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