1 /*
2 * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #ifndef SHARE_GC_SHARED_GENERATION_HPP
26 #define SHARE_GC_SHARED_GENERATION_HPP
27
28 #include "gc/shared/collectorCounters.hpp"
29 #include "gc/shared/referenceProcessor.hpp"
30 #include "logging/log.hpp"
31 #include "memory/allocation.hpp"
32 #include "memory/memRegion.hpp"
33 #include "memory/virtualspace.hpp"
34 #include "runtime/mutex.hpp"
35 #include "runtime/perfData.hpp"
36
37 // A Generation models a heap area for similarly-aged objects.
38 // It will contain one ore more spaces holding the actual objects.
39 //
40 // The Generation class hierarchy:
41 //
42 // Generation - abstract base class
43 // - DefNewGeneration - allocation area (copy collected)
44 // - CardGeneration - abstract class adding offset array behavior
45 // - TenuredGeneration - tenured (old object) space (markSweepCompact)
46 //
47 // The system configuration currently allowed is:
48 //
49 // DefNewGeneration + TenuredGeneration
50 //
51
52 class DefNewGeneration;
53 class GCMemoryManager;
54 class GenerationSpec;
55 class CompactibleSpace;
56 class ContiguousSpace;
57 class CompactPoint;
58 class OopClosure;
59 class FastScanClosure;
60 class GenCollectedHeap;
61 class GCStats;
62
63 // A "ScratchBlock" represents a block of memory in one generation usable by
64 // another. It represents "num_words" free words, starting at and including
65 // the address of "this".
66 struct ScratchBlock {
67 ScratchBlock* next;
68 size_t num_words;
69 HeapWord scratch_space[1]; // Actually, of size "num_words-2" (assuming
70 // first two fields are word-sized.)
71 };
72
73 class Generation: public CHeapObj<mtGC> {
74 friend class VMStructs;
75 private:
76 MemRegion _prev_used_region; // for collectors that want to "remember" a value for
77 // used region at some specific point during collection.
78
79 GCMemoryManager* _gc_manager;
80
81 protected:
82 // Minimum and maximum addresses for memory reserved (not necessarily
83 // committed) for generation.
84 // Used by card marking code. Must not overlap with address ranges of
85 // other generations.
86 MemRegion _reserved;
87
88 // Memory area reserved for generation
89 VirtualSpace _virtual_space;
90
91 // ("Weak") Reference processing support
92 SpanSubjectToDiscoveryClosure _span_based_discoverer;
93 ReferenceProcessor* _ref_processor;
94
95 // Performance Counters
96 CollectorCounters* _gc_counters;
97
98 // Statistics for garbage collection
99 GCStats* _gc_stats;
100
101 // Initialize the generation.
102 Generation(ReservedSpace rs, size_t initial_byte_size);
103
104 public:
105 // The set of possible generation kinds.
106 enum Name {
107 DefNew,
108 MarkSweepCompact,
109 Other
110 };
111
112 enum SomePublicConstants {
113 // Generations are GenGrain-aligned and have size that are multiples of
114 // GenGrain.
115 // Note: on ARM we add 1 bit for card_table_base to be properly aligned
116 // (we expect its low byte to be zero - see implementation of post_barrier)
117 LogOfGenGrain = 16 ARM32_ONLY(+1),
118 GenGrain = 1 << LogOfGenGrain
119 };
120
121 // allocate and initialize ("weak") refs processing support
122 virtual void ref_processor_init();
123 void set_ref_processor(ReferenceProcessor* rp) {
124 assert(_ref_processor == NULL, "clobbering existing _ref_processor");
125 _ref_processor = rp;
126 }
127
128 virtual Generation::Name kind() { return Generation::Other; }
129
130 // This properly belongs in the collector, but for now this
131 // will do.
132 virtual bool refs_discovery_is_atomic() const { return true; }
133 virtual bool refs_discovery_is_mt() const { return false; }
134
135 // Space inquiries (results in bytes)
136 size_t initial_size();
137 virtual size_t capacity() const = 0; // The maximum number of object bytes the
138 // generation can currently hold.
139 virtual size_t used() const = 0; // The number of used bytes in the gen.
140 virtual size_t free() const = 0; // The number of free bytes in the gen.
141
142 // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.
143 // Returns the total number of bytes available in a generation
144 // for the allocation of objects.
145 virtual size_t max_capacity() const;
146
147 // If this is a young generation, the maximum number of bytes that can be
148 // allocated in this generation before a GC is triggered.
149 virtual size_t capacity_before_gc() const { return 0; }
150
151 // The largest number of contiguous free bytes in the generation,
152 // including expansion (Assumes called at a safepoint.)
153 virtual size_t contiguous_available() const = 0;
154 // The largest number of contiguous free bytes in this or any higher generation.
155 virtual size_t max_contiguous_available() const;
156
157 // Returns true if promotions of the specified amount are
158 // likely to succeed without a promotion failure.
159 // Promotion of the full amount is not guaranteed but
160 // might be attempted in the worst case.
161 virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const;
162
163 // For a non-young generation, this interface can be used to inform a
164 // generation that a promotion attempt into that generation failed.
165 // Typically used to enable diagnostic output for post-mortem analysis,
166 // but other uses of the interface are not ruled out.
167 virtual void promotion_failure_occurred() { /* does nothing */ }
168
169 // Return an estimate of the maximum allocation that could be performed
170 // in the generation without triggering any collection or expansion
171 // activity. It is "unsafe" because no locks are taken; the result
172 // should be treated as an approximation, not a guarantee, for use in
173 // heuristic resizing decisions.
174 virtual size_t unsafe_max_alloc_nogc() const = 0;
175
176 // Returns true if this generation cannot be expanded further
177 // without a GC. Override as appropriate.
178 virtual bool is_maximal_no_gc() const {
179 return _virtual_space.uncommitted_size() == 0;
180 }
181
182 MemRegion reserved() const { return _reserved; }
183
184 // Returns a region guaranteed to contain all the objects in the
185 // generation.
186 virtual MemRegion used_region() const { return _reserved; }
187
188 MemRegion prev_used_region() const { return _prev_used_region; }
189 virtual void save_used_region() { _prev_used_region = used_region(); }
190
191 // Returns "TRUE" iff "p" points into the committed areas in the generation.
192 // For some kinds of generations, this may be an expensive operation.
193 // To avoid performance problems stemming from its inadvertent use in
194 // product jvm's, we restrict its use to assertion checking or
195 // verification only.
196 virtual bool is_in(const void* p) const;
197
198 /* Returns "TRUE" iff "p" points into the reserved area of the generation. */
199 bool is_in_reserved(const void* p) const {
200 return _reserved.contains(p);
201 }
202
203 // If some space in the generation contains the given "addr", return a
204 // pointer to that space, else return "NULL".
205 virtual Space* space_containing(const void* addr) const;
206
207 // Iteration - do not use for time critical operations
208 virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;
209
210 // Returns the first space, if any, in the generation that can participate
211 // in compaction, or else "NULL".
212 virtual CompactibleSpace* first_compaction_space() const = 0;
213
214 // Returns "true" iff this generation should be used to allocate an
215 // object of the given size. Young generations might
216 // wish to exclude very large objects, for example, since, if allocated
217 // often, they would greatly increase the frequency of young-gen
218 // collection.
219 virtual bool should_allocate(size_t word_size, bool is_tlab) {
220 bool result = false;
221 size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);
222 if (!is_tlab || supports_tlab_allocation()) {
223 result = (word_size > 0) && (word_size < overflow_limit);
224 }
225 return result;
226 }
227
228 // Allocate and returns a block of the requested size, or returns "NULL".
229 // Assumes the caller has done any necessary locking.
230 virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0;
231
232 // Like "allocate", but performs any necessary locking internally.
233 virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;
234
235 // Some generation may offer a region for shared, contiguous allocation,
236 // via inlined code (by exporting the address of the top and end fields
237 // defining the extent of the contiguous allocation region.)
238
239 // This function returns "true" iff the heap supports this kind of
240 // allocation. (More precisely, this means the style of allocation that
241 // increments *top_addr()" with a CAS.) (Default is "no".)
242 // A generation that supports this allocation style must use lock-free
243 // allocation for *all* allocation, since there are times when lock free
244 // allocation will be concurrent with plain "allocate" calls.
245 virtual bool supports_inline_contig_alloc() const { return false; }
246
247 // These functions return the addresses of the fields that define the
248 // boundaries of the contiguous allocation area. (These fields should be
249 // physically near to one another.)
250 virtual HeapWord* volatile* top_addr() const { return NULL; }
251 virtual HeapWord** end_addr() const { return NULL; }
252
253 // Thread-local allocation buffers
254 virtual bool supports_tlab_allocation() const { return false; }
255 virtual size_t tlab_capacity() const {
256 guarantee(false, "Generation doesn't support thread local allocation buffers");
257 return 0;
258 }
259 virtual size_t tlab_used() const {
260 guarantee(false, "Generation doesn't support thread local allocation buffers");
261 return 0;
262 }
263 virtual size_t unsafe_max_tlab_alloc() const {
264 guarantee(false, "Generation doesn't support thread local allocation buffers");
265 return 0;
266 }
267
268 // "obj" is the address of an object in a younger generation. Allocate space
269 // for "obj" in the current (or some higher) generation, and copy "obj" into
270 // the newly allocated space, if possible, returning the result (or NULL if
271 // the allocation failed).
272 //
273 // The "obj_size" argument is just obj->size(), passed along so the caller can
274 // avoid repeating the virtual call to retrieve it.
275 virtual oop promote(oop obj, size_t obj_size);
276
277 // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote
278 // object "obj", whose original mark word was "m", and whose size is
279 // "word_sz". If possible, allocate space for "obj", copy obj into it
280 // (taking care to copy "m" into the mark word when done, since the mark
281 // word of "obj" may have been overwritten with a forwarding pointer, and
282 // also taking care to copy the klass pointer *last*. Returns the new
283 // object if successful, or else NULL.
284 virtual oop par_promote(int thread_num, oop obj, markWord m, size_t word_sz);
285
286 // Informs the current generation that all par_promote_alloc's in the
287 // collection have been completed; any supporting data structures can be
288 // reset. Default is to do nothing.
289 virtual void par_promote_alloc_done(int thread_num) {}
290
291 // Informs the current generation that all oop_since_save_marks_iterates
292 // performed by "thread_num" in the current collection, if any, have been
293 // completed; any supporting data structures can be reset. Default is to
294 // do nothing.
295 virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}
296
297 // Returns "true" iff collect() should subsequently be called on this
298 // this generation. See comment below.
299 // This is a generic implementation which can be overridden.
300 //
301 // Note: in the current (1.4) implementation, when genCollectedHeap's
302 // incremental_collection_will_fail flag is set, all allocations are
303 // slow path (the only fast-path place to allocate is DefNew, which
304 // will be full if the flag is set).
305 // Thus, older generations which collect younger generations should
306 // test this flag and collect if it is set.
307 virtual bool should_collect(bool full,
308 size_t word_size,
309 bool is_tlab) {
310 return (full || should_allocate(word_size, is_tlab));
311 }
312
313 // Returns true if the collection is likely to be safely
314 // completed. Even if this method returns true, a collection
315 // may not be guaranteed to succeed, and the system should be
316 // able to safely unwind and recover from that failure, albeit
317 // at some additional cost.
318 virtual bool collection_attempt_is_safe() {
319 guarantee(false, "Are you sure you want to call this method?");
320 return true;
321 }
322
323 // Perform a garbage collection.
324 // If full is true attempt a full garbage collection of this generation.
325 // Otherwise, attempting to (at least) free enough space to support an
326 // allocation of the given "word_size".
327 virtual void collect(bool full,
328 bool clear_all_soft_refs,
329 size_t word_size,
330 bool is_tlab) = 0;
331
332 // Perform a heap collection, attempting to create (at least) enough
333 // space to support an allocation of the given "word_size". If
334 // successful, perform the allocation and return the resulting
335 // "oop" (initializing the allocated block). If the allocation is
336 // still unsuccessful, return "NULL".
337 virtual HeapWord* expand_and_allocate(size_t word_size,
338 bool is_tlab,
339 bool parallel = false) = 0;
340
341 // Some generations may require some cleanup or preparation actions before
342 // allowing a collection. The default is to do nothing.
343 virtual void gc_prologue(bool full) {}
344
345 // Some generations may require some cleanup actions after a collection.
346 // The default is to do nothing.
347 virtual void gc_epilogue(bool full) {}
348
349 // Save the high water marks for the used space in a generation.
350 virtual void record_spaces_top() {}
351
352 // Some generations may need to be "fixed-up" after some allocation
353 // activity to make them parsable again. The default is to do nothing.
354 virtual void ensure_parsability() {}
355
356 // Generations may keep statistics about collection. This method
357 // updates those statistics. current_generation is the generation
358 // that was most recently collected. This allows the generation to
359 // decide what statistics are valid to collect. For example, the
360 // generation can decide to gather the amount of promoted data if
361 // the collection of the young generation has completed.
362 GCStats* gc_stats() const { return _gc_stats; }
363 virtual void update_gc_stats(Generation* current_generation, bool full) {}
364
365 #if INCLUDE_SERIALGC
366 // Mark sweep support phase2
367 virtual void prepare_for_compaction(CompactPoint* cp);
368 // Mark sweep support phase3
369 virtual void adjust_pointers();
370 // Mark sweep support phase4
371 virtual void compact();
372 virtual void post_compact() { ShouldNotReachHere(); }
373 #endif
374
375 // Support for CMS's rescan. In this general form we return a pointer
376 // to an abstract object that can be used, based on specific previously
377 // decided protocols, to exchange information between generations,
378 // information that may be useful for speeding up certain types of
379 // garbage collectors. A NULL value indicates to the client that
380 // no data recording is expected by the provider. The data-recorder is
381 // expected to be GC worker thread-local, with the worker index
382 // indicated by "thr_num".
383 virtual void* get_data_recorder(int thr_num) { return NULL; }
384 virtual void sample_eden_chunk() {}
385
386 // Some generations may require some cleanup actions before allowing
387 // a verification.
388 virtual void prepare_for_verify() {}
389
390 // Accessing "marks".
391
392 // This function gives a generation a chance to note a point between
393 // collections. For example, a contiguous generation might note the
394 // beginning allocation point post-collection, which might allow some later
395 // operations to be optimized.
396 virtual void save_marks() {}
397
398 // This function allows generations to initialize any "saved marks". That
399 // is, should only be called when the generation is empty.
400 virtual void reset_saved_marks() {}
401
402 // This function is "true" iff any no allocations have occurred in the
403 // generation since the last call to "save_marks".
404 virtual bool no_allocs_since_save_marks() = 0;
405
406 // The "requestor" generation is performing some garbage collection
407 // action for which it would be useful to have scratch space. If
408 // the target is not the requestor, no gc actions will be required
409 // of the target. The requestor promises to allocate no more than
410 // "max_alloc_words" in the target generation (via promotion say,
411 // if the requestor is a young generation and the target is older).
412 // If the target generation can provide any scratch space, it adds
413 // it to "list", leaving "list" pointing to the head of the
414 // augmented list. The default is to offer no space.
415 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
416 size_t max_alloc_words) {}
417
418 // Give each generation an opportunity to do clean up for any
419 // contributed scratch.
420 virtual void reset_scratch() {}
421
422 // When an older generation has been collected, and perhaps resized,
423 // this method will be invoked on all younger generations (from older to
424 // younger), allowing them to resize themselves as appropriate.
425 virtual void compute_new_size() = 0;
426
427 // Printing
428 virtual const char* name() const = 0;
429 virtual const char* short_name() const = 0;
430
431 // Reference Processing accessor
432 ReferenceProcessor* const ref_processor() { return _ref_processor; }
433
434 // Iteration.
435
436 // Iterate over all the ref-containing fields of all objects in the
437 // generation, calling "cl.do_oop" on each.
438 virtual void oop_iterate(OopIterateClosure* cl);
439
440 // Iterate over all objects in the generation, calling "cl.do_object" on
441 // each.
442 virtual void object_iterate(ObjectClosure* cl);
443
444 // Inform a generation that it longer contains references to objects
445 // in any younger generation. [e.g. Because younger gens are empty,
446 // clear the card table.]
447 virtual void clear_remembered_set() { }
448
449 // Inform a generation that some of its objects have moved. [e.g. The
450 // generation's spaces were compacted, invalidating the card table.]
451 virtual void invalidate_remembered_set() { }
452
453 // Block abstraction.
454
455 // Returns the address of the start of the "block" that contains the
456 // address "addr". We say "blocks" instead of "object" since some heaps
457 // may not pack objects densely; a chunk may either be an object or a
458 // non-object.
459 virtual HeapWord* block_start(const void* addr) const;
460
461 // Requires "addr" to be the start of a chunk, and returns its size.
462 // "addr + size" is required to be the start of a new chunk, or the end
463 // of the active area of the heap.
464 virtual size_t block_size(const HeapWord* addr) const ;
465
466 // Requires "addr" to be the start of a block, and returns "TRUE" iff
467 // the block is an object.
468 virtual bool block_is_obj(const HeapWord* addr) const;
469
470 void print_heap_change(size_t prev_used) const;
471
472 virtual void print() const;
473 virtual void print_on(outputStream* st) const;
474
475 virtual void verify() = 0;
476
477 struct StatRecord {
478 int invocations;
479 elapsedTimer accumulated_time;
480 StatRecord() :
481 invocations(0),
482 accumulated_time(elapsedTimer()) {}
483 };
484 private:
485 StatRecord _stat_record;
486 public:
487 StatRecord* stat_record() { return &_stat_record; }
488
489 virtual void print_summary_info_on(outputStream* st);
490
491 // Performance Counter support
492 virtual void update_counters() = 0;
493 virtual CollectorCounters* counters() { return _gc_counters; }
494
495 GCMemoryManager* gc_manager() const {
496 assert(_gc_manager != NULL, "not initialized yet");
497 return _gc_manager;
498 }
499
500 void set_gc_manager(GCMemoryManager* gc_manager) {
501 _gc_manager = gc_manager;
502 }
503
504 };
505
506 #endif // SHARE_GC_SHARED_GENERATION_HPP