1 /*
2 * Copyright (c) 2001, 2026, 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
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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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20 * or visit www.oracle.com if you need additional information or have any
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23 */
24
25 #ifndef SHARE_GC_SHARED_COLLECTEDHEAP_HPP
26 #define SHARE_GC_SHARED_COLLECTEDHEAP_HPP
27
28 #include "gc/shared/gcCause.hpp"
29 #include "gc/shared/gcWhen.hpp"
30 #include "gc/shared/verifyOption.hpp"
31 #include "memory/allocation.hpp"
32 #include "memory/metaspace.hpp"
33 #include "memory/universe.hpp"
34 #include "oops/stackChunkOop.hpp"
35 #include "runtime/handles.hpp"
36 #include "runtime/perfDataTypes.hpp"
37 #include "runtime/safepoint.hpp"
38 #include "services/cpuTimeUsage.hpp"
39 #include "services/memoryUsage.hpp"
40 #include "utilities/debug.hpp"
41 #include "utilities/formatBuffer.hpp"
42 #include "utilities/growableArray.hpp"
43
44 // A "CollectedHeap" is an implementation of a java heap for HotSpot. This
45 // is an abstract class: there may be many different kinds of heaps. This
46 // class defines the functions that a heap must implement, and contains
47 // infrastructure common to all heaps.
48
49 class GCHeapLog;
50 class GCHeapSummary;
51 class GCMemoryManager;
52 class GCMetaspaceLog;
53 class GCTimer;
54 class GCTracer;
55 class MemoryPool;
56 class MetaspaceSummary;
57 class ReservedHeapSpace;
58 class Thread;
59 class ThreadClosure;
60 class VirtualSpaceSummary;
61 class WorkerThreads;
62 class nmethod;
63
64 class ParallelObjectIteratorImpl : public CHeapObj<mtGC> {
65 public:
66 virtual ~ParallelObjectIteratorImpl() {}
67 virtual void object_iterate(ObjectClosure* cl, uint worker_id) = 0;
68 };
69
70 // User facing parallel object iterator. This is a StackObj, which ensures that
71 // the _impl is allocated and deleted in the scope of this object. This ensures
72 // the life cycle of the implementation is as required by ThreadsListHandle,
73 // which is sometimes used by the root iterators.
74 class ParallelObjectIterator : public StackObj {
75 ParallelObjectIteratorImpl* _impl;
76
77 public:
78 ParallelObjectIterator(uint thread_num);
79 ~ParallelObjectIterator();
80 void object_iterate(ObjectClosure* cl, uint worker_id);
81 };
82
83 //
84 // CollectedHeap
85 // SerialHeap
86 // G1CollectedHeap
87 // ParallelScavengeHeap
88 // ShenandoahHeap
89 // ZCollectedHeap
90 //
91 class CollectedHeap : public CHeapObj<mtGC> {
92 friend class CPUTimeUsage::GC;
93 friend class VMStructs;
94 friend class JVMCIVMStructs;
95 friend class IsSTWGCActiveMark; // Block structured external access to _is_stw_gc_active
96 friend class MemAllocator;
97
98 private:
99 static bool _is_shutting_down;
100
101 GCHeapLog* _heap_log;
102 GCMetaspaceLog* _metaspace_log;
103
104 // Historic gc information
105 size_t _capacity_at_last_gc;
106 size_t _used_at_last_gc;
107
108 // First, set it to java_lang_Object.
109 // Then, set it to FillerObject after the FillerObject_klass loading is complete.
110 static Klass* _filler_object_klass;
111
112 protected:
113 // Not used by all GCs
114 MemRegion _reserved;
115
116 bool _is_stw_gc_active;
117
118 // (Minimum) Alignment reserve for TLABs and PLABs.
119 static size_t _lab_alignment_reserve;
120 // Used for filler objects (static, but initialized in ctor).
121 static size_t _filler_array_max_size;
122
123 static size_t _stack_chunk_max_size; // 0 for no limit
124
125 // Last time the whole heap has been examined in support of RMI
126 // MaxObjectInspectionAge.
127 // This timestamp must be monotonically non-decreasing to avoid
128 // time-warp warnings.
129 jlong _last_whole_heap_examined_time_ns;
130
131 unsigned int _total_collections; // ... started
132 unsigned int _total_full_collections; // ... started
133 NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;)
134 NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;)
135
136 jlong _vmthread_cpu_time;
137
138 // Reason for current garbage collection. Should be set to
139 // a value reflecting no collection between collections.
140 GCCause::Cause _gc_cause;
141 GCCause::Cause _gc_lastcause;
142 PerfStringVariable* _perf_gc_cause;
143 PerfStringVariable* _perf_gc_lastcause;
144
145 // Constructor
146 CollectedHeap();
147
148 // Create a new tlab. All TLAB allocations must go through this.
149 // To allow more flexible TLAB allocations min_size specifies
150 // the minimum size needed, while requested_size is the requested
151 // size based on ergonomics. The actually allocated size will be
152 // returned in actual_size.
153 virtual HeapWord* allocate_new_tlab(size_t min_size,
154 size_t requested_size,
155 size_t* actual_size) = 0;
156
157 // Reinitialize tlabs before resuming mutators.
158 virtual void resize_all_tlabs();
159
160 // Raw memory allocation facilities
161 // The obj and array allocate methods are covers for these methods.
162 // mem_allocate() should never be
163 // called to allocate TLABs, only individual objects.
164 virtual HeapWord* mem_allocate(size_t size) = 0;
165
166 // Filler object utilities.
167 static inline size_t filler_array_hdr_size();
168
169 static size_t filler_array_min_size();
170
171 protected:
172 static inline void zap_filler_array_with(HeapWord* start, size_t words, juint value);
173 DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);)
174
175 // Fill with a single array; caller must ensure filler_array_min_size() <=
176 // words <= filler_array_max_size().
177 static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true);
178
179 // Fill with a single object (either an int array or a java.lang.Object).
180 static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true);
181
182 virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer);
183
184 // Verification functions
185 DEBUG_ONLY(static void check_for_valid_allocation_state();)
186
187 public:
188 enum Name {
189 None,
190 Serial,
191 Parallel,
192 G1,
193 Epsilon,
194 Z,
195 Shenandoah
196 };
197
198 protected:
199 // Get a pointer to the derived heap object. Used to implement
200 // derived class heap() functions rather than being called directly.
201 template<typename T>
202 static T* named_heap(Name kind) {
203 CollectedHeap* heap = Universe::heap();
204 assert(heap != nullptr, "Uninitialized heap");
205 assert(kind == heap->kind(), "Heap kind %u should be %u",
206 static_cast<uint>(heap->kind()), static_cast<uint>(kind));
207 return static_cast<T*>(heap);
208 }
209
210 // Print any relevant tracing info that flags imply.
211 // Default implementation does nothing.
212 virtual void print_tracing_info() const = 0;
213
214 public:
215 // Stop any onging concurrent work and prepare for exit.
216 virtual void stop() = 0;
217
218 static inline size_t filler_array_max_size() {
219 return _filler_array_max_size;
220 }
221
222 static inline size_t stack_chunk_max_size() {
223 return _stack_chunk_max_size;
224 }
225
226 static inline Klass* filler_object_klass() {
227 return _filler_object_klass;
228 }
229
230 static inline void set_filler_object_klass(Klass* k) {
231 _filler_object_klass = k;
232 }
233
234 virtual Name kind() const = 0;
235
236 virtual const char* name() const = 0;
237
238 /**
239 * Returns JNI error code JNI_ENOMEM if memory could not be allocated,
240 * and JNI_OK on success.
241 */
242 virtual jint initialize() = 0;
243
244 // Initialize serviceability support. This should prepare the implementation
245 // for accepting serviceability-related calls, like memory_managers(), memory_pools().
246 virtual void initialize_serviceability() = 0;
247
248 // In many heaps, there will be a need to perform some initialization activities
249 // after the Universe is fully formed, but before general heap allocation is allowed.
250 // This is the correct place to place such initialization methods.
251 virtual void post_initialize();
252
253 static bool is_shutting_down();
254
255 void initiate_shutdown();
256
257 // Stop and resume concurrent GC threads interfering with safepoint operations
258 virtual void safepoint_synchronize_begin() {}
259 virtual void safepoint_synchronize_end() {}
260
261 void add_vmthread_cpu_time(jlong time);
262
263 void initialize_reserved_region(const ReservedHeapSpace& rs);
264
265 virtual size_t capacity() const = 0;
266 virtual size_t used() const = 0;
267
268 // Returns unused capacity.
269 virtual size_t unused() const;
270
271 // Historic gc information
272 size_t free_at_last_gc() const { return _capacity_at_last_gc - _used_at_last_gc; }
273 size_t used_at_last_gc() const { return _used_at_last_gc; }
274 void update_capacity_and_used_at_gc();
275
276 // Support for java.lang.Runtime.maxMemory(): return the maximum amount of
277 // memory that the vm could make available for storing 'normal' java objects.
278 // This is based on the reserved address space, but should not include space
279 // that the vm uses internally for bookkeeping or temporary storage
280 // (e.g., in the case of the young gen, one of the survivor
281 // spaces).
282 virtual size_t max_capacity() const = 0;
283
284 // Returns "TRUE" iff "p" points into the committed areas of the heap.
285 // This method can be expensive so avoid using it in performance critical
286 // code.
287 virtual bool is_in(const void* p) const = 0;
288
289 DEBUG_ONLY(bool is_in_or_null(const void* p) const { return p == nullptr || is_in(p); })
290
291 void set_gc_cause(GCCause::Cause v);
292 GCCause::Cause gc_cause() const { return _gc_cause; }
293
294 oop obj_allocate(Klass* klass, size_t size, TRAPS);
295 virtual oop array_allocate(Klass* klass, size_t size, int length, bool do_zero, TRAPS);
296 oop class_allocate(Klass* klass, size_t size, size_t base_size, TRAPS);
297
298 // Utilities for turning raw memory into filler objects.
299 //
300 // min_fill_size() is the smallest region that can be filled.
301 // fill_with_objects() can fill arbitrary-sized regions of the heap using
302 // multiple objects. fill_with_object() is for regions known to be smaller
303 // than the largest array of integers; it uses a single object to fill the
304 // region and has slightly less overhead.
305 static size_t min_fill_size() {
306 return size_t(align_object_size(oopDesc::header_size()));
307 }
308
309 static void fill_with_objects(HeapWord* start, size_t words, bool zap = true);
310
311 static void fill_with_object(HeapWord* start, size_t words, bool zap = true);
312 static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) {
313 fill_with_object(start, pointer_delta(end, start), zap);
314 }
315
316 inline static bool is_filler_object(oop obj);
317
318 virtual void fill_with_dummy_object(HeapWord* start, HeapWord* end, bool zap);
319 static size_t min_dummy_object_size() {
320 return oopDesc::header_size();
321 }
322
323 static size_t lab_alignment_reserve() {
324 assert(_lab_alignment_reserve != SIZE_MAX, "uninitialized");
325 return _lab_alignment_reserve;
326 }
327
328 // Some heaps may be in an unparseable state at certain times between
329 // collections. This may be necessary for efficient implementation of
330 // certain allocation-related activities. Calling this function before
331 // attempting to parse a heap ensures that the heap is in a parsable
332 // state (provided other concurrent activity does not introduce
333 // unparsability). It is normally expected, therefore, that this
334 // method is invoked with the world stopped.
335 // NOTE: if you override this method, make sure you call
336 // super::ensure_parsability so that the non-generational
337 // part of the work gets done. See implementation of
338 // CollectedHeap::ensure_parsability and, for instance,
339 // that of ParallelScavengeHeap::ensure_parsability().
340 // The argument "retire_tlabs" controls whether existing TLABs
341 // are merely filled or also retired, thus preventing further
342 // allocation from them and necessitating allocation of new TLABs.
343 virtual void ensure_parsability(bool retire_tlabs);
344
345 // The amount of space available for thread-local allocation buffers.
346 virtual size_t tlab_capacity() const = 0;
347
348 // The amount of space used for thread-local allocation buffers.
349 virtual size_t tlab_used() const = 0;
350
351 virtual size_t max_tlab_size() const;
352
353 // An estimate of the maximum allocation that could be performed
354 // for thread-local allocation buffers without triggering any
355 // collection or expansion activity.
356 virtual size_t unsafe_max_tlab_alloc() const = 0;
357
358 // Perform a collection of the heap of a type depending on the given cause.
359 virtual void collect(GCCause::Cause cause) = 0;
360
361 // Perform a full collection
362 virtual void do_full_collection(bool clear_all_soft_refs) = 0;
363
364 // This interface assumes that it's being called by the
365 // vm thread. It collects the heap assuming that the
366 // heap lock is already held and that we are executing in
367 // the context of the vm thread.
368 virtual void collect_as_vm_thread(GCCause::Cause cause);
369
370 virtual MetaWord* satisfy_failed_metadata_allocation(ClassLoaderData* loader_data,
371 size_t size,
372 Metaspace::MetadataType mdtype);
373
374 // Return true, if accesses to the object would require barriers.
375 // This is used by continuations to copy chunks of a thread stack into StackChunk object or out of a StackChunk
376 // object back into the thread stack. These chunks may contain references to objects. It is crucial that
377 // the GC does not attempt to traverse the object while we modify it, because its structure (oopmap) is changed
378 // when stack chunks are stored into it.
379 // StackChunk objects may be reused, the GC must not assume that a StackChunk object is always a freshly
380 // allocated object.
381 virtual bool requires_barriers(stackChunkOop obj) const = 0;
382
383 // Returns "true" iff there is a stop-world GC in progress.
384 bool is_stw_gc_active() const { return _is_stw_gc_active; }
385
386 // Total number of GC collections (started)
387 unsigned int total_collections() const { return _total_collections; }
388 unsigned int total_full_collections() const { return _total_full_collections;}
389
390 // Increment total number of GC collections (started)
391 void increment_total_collections(bool full = false) {
392 _total_collections++;
393 if (full) {
394 _total_full_collections++;
395 }
396 }
397
398 virtual MemoryUsage memory_usage();
399 virtual GrowableArray<GCMemoryManager*> memory_managers() = 0;
400 virtual GrowableArray<MemoryPool*> memory_pools() = 0;
401
402 // Iterate over all objects, calling "cl.do_object" on each.
403 virtual void object_iterate(ObjectClosure* cl) = 0;
404
405 virtual ParallelObjectIteratorImpl* parallel_object_iterator(uint thread_num) {
406 return nullptr;
407 }
408
409 // Keep alive an object that was loaded with AS_NO_KEEPALIVE.
410 virtual void keep_alive(oop obj) {}
411
412 // Perform any cleanup actions necessary before allowing a verification.
413 virtual void prepare_for_verify() = 0;
414
415 // Returns the longest time (in ms) that has elapsed since the last
416 // time that the whole heap has been examined by a garbage collection.
417 jlong millis_since_last_whole_heap_examined();
418 // GC should call this when the next whole heap analysis has completed to
419 // satisfy above requirement.
420 void record_whole_heap_examined_timestamp();
421
422 private:
423 // Generate any dumps preceding or following a full gc
424 void full_gc_dump(GCTimer* timer, bool before);
425
426 void print_relative_to_gc(GCWhen::Type when) const;
427
428 public:
429 void pre_full_gc_dump(GCTimer* timer);
430 void post_full_gc_dump(GCTimer* timer);
431
432 virtual VirtualSpaceSummary create_heap_space_summary();
433 GCHeapSummary create_heap_summary();
434
435 MetaspaceSummary create_metaspace_summary();
436
437 // GCs are free to represent the bit representation for null differently in memory,
438 // which is typically not observable when using the Access API. However, if for
439 // some reason a context doesn't allow using the Access API, then this function
440 // explicitly checks if the given memory location contains a null value.
441 virtual bool contains_null(const oop* p) const;
442
443 void print_invocation_on(outputStream* st, const char* type, GCWhen::Type when) const;
444
445 // Print heap information.
446 virtual void print_heap_on(outputStream* st) const = 0;
447
448 // Print additional information about the GC that is not included in print_heap_on().
449 virtual void print_gc_on(outputStream* st) const = 0;
450
451 // The default behavior is to call print_heap_on() and print_gc_on() on tty.
452 virtual void print() const;
453
454 // Used to print information about locations in the hs_err file.
455 virtual bool print_location(outputStream* st, void* addr) const = 0;
456
457 // Iterator for all GC threads (other than VM thread)
458 virtual void gc_threads_do(ThreadClosure* tc) const = 0;
459
460 void print_before_gc() const;
461 void print_after_gc() const;
462
463 // Registering and unregistering an nmethod (compiled code) with the heap.
464 virtual void register_nmethod(nmethod* nm) = 0;
465 virtual void unregister_nmethod(nmethod* nm) = 0;
466 virtual void verify_nmethod(nmethod* nm) = 0;
467
468 void trace_heap_before_gc(const GCTracer* gc_tracer);
469 void trace_heap_after_gc(const GCTracer* gc_tracer);
470
471 // Heap verification
472 virtual void verify(VerifyOption option) = 0;
473
474 // Return true if concurrent gc control via WhiteBox is supported by
475 // this collector. The default implementation returns false.
476 virtual bool supports_concurrent_gc_breakpoints() const;
477
478 // Workers used in non-GC safepoints for parallel safepoint cleanup. If this
479 // method returns null, cleanup tasks are done serially in the VMThread. See
480 // `SafepointSynchronize::do_cleanup_tasks` for details.
481 // GCs using a GC worker thread pool inside GC safepoints may opt to share
482 // that pool with non-GC safepoints, avoiding creating extraneous threads.
483 // Such sharing is safe, because GC safepoints and non-GC safepoints never
484 // overlap. For example, `G1CollectedHeap::workers()` (for GC safepoints) and
485 // `G1CollectedHeap::safepoint_workers()` (for non-GC safepoints) return the
486 // same thread-pool.
487 virtual WorkerThreads* safepoint_workers() { return nullptr; }
488
489 // Support for object pinning. This is used by JNI Get*Critical()
490 // and Release*Critical() family of functions. The GC must guarantee
491 // that pinned objects never move and don't get reclaimed as garbage.
492 // These functions are potentially safepointing.
493 virtual void pin_object(JavaThread* thread, oop obj) = 0;
494 virtual void unpin_object(JavaThread* thread, oop obj) = 0;
495
496 // Support for loading objects from CDS archive into the heap
497 // (usually as a snapshot of the old generation).
498 virtual bool can_load_archived_objects() const { return false; }
499 virtual HeapWord* allocate_loaded_archive_space(size_t size) { return nullptr; }
500 virtual void complete_loaded_archive_space(MemRegion archive_space) { }
501 virtual size_t bootstrap_max_memory() const;
502
503 virtual bool is_oop(oop object) const;
504 // Non product verification and debugging.
505 #ifndef PRODUCT
506 // Support for PromotionFailureALot. Return true if it's time to cause a
507 // promotion failure. The no-argument version uses
508 // this->_promotion_failure_alot_count as the counter.
509 bool promotion_should_fail(volatile size_t* count);
510 bool promotion_should_fail();
511
512 // Reset the PromotionFailureALot counters. Should be called at the end of a
513 // GC in which promotion failure occurred.
514 void reset_promotion_should_fail(volatile size_t* count);
515 void reset_promotion_should_fail();
516 #endif // #ifndef PRODUCT
517 };
518
519 // Class to set and reset the GC cause for a CollectedHeap.
520
521 class GCCauseSetter : StackObj {
522 CollectedHeap* _heap;
523 GCCause::Cause _previous_cause;
524 public:
525 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) {
526 _heap = heap;
527 _previous_cause = _heap->gc_cause();
528 _heap->set_gc_cause(cause);
529 }
530
531 ~GCCauseSetter() {
532 _heap->set_gc_cause(_previous_cause);
533 }
534 };
535
536 #endif // SHARE_GC_SHARED_COLLECTEDHEAP_HPP