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