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