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