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 // Returns "true" iff collect() should subsequently be called on this
313 // this generation. See comment below.
314 // This is a generic implementation which can be overridden.
315 //
316 // Note: in the current (1.4) implementation, when genCollectedHeap's
317 // incremental_collection_will_fail flag is set, all allocations are
318 // slow path (the only fast-path place to allocate is DefNew, which
319 // will be full if the flag is set).
320 // Thus, older generations which collect younger generations should
321 // test this flag and collect if it is set.
322 virtual bool should_collect(bool full,
323 size_t word_size,
324 bool is_tlab) {
325 return (full || should_allocate(word_size, is_tlab));
326 }
327
328 // Returns true if the collection is likely to be safely
329 // completed. Even if this method returns true, a collection
330 // may not be guaranteed to succeed, and the system should be
331 // able to safely unwind and recover from that failure, albeit
332 // at some additional cost.
333 virtual bool collection_attempt_is_safe() {
334 guarantee(false, "Are you sure you want to call this method?");
335 return true;
336 }
337
338 // Perform a garbage collection.
339 // If full is true attempt a full garbage collection of this generation.
340 // Otherwise, attempting to (at least) free enough space to support an
341 // allocation of the given "word_size".
342 virtual void collect(bool full,
343 bool clear_all_soft_refs,
344 size_t word_size,
345 bool is_tlab) = 0;
346
347 // Perform a heap collection, attempting to create (at least) enough
348 // space to support an allocation of the given "word_size". If
349 // successful, perform the allocation and return the resulting
350 // "oop" (initializing the allocated block). If the allocation is
351 // still unsuccessful, return "NULL".
352 virtual HeapWord* expand_and_allocate(size_t word_size,
353 bool is_tlab,
354 bool parallel = false) = 0;
355
356 // Some generations may require some cleanup or preparation actions before
357 // allowing a collection. The default is to do nothing.
358 virtual void gc_prologue(bool full) {}
359
360 // Some generations may require some cleanup actions after a collection.
361 // The default is to do nothing.
362 virtual void gc_epilogue(bool full) {}
363
364 // Save the high water marks for the used space in a generation.
365 virtual void record_spaces_top() {}
366
367 // Some generations may need to be "fixed-up" after some allocation
368 // activity to make them parsable again. The default is to do nothing.
369 virtual void ensure_parsability() {}
370
371 // Time (in ms) when we were last collected or now if a collection is
372 // in progress.
373 virtual jlong time_of_last_gc(jlong now) {
374 // Both _time_of_last_gc and now are set using a time source
375 // that guarantees monotonically non-decreasing values provided
376 // the underlying platform provides such a source. So we still
377 // have to guard against non-monotonicity.
378 NOT_PRODUCT(
379 if (now < _time_of_last_gc) {
380 warning("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _time_of_last_gc, now);
381 }
382 )
383 return _time_of_last_gc;
384 }
385
386 virtual void update_time_of_last_gc(jlong now) {
387 _time_of_last_gc = now;
388 }
389
390 // Generations may keep statistics about collection. This method
391 // updates those statistics. current_generation is the generation
392 // that was most recently collected. This allows the generation to
393 // decide what statistics are valid to collect. For example, the
394 // generation can decide to gather the amount of promoted data if
395 // the collection of the young generation has completed.
396 GCStats* gc_stats() const { return _gc_stats; }
397 virtual void update_gc_stats(Generation* current_generation, bool full) {}
398
399 // Mark sweep support phase2
400 virtual void prepare_for_compaction(CompactPoint* cp);
401 // Mark sweep support phase3
402 virtual void adjust_pointers();
403 // Mark sweep support phase4
404 virtual void compact();
405 virtual void post_compact() { ShouldNotReachHere(); }
406
407 // Support for CMS's rescan. In this general form we return a pointer
408 // to an abstract object that can be used, based on specific previously
409 // decided protocols, to exchange information between generations,
410 // information that may be useful for speeding up certain types of
411 // garbage collectors. A NULL value indicates to the client that
412 // no data recording is expected by the provider. The data-recorder is
413 // expected to be GC worker thread-local, with the worker index
414 // indicated by "thr_num".
415 virtual void* get_data_recorder(int thr_num) { return NULL; }
416 virtual void sample_eden_chunk() {}
417
418 // Some generations may require some cleanup actions before allowing
419 // a verification.
420 virtual void prepare_for_verify() {}
421
422 // Accessing "marks".
423
424 // This function gives a generation a chance to note a point between
425 // collections. For example, a contiguous generation might note the
426 // beginning allocation point post-collection, which might allow some later
427 // operations to be optimized.
428 virtual void save_marks() {}
429
430 // This function allows generations to initialize any "saved marks". That
431 // is, should only be called when the generation is empty.
432 virtual void reset_saved_marks() {}
433
434 // This function is "true" iff any no allocations have occurred in the
435 // generation since the last call to "save_marks".
436 virtual bool no_allocs_since_save_marks() = 0;
437
438 // Apply "cl->apply" to (the addresses of) all reference fields in objects
439 // allocated in the current generation since the last call to "save_marks".
440 // If more objects are allocated in this generation as a result of applying
441 // the closure, iterates over reference fields in those objects as well.
442 // Calls "save_marks" at the end of the iteration.
443 // General signature...
444 virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0;
445 // ...and specializations for de-virtualization. (The general
446 // implementation of the _nv versions call the virtual version.
447 // Note that the _nv suffix is not really semantically necessary,
448 // but it avoids some not-so-useful warnings on Solaris.)
449 #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
450 virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
451 oop_since_save_marks_iterate_v((OopsInGenClosure*)cl); \
452 }
453 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL)
454
455 #undef Generation_SINCE_SAVE_MARKS_DECL
456
457 // The "requestor" generation is performing some garbage collection
458 // action for which it would be useful to have scratch space. If
459 // the target is not the requestor, no gc actions will be required
460 // of the target. The requestor promises to allocate no more than
461 // "max_alloc_words" in the target generation (via promotion say,
462 // if the requestor is a young generation and the target is older).
463 // If the target generation can provide any scratch space, it adds
464 // it to "list", leaving "list" pointing to the head of the
465 // augmented list. The default is to offer no space.
466 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
467 size_t max_alloc_words) {}
468
469 // Give each generation an opportunity to do clean up for any
470 // contributed scratch.
471 virtual void reset_scratch() {}
472
473 // When an older generation has been collected, and perhaps resized,
474 // this method will be invoked on all younger generations (from older to
475 // younger), allowing them to resize themselves as appropriate.
476 virtual void compute_new_size() = 0;
477
478 // Printing
479 virtual const char* name() const = 0;
480 virtual const char* short_name() const = 0;
481
482 // Reference Processing accessor
483 ReferenceProcessor* const ref_processor() { return _ref_processor; }
484
485 // Iteration.
486
487 // Iterate over all the ref-containing fields of all objects in the
488 // generation, calling "cl.do_oop" on each.
489 virtual void oop_iterate(ExtendedOopClosure* cl);
490
491 // Iterate over all objects in the generation, calling "cl.do_object" on
492 // each.
493 virtual void object_iterate(ObjectClosure* cl);
494
495 // Iterate over all safe objects in the generation, calling "cl.do_object" on
496 // each. An object is safe if its references point to other objects in
497 // the heap. This defaults to object_iterate() unless overridden.
498 virtual void safe_object_iterate(ObjectClosure* cl);
499
500 // Apply "cl->do_oop" to (the address of) all and only all the ref fields
501 // in the current generation that contain pointers to objects in younger
502 // generations. Objects allocated since the last "save_marks" call are
503 // excluded.
504 virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0;
505
506 // Inform a generation that it longer contains references to objects
507 // in any younger generation. [e.g. Because younger gens are empty,
508 // clear the card table.]
509 virtual void clear_remembered_set() { }
510
511 // Inform a generation that some of its objects have moved. [e.g. The
512 // generation's spaces were compacted, invalidating the card table.]
513 virtual void invalidate_remembered_set() { }
514
515 // Block abstraction.
516
517 // Returns the address of the start of the "block" that contains the
518 // address "addr". We say "blocks" instead of "object" since some heaps
519 // may not pack objects densely; a chunk may either be an object or a
520 // non-object.
521 virtual HeapWord* block_start(const void* addr) const;
522
523 // Requires "addr" to be the start of a chunk, and returns its size.
524 // "addr + size" is required to be the start of a new chunk, or the end
525 // of the active area of the heap.
526 virtual size_t block_size(const HeapWord* addr) const ;
527
528 // Requires "addr" to be the start of a block, and returns "TRUE" iff
529 // the block is an object.
530 virtual bool block_is_obj(const HeapWord* addr) const;
531
532 void print_heap_change(size_t prev_used) const;
533
534 virtual void print() const;
535 virtual void print_on(outputStream* st) const;
536
537 virtual void verify() = 0;
538
539 struct StatRecord {
540 int invocations;
541 elapsedTimer accumulated_time;
542 StatRecord() :
543 invocations(0),
544 accumulated_time(elapsedTimer()) {}
545 };
546 private:
547 StatRecord _stat_record;
548 public:
549 StatRecord* stat_record() { return &_stat_record; }
550
551 virtual void print_summary_info();
552 virtual void print_summary_info_on(outputStream* st);
553
554 // Performance Counter support
555 virtual void update_counters() = 0;
556 virtual CollectorCounters* counters() { return _gc_counters; }
557 };
558
559 #endif // SHARE_VM_GC_SHARED_GENERATION_HPP