Tue, 12 Jan 2010 14:56:46 -0800
6902115: G1:assert(ignore_max_completed||thread->is_Java_thread()||SafepointSynchronize::is_at_safepoint())
Summary: Remove invalid assert and mangle filler objects in TLABs that are being retired.
Reviewed-by: ysr, jmasa
1 /*
2 * Copyright 2001-2009 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
25 // A "CollectedHeap" is an implementation of a java heap for HotSpot. This
26 // is an abstract class: there may be many different kinds of heaps. This
27 // class defines the functions that a heap must implement, and contains
28 // infrastructure common to all heaps.
30 class BarrierSet;
31 class ThreadClosure;
32 class AdaptiveSizePolicy;
33 class Thread;
35 //
36 // CollectedHeap
37 // SharedHeap
38 // GenCollectedHeap
39 // G1CollectedHeap
40 // ParallelScavengeHeap
41 //
42 class CollectedHeap : public CHeapObj {
43 friend class VMStructs;
44 friend class IsGCActiveMark; // Block structured external access to _is_gc_active
45 friend class constantPoolCacheKlass; // allocate() method inserts is_conc_safe
47 #ifdef ASSERT
48 static int _fire_out_of_memory_count;
49 #endif
51 // Used for filler objects (static, but initialized in ctor).
52 static size_t _filler_array_max_size;
54 protected:
55 MemRegion _reserved;
56 BarrierSet* _barrier_set;
57 bool _is_gc_active;
58 unsigned int _total_collections; // ... started
59 unsigned int _total_full_collections; // ... started
60 NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;)
61 NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;)
63 // Reason for current garbage collection. Should be set to
64 // a value reflecting no collection between collections.
65 GCCause::Cause _gc_cause;
66 GCCause::Cause _gc_lastcause;
67 PerfStringVariable* _perf_gc_cause;
68 PerfStringVariable* _perf_gc_lastcause;
70 // Constructor
71 CollectedHeap();
73 // Create a new tlab
74 virtual HeapWord* allocate_new_tlab(size_t size);
76 // Fix up tlabs to make the heap well-formed again,
77 // optionally retiring the tlabs.
78 virtual void fill_all_tlabs(bool retire);
80 // Accumulate statistics on all tlabs.
81 virtual void accumulate_statistics_all_tlabs();
83 // Reinitialize tlabs before resuming mutators.
84 virtual void resize_all_tlabs();
86 protected:
87 // Allocate from the current thread's TLAB, with broken-out slow path.
88 inline static HeapWord* allocate_from_tlab(Thread* thread, size_t size);
89 static HeapWord* allocate_from_tlab_slow(Thread* thread, size_t size);
91 // Allocate an uninitialized block of the given size, or returns NULL if
92 // this is impossible.
93 inline static HeapWord* common_mem_allocate_noinit(size_t size, bool is_noref, TRAPS);
95 // Like allocate_init, but the block returned by a successful allocation
96 // is guaranteed initialized to zeros.
97 inline static HeapWord* common_mem_allocate_init(size_t size, bool is_noref, TRAPS);
99 // Same as common_mem version, except memory is allocated in the permanent area
100 // If there is no permanent area, revert to common_mem_allocate_noinit
101 inline static HeapWord* common_permanent_mem_allocate_noinit(size_t size, TRAPS);
103 // Same as common_mem version, except memory is allocated in the permanent area
104 // If there is no permanent area, revert to common_mem_allocate_init
105 inline static HeapWord* common_permanent_mem_allocate_init(size_t size, TRAPS);
107 // Helper functions for (VM) allocation.
108 inline static void post_allocation_setup_common(KlassHandle klass,
109 HeapWord* obj, size_t size);
110 inline static void post_allocation_setup_no_klass_install(KlassHandle klass,
111 HeapWord* objPtr,
112 size_t size);
114 inline static void post_allocation_setup_obj(KlassHandle klass,
115 HeapWord* obj, size_t size);
117 inline static void post_allocation_setup_array(KlassHandle klass,
118 HeapWord* obj, size_t size,
119 int length);
121 // Clears an allocated object.
122 inline static void init_obj(HeapWord* obj, size_t size);
124 // Filler object utilities.
125 static inline size_t filler_array_hdr_size();
126 static inline size_t filler_array_min_size();
127 static inline size_t filler_array_max_size();
129 DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);)
130 DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);)
132 // Fill with a single array; caller must ensure filler_array_min_size() <=
133 // words <= filler_array_max_size().
134 static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true);
136 // Fill with a single object (either an int array or a java.lang.Object).
137 static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true);
139 // Verification functions
140 virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size)
141 PRODUCT_RETURN;
142 virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size)
143 PRODUCT_RETURN;
144 debug_only(static void check_for_valid_allocation_state();)
146 public:
147 enum Name {
148 Abstract,
149 SharedHeap,
150 GenCollectedHeap,
151 ParallelScavengeHeap,
152 G1CollectedHeap
153 };
155 virtual CollectedHeap::Name kind() const { return CollectedHeap::Abstract; }
157 /**
158 * Returns JNI error code JNI_ENOMEM if memory could not be allocated,
159 * and JNI_OK on success.
160 */
161 virtual jint initialize() = 0;
163 // In many heaps, there will be a need to perform some initialization activities
164 // after the Universe is fully formed, but before general heap allocation is allowed.
165 // This is the correct place to place such initialization methods.
166 virtual void post_initialize() = 0;
168 MemRegion reserved_region() const { return _reserved; }
169 address base() const { return (address)reserved_region().start(); }
171 // Future cleanup here. The following functions should specify bytes or
172 // heapwords as part of their signature.
173 virtual size_t capacity() const = 0;
174 virtual size_t used() const = 0;
176 // Return "true" if the part of the heap that allocates Java
177 // objects has reached the maximal committed limit that it can
178 // reach, without a garbage collection.
179 virtual bool is_maximal_no_gc() const = 0;
181 virtual size_t permanent_capacity() const = 0;
182 virtual size_t permanent_used() const = 0;
184 // Support for java.lang.Runtime.maxMemory(): return the maximum amount of
185 // memory that the vm could make available for storing 'normal' java objects.
186 // This is based on the reserved address space, but should not include space
187 // that the vm uses internally for bookkeeping or temporary storage (e.g.,
188 // perm gen space or, in the case of the young gen, one of the survivor
189 // spaces).
190 virtual size_t max_capacity() const = 0;
192 // Returns "TRUE" if "p" points into the reserved area of the heap.
193 bool is_in_reserved(const void* p) const {
194 return _reserved.contains(p);
195 }
197 bool is_in_reserved_or_null(const void* p) const {
198 return p == NULL || is_in_reserved(p);
199 }
201 // Returns "TRUE" if "p" points to the head of an allocated object in the
202 // heap. Since this method can be expensive in general, we restrict its
203 // use to assertion checking only.
204 virtual bool is_in(const void* p) const = 0;
206 bool is_in_or_null(const void* p) const {
207 return p == NULL || is_in(p);
208 }
210 // Let's define some terms: a "closed" subset of a heap is one that
211 //
212 // 1) contains all currently-allocated objects, and
213 //
214 // 2) is closed under reference: no object in the closed subset
215 // references one outside the closed subset.
216 //
217 // Membership in a heap's closed subset is useful for assertions.
218 // Clearly, the entire heap is a closed subset, so the default
219 // implementation is to use "is_in_reserved". But this may not be too
220 // liberal to perform useful checking. Also, the "is_in" predicate
221 // defines a closed subset, but may be too expensive, since "is_in"
222 // verifies that its argument points to an object head. The
223 // "closed_subset" method allows a heap to define an intermediate
224 // predicate, allowing more precise checking than "is_in_reserved" at
225 // lower cost than "is_in."
227 // One important case is a heap composed of disjoint contiguous spaces,
228 // such as the Garbage-First collector. Such heaps have a convenient
229 // closed subset consisting of the allocated portions of those
230 // contiguous spaces.
232 // Return "TRUE" iff the given pointer points into the heap's defined
233 // closed subset (which defaults to the entire heap).
234 virtual bool is_in_closed_subset(const void* p) const {
235 return is_in_reserved(p);
236 }
238 bool is_in_closed_subset_or_null(const void* p) const {
239 return p == NULL || is_in_closed_subset(p);
240 }
242 // XXX is_permanent() and is_in_permanent() should be better named
243 // to distinguish one from the other.
245 // Returns "TRUE" if "p" is allocated as "permanent" data.
246 // If the heap does not use "permanent" data, returns the same
247 // value is_in_reserved() would return.
248 // NOTE: this actually returns true if "p" is in reserved space
249 // for the space not that it is actually allocated (i.e. in committed
250 // space). If you need the more conservative answer use is_permanent().
251 virtual bool is_in_permanent(const void *p) const = 0;
253 bool is_in_permanent_or_null(const void *p) const {
254 return p == NULL || is_in_permanent(p);
255 }
257 // Returns "TRUE" if "p" is in the committed area of "permanent" data.
258 // If the heap does not use "permanent" data, returns the same
259 // value is_in() would return.
260 virtual bool is_permanent(const void *p) const = 0;
262 bool is_permanent_or_null(const void *p) const {
263 return p == NULL || is_permanent(p);
264 }
266 // An object is scavengable if its location may move during a scavenge.
267 // (A scavenge is a GC which is not a full GC.)
268 // Currently, this just means it is not perm (and not null).
269 // This could change if we rethink what's in perm-gen.
270 bool is_scavengable(const void *p) const {
271 return !is_in_permanent_or_null(p);
272 }
274 // Returns "TRUE" if "p" is a method oop in the
275 // current heap, with high probability. This predicate
276 // is not stable, in general.
277 bool is_valid_method(oop p) const;
279 void set_gc_cause(GCCause::Cause v) {
280 if (UsePerfData) {
281 _gc_lastcause = _gc_cause;
282 _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause));
283 _perf_gc_cause->set_value(GCCause::to_string(v));
284 }
285 _gc_cause = v;
286 }
287 GCCause::Cause gc_cause() { return _gc_cause; }
289 // Preload classes into the shared portion of the heap, and then dump
290 // that data to a file so that it can be loaded directly by another
291 // VM (then terminate).
292 virtual void preload_and_dump(TRAPS) { ShouldNotReachHere(); }
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 large_typearray_allocate(KlassHandle klass, int size, int length, TRAPS);
299 // Special obj/array allocation facilities.
300 // Some heaps may want to manage "permanent" data uniquely. These default
301 // to the general routines if the heap does not support such handling.
302 inline static oop permanent_obj_allocate(KlassHandle klass, int size, TRAPS);
303 // permanent_obj_allocate_no_klass_install() does not do the installation of
304 // the klass pointer in the newly created object (as permanent_obj_allocate()
305 // above does). This allows for a delay in the installation of the klass
306 // pointer that is needed during the create of klassKlass's. The
307 // method post_allocation_install_obj_klass() is used to install the
308 // klass pointer.
309 inline static oop permanent_obj_allocate_no_klass_install(KlassHandle klass,
310 int size,
311 TRAPS);
312 inline static void post_allocation_install_obj_klass(KlassHandle klass,
313 oop obj,
314 int size);
315 inline static oop permanent_array_allocate(KlassHandle klass, int size, int length, TRAPS);
317 // Raw memory allocation facilities
318 // The obj and array allocate methods are covers for these methods.
319 // The permanent allocation method should default to mem_allocate if
320 // permanent memory isn't supported.
321 virtual HeapWord* mem_allocate(size_t size,
322 bool is_noref,
323 bool is_tlab,
324 bool* gc_overhead_limit_was_exceeded) = 0;
325 virtual HeapWord* permanent_mem_allocate(size_t size) = 0;
327 // The boundary between a "large" and "small" array of primitives, in words.
328 virtual size_t large_typearray_limit() = 0;
330 // Utilities for turning raw memory into filler objects.
331 //
332 // min_fill_size() is the smallest region that can be filled.
333 // fill_with_objects() can fill arbitrary-sized regions of the heap using
334 // multiple objects. fill_with_object() is for regions known to be smaller
335 // than the largest array of integers; it uses a single object to fill the
336 // region and has slightly less overhead.
337 static size_t min_fill_size() {
338 return size_t(align_object_size(oopDesc::header_size()));
339 }
341 static void fill_with_objects(HeapWord* start, size_t words, bool zap = true);
343 static void fill_with_object(HeapWord* start, size_t words, bool zap = true);
344 static void fill_with_object(MemRegion region, bool zap = true) {
345 fill_with_object(region.start(), region.word_size(), zap);
346 }
347 static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) {
348 fill_with_object(start, pointer_delta(end, start), zap);
349 }
351 // Some heaps may offer a contiguous region for shared non-blocking
352 // allocation, via inlined code (by exporting the address of the top and
353 // end fields defining the extent of the contiguous allocation region.)
355 // This function returns "true" iff the heap supports this kind of
356 // allocation. (Default is "no".)
357 virtual bool supports_inline_contig_alloc() const {
358 return false;
359 }
360 // These functions return the addresses of the fields that define the
361 // boundaries of the contiguous allocation area. (These fields should be
362 // physically near to one another.)
363 virtual HeapWord** top_addr() const {
364 guarantee(false, "inline contiguous allocation not supported");
365 return NULL;
366 }
367 virtual HeapWord** end_addr() const {
368 guarantee(false, "inline contiguous allocation not supported");
369 return NULL;
370 }
372 // Some heaps may be in an unparseable state at certain times between
373 // collections. This may be necessary for efficient implementation of
374 // certain allocation-related activities. Calling this function before
375 // attempting to parse a heap ensures that the heap is in a parsable
376 // state (provided other concurrent activity does not introduce
377 // unparsability). It is normally expected, therefore, that this
378 // method is invoked with the world stopped.
379 // NOTE: if you override this method, make sure you call
380 // super::ensure_parsability so that the non-generational
381 // part of the work gets done. See implementation of
382 // CollectedHeap::ensure_parsability and, for instance,
383 // that of GenCollectedHeap::ensure_parsability().
384 // The argument "retire_tlabs" controls whether existing TLABs
385 // are merely filled or also retired, thus preventing further
386 // allocation from them and necessitating allocation of new TLABs.
387 virtual void ensure_parsability(bool retire_tlabs);
389 // Return an estimate of the maximum allocation that could be performed
390 // without triggering any collection or expansion activity. In a
391 // generational collector, for example, this is probably the largest
392 // allocation that could be supported (without expansion) in the youngest
393 // generation. It is "unsafe" because no locks are taken; the result
394 // should be treated as an approximation, not a guarantee, for use in
395 // heuristic resizing decisions.
396 virtual size_t unsafe_max_alloc() = 0;
398 // Section on thread-local allocation buffers (TLABs)
399 // If the heap supports thread-local allocation buffers, it should override
400 // the following methods:
401 // Returns "true" iff the heap supports thread-local allocation buffers.
402 // The default is "no".
403 virtual bool supports_tlab_allocation() const {
404 return false;
405 }
406 // The amount of space available for thread-local allocation buffers.
407 virtual size_t tlab_capacity(Thread *thr) const {
408 guarantee(false, "thread-local allocation buffers not supported");
409 return 0;
410 }
411 // An estimate of the maximum allocation that could be performed
412 // for thread-local allocation buffers without triggering any
413 // collection or expansion activity.
414 virtual size_t unsafe_max_tlab_alloc(Thread *thr) const {
415 guarantee(false, "thread-local allocation buffers not supported");
416 return 0;
417 }
419 // Can a compiler initialize a new object without store barriers?
420 // This permission only extends from the creation of a new object
421 // via a TLAB up to the first subsequent safepoint. If such permission
422 // is granted for this heap type, the compiler promises to call
423 // defer_store_barrier() below on any slow path allocation of
424 // a new object for which such initializing store barriers will
425 // have been elided.
426 virtual bool can_elide_tlab_store_barriers() const = 0;
428 // If a compiler is eliding store barriers for TLAB-allocated objects,
429 // there is probably a corresponding slow path which can produce
430 // an object allocated anywhere. The compiler's runtime support
431 // promises to call this function on such a slow-path-allocated
432 // object before performing initializations that have elided
433 // store barriers. Returns new_obj, or maybe a safer copy thereof.
434 virtual oop defer_store_barrier(JavaThread* thread, oop new_obj);
436 // Answers whether an initializing store to a new object currently
437 // allocated at the given address doesn't need a (deferred) store
438 // barrier. Returns "true" if it doesn't need an initializing
439 // store barrier; answers "false" if it does.
440 virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0;
442 // If the CollectedHeap was asked to defer a store barrier above,
443 // this informs it to flush such a deferred store barrier to the
444 // remembered set.
445 virtual void flush_deferred_store_barrier(JavaThread* thread);
447 // Can a compiler elide a store barrier when it writes
448 // a permanent oop into the heap? Applies when the compiler
449 // is storing x to the heap, where x->is_perm() is true.
450 virtual bool can_elide_permanent_oop_store_barriers() const = 0;
452 // Does this heap support heap inspection (+PrintClassHistogram?)
453 virtual bool supports_heap_inspection() const = 0;
455 // Perform a collection of the heap; intended for use in implementing
456 // "System.gc". This probably implies as full a collection as the
457 // "CollectedHeap" supports.
458 virtual void collect(GCCause::Cause cause) = 0;
460 // This interface assumes that it's being called by the
461 // vm thread. It collects the heap assuming that the
462 // heap lock is already held and that we are executing in
463 // the context of the vm thread.
464 virtual void collect_as_vm_thread(GCCause::Cause cause) = 0;
466 // Returns the barrier set for this heap
467 BarrierSet* barrier_set() { return _barrier_set; }
469 // Returns "true" iff there is a stop-world GC in progress. (I assume
470 // that it should answer "false" for the concurrent part of a concurrent
471 // collector -- dld).
472 bool is_gc_active() const { return _is_gc_active; }
474 // Total number of GC collections (started)
475 unsigned int total_collections() const { return _total_collections; }
476 unsigned int total_full_collections() const { return _total_full_collections;}
478 // Increment total number of GC collections (started)
479 // Should be protected but used by PSMarkSweep - cleanup for 1.4.2
480 void increment_total_collections(bool full = false) {
481 _total_collections++;
482 if (full) {
483 increment_total_full_collections();
484 }
485 }
487 void increment_total_full_collections() { _total_full_collections++; }
489 // Return the AdaptiveSizePolicy for the heap.
490 virtual AdaptiveSizePolicy* size_policy() = 0;
492 // Iterate over all the ref-containing fields of all objects, calling
493 // "cl.do_oop" on each. This includes objects in permanent memory.
494 virtual void oop_iterate(OopClosure* cl) = 0;
496 // Iterate over all objects, calling "cl.do_object" on each.
497 // This includes objects in permanent memory.
498 virtual void object_iterate(ObjectClosure* cl) = 0;
500 // Similar to object_iterate() except iterates only
501 // over live objects.
502 virtual void safe_object_iterate(ObjectClosure* cl) = 0;
504 // Behaves the same as oop_iterate, except only traverses
505 // interior pointers contained in permanent memory. If there
506 // is no permanent memory, does nothing.
507 virtual void permanent_oop_iterate(OopClosure* cl) = 0;
509 // Behaves the same as object_iterate, except only traverses
510 // object contained in permanent memory. If there is no
511 // permanent memory, does nothing.
512 virtual void permanent_object_iterate(ObjectClosure* cl) = 0;
514 // NOTE! There is no requirement that a collector implement these
515 // functions.
516 //
517 // A CollectedHeap is divided into a dense sequence of "blocks"; that is,
518 // each address in the (reserved) heap is a member of exactly
519 // one block. The defining characteristic of a block is that it is
520 // possible to find its size, and thus to progress forward to the next
521 // block. (Blocks may be of different sizes.) Thus, blocks may
522 // represent Java objects, or they might be free blocks in a
523 // free-list-based heap (or subheap), as long as the two kinds are
524 // distinguishable and the size of each is determinable.
526 // Returns the address of the start of the "block" that contains the
527 // address "addr". We say "blocks" instead of "object" since some heaps
528 // may not pack objects densely; a chunk may either be an object or a
529 // non-object.
530 virtual HeapWord* block_start(const void* addr) const = 0;
532 // Requires "addr" to be the start of a chunk, and returns its size.
533 // "addr + size" is required to be the start of a new chunk, or the end
534 // of the active area of the heap.
535 virtual size_t block_size(const HeapWord* addr) const = 0;
537 // Requires "addr" to be the start of a block, and returns "TRUE" iff
538 // the block is an object.
539 virtual bool block_is_obj(const HeapWord* addr) const = 0;
541 // Returns the longest time (in ms) that has elapsed since the last
542 // time that any part of the heap was examined by a garbage collection.
543 virtual jlong millis_since_last_gc() = 0;
545 // Perform any cleanup actions necessary before allowing a verification.
546 virtual void prepare_for_verify() = 0;
548 // Generate any dumps preceding or following a full gc
549 void pre_full_gc_dump();
550 void post_full_gc_dump();
552 virtual void print() const = 0;
553 virtual void print_on(outputStream* st) const = 0;
555 // Print all GC threads (other than the VM thread)
556 // used by this heap.
557 virtual void print_gc_threads_on(outputStream* st) const = 0;
558 void print_gc_threads() { print_gc_threads_on(tty); }
559 // Iterator for all GC threads (other than VM thread)
560 virtual void gc_threads_do(ThreadClosure* tc) const = 0;
562 // Print any relevant tracing info that flags imply.
563 // Default implementation does nothing.
564 virtual void print_tracing_info() const = 0;
566 // Heap verification
567 virtual void verify(bool allow_dirty, bool silent, bool option) = 0;
569 // Non product verification and debugging.
570 #ifndef PRODUCT
571 // Support for PromotionFailureALot. Return true if it's time to cause a
572 // promotion failure. The no-argument version uses
573 // this->_promotion_failure_alot_count as the counter.
574 inline bool promotion_should_fail(volatile size_t* count);
575 inline bool promotion_should_fail();
577 // Reset the PromotionFailureALot counters. Should be called at the end of a
578 // GC in which promotion failure ocurred.
579 inline void reset_promotion_should_fail(volatile size_t* count);
580 inline void reset_promotion_should_fail();
581 #endif // #ifndef PRODUCT
583 #ifdef ASSERT
584 static int fired_fake_oom() {
585 return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt);
586 }
587 #endif
588 };
590 // Class to set and reset the GC cause for a CollectedHeap.
592 class GCCauseSetter : StackObj {
593 CollectedHeap* _heap;
594 GCCause::Cause _previous_cause;
595 public:
596 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) {
597 assert(SafepointSynchronize::is_at_safepoint(),
598 "This method manipulates heap state without locking");
599 _heap = heap;
600 _previous_cause = _heap->gc_cause();
601 _heap->set_gc_cause(cause);
602 }
604 ~GCCauseSetter() {
605 assert(SafepointSynchronize::is_at_safepoint(),
606 "This method manipulates heap state without locking");
607 _heap->set_gc_cause(_previous_cause);
608 }
609 };