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 * published by the Free Software Foundation.

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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

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 */

// 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;

  // 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