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