1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_VM_GC_SHARED_GENERATION_HPP
26 #define SHARE_VM_GC_SHARED_GENERATION_HPP
27
28 #include "gc/shared/collectorCounters.hpp"
29 #include "gc/shared/referenceProcessor.hpp"
30 #include "gc/shared/watermark.hpp"
31 #include "memory/allocation.hpp"
32 #include "memory/memRegion.hpp"
33 #include "memory/universe.hpp"
34 #include "memory/virtualspace.hpp"
35 #include "runtime/mutex.hpp"
36 #include "runtime/perfData.hpp"
37
38 // A Generation models a heap area for similarly-aged objects.
39 // It will contain one ore more spaces holding the actual objects.
40 //
41 // The Generation class hierarchy:
42 //
43 // Generation - abstract base class
44 // - DefNewGeneration - allocation area (copy collected)
45 // - ParNewGeneration - a DefNewGeneration that is collected by
46 // several threads
47 // - CardGeneration - abstract class adding offset array behavior
48 // - TenuredGeneration - tenured (old object) space (markSweepCompact)
49 // - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation
50 // (Detlefs-Printezis refinement of
51 // Boehm-Demers-Schenker)
52 //
53 // The system configurations currently allowed are:
54 //
55 // DefNewGeneration + TenuredGeneration
56 //
57 // ParNewGeneration + ConcurrentMarkSweepGeneration
58 //
59
60 class DefNewGeneration;
61 class GenerationSpec;
62 class CompactibleSpace;
63 class ContiguousSpace;
64 class CompactPoint;
65 class OopsInGenClosure;
66 class OopClosure;
67 class ScanClosure;
68 class FastScanClosure;
69 class GenCollectedHeap;
70 class GenRemSet;
71 class GCStats;
72
73 // A "ScratchBlock" represents a block of memory in one generation usable by
74 // another. It represents "num_words" free words, starting at and including
75 // the address of "this".
76 struct ScratchBlock {
77 ScratchBlock* next;
78 size_t num_words;
79 HeapWord scratch_space[1]; // Actually, of size "num_words-2" (assuming
80 // first two fields are word-sized.)
81 };
82
83 class Generation: public CHeapObj<mtGC> {
84 friend class VMStructs;
85 private:
86 jlong _time_of_last_gc; // time when last gc on this generation happened (ms)
87 MemRegion _prev_used_region; // for collectors that want to "remember" a value for
88 // used region at some specific point during collection.
89
90 protected:
91 // Minimum and maximum addresses for memory reserved (not necessarily
92 // committed) for generation.
93 // Used by card marking code. Must not overlap with address ranges of
94 // other generations.
95 MemRegion _reserved;
96
97 // Memory area reserved for generation
98 VirtualSpace _virtual_space;
99
100 // ("Weak") Reference processing support
101 ReferenceProcessor* _ref_processor;
102
103 // Performance Counters
104 CollectorCounters* _gc_counters;
105
106 // Statistics for garbage collection
107 GCStats* _gc_stats;
108
109 // Initialize the generation.
110 Generation(ReservedSpace rs, size_t initial_byte_size);
111
112 // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in
113 // "sp" that point into younger generations.
114 // The iteration is only over objects allocated at the start of the
115 // iterations; objects allocated as a result of applying the closure are
116 // not included.
117 void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl, uint n_threads);
118
119 public:
120 // The set of possible generation kinds.
121 enum Name {
122 DefNew,
123 ParNew,
124 MarkSweepCompact,
125 ConcurrentMarkSweep,
126 Other
127 };
128
129 enum SomePublicConstants {
130 // Generations are GenGrain-aligned and have size that are multiples of
131 // GenGrain.
132 // Note: on ARM we add 1 bit for card_table_base to be properly aligned
133 // (we expect its low byte to be zero - see implementation of post_barrier)
134 LogOfGenGrain = 16 ARM32_ONLY(+1),
135 GenGrain = 1 << LogOfGenGrain
136 };
137
138 // allocate and initialize ("weak") refs processing support
139 virtual void ref_processor_init();
140 void set_ref_processor(ReferenceProcessor* rp) {
141 assert(_ref_processor == NULL, "clobbering existing _ref_processor");
142 _ref_processor = rp;
143 }
144
145 virtual Generation::Name kind() { return Generation::Other; }
146 GenerationSpec* spec();
147
148 // This properly belongs in the collector, but for now this
149 // will do.
150 virtual bool refs_discovery_is_atomic() const { return true; }
151 virtual bool refs_discovery_is_mt() const { return false; }
152
153 // Space enquiries (results in bytes)
154 virtual size_t capacity() const = 0; // The maximum number of object bytes the
155 // generation can currently hold.
156 virtual size_t used() const = 0; // The number of used bytes in the gen.
157 virtual size_t free() const = 0; // The number of free bytes in the gen.
158
159 // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.
160 // Returns the total number of bytes available in a generation
161 // for the allocation of objects.
162 virtual size_t max_capacity() const;
163
164 // If this is a young generation, the maximum number of bytes that can be
165 // allocated in this generation before a GC is triggered.
166 virtual size_t capacity_before_gc() const { return 0; }
167
168 // The largest number of contiguous free bytes in the generation,
169 // including expansion (Assumes called at a safepoint.)
170 virtual size_t contiguous_available() const = 0;
171 // The largest number of contiguous free bytes in this or any higher generation.
172 virtual size_t max_contiguous_available() const;
173
174 // Returns true if promotions of the specified amount are
175 // likely to succeed without a promotion failure.
176 // Promotion of the full amount is not guaranteed but
177 // might be attempted in the worst case.
178 virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const;
179
180 // For a non-young generation, this interface can be used to inform a
181 // generation that a promotion attempt into that generation failed.
182 // Typically used to enable diagnostic output for post-mortem analysis,
183 // but other uses of the interface are not ruled out.
184 virtual void promotion_failure_occurred() { /* does nothing */ }
185
186 // Return an estimate of the maximum allocation that could be performed
187 // in the generation without triggering any collection or expansion
188 // activity. It is "unsafe" because no locks are taken; the result
189 // should be treated as an approximation, not a guarantee, for use in
190 // heuristic resizing decisions.
191 virtual size_t unsafe_max_alloc_nogc() const = 0;
192
193 // Returns true if this generation cannot be expanded further
194 // without a GC. Override as appropriate.
195 virtual bool is_maximal_no_gc() const {
196 return _virtual_space.uncommitted_size() == 0;
197 }
198
199 MemRegion reserved() const { return _reserved; }
200
201 // Returns a region guaranteed to contain all the objects in the
202 // generation.
203 virtual MemRegion used_region() const { return _reserved; }
204
205 MemRegion prev_used_region() const { return _prev_used_region; }
206 virtual void save_used_region() { _prev_used_region = used_region(); }
207
208 // Returns "TRUE" iff "p" points into the committed areas in the generation.
209 // For some kinds of generations, this may be an expensive operation.
210 // To avoid performance problems stemming from its inadvertent use in
211 // product jvm's, we restrict its use to assertion checking or
212 // verification only.
213 virtual bool is_in(const void* p) const;
214
215 /* Returns "TRUE" iff "p" points into the reserved area of the generation. */
216 bool is_in_reserved(const void* p) const {
217 return _reserved.contains(p);
218 }
219
220 // If some space in the generation contains the given "addr", return a
221 // pointer to that space, else return "NULL".
222 virtual Space* space_containing(const void* addr) const;
223
224 // Iteration - do not use for time critical operations
225 virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;
226
227 // Returns the first space, if any, in the generation that can participate
228 // in compaction, or else "NULL".
229 virtual CompactibleSpace* first_compaction_space() const = 0;
230
231 // Returns "true" iff this generation should be used to allocate an
232 // object of the given size. Young generations might
233 // wish to exclude very large objects, for example, since, if allocated
234 // often, they would greatly increase the frequency of young-gen
235 // collection.
236 virtual bool should_allocate(size_t word_size, bool is_tlab) {
237 bool result = false;
238 size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);
239 if (!is_tlab || supports_tlab_allocation()) {
240 result = (word_size > 0) && (word_size < overflow_limit);
241 }
242 return result;
243 }
244
245 // Allocate and returns a block of the requested size, or returns "NULL".
246 // Assumes the caller has done any necessary locking.
247 virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0;
248
249 // Like "allocate", but performs any necessary locking internally.
250 virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;
251
252 // Some generation may offer a region for shared, contiguous allocation,
253 // via inlined code (by exporting the address of the top and end fields
254 // defining the extent of the contiguous allocation region.)
255
256 // This function returns "true" iff the heap supports this kind of
257 // allocation. (More precisely, this means the style of allocation that
258 // increments *top_addr()" with a CAS.) (Default is "no".)
259 // A generation that supports this allocation style must use lock-free
260 // allocation for *all* allocation, since there are times when lock free
261 // allocation will be concurrent with plain "allocate" calls.
262 virtual bool supports_inline_contig_alloc() const { return false; }
263
264 // These functions return the addresses of the fields that define the
265 // boundaries of the contiguous allocation area. (These fields should be
266 // physically near to one another.)
267 virtual HeapWord** top_addr() const { return NULL; }
268 virtual HeapWord** end_addr() const { return NULL; }
269
270 // Thread-local allocation buffers
271 virtual bool supports_tlab_allocation() const { return false; }
272 virtual size_t tlab_capacity() const {
273 guarantee(false, "Generation doesn't support thread local allocation buffers");
274 return 0;
275 }
276 virtual size_t tlab_used() const {
277 guarantee(false, "Generation doesn't support thread local allocation buffers");
278 return 0;
279 }
280 virtual size_t unsafe_max_tlab_alloc() const {
281 guarantee(false, "Generation doesn't support thread local allocation buffers");
282 return 0;
283 }
284
285 // "obj" is the address of an object in a younger generation. Allocate space
286 // for "obj" in the current (or some higher) generation, and copy "obj" into
287 // the newly allocated space, if possible, returning the result (or NULL if
288 // the allocation failed).
289 //
290 // The "obj_size" argument is just obj->size(), passed along so the caller can
291 // avoid repeating the virtual call to retrieve it.
292 virtual oop promote(oop obj, size_t obj_size);
293
294 // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote
295 // object "obj", whose original mark word was "m", and whose size is
296 // "word_sz". If possible, allocate space for "obj", copy obj into it
297 // (taking care to copy "m" into the mark word when done, since the mark
298 // word of "obj" may have been overwritten with a forwarding pointer, and
299 // also taking care to copy the klass pointer *last*. Returns the new
300 // object if successful, or else NULL.
301 virtual oop par_promote(int thread_num, oop obj, markOop m, size_t word_sz);
302
303 // Informs the current generation that all par_promote_alloc's in the
304 // collection have been completed; any supporting data structures can be
305 // reset. Default is to do nothing.
306 virtual void par_promote_alloc_done(int thread_num) {}
307
308 // Informs the current generation that all oop_since_save_marks_iterates
309 // performed by "thread_num" in the current collection, if any, have been
310 // completed; any supporting data structures can be reset. Default is to
311 // do nothing.
312 virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}
313
314 // This generation will collect all younger generations
315 // during a full collection.
316 virtual bool full_collects_young_generation() const { return false; }
317
318 // This generation does in-place marking, meaning that mark words
319 // are mutated during the marking phase and presumably reinitialized
320 // to a canonical value after the GC. This is currently used by the
321 // biased locking implementation to determine whether additional
322 // work is required during the GC prologue and epilogue.
323 virtual bool performs_in_place_marking() const { return true; }
324
325 // Returns "true" iff collect() should subsequently be called on this
326 // this generation. See comment below.
327 // This is a generic implementation which can be overridden.
328 //
329 // Note: in the current (1.4) implementation, when genCollectedHeap's
330 // incremental_collection_will_fail flag is set, all allocations are
331 // slow path (the only fast-path place to allocate is DefNew, which
332 // will be full if the flag is set).
333 // Thus, older generations which collect younger generations should
334 // test this flag and collect if it is set.
335 virtual bool should_collect(bool full,
336 size_t word_size,
337 bool is_tlab) {
338 return (full || should_allocate(word_size, is_tlab));
339 }
340
341 // Returns true if the collection is likely to be safely
342 // completed. Even if this method returns true, a collection
343 // may not be guaranteed to succeed, and the system should be
344 // able to safely unwind and recover from that failure, albeit
345 // at some additional cost.
346 virtual bool collection_attempt_is_safe() {
347 guarantee(false, "Are you sure you want to call this method?");
348 return true;
349 }
350
351 // Perform a garbage collection.
352 // If full is true attempt a full garbage collection of this generation.
353 // Otherwise, attempting to (at least) free enough space to support an
354 // allocation of the given "word_size".
355 virtual void collect(bool full,
356 bool clear_all_soft_refs,
357 size_t word_size,
358 bool is_tlab) = 0;
359
360 // Perform a heap collection, attempting to create (at least) enough
361 // space to support an allocation of the given "word_size". If
362 // successful, perform the allocation and return the resulting
363 // "oop" (initializing the allocated block). If the allocation is
364 // still unsuccessful, return "NULL".
365 virtual HeapWord* expand_and_allocate(size_t word_size,
366 bool is_tlab,
367 bool parallel = false) = 0;
368
369 // Some generations may require some cleanup or preparation actions before
370 // allowing a collection. The default is to do nothing.
371 virtual void gc_prologue(bool full) {}
372
373 // Some generations may require some cleanup actions after a collection.
374 // The default is to do nothing.
375 virtual void gc_epilogue(bool full) {}
376
377 // Save the high water marks for the used space in a generation.
378 virtual void record_spaces_top() {}
379
380 // Some generations may need to be "fixed-up" after some allocation
381 // activity to make them parsable again. The default is to do nothing.
382 virtual void ensure_parsability() {}
383
384 // Time (in ms) when we were last collected or now if a collection is
385 // in progress.
386 virtual jlong time_of_last_gc(jlong now) {
387 // Both _time_of_last_gc and now are set using a time source
388 // that guarantees monotonically non-decreasing values provided
389 // the underlying platform provides such a source. So we still
390 // have to guard against non-monotonicity.
391 NOT_PRODUCT(
392 if (now < _time_of_last_gc) {
393 warning("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _time_of_last_gc, now);
394 }
395 )
396 return _time_of_last_gc;
397 }
398
399 virtual void update_time_of_last_gc(jlong now) {
400 _time_of_last_gc = now;
401 }
402
403 // Generations may keep statistics about collection. This method
404 // updates those statistics. current_generation is the generation
405 // that was most recently collected. This allows the generation to
406 // decide what statistics are valid to collect. For example, the
407 // generation can decide to gather the amount of promoted data if
408 // the collection of the younger generations has completed.
409 GCStats* gc_stats() const { return _gc_stats; }
410 virtual void update_gc_stats(Generation* current_generation, bool full) {}
411
412 // Mark sweep support phase2
413 virtual void prepare_for_compaction(CompactPoint* cp);
414 // Mark sweep support phase3
415 virtual void adjust_pointers();
416 // Mark sweep support phase4
417 virtual void compact();
418 virtual void post_compact() { ShouldNotReachHere(); }
419
420 // Support for CMS's rescan. In this general form we return a pointer
421 // to an abstract object that can be used, based on specific previously
422 // decided protocols, to exchange information between generations,
423 // information that may be useful for speeding up certain types of
424 // garbage collectors. A NULL value indicates to the client that
425 // no data recording is expected by the provider. The data-recorder is
426 // expected to be GC worker thread-local, with the worker index
427 // indicated by "thr_num".
428 virtual void* get_data_recorder(int thr_num) { return NULL; }
429 virtual void sample_eden_chunk() {}
430
431 // Some generations may require some cleanup actions before allowing
432 // a verification.
433 virtual void prepare_for_verify() {}
434
435 // Accessing "marks".
436
437 // This function gives a generation a chance to note a point between
438 // collections. For example, a contiguous generation might note the
439 // beginning allocation point post-collection, which might allow some later
440 // operations to be optimized.
441 virtual void save_marks() {}
442
443 // This function allows generations to initialize any "saved marks". That
444 // is, should only be called when the generation is empty.
445 virtual void reset_saved_marks() {}
446
447 // This function is "true" iff any no allocations have occurred in the
448 // generation since the last call to "save_marks".
449 virtual bool no_allocs_since_save_marks() = 0;
450
451 // Apply "cl->apply" to (the addresses of) all reference fields in objects
452 // allocated in the current generation since the last call to "save_marks".
453 // If more objects are allocated in this generation as a result of applying
454 // the closure, iterates over reference fields in those objects as well.
455 // Calls "save_marks" at the end of the iteration.
456 // General signature...
457 virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0;
458 // ...and specializations for de-virtualization. (The general
459 // implementation of the _nv versions call the virtual version.
460 // Note that the _nv suffix is not really semantically necessary,
461 // but it avoids some not-so-useful warnings on Solaris.)
462 #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
463 virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
464 oop_since_save_marks_iterate_v((OopsInGenClosure*)cl); \
465 }
466 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL)
467
468 #undef Generation_SINCE_SAVE_MARKS_DECL
469
470 // The "requestor" generation is performing some garbage collection
471 // action for which it would be useful to have scratch space. If
472 // the target is not the requestor, no gc actions will be required
473 // of the target. The requestor promises to allocate no more than
474 // "max_alloc_words" in the target generation (via promotion say,
475 // if the requestor is a young generation and the target is older).
476 // If the target generation can provide any scratch space, it adds
477 // it to "list", leaving "list" pointing to the head of the
478 // augmented list. The default is to offer no space.
479 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
480 size_t max_alloc_words) {}
481
482 // Give each generation an opportunity to do clean up for any
483 // contributed scratch.
484 virtual void reset_scratch() {}
485
486 // When an older generation has been collected, and perhaps resized,
487 // this method will be invoked on all younger generations (from older to
488 // younger), allowing them to resize themselves as appropriate.
489 virtual void compute_new_size() = 0;
490
491 // Printing
492 virtual const char* name() const = 0;
493 virtual const char* short_name() const = 0;
494
495 // Reference Processing accessor
496 ReferenceProcessor* const ref_processor() { return _ref_processor; }
497
498 // Iteration.
499
500 // Iterate over all the ref-containing fields of all objects in the
501 // generation, calling "cl.do_oop" on each.
502 virtual void oop_iterate(ExtendedOopClosure* cl);
503
504 // Iterate over all objects in the generation, calling "cl.do_object" on
505 // each.
506 virtual void object_iterate(ObjectClosure* cl);
507
508 // Iterate over all safe objects in the generation, calling "cl.do_object" on
509 // each. An object is safe if its references point to other objects in
510 // the heap. This defaults to object_iterate() unless overridden.
511 virtual void safe_object_iterate(ObjectClosure* cl);
512
513 // Apply "cl->do_oop" to (the address of) all and only all the ref fields
514 // in the current generation that contain pointers to objects in younger
515 // generations. Objects allocated since the last "save_marks" call are
516 // excluded.
517 virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0;
518
519 // Inform a generation that it longer contains references to objects
520 // in any younger generation. [e.g. Because younger gens are empty,
521 // clear the card table.]
522 virtual void clear_remembered_set() { }
523
524 // Inform a generation that some of its objects have moved. [e.g. The
525 // generation's spaces were compacted, invalidating the card table.]
526 virtual void invalidate_remembered_set() { }
527
528 // Block abstraction.
529
530 // Returns the address of the start of the "block" that contains the
531 // address "addr". We say "blocks" instead of "object" since some heaps
532 // may not pack objects densely; a chunk may either be an object or a
533 // non-object.
534 virtual HeapWord* block_start(const void* addr) const;
535
536 // Requires "addr" to be the start of a chunk, and returns its size.
537 // "addr + size" is required to be the start of a new chunk, or the end
538 // of the active area of the heap.
539 virtual size_t block_size(const HeapWord* addr) const ;
540
541 // Requires "addr" to be the start of a block, and returns "TRUE" iff
542 // the block is an object.
543 virtual bool block_is_obj(const HeapWord* addr) const;
544
545
546 // PrintGC, PrintGCDetails support
547 void print_heap_change(size_t prev_used) const;
548
549 // PrintHeapAtGC support
550 virtual void print() const;
551 virtual void print_on(outputStream* st) const;
552
553 virtual void verify() = 0;
554
555 struct StatRecord {
556 int invocations;
557 elapsedTimer accumulated_time;
558 StatRecord() :
559 invocations(0),
560 accumulated_time(elapsedTimer()) {}
561 };
562 private:
563 StatRecord _stat_record;
564 public:
565 StatRecord* stat_record() { return &_stat_record; }
566
567 virtual void print_summary_info();
568 virtual void print_summary_info_on(outputStream* st);
569
570 // Performance Counter support
571 virtual void update_counters() = 0;
572 virtual CollectorCounters* counters() { return _gc_counters; }
573 };
574
575 #endif // SHARE_VM_GC_SHARED_GENERATION_HPP