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