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