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.
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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
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23 */
24
25 #ifndef SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP
26 #define SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP
27
28 #include "gc_interface/gcCause.hpp"
29 #include "gc_implementation/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 // SharedHeap
79 // GenCollectedHeap
80 // G1CollectedHeap
81 // ParallelScavengeHeap
82 //
83 class CollectedHeap : public CHeapObj<mtInternal> {
84 friend class VMStructs;
85 friend class IsGCActiveMark; // Block structured external access to _is_gc_active
86
87 private:
88 #ifdef ASSERT
89 static int _fire_out_of_memory_count;
90 #endif
91
92 // Used for filler objects (static, but initialized in ctor).
93 static size_t _filler_array_max_size;
94
95 GCHeapLog* _gc_heap_log;
96
97 // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2 is being used
98 bool _defer_initial_card_mark;
99
100 MemRegion _reserved;
101
102 protected:
103 BarrierSet* _barrier_set;
104 bool _is_gc_active;
105 uint _n_par_threads;
106
107 unsigned int _total_collections; // ... started
108 unsigned int _total_full_collections; // ... started
109 NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;)
110 NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;)
111
112 // Reason for current garbage collection. Should be set to
113 // a value reflecting no collection between collections.
114 GCCause::Cause _gc_cause;
115 GCCause::Cause _gc_lastcause;
116 PerfStringVariable* _perf_gc_cause;
117 PerfStringVariable* _perf_gc_lastcause;
118
119 // Constructor
120 CollectedHeap();
121
122 // Do common initializations that must follow instance construction,
123 // for example, those needing virtual calls.
124 // This code could perhaps be moved into initialize() but would
125 // be slightly more awkward because we want the latter to be a
126 // pure virtual.
127 void pre_initialize();
128
129 // Create a new tlab. All TLAB allocations must go through this.
130 virtual HeapWord* allocate_new_tlab(size_t size);
131
132 // Accumulate statistics on all tlabs.
133 virtual void accumulate_statistics_all_tlabs();
134
135 // Reinitialize tlabs before resuming mutators.
136 virtual void resize_all_tlabs();
137
138 // Allocate from the current thread's TLAB, with broken-out slow path.
139 inline static HeapWord* allocate_from_tlab(KlassHandle klass, Thread* thread, size_t size);
140 static HeapWord* allocate_from_tlab_slow(KlassHandle klass, Thread* thread, size_t size);
141
142 // Allocate an uninitialized block of the given size, or returns NULL if
143 // this is impossible.
144 inline static HeapWord* common_mem_allocate_noinit(KlassHandle klass, size_t size, TRAPS);
145
146 // Like allocate_init, but the block returned by a successful allocation
147 // is guaranteed initialized to zeros.
148 inline static HeapWord* common_mem_allocate_init(KlassHandle klass, size_t size, TRAPS);
149
150 // Helper functions for (VM) allocation.
151 inline static void post_allocation_setup_common(KlassHandle klass, HeapWord* obj);
152 inline static void post_allocation_setup_no_klass_install(KlassHandle klass,
153 HeapWord* objPtr);
154
155 inline static void post_allocation_setup_obj(KlassHandle klass, HeapWord* obj, int size);
156
157 inline static void post_allocation_setup_array(KlassHandle klass,
158 HeapWord* obj, int length);
159
160 // Clears an allocated object.
161 inline static void init_obj(HeapWord* obj, size_t size);
162
163 // Filler object utilities.
164 static inline size_t filler_array_hdr_size();
165 static inline size_t filler_array_min_size();
166
167 DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);)
168 DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);)
169
170 // Fill with a single array; caller must ensure filler_array_min_size() <=
171 // words <= filler_array_max_size().
172 static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true);
173
174 // Fill with a single object (either an int array or a java.lang.Object).
175 static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true);
176
177 virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer);
178
179 // Verification functions
180 virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size)
181 PRODUCT_RETURN;
182 virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size)
183 PRODUCT_RETURN;
184 debug_only(static void check_for_valid_allocation_state();)
185
186 public:
187 enum Name {
188 Abstract,
189 SharedHeap,
190 GenCollectedHeap,
191 ParallelScavengeHeap,
192 G1CollectedHeap
193 };
194
195 static inline size_t filler_array_max_size() {
196 return _filler_array_max_size;
197 }
198
199 virtual CollectedHeap::Name kind() const { return CollectedHeap::Abstract; }
200
201 /**
202 * Returns JNI error code JNI_ENOMEM if memory could not be allocated,
203 * and JNI_OK on success.
204 */
205 virtual jint initialize() = 0;
206
207 // In many heaps, there will be a need to perform some initialization activities
208 // after the Universe is fully formed, but before general heap allocation is allowed.
209 // This is the correct place to place such initialization methods.
210 virtual void post_initialize() = 0;
211
212 // Stop any onging concurrent work and prepare for exit.
213 virtual void stop() {}
214
215 void initialize_reserved_region(HeapWord *start, HeapWord *end);
216 MemRegion reserved_region() const { return _reserved; }
217 address base() const { return (address)reserved_region().start(); }
218
219 virtual size_t capacity() const = 0;
220 virtual size_t used() const = 0;
221
222 // Return "true" if the part of the heap that allocates Java
223 // objects has reached the maximal committed limit that it can
224 // reach, without a garbage collection.
225 virtual bool is_maximal_no_gc() const = 0;
226
227 // Support for java.lang.Runtime.maxMemory(): return the maximum amount of
228 // memory that the vm could make available for storing 'normal' java objects.
229 // This is based on the reserved address space, but should not include space
230 // that the vm uses internally for bookkeeping or temporary storage
231 // (e.g., in the case of the young gen, one of the survivor
232 // spaces).
233 virtual size_t max_capacity() const = 0;
234
235 // Returns "TRUE" if "p" points into the reserved area of the heap.
236 bool is_in_reserved(const void* p) const {
237 return _reserved.contains(p);
238 }
239
240 bool is_in_reserved_or_null(const void* p) const {
241 return p == NULL || is_in_reserved(p);
242 }
243
244 // Returns "TRUE" iff "p" points into the committed areas of the heap.
245 // Since this method can be expensive in general, we restrict its
246 // use to assertion checking only.
247 virtual bool is_in(const void* p) const = 0;
248
249 bool is_in_or_null(const void* p) const {
250 return p == NULL || is_in(p);
251 }
252
253 bool is_in_place(Metadata** p) {
254 return !Universe::heap()->is_in(p);
255 }
256 bool is_in_place(oop* p) { return Universe::heap()->is_in(p); }
257 bool is_in_place(narrowOop* p) {
258 oop o = oopDesc::load_decode_heap_oop_not_null(p);
259 return Universe::heap()->is_in((const void*)o);
260 }
261
262 // Let's define some terms: a "closed" subset of a heap is one that
263 //
264 // 1) contains all currently-allocated objects, and
265 //
266 // 2) is closed under reference: no object in the closed subset
267 // references one outside the closed subset.
268 //
269 // Membership in a heap's closed subset is useful for assertions.
270 // Clearly, the entire heap is a closed subset, so the default
271 // implementation is to use "is_in_reserved". But this may not be too
272 // liberal to perform useful checking. Also, the "is_in" predicate
273 // defines a closed subset, but may be too expensive, since "is_in"
274 // verifies that its argument points to an object head. The
275 // "closed_subset" method allows a heap to define an intermediate
276 // predicate, allowing more precise checking than "is_in_reserved" at
277 // lower cost than "is_in."
278
279 // One important case is a heap composed of disjoint contiguous spaces,
280 // such as the Garbage-First collector. Such heaps have a convenient
281 // closed subset consisting of the allocated portions of those
282 // contiguous spaces.
283
284 // Return "TRUE" iff the given pointer points into the heap's defined
285 // closed subset (which defaults to the entire heap).
286 virtual bool is_in_closed_subset(const void* p) const {
287 return is_in_reserved(p);
288 }
289
290 bool is_in_closed_subset_or_null(const void* p) const {
291 return p == NULL || is_in_closed_subset(p);
292 }
293
294 // An object is scavengable if its location may move during a scavenge.
295 // (A scavenge is a GC which is not a full GC.)
296 virtual bool is_scavengable(const void *p) = 0;
297
298 void set_gc_cause(GCCause::Cause v) {
299 if (UsePerfData) {
300 _gc_lastcause = _gc_cause;
301 _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause));
302 _perf_gc_cause->set_value(GCCause::to_string(v));
303 }
304 _gc_cause = v;
305 }
306 GCCause::Cause gc_cause() { return _gc_cause; }
307
308 // Number of threads currently working on GC tasks.
309 uint n_par_threads() { return _n_par_threads; }
310
311 // May be overridden to set additional parallelism.
312 virtual void set_par_threads(uint t) { _n_par_threads = t; };
313
314 // General obj/array allocation facilities.
315 inline static oop obj_allocate(KlassHandle klass, int size, TRAPS);
316 inline static oop array_allocate(KlassHandle klass, int size, int length, TRAPS);
317 inline static oop array_allocate_nozero(KlassHandle klass, int size, int length, TRAPS);
318
319 inline static void post_allocation_install_obj_klass(KlassHandle klass,
320 oop obj);
321
322 // Raw memory allocation facilities
323 // The obj and array allocate methods are covers for these methods.
324 // mem_allocate() should never be
325 // called to allocate TLABs, only individual objects.
326 virtual HeapWord* mem_allocate(size_t size,
327 bool* gc_overhead_limit_was_exceeded) = 0;
328
329 // Utilities for turning raw memory into filler objects.
330 //
331 // min_fill_size() is the smallest region that can be filled.
332 // fill_with_objects() can fill arbitrary-sized regions of the heap using
333 // multiple objects. fill_with_object() is for regions known to be smaller
334 // than the largest array of integers; it uses a single object to fill the
335 // region and has slightly less overhead.
336 static size_t min_fill_size() {
337 return size_t(align_object_size(oopDesc::header_size()));
338 }
339
340 static void fill_with_objects(HeapWord* start, size_t words, bool zap = true);
341
342 static void fill_with_object(HeapWord* start, size_t words, bool zap = true);
343 static void fill_with_object(MemRegion region, bool zap = true) {
344 fill_with_object(region.start(), region.word_size(), zap);
345 }
346 static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) {
347 fill_with_object(start, pointer_delta(end, start), zap);
348 }
349
350 // Return the address "addr" aligned by "alignment_in_bytes" if such
351 // an address is below "end". Return NULL otherwise.
352 inline static HeapWord* align_allocation_or_fail(HeapWord* addr,
353 HeapWord* end,
354 unsigned short alignment_in_bytes);
355
356 // Some heaps may offer a contiguous region for shared non-blocking
357 // allocation, via inlined code (by exporting the address of the top and
358 // end fields defining the extent of the contiguous allocation region.)
359
360 // This function returns "true" iff the heap supports this kind of
361 // allocation. (Default is "no".)
362 virtual bool supports_inline_contig_alloc() const {
363 return false;
364 }
365 // These functions return the addresses of the fields that define the
366 // boundaries of the contiguous allocation area. (These fields should be
367 // physically near to one another.)
368 virtual HeapWord** top_addr() const {
369 guarantee(false, "inline contiguous allocation not supported");
370 return NULL;
371 }
372 virtual HeapWord** end_addr() const {
373 guarantee(false, "inline contiguous allocation not supported");
374 return NULL;
375 }
376
377 // Some heaps may be in an unparseable state at certain times between
378 // collections. This may be necessary for efficient implementation of
379 // certain allocation-related activities. Calling this function before
380 // attempting to parse a heap ensures that the heap is in a parsable
381 // state (provided other concurrent activity does not introduce
382 // unparsability). It is normally expected, therefore, that this
383 // method is invoked with the world stopped.
384 // NOTE: if you override this method, make sure you call
385 // super::ensure_parsability so that the non-generational
386 // part of the work gets done. See implementation of
387 // CollectedHeap::ensure_parsability and, for instance,
388 // that of GenCollectedHeap::ensure_parsability().
389 // The argument "retire_tlabs" controls whether existing TLABs
390 // are merely filled or also retired, thus preventing further
391 // allocation from them and necessitating allocation of new TLABs.
392 virtual void ensure_parsability(bool retire_tlabs);
393
394 // Section on thread-local allocation buffers (TLABs)
395 // If the heap supports thread-local allocation buffers, it should override
396 // the following methods:
397 // Returns "true" iff the heap supports thread-local allocation buffers.
398 // The default is "no".
399 virtual bool supports_tlab_allocation() const = 0;
400
401 // The amount of space available for thread-local allocation buffers.
402 virtual size_t tlab_capacity(Thread *thr) const = 0;
403
404 // The amount of used space for thread-local allocation buffers for the given thread.
405 virtual size_t tlab_used(Thread *thr) const = 0;
406
407 virtual size_t max_tlab_size() const;
408
409 // An estimate of the maximum allocation that could be performed
410 // for thread-local allocation buffers without triggering any
411 // collection or expansion activity.
412 virtual size_t unsafe_max_tlab_alloc(Thread *thr) const {
413 guarantee(false, "thread-local allocation buffers not supported");
414 return 0;
415 }
416
417 // Can a compiler initialize a new object without store barriers?
418 // This permission only extends from the creation of a new object
419 // via a TLAB up to the first subsequent safepoint. If such permission
420 // is granted for this heap type, the compiler promises to call
421 // defer_store_barrier() below on any slow path allocation of
422 // a new object for which such initializing store barriers will
423 // have been elided.
424 virtual bool can_elide_tlab_store_barriers() const = 0;
425
426 // If a compiler is eliding store barriers for TLAB-allocated objects,
427 // there is probably a corresponding slow path which can produce
428 // an object allocated anywhere. The compiler's runtime support
429 // promises to call this function on such a slow-path-allocated
430 // object before performing initializations that have elided
431 // store barriers. Returns new_obj, or maybe a safer copy thereof.
432 virtual oop new_store_pre_barrier(JavaThread* thread, oop new_obj);
433
434 // Answers whether an initializing store to a new object currently
435 // allocated at the given address doesn't need a store
436 // barrier. Returns "true" if it doesn't need an initializing
437 // store barrier; answers "false" if it does.
438 virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0;
439
440 // If a compiler is eliding store barriers for TLAB-allocated objects,
441 // we will be informed of a slow-path allocation by a call
442 // to new_store_pre_barrier() above. Such a call precedes the
443 // initialization of the object itself, and no post-store-barriers will
444 // be issued. Some heap types require that the barrier strictly follows
445 // the initializing stores. (This is currently implemented by deferring the
446 // barrier until the next slow-path allocation or gc-related safepoint.)
447 // This interface answers whether a particular heap type needs the card
448 // mark to be thus strictly sequenced after the stores.
449 virtual bool card_mark_must_follow_store() const = 0;
450
451 // If the CollectedHeap was asked to defer a store barrier above,
452 // this informs it to flush such a deferred store barrier to the
453 // remembered set.
454 virtual void flush_deferred_store_barrier(JavaThread* thread);
455
456 // Does this heap support heap inspection (+PrintClassHistogram?)
457 virtual bool supports_heap_inspection() const = 0;
458
459 // Perform a collection of the heap; intended for use in implementing
460 // "System.gc". This probably implies as full a collection as the
461 // "CollectedHeap" supports.
462 virtual void collect(GCCause::Cause cause) = 0;
463
464 // Perform a full collection
465 virtual void do_full_collection(bool clear_all_soft_refs) = 0;
466
467 // This interface assumes that it's being called by the
468 // vm thread. It collects the heap assuming that the
469 // heap lock is already held and that we are executing in
470 // the context of the vm thread.
471 virtual void collect_as_vm_thread(GCCause::Cause cause);
472
473 // Returns the barrier set for this heap
474 BarrierSet* barrier_set() { return _barrier_set; }
475
476 // Returns "true" iff there is a stop-world GC in progress. (I assume
477 // that it should answer "false" for the concurrent part of a concurrent
478 // collector -- dld).
479 bool is_gc_active() const { return _is_gc_active; }
480
481 // Total number of GC collections (started)
482 unsigned int total_collections() const { return _total_collections; }
483 unsigned int total_full_collections() const { return _total_full_collections;}
484
485 // Increment total number of GC collections (started)
486 // Should be protected but used by PSMarkSweep - cleanup for 1.4.2
487 void increment_total_collections(bool full = false) {
488 _total_collections++;
489 if (full) {
490 increment_total_full_collections();
491 }
492 }
493
494 void increment_total_full_collections() { _total_full_collections++; }
495
496 // Return the AdaptiveSizePolicy for the heap.
497 virtual AdaptiveSizePolicy* size_policy() = 0;
498
499 // Return the CollectorPolicy for the heap
500 virtual CollectorPolicy* collector_policy() const = 0;
501
502 void oop_iterate_no_header(OopClosure* cl);
503
504 // Iterate over all the ref-containing fields of all objects, calling
505 // "cl.do_oop" on each.
506 virtual void oop_iterate(ExtendedOopClosure* cl) = 0;
507
508 // Iterate over all objects, calling "cl.do_object" on each.
509 virtual void object_iterate(ObjectClosure* cl) = 0;
510
511 // Similar to object_iterate() except iterates only
512 // over live objects.
513 virtual void safe_object_iterate(ObjectClosure* cl) = 0;
514
515 // NOTE! There is no requirement that a collector implement these
516 // functions.
517 //
518 // A CollectedHeap is divided into a dense sequence of "blocks"; that is,
519 // each address in the (reserved) heap is a member of exactly
520 // one block. The defining characteristic of a block is that it is
521 // possible to find its size, and thus to progress forward to the next
522 // block. (Blocks may be of different sizes.) Thus, blocks may
523 // represent Java objects, or they might be free blocks in a
524 // free-list-based heap (or subheap), as long as the two kinds are
525 // distinguishable and the size of each is determinable.
526
527 // Returns the address of the start of the "block" that contains the
528 // address "addr". We say "blocks" instead of "object" since some heaps
529 // may not pack objects densely; a chunk may either be an object or a
530 // non-object.
531 virtual HeapWord* block_start(const void* addr) const = 0;
532
533 // Requires "addr" to be the start of a chunk, and returns its size.
534 // "addr + size" is required to be the start of a new chunk, or the end
535 // of the active area of the heap.
536 virtual size_t block_size(const HeapWord* addr) const = 0;
537
538 // Requires "addr" to be the start of a block, and returns "TRUE" iff
539 // the block is an object.
540 virtual bool block_is_obj(const HeapWord* addr) const = 0;
541
542 // Returns the longest time (in ms) that has elapsed since the last
543 // time that any part of the heap was examined by a garbage collection.
544 virtual jlong millis_since_last_gc() = 0;
545
546 // Perform any cleanup actions necessary before allowing a verification.
547 virtual void prepare_for_verify() = 0;
548
549 // Generate any dumps preceding or following a full gc
550 void pre_full_gc_dump(GCTimer* timer);
551 void post_full_gc_dump(GCTimer* timer);
552
553 VirtualSpaceSummary create_heap_space_summary();
554 GCHeapSummary create_heap_summary();
555
556 MetaspaceSummary create_metaspace_summary();
557
558 // Print heap information on the given outputStream.
559 virtual void print_on(outputStream* st) const = 0;
560 // The default behavior is to call print_on() on tty.
561 virtual void print() const {
562 print_on(tty);
563 }
564 // Print more detailed heap information on the given
565 // outputStream. The default behavior is to call print_on(). It is
566 // up to each subclass to override it and add any additional output
567 // it needs.
568 virtual void print_extended_on(outputStream* st) const {
569 print_on(st);
570 }
571
572 virtual void print_on_error(outputStream* st) const;
573
574 // Print all GC threads (other than the VM thread)
575 // used by this heap.
576 virtual void print_gc_threads_on(outputStream* st) const = 0;
577 // The default behavior is to call print_gc_threads_on() on tty.
578 void print_gc_threads() {
579 print_gc_threads_on(tty);
580 }
581 // Iterator for all GC threads (other than VM thread)
582 virtual void gc_threads_do(ThreadClosure* tc) const = 0;
583
584 // Print any relevant tracing info that flags imply.
585 // Default implementation does nothing.
586 virtual void print_tracing_info() const = 0;
587
588 void print_heap_before_gc();
589 void print_heap_after_gc();
590
591 // Registering and unregistering an nmethod (compiled code) with the heap.
592 // Override with specific mechanism for each specialized heap type.
593 virtual void register_nmethod(nmethod* nm);
594 virtual void unregister_nmethod(nmethod* nm);
595
596 void trace_heap_before_gc(const GCTracer* gc_tracer);
597 void trace_heap_after_gc(const GCTracer* gc_tracer);
598
599 // Heap verification
600 virtual void verify(bool silent, VerifyOption option) = 0;
601
602 // Non product verification and debugging.
603 #ifndef PRODUCT
604 // Support for PromotionFailureALot. Return true if it's time to cause a
605 // promotion failure. The no-argument version uses
606 // this->_promotion_failure_alot_count as the counter.
607 inline bool promotion_should_fail(volatile size_t* count);
608 inline bool promotion_should_fail();
609
610 // Reset the PromotionFailureALot counters. Should be called at the end of a
611 // GC in which promotion failure occurred.
612 inline void reset_promotion_should_fail(volatile size_t* count);
613 inline void reset_promotion_should_fail();
614 #endif // #ifndef PRODUCT
615
616 #ifdef ASSERT
617 static int fired_fake_oom() {
618 return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt);
619 }
620 #endif
621
622 public:
623 // This is a convenience method that is used in cases where
624 // the actual number of GC worker threads is not pertinent but
625 // only whether there more than 0. Use of this method helps
626 // reduce the occurrence of ParallelGCThreads to uses where the
627 // actual number may be germane.
628 static bool use_parallel_gc_threads() { return ParallelGCThreads > 0; }
629
630 // Copy the current allocation context statistics for the specified contexts.
631 // For each context in contexts, set the corresponding entries in the totals
632 // and accuracy arrays to the current values held by the statistics. Each
633 // array should be of length len.
634 // Returns true if there are more stats available.
635 virtual bool copy_allocation_context_stats(const jint* contexts,
636 jlong* totals,
637 jbyte* accuracy,
638 jint len) {
639 return false;
640 }
641
642 /////////////// Unit tests ///////////////
643
644 NOT_PRODUCT(static void test_is_in();)
645 };
646
647 // Class to set and reset the GC cause for a CollectedHeap.
648
649 class GCCauseSetter : StackObj {
650 CollectedHeap* _heap;
651 GCCause::Cause _previous_cause;
652 public:
653 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) {
654 assert(SafepointSynchronize::is_at_safepoint(),
655 "This method manipulates heap state without locking");
656 _heap = heap;
657 _previous_cause = _heap->gc_cause();
658 _heap->set_gc_cause(cause);
659 }
660
661 ~GCCauseSetter() {
662 assert(SafepointSynchronize::is_at_safepoint(),
663 "This method manipulates heap state without locking");
664 _heap->set_gc_cause(_previous_cause);
665 }
666 };
667
668 #endif // SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP