/* * Copyright 1997-2009 Sun Microsystems, Inc. All Rights Reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, * CA 95054 USA or visit www.sun.com if you need additional information or * have any questions. * */ // A Generation models a heap area for similarly-aged objects. // It will contain one ore more spaces holding the actual objects. // // The Generation class hierarchy: // // Generation - abstract base class // - DefNewGeneration - allocation area (copy collected) // - ParNewGeneration - a DefNewGeneration that is collected by // several threads // - CardGeneration - abstract class adding offset array behavior // - OneContigSpaceCardGeneration - abstract class holding a single // contiguous space with card marking // - TenuredGeneration - tenured (old object) space (markSweepCompact) // - CompactingPermGenGen - reflective object area (klasses, methods, symbols, ...) // - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation // (Detlefs-Printezis refinement of // Boehm-Demers-Schenker) // // The system configurations currently allowed are: // // DefNewGeneration + TenuredGeneration + PermGeneration // DefNewGeneration + ConcurrentMarkSweepGeneration + ConcurrentMarkSweepPermGen // // ParNewGeneration + TenuredGeneration + PermGeneration // ParNewGeneration + ConcurrentMarkSweepGeneration + ConcurrentMarkSweepPermGen // class DefNewGeneration; class GenerationSpec; class CompactibleSpace; class ContiguousSpace; class CompactPoint; class OopsInGenClosure; class OopClosure; class ScanClosure; class FastScanClosure; class GenCollectedHeap; class GenRemSet; class GCStats; // A "ScratchBlock" represents a block of memory in one generation usable by // another. It represents "num_words" free words, starting at and including // the address of "this". struct ScratchBlock { ScratchBlock* next; size_t num_words; HeapWord scratch_space[1]; // Actually, of size "num_words-2" (assuming // first two fields are word-sized.) }; class Generation: public CHeapObj { friend class VMStructs; private: jlong _time_of_last_gc; // time when last gc on this generation happened (ms) MemRegion _prev_used_region; // for collectors that want to "remember" a value for // used region at some specific point during collection. protected: // Minimum and maximum addresses for memory reserved (not necessarily // committed) for generation. // Used by card marking code. Must not overlap with address ranges of // other generations. MemRegion _reserved; // Memory area reserved for generation VirtualSpace _virtual_space; // Level in the generation hierarchy. int _level; // ("Weak") Reference processing support ReferenceProcessor* _ref_processor; // Performance Counters CollectorCounters* _gc_counters; // Statistics for garbage collection GCStats* _gc_stats; // Returns the next generation in the configuration, or else NULL if this // is the highest generation. Generation* next_gen() const; // Initialize the generation. Generation(ReservedSpace rs, size_t initial_byte_size, int level); // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in // "sp" that point into younger generations. // The iteration is only over objects allocated at the start of the // iterations; objects allocated as a result of applying the closure are // not included. void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl); public: // The set of possible generation kinds. enum Name { ASParNew, ASConcurrentMarkSweep, DefNew, ParNew, MarkSweepCompact, ConcurrentMarkSweep, Other }; enum SomePublicConstants { // Generations are GenGrain-aligned and have size that are multiples of // GenGrain. LogOfGenGrain = 16, GenGrain = 1 << LogOfGenGrain }; // allocate and initialize ("weak") refs processing support virtual void ref_processor_init(); void set_ref_processor(ReferenceProcessor* rp) { assert(_ref_processor == NULL, "clobbering existing _ref_processor"); _ref_processor = rp; } virtual Generation::Name kind() { return Generation::Other; } GenerationSpec* spec(); // This properly belongs in the collector, but for now this // will do. virtual bool refs_discovery_is_atomic() const { return true; } virtual bool refs_discovery_is_mt() const { return false; } // Space enquiries (results in bytes) virtual size_t capacity() const = 0; // The maximum number of object bytes the // generation can currently hold. virtual size_t used() const = 0; // The number of used bytes in the gen. virtual size_t free() const = 0; // The number of free bytes in the gen. // Support for java.lang.Runtime.maxMemory(); see CollectedHeap. // Returns the total number of bytes available in a generation // for the allocation of objects. virtual size_t max_capacity() const; // If this is a young generation, the maximum number of bytes that can be // allocated in this generation before a GC is triggered. virtual size_t capacity_before_gc() const { return 0; } // The largest number of contiguous free bytes in the generation, // including expansion (Assumes called at a safepoint.) virtual size_t contiguous_available() const = 0; // The largest number of contiguous free bytes in this or any higher generation. virtual size_t max_contiguous_available() const; // Returns true if promotions of the specified amount can // be attempted safely (without a vm failure). // Promotion of the full amount is not guaranteed but // can be attempted. // younger_handles_promotion_failure // is true if the younger generation handles a promotion // failure. virtual bool promotion_attempt_is_safe(size_t promotion_in_bytes, bool younger_handles_promotion_failure) const; // For a non-young generation, this interface can be used to inform a // generation that a promotion attempt into that generation failed. // Typically used to enable diagnostic output for post-mortem analysis, // but other uses of the interface are not ruled out. virtual void promotion_failure_occurred() { /* does nothing */ } // Return an estimate of the maximum allocation that could be performed // in the generation without triggering any collection or expansion // activity. It is "unsafe" because no locks are taken; the result // should be treated as an approximation, not a guarantee, for use in // heuristic resizing decisions. virtual size_t unsafe_max_alloc_nogc() const = 0; // Returns true if this generation cannot be expanded further // without a GC. Override as appropriate. virtual bool is_maximal_no_gc() const { return _virtual_space.uncommitted_size() == 0; } MemRegion reserved() const { return _reserved; } // Returns a region guaranteed to contain all the objects in the // generation. virtual MemRegion used_region() const { return _reserved; } MemRegion prev_used_region() const { return _prev_used_region; } virtual void save_used_region() { _prev_used_region = used_region(); } // Returns "TRUE" iff "p" points into an allocated object in the generation. // For some kinds of generations, this may be an expensive operation. // To avoid performance problems stemming from its inadvertent use in // product jvm's, we restrict its use to assertion checking or // verification only. virtual bool is_in(const void* p) const; /* Returns "TRUE" iff "p" points into the reserved area of the generation. */ bool is_in_reserved(const void* p) const { return _reserved.contains(p); } // Check that the generation kind is DefNewGeneration or a sub // class of DefNewGeneration and return a DefNewGeneration* DefNewGeneration* as_DefNewGeneration(); // If some space in the generation contains the given "addr", return a // pointer to that space, else return "NULL". virtual Space* space_containing(const void* addr) const; // Iteration - do not use for time critical operations virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0; // Returns the first space, if any, in the generation that can participate // in compaction, or else "NULL". virtual CompactibleSpace* first_compaction_space() const = 0; // Returns "true" iff this generation should be used to allocate an // object of the given size. Young generations might // wish to exclude very large objects, for example, since, if allocated // often, they would greatly increase the frequency of young-gen // collection. virtual bool should_allocate(size_t word_size, bool is_tlab) { bool result = false; size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize); if (!is_tlab || supports_tlab_allocation()) { result = (word_size > 0) && (word_size < overflow_limit); } return result; } // Allocate and returns a block of the requested size, or returns "NULL". // Assumes the caller has done any necessary locking. virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0; // Like "allocate", but performs any necessary locking internally. virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0; // A 'younger' gen has reached an allocation limit, and uses this to notify // the next older gen. The return value is a new limit, or NULL if none. The // caller must do the necessary locking. virtual HeapWord* allocation_limit_reached(Space* space, HeapWord* top, size_t word_size) { return NULL; } // Some generation may offer a region for shared, contiguous allocation, // via inlined code (by exporting the address of the top and end fields // defining the extent of the contiguous allocation region.) // This function returns "true" iff the heap supports this kind of // allocation. (More precisely, this means the style of allocation that // increments *top_addr()" with a CAS.) (Default is "no".) // A generation that supports this allocation style must use lock-free // allocation for *all* allocation, since there are times when lock free // allocation will be concurrent with plain "allocate" calls. virtual bool supports_inline_contig_alloc() const { return false; } // These functions return the addresses of the fields that define the // boundaries of the contiguous allocation area. (These fields should be // physicall near to one another.) virtual HeapWord** top_addr() const { return NULL; } virtual HeapWord** end_addr() const { return NULL; } // Thread-local allocation buffers virtual bool supports_tlab_allocation() const { return false; } virtual size_t tlab_capacity() const { guarantee(false, "Generation doesn't support thread local allocation buffers"); return 0; } virtual size_t unsafe_max_tlab_alloc() const { guarantee(false, "Generation doesn't support thread local allocation buffers"); return 0; } // "obj" is the address of an object in a younger generation. Allocate space // for "obj" in the current (or some higher) generation, and copy "obj" into // the newly allocated space, if possible, returning the result (or NULL if // the allocation failed). // // The "obj_size" argument is just obj->size(), passed along so the caller can // avoid repeating the virtual call to retrieve it. virtual oop promote(oop obj, size_t obj_size); // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote // object "obj", whose original mark word was "m", and whose size is // "word_sz". If possible, allocate space for "obj", copy obj into it // (taking care to copy "m" into the mark word when done, since the mark // word of "obj" may have been overwritten with a forwarding pointer, and // also taking care to copy the klass pointer *last*. Returns the new // object if successful, or else NULL. virtual oop par_promote(int thread_num, oop obj, markOop m, size_t word_sz); // Undo, if possible, the most recent par_promote_alloc allocation by // "thread_num" ("obj", of "word_sz"). virtual void par_promote_alloc_undo(int thread_num, HeapWord* obj, size_t word_sz); // Informs the current generation that all par_promote_alloc's in the // collection have been completed; any supporting data structures can be // reset. Default is to do nothing. virtual void par_promote_alloc_done(int thread_num) {} // Informs the current generation that all oop_since_save_marks_iterates // performed by "thread_num" in the current collection, if any, have been // completed; any supporting data structures can be reset. Default is to // do nothing. virtual void par_oop_since_save_marks_iterate_done(int thread_num) {} // This generation will collect all younger generations // during a full collection. virtual bool full_collects_younger_generations() const { return false; } // This generation does in-place marking, meaning that mark words // are mutated during the marking phase and presumably reinitialized // to a canonical value after the GC. This is currently used by the // biased locking implementation to determine whether additional // work is required during the GC prologue and epilogue. virtual bool performs_in_place_marking() const { return true; } // Returns "true" iff collect() should subsequently be called on this // this generation. See comment below. // This is a generic implementation which can be overridden. // // Note: in the current (1.4) implementation, when genCollectedHeap's // incremental_collection_will_fail flag is set, all allocations are // slow path (the only fast-path place to allocate is DefNew, which // will be full if the flag is set). // Thus, older generations which collect younger generations should // test this flag and collect if it is set. virtual bool should_collect(bool full, size_t word_size, bool is_tlab) { return (full || should_allocate(word_size, is_tlab)); } // Perform a garbage collection. // If full is true attempt a full garbage collection of this generation. // Otherwise, attempting to (at least) free enough space to support an // allocation of the given "word_size". virtual void collect(bool full, bool clear_all_soft_refs, size_t word_size, bool is_tlab) = 0; // Perform a heap collection, attempting to create (at least) enough // space to support an allocation of the given "word_size". If // successful, perform the allocation and return the resulting // "oop" (initializing the allocated block). If the allocation is // still unsuccessful, return "NULL". virtual HeapWord* expand_and_allocate(size_t word_size, bool is_tlab, bool parallel = false) = 0; // Some generations may require some cleanup or preparation actions before // allowing a collection. The default is to do nothing. virtual void gc_prologue(bool full) {}; // Some generations may require some cleanup actions after a collection. // The default is to do nothing. virtual void gc_epilogue(bool full) {}; // Save the high water marks for the used space in a generation. virtual void record_spaces_top() {}; // Some generations may need to be "fixed-up" after some allocation // activity to make them parsable again. The default is to do nothing. virtual void ensure_parsability() {}; // Time (in ms) when we were last collected or now if a collection is // in progress. virtual jlong time_of_last_gc(jlong now) { // XXX See note in genCollectedHeap::millis_since_last_gc() NOT_PRODUCT( if (now < _time_of_last_gc) { warning("time warp: %d to %d", _time_of_last_gc, now); } ) return _time_of_last_gc; } virtual void update_time_of_last_gc(jlong now) { _time_of_last_gc = now; } // Generations may keep statistics about collection. This // method updates those statistics. current_level is // the level of the collection that has most recently // occurred. This allows the generation to decide what // statistics are valid to collect. For example, the // generation can decide to gather the amount of promoted data // if the collection of the younger generations has completed. GCStats* gc_stats() const { return _gc_stats; } virtual void update_gc_stats(int current_level, bool full) {} // Mark sweep support phase2 virtual void prepare_for_compaction(CompactPoint* cp); // Mark sweep support phase3 virtual void pre_adjust_pointers() {ShouldNotReachHere();} virtual void adjust_pointers(); // Mark sweep support phase4 virtual void compact(); virtual void post_compact() {ShouldNotReachHere();} // Support for CMS's rescan. In this general form we return a pointer // to an abstract object that can be used, based on specific previously // decided protocols, to exchange information between generations, // information that may be useful for speeding up certain types of // garbage collectors. A NULL value indicates to the client that // no data recording is expected by the provider. The data-recorder is // expected to be GC worker thread-local, with the worker index // indicated by "thr_num". virtual void* get_data_recorder(int thr_num) { return NULL; } // Some generations may require some cleanup actions before allowing // a verification. virtual void prepare_for_verify() {}; // Accessing "marks". // This function gives a generation a chance to note a point between // collections. For example, a contiguous generation might note the // beginning allocation point post-collection, which might allow some later // operations to be optimized. virtual void save_marks() {} // This function allows generations to initialize any "saved marks". That // is, should only be called when the generation is empty. virtual void reset_saved_marks() {} // This function is "true" iff any no allocations have occurred in the // generation since the last call to "save_marks". virtual bool no_allocs_since_save_marks() = 0; // Apply "cl->apply" to (the addresses of) all reference fields in objects // allocated in the current generation since the last call to "save_marks". // If more objects are allocated in this generation as a result of applying // the closure, iterates over reference fields in those objects as well. // Calls "save_marks" at the end of the iteration. // General signature... virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0; // ...and specializations for de-virtualization. (The general // implemention of the _nv versions call the virtual version. // Note that the _nv suffix is not really semantically necessary, // but it avoids some not-so-useful warnings on Solaris.) #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \ virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ oop_since_save_marks_iterate_v((OopsInGenClosure*)cl); \ } SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL) #undef Generation_SINCE_SAVE_MARKS_DECL // The "requestor" generation is performing some garbage collection // action for which it would be useful to have scratch space. If // the target is not the requestor, no gc actions will be required // of the target. The requestor promises to allocate no more than // "max_alloc_words" in the target generation (via promotion say, // if the requestor is a young generation and the target is older). // If the target generation can provide any scratch space, it adds // it to "list", leaving "list" pointing to the head of the // augmented list. The default is to offer no space. virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor, size_t max_alloc_words) {} // Give each generation an opportunity to do clean up for any // contributed scratch. virtual void reset_scratch() {}; // When an older generation has been collected, and perhaps resized, // this method will be invoked on all younger generations (from older to // younger), allowing them to resize themselves as appropriate. virtual void compute_new_size() = 0; // Printing virtual const char* name() const = 0; virtual const char* short_name() const = 0; int level() const { return _level; } // Attributes // True iff the given generation may only be the youngest generation. virtual bool must_be_youngest() const = 0; // True iff the given generation may only be the oldest generation. virtual bool must_be_oldest() const = 0; // Reference Processing accessor ReferenceProcessor* const ref_processor() { return _ref_processor; } // Iteration. // Iterate over all the ref-containing fields of all objects in the // generation, calling "cl.do_oop" on each. virtual void oop_iterate(OopClosure* cl); // Same as above, restricted to the intersection of a memory region and // the generation. virtual void oop_iterate(MemRegion mr, OopClosure* cl); // Iterate over all objects in the generation, calling "cl.do_object" on // each. virtual void object_iterate(ObjectClosure* cl); // Iterate over all safe objects in the generation, calling "cl.do_object" on // each. An object is safe if its references point to other objects in // the heap. This defaults to object_iterate() unless overridden. virtual void safe_object_iterate(ObjectClosure* cl); // Iterate over all objects allocated in the generation since the last // collection, calling "cl.do_object" on each. The generation must have // been initialized properly to support this function, or else this call // will fail. virtual void object_iterate_since_last_GC(ObjectClosure* cl) = 0; // Apply "cl->do_oop" to (the address of) all and only all the ref fields // in the current generation that contain pointers to objects in younger // generations. Objects allocated since the last "save_marks" call are // excluded. virtual void younger_refs_iterate(OopsInGenClosure* cl) = 0; // Inform a generation that it longer contains references to objects // in any younger generation. [e.g. Because younger gens are empty, // clear the card table.] virtual void clear_remembered_set() { } // Inform a generation that some of its objects have moved. [e.g. The // generation's spaces were compacted, invalidating the card table.] virtual void invalidate_remembered_set() { } // Block abstraction. // Returns the address of the start of the "block" that contains the // address "addr". We say "blocks" instead of "object" since some heaps // may not pack objects densely; a chunk may either be an object or a // non-object. virtual HeapWord* block_start(const void* addr) const; // Requires "addr" to be the start of a chunk, and returns its size. // "addr + size" is required to be the start of a new chunk, or the end // of the active area of the heap. virtual size_t block_size(const HeapWord* addr) const ; // Requires "addr" to be the start of a block, and returns "TRUE" iff // the block is an object. virtual bool block_is_obj(const HeapWord* addr) const; // PrintGC, PrintGCDetails support void print_heap_change(size_t prev_used) const; // PrintHeapAtGC support virtual void print() const; virtual void print_on(outputStream* st) const; virtual void verify(bool allow_dirty) = 0; struct StatRecord { int invocations; elapsedTimer accumulated_time; StatRecord() : invocations(0), accumulated_time(elapsedTimer()) {} }; private: StatRecord _stat_record; public: StatRecord* stat_record() { return &_stat_record; } virtual void print_summary_info(); virtual void print_summary_info_on(outputStream* st); // Performance Counter support virtual void update_counters() = 0; virtual CollectorCounters* counters() { return _gc_counters; } }; // Class CardGeneration is a generation that is covered by a card table, // and uses a card-size block-offset array to implement block_start. // class BlockOffsetArray; // class BlockOffsetArrayContigSpace; class BlockOffsetSharedArray; class CardGeneration: public Generation { friend class VMStructs; protected: // This is shared with other generations. GenRemSet* _rs; // This is local to this generation. BlockOffsetSharedArray* _bts; CardGeneration(ReservedSpace rs, size_t initial_byte_size, int level, GenRemSet* remset); public: // Attempt to expand the generation by "bytes". Expand by at a // minimum "expand_bytes". Return true if some amount (not // necessarily the full "bytes") was done. virtual bool expand(size_t bytes, size_t expand_bytes); virtual void clear_remembered_set(); virtual void invalidate_remembered_set(); virtual void prepare_for_verify(); // Grow generation with specified size (returns false if unable to grow) virtual bool grow_by(size_t bytes) = 0; // Grow generation to reserved size. virtual bool grow_to_reserved() = 0; }; // OneContigSpaceCardGeneration models a heap of old objects contained in a single // contiguous space. // // Garbage collection is performed using mark-compact. class OneContigSpaceCardGeneration: public CardGeneration { friend class VMStructs; // Abstractly, this is a subtype that gets access to protected fields. friend class CompactingPermGen; friend class VM_PopulateDumpSharedSpace; protected: size_t _min_heap_delta_bytes; // Minimum amount to expand. ContiguousSpace* _the_space; // actual space holding objects WaterMark _last_gc; // watermark between objects allocated before // and after last GC. // Grow generation with specified size (returns false if unable to grow) virtual bool grow_by(size_t bytes); // Grow generation to reserved size. virtual bool grow_to_reserved(); // Shrink generation with specified size (returns false if unable to shrink) void shrink_by(size_t bytes); // Allocation failure virtual bool expand(size_t bytes, size_t expand_bytes); void shrink(size_t bytes); // Accessing spaces ContiguousSpace* the_space() const { return _the_space; } public: OneContigSpaceCardGeneration(ReservedSpace rs, size_t initial_byte_size, size_t min_heap_delta_bytes, int level, GenRemSet* remset, ContiguousSpace* space) : CardGeneration(rs, initial_byte_size, level, remset), _the_space(space), _min_heap_delta_bytes(min_heap_delta_bytes) {} inline bool is_in(const void* p) const; // Space enquiries size_t capacity() const; size_t used() const; size_t free() const; MemRegion used_region() const; size_t unsafe_max_alloc_nogc() const; size_t contiguous_available() const; // Iteration void object_iterate(ObjectClosure* blk); void space_iterate(SpaceClosure* blk, bool usedOnly = false); void object_iterate_since_last_GC(ObjectClosure* cl); void younger_refs_iterate(OopsInGenClosure* blk); inline CompactibleSpace* first_compaction_space() const; virtual inline HeapWord* allocate(size_t word_size, bool is_tlab); virtual inline HeapWord* par_allocate(size_t word_size, bool is_tlab); // Accessing marks inline WaterMark top_mark(); inline WaterMark bottom_mark(); #define OneContig_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \ void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl); OneContig_SINCE_SAVE_MARKS_DECL(OopsInGenClosure,_v) SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(OneContig_SINCE_SAVE_MARKS_DECL) void save_marks(); void reset_saved_marks(); bool no_allocs_since_save_marks(); inline size_t block_size(const HeapWord* addr) const; inline bool block_is_obj(const HeapWord* addr) const; virtual void collect(bool full, bool clear_all_soft_refs, size_t size, bool is_tlab); HeapWord* expand_and_allocate(size_t size, bool is_tlab, bool parallel = false); virtual void prepare_for_verify(); virtual void gc_epilogue(bool full); virtual void record_spaces_top(); virtual void verify(bool allow_dirty); virtual void print_on(outputStream* st) const; };