtual void flush_deferred_store_barrier(JavaThread* thread); 434 435 // Perform a collection of the heap; intended for use in implementing 436 // "System.gc". This probably implies as full a collection as the 437 // "CollectedHeap" supports. 438 virtual void collect(GCCause::Cause cause) = 0; 439 440 // Perform a full collection 441 virtual void do_full_collection(bool clear_all_soft_refs) = 0; 442 443 // This interface assumes that it's being called by the 444 // vm thread. It collects the heap assuming that the 445 // heap lock is already held and that we are executing in 446 // the context of the vm thread. 447 virtual void collect_as_vm_thread(GCCause::Cause cause); 448 449 // Returns the barrier set for this heap 450 BarrierSet* barrier_set() { return _barrier_set; } 451 void set_barrier_set(BarrierSet* barrier_set); 452 453 // Returns "true" iff there is a stop-world GC in progress. (I assume 454 // that it should answer "false" for the concurrent part of a concurrent 455 // collector -- dld). 456 bool is_gc_active() const { return _is_gc_active; } 457 458 // Total number of GC collections (started) 459 unsigned int total_collections() const { return _total_collections; } 460 unsigned int total_full_collections() const { return _total_full_collections;} 461 462 // Increment total number of GC collections (started) 463 // Should be protected but used by PSMarkSweep - cleanup for 1.4.2 464 void increment_total_collections(bool full = false) { 465 _total_collections++; 466 if (full) { 467 increment_total_full_collections(); 468 } 469 } 470 471 void increment_total_full_collections() { _total_full_collections++; } 472 473 // Return the AdaptiveSizePolicy for the heap. 474 virtual AdaptiveSizePolicy* size_policy() = 0; 475 476 // Return the CollectorPolicy for the heap 477 virtual CollectorPolicy* collector_policy() const = 0; 478 479 // Iterate over all objects, calling "cl.do_object" on each. 480 virtual void object_iterate(ObjectClosure* cl) = 0; 481 482 // Similar to object_iterate() except iterates only 483 // over live objects. 484 virtual void safe_object_iterate(ObjectClosure* cl) = 0; 485 486 // NOTE! There is no requirement that a collector implement these 487 // functions. 488 // 489 // A CollectedHeap is divided into a dense sequence of "blocks"; that is, 490 // each address in the (reserved) heap is a member of exactly 491 // one block. The defining characteristic of a block is that it is 492 // possible to find its size, and thus to progress forward to the next 493 // block. (Blocks may be of different sizes.) Thus, blocks may 494 // represent Java objects, or they might be free blocks in a 495 // free-list-based heap (or subheap), as long as the two kinds are 496 // distinguishable and the size of each is determinable. 497 498 // Returns the address of the start of the "block" that contains the 499 // address "addr". We say "blocks" instead of "object" since some heaps 500 // may not pack objects densely; a chunk may either be an object or a 501 // non-object. 502 virtual HeapWord* block_start(const void* addr) const = 0; 503 504 // Requires "addr" to be the start of a chunk, and returns its size. 505 // "addr + size" is required to be the start of a new chunk, or the end 506 // of the active area of the heap. 507 virtual size_t block_size(const HeapWord* addr) const = 0; 508 509 // Requires "addr" to be the start of a block, and returns "TRUE" iff 510 // the block is an object. 511 virtual bool block_is_obj(const HeapWord* addr) const = 0; 512 513 // Returns the longest time (in ms) that has elapsed since the last 514 // time that any part of the heap was examined by a garbage collection. 515 virtual jlong millis_since_last_gc() = 0; 516 517 // Perform any cleanup actions necessary before allowing a verification. 518 virtual void prepare_for_verify() = 0; 519 520 // Generate any dumps preceding or following a full gc 521 void pre_full_gc_dump(GCTimer* timer); 522 void post_full_gc_dump(GCTimer* timer); 523 524 VirtualSpaceSummary create_heap_space_summary(); 525 GCHeapSummary create_heap_summary(); 526 527 MetaspaceSummary create_metaspace_summary(); 528 529 // Print heap information on the given outputStream. 530 virtual void print_on(outputStream* st) const = 0; 531 // The default behavior is to call print_on() on tty. 532 virtual void print() const { 533 print_on(tty); 534 } 535 // Print more detailed heap information on the given 536 // outputStream. The default behavior is to call print_on(). It is 537 // up to each subclass to override it and add any additional output 538 // it needs. 539 virtual void print_extended_on(outputStream* st) const { 540 print_on(st); 541 } 542 543 virtual void print_on_error(outputStream* st) const; 544 545 // Print all GC threads (other than the VM thread) 546 // used by this heap. 547 virtual void print_gc_threads_on(outputStream* st) const = 0; 548 // The default behavior is to call print_gc_threads_on() on tty. 549 void print_gc_threads() { 550 print_gc_threads_on(tty); 551 } 552 // Iterator for all GC threads (other than VM thread) 553 virtual void gc_threads_do(ThreadClosure* tc) const = 0; 554 555 // Print any relevant tracing info that flags imply. 556 // Default implementation does nothing. 557 virtual void print_tracing_info() const = 0; 558 559 void print_heap_before_gc(); 560 void print_heap_after_gc(); 561 562 // Registering and unregistering an nmethod (compiled code) with the heap. 563 // Override with specific mechanism for each specialized heap type. 564 virtual void register_nmethod(nmethod* nm); 565 virtual void unregister_nmethod(nmethod* nm); 566 567 void trace_heap_before_gc(const GCTracer* gc_tracer); 568 void trace_heap_after_gc(const GCTracer* gc_tracer); 569 570 // Heap verification 571 virtual void verify(bool silent, VerifyOption option) = 0; 572 573 // Non product verification and debugging. 574 #ifndef PRODUCT 575 // Support for PromotionFailureALot. Return true if it's time to cause a 576 // promotion failure. The no-argument version uses 577 // this->_promotion_failure_alot_count as the counter. 578 inline bool promotion_should_fail(volatile size_t* count); 579 inline bool promotion_should_fail(); 580 581 // Reset the PromotionFailureALot counters. Should be called at the end of a 582 // GC in which promotion failure occurred. 583 inline void reset_promotion_should_fail(volatile size_t* count); 584 inline void reset_promotion_should_fail(); 585 #endif // #ifndef PRODUCT 586 587 #ifdef ASSERT 588 static int fired_fake_oom() { 589 return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt); 590 } 591 #endif 592 593 public: 594 // Copy the current allocation context statistics for the specified contexts. 595 // For each context in contexts, set the corresponding entries in the totals 596 // and accuracy arrays to the current values held by the statistics. Each 597 // array should be of length len. 598 // Returns true if there are more stats available. 599 virtual bool copy_allocation_context_stats(const jint* contexts, 600 jlong* totals, 601 jbyte* accuracy, 602 jint len) { 603 return false; 604 } 605 606 /////////////// Unit tests /////////////// 607 608 NOT_PRODUCT(static void test_is_in();) 609 }; 610 611 // Class to set and reset the GC cause for a CollectedHeap. 612 613 class GCCauseSetter : StackObj { 614 CollectedHeap* _heap; 615 GCCause::Cause _previous_cause; 616 public: 617 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) { 618 assert(SafepointSynchronize::is_at_safepoint(), 619 "This method manipulates heap state without locking"); 620 _heap = heap; 621 _previous_cause = _heap->gc_cause(); 622 _heap->set_gc_cause(cause); 623 } 624 625 ~GCCauseSetter() { 626 assert(SafepointSynchronize::is_at_safepoint(), 627 "This method manipulates heap state without locking"); 628 _heap->set_gc_cause(_previous_cause); 629 } 630 }; 631 632 #endif // SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP