Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright 1997-2008 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 space is an abstraction for the "storage units" backing

 // up the generation abstraction. It includes specific

 // implementations for keeping track of free and used space,

 // for iterating over objects and free blocks, etc.

 // Here's the Space hierarchy:

 //

 // - Space               -- an asbtract base class describing a heap area

 //   - CompactibleSpace  -- a space supporting compaction

 //     - CompactibleFreeListSpace -- (used for CMS generation)

 //     - ContiguousSpace -- a compactible space in which all free space

 //                          is contiguous

 //       - EdenSpace     -- contiguous space used as nursery

 //         - ConcEdenSpace -- contiguous space with a 'soft end safe' allocation

 //       - OffsetTableContigSpace -- contiguous space with a block offset array

 //                          that allows "fast" block_start calls

 //         - TenuredSpace -- (used for TenuredGeneration)

 //         - ContigPermSpace -- an offset table contiguous space for perm gen

 // Forward decls.

 class Space;

 class BlockOffsetArray;

 class BlockOffsetArrayContigSpace;

 class Generation;

 class CompactibleSpace;

 class BlockOffsetTable;

 class GenRemSet;

 class CardTableRS;

 class DirtyCardToOopClosure;

 // An oop closure that is circumscribed by a filtering memory region.

 class SpaceMemRegionOopsIterClosure: public OopClosure {

  private:

   OopClosure* _cl;

   MemRegion   _mr;

  protected:

   template <class T> void do_oop_work(T* p) {

     if (_mr.contains(p)) {

       _cl->do_oop(p);

     }

   }

  public:

   SpaceMemRegionOopsIterClosure(OopClosure* cl, MemRegion mr):

     _cl(cl), _mr(mr) {}

   virtual void do_oop(oop* p);

   virtual void do_oop(narrowOop* p);

 };

 // A Space describes a heap area. Class Space is an abstract

 // base class.

 //

 // Space supports allocation, size computation and GC support is provided.

 //

 // Invariant: bottom() and end() are on page_size boundaries and

 // bottom() <= top() <= end()

 // top() is inclusive and end() is exclusive.

 class Space: public CHeapObj {

   friend class VMStructs;

  protected:

   HeapWord* _bottom;

   HeapWord* _end;

   // Used in support of save_marks()

   HeapWord* _saved_mark_word;

   MemRegionClosure* _preconsumptionDirtyCardClosure;

   // A sequential tasks done structure. This supports

   // parallel GC, where we have threads dynamically

   // claiming sub-tasks from a larger parallel task.

   SequentialSubTasksDone _par_seq_tasks;

   Space():

     _bottom(NULL), _end(NULL), _preconsumptionDirtyCardClosure(NULL) { }

  public:

   // Accessors

   HeapWord* bottom() const         { return _bottom; }

   HeapWord* end() const            { return _end;    }

   virtual void set_bottom(HeapWord* value) { _bottom = value; }

   virtual void set_end(HeapWord* value)    { _end = value; }

   virtual HeapWord* saved_mark_word() const  { return _saved_mark_word; }

   void set_saved_mark_word(HeapWord* p) { _saved_mark_word = p; }

   MemRegionClosure* preconsumptionDirtyCardClosure() const {

     return _preconsumptionDirtyCardClosure;

   }

   void setPreconsumptionDirtyCardClosure(MemRegionClosure* cl) {

     _preconsumptionDirtyCardClosure = cl;

   }

   // Returns a subregion of the space containing all the objects in

   // the space.

   virtual MemRegion used_region() const { return MemRegion(bottom(), end()); }

   // Returns a region that is guaranteed to contain (at least) all objects

   // allocated at the time of the last call to "save_marks".  If the space

   // initializes its DirtyCardToOopClosure's specifying the "contig" option

   // (that is, if the space is contiguous), then this region must contain only

   // such objects: the memregion will be from the bottom of the region to the

   // saved mark.  Otherwise, the "obj_allocated_since_save_marks" method of

   // the space must distiguish between objects in the region allocated before

   // and after the call to save marks.

   virtual MemRegion used_region_at_save_marks() const {

     return MemRegion(bottom(), saved_mark_word());

   }

   // Initialization.

   // "initialize" should be called once on a space, before it is used for

   // any purpose.  The "mr" arguments gives the bounds of the space, and

   // the "clear_space" argument should be true unless the memory in "mr" is

   // known to be zeroed.

   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);

   // The "clear" method must be called on a region that may have

   // had allocation performed in it, but is now to be considered empty.

   virtual void clear(bool mangle_space);

   // For detecting GC bugs.  Should only be called at GC boundaries, since

   // some unused space may be used as scratch space during GC's.

   // Default implementation does nothing. We also call this when expanding

   // a space to satisfy an allocation request. See bug #4668531

   virtual void mangle_unused_area() {}

   virtual void mangle_unused_area_complete() {}

   virtual void mangle_region(MemRegion mr) {}

   // Testers

   bool is_empty() const              { return used() == 0; }

   bool not_empty() const             { return used() > 0; }

   // Returns true iff the given the space contains the

   // given address as part of an allocated object. For

   // ceratin kinds of spaces, this might be a potentially

   // expensive operation. To prevent performance problems

   // on account of its inadvertent use in product jvm's,

   // we restrict its use to assertion checks only.

   virtual bool is_in(const void* p) const;

   // Returns true iff the given reserved memory of the space contains the

   // given address.

   bool is_in_reserved(const void* p) const { return _bottom <= p && p < _end; }

   // Returns true iff the given block is not allocated.

   virtual bool is_free_block(const HeapWord* p) const = 0;

   // Test whether p is double-aligned

   static bool is_aligned(void* p) {

     return ((intptr_t)p & (sizeof(double)-1)) == 0;

   }

   // Size computations.  Sizes are in bytes.

   size_t capacity()     const { return byte_size(bottom(), end()); }

   virtual size_t used() const = 0;

   virtual size_t free() const = 0;

   // Iterate over all the ref-containing fields of all objects in the

   // space, calling "cl.do_oop" on each.  Fields in objects allocated by

   // applications of the closure are not included in the iteration.

   virtual void oop_iterate(OopClosure* cl);

   // Same as above, restricted to the intersection of a memory region and

   // the space.  Fields in objects allocated by applications of the closure

   // are not included in the iteration.

   virtual void oop_iterate(MemRegion mr, OopClosure* cl) = 0;

   // Iterate over all objects in the space, calling "cl.do_object" on

   // each.  Objects allocated by applications of the closure are not

   // included in the iteration.

   virtual void object_iterate(ObjectClosure* blk) = 0;

   // Iterate over all objects that intersect with mr, calling "cl->do_object"

   // on each.  There is an exception to this: if this closure has already

   // been invoked on an object, it may skip such objects in some cases.  This is

   // Most likely to happen in an "upwards" (ascending address) iteration of

   // MemRegions.

   virtual void object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl);

   // Iterate over as many initialized objects in the space as possible,

   // calling "cl.do_object_careful" on each. Return NULL if all objects

   // in the space (at the start of the iteration) were iterated over.

   // Return an address indicating the extent of the iteration in the

   // event that the iteration had to return because of finding an

   // uninitialized object in the space, or if the closure "cl"

   // signalled early termination.

   virtual HeapWord* object_iterate_careful(ObjectClosureCareful* cl);

   virtual HeapWord* object_iterate_careful_m(MemRegion mr,

                                              ObjectClosureCareful* cl);

   // Create and return a new dirty card to oop closure. Can be

   // overriden to return the appropriate type of closure

   // depending on the type of space in which the closure will

   // operate. ResourceArea allocated.

   virtual DirtyCardToOopClosure* new_dcto_cl(OopClosure* cl,

                                              CardTableModRefBS::PrecisionStyle precision,

                                              HeapWord* boundary = NULL);

   // If "p" is in the space, returns the address of the start of the

   // "block" that contains "p".  We say "block" instead of "object" since

   // some heaps may not pack objects densely; a chunk may either be an

   // object or a non-object.  If "p" is not in the space, return NULL.

   virtual HeapWord* block_start_const(const void* p) const = 0;

   // The non-const version may have benevolent side effects on the data

   // structure supporting these calls, possibly speeding up future calls.

   // The default implementation, however, is simply to call the const

   // version.

   inline virtual HeapWord* block_start(const void* p);

   // 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 = 0;

   // 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 = 0;

   // Requires "addr" to be the start of a block, and returns "TRUE" iff

   // the block is an object and the object is alive.

   virtual bool obj_is_alive(const HeapWord* addr) const;

   // Allocation (return NULL if full).  Assumes the caller has established

   // mutually exclusive access to the space.

   virtual HeapWord* allocate(size_t word_size) = 0;

   // Allocation (return NULL if full).  Enforces mutual exclusion internally.

   virtual HeapWord* par_allocate(size_t word_size) = 0;

   // Returns true if this object has been allocated since a

   // generation's "save_marks" call.

   virtual bool obj_allocated_since_save_marks(const oop obj) const = 0;

   // Mark-sweep-compact support: all spaces can update pointers to objects

   // moving as a part of compaction.

   virtual void adjust_pointers();

   // PrintHeapAtGC support

   virtual void print() const;

   virtual void print_on(outputStream* st) const;

   virtual void print_short() const;

   virtual void print_short_on(outputStream* st) const;

   // Accessor for parallel sequential tasks.

   SequentialSubTasksDone* par_seq_tasks() { return &_par_seq_tasks; }

   // IF "this" is a ContiguousSpace, return it, else return NULL.

   virtual ContiguousSpace* toContiguousSpace() {

     return NULL;

   }

   // Debugging

   virtual void verify(bool allow_dirty) const = 0;

 };

 // A MemRegionClosure (ResourceObj) whose "do_MemRegion" function applies an

 // OopClosure to (the addresses of) all the ref-containing fields that could

 // be modified by virtue of the given MemRegion being dirty. (Note that

 // because of the imprecise nature of the write barrier, this may iterate

 // over oops beyond the region.)

 // This base type for dirty card to oop closures handles memory regions

 // in non-contiguous spaces with no boundaries, and should be sub-classed

 // to support other space types. See ContiguousDCTOC for a sub-class

 // that works with ContiguousSpaces.

 class DirtyCardToOopClosure: public MemRegionClosureRO {

 protected:

   OopClosure* _cl;

   Space* _sp;

   CardTableModRefBS::PrecisionStyle _precision;

   HeapWord* _boundary;          // If non-NULL, process only non-NULL oops

                                 // pointing below boundary.

   HeapWord* _min_done;          // ObjHeadPreciseArray precision requires

                                 // a downwards traversal; this is the

                                 // lowest location already done (or,

                                 // alternatively, the lowest address that

                                 // shouldn't be done again.  NULL means infinity.)

   NOT_PRODUCT(HeapWord* _last_bottom;)

   NOT_PRODUCT(HeapWord* _last_explicit_min_done;)

   // Get the actual top of the area on which the closure will

   // operate, given where the top is assumed to be (the end of the

   // memory region passed to do_MemRegion) and where the object

   // at the top is assumed to start. For example, an object may

   // start at the top but actually extend past the assumed top,

   // in which case the top becomes the end of the object.

   virtual HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);

   // Walk the given memory region from bottom to (actual) top

   // looking for objects and applying the oop closure (_cl) to

   // them. The base implementation of this treats the area as

   // blocks, where a block may or may not be an object. Sub-

   // classes should override this to provide more accurate

   // or possibly more efficient walking.

   virtual void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top);

 public:

   DirtyCardToOopClosure(Space* sp, OopClosure* cl,

                         CardTableModRefBS::PrecisionStyle precision,

                         HeapWord* boundary) :

     _sp(sp), _cl(cl), _precision(precision), _boundary(boundary),

     _min_done(NULL) {

     NOT_PRODUCT(_last_bottom = NULL);

     NOT_PRODUCT(_last_explicit_min_done = NULL);

   }

   void do_MemRegion(MemRegion mr);

   void set_min_done(HeapWord* min_done) {

     _min_done = min_done;

     NOT_PRODUCT(_last_explicit_min_done = _min_done);

   }

 #ifndef PRODUCT

   void set_last_bottom(HeapWord* last_bottom) {

     _last_bottom = last_bottom;

   }

 #endif

 };

 // A structure to represent a point at which objects are being copied

 // during compaction.

 class CompactPoint : public StackObj {

 public:

   Generation* gen;

   CompactibleSpace* space;

   HeapWord* threshold;

   CompactPoint(Generation* _gen, CompactibleSpace* _space,

                HeapWord* _threshold) :

     gen(_gen), space(_space), threshold(_threshold) {}

 };

 // A space that supports compaction operations.  This is usually, but not

 // necessarily, a space that is normally contiguous.  But, for example, a

 // free-list-based space whose normal collection is a mark-sweep without

 // compaction could still support compaction in full GC's.

 class CompactibleSpace: public Space {

   friend class VMStructs;

   friend class CompactibleFreeListSpace;

   friend class CompactingPermGenGen;

   friend class CMSPermGenGen;

 private:

   HeapWord* _compaction_top;

   CompactibleSpace* _next_compaction_space;

 public:

   CompactibleSpace() :

    _compaction_top(NULL), _next_compaction_space(NULL) {}

   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);

   virtual void clear(bool mangle_space);

   // Used temporarily during a compaction phase to hold the value

   // top should have when compaction is complete.

   HeapWord* compaction_top() const { return _compaction_top;    }

   void set_compaction_top(HeapWord* value) {

     assert(value == NULL || (value >= bottom() && value <= end()),

       "should point inside space");

     _compaction_top = value;

   }

   // Perform operations on the space needed after a compaction

   // has been performed.

   virtual void reset_after_compaction() {}

   // Returns the next space (in the current generation) to be compacted in

   // the global compaction order.  Also is used to select the next

   // space into which to compact.

   virtual CompactibleSpace* next_compaction_space() const {

     return _next_compaction_space;

   }

   void set_next_compaction_space(CompactibleSpace* csp) {

     _next_compaction_space = csp;

   }

   // MarkSweep support phase2

   // Start the process of compaction of the current space: compute

   // post-compaction addresses, and insert forwarding pointers.  The fields

   // "cp->gen" and "cp->compaction_space" are the generation and space into

   // which we are currently compacting.  This call updates "cp" as necessary,

   // and leaves the "compaction_top" of the final value of

   // "cp->compaction_space" up-to-date.  Offset tables may be updated in

   // this phase as if the final copy had occurred; if so, "cp->threshold"

   // indicates when the next such action should be taken.

   virtual void prepare_for_compaction(CompactPoint* cp);

   // MarkSweep support phase3

   virtual void adjust_pointers();

   // MarkSweep support phase4

   virtual void compact();

   // The maximum percentage of objects that can be dead in the compacted

   // live part of a compacted space ("deadwood" support.)

   virtual size_t allowed_dead_ratio() const { return 0; };

   // Some contiguous spaces may maintain some data structures that should

   // be updated whenever an allocation crosses a boundary.  This function

   // returns the first such boundary.

   // (The default implementation returns the end of the space, so the

   // boundary is never crossed.)

   virtual HeapWord* initialize_threshold() { return end(); }

   // "q" is an object of the given "size" that should be forwarded;

   // "cp" names the generation ("gen") and containing "this" (which must

   // also equal "cp->space").  "compact_top" is where in "this" the

   // next object should be forwarded to.  If there is room in "this" for

   // the object, insert an appropriate forwarding pointer in "q".

   // If not, go to the next compaction space (there must

   // be one, since compaction must succeed -- we go to the first space of

   // the previous generation if necessary, updating "cp"), reset compact_top

   // and then forward.  In either case, returns the new value of "compact_top".

   // If the forwarding crosses "cp->threshold", invokes the "cross_threhold"

   // function of the then-current compaction space, and updates "cp->threshold

   // accordingly".

   virtual HeapWord* forward(oop q, size_t size, CompactPoint* cp,

                     HeapWord* compact_top);

   // Return a size with adjusments as required of the space.

   virtual size_t adjust_object_size_v(size_t size) const { return size; }

 protected:

   // Used during compaction.

   HeapWord* _first_dead;

   HeapWord* _end_of_live;

   // Minimum size of a free block.

   virtual size_t minimum_free_block_size() const = 0;

   // This the function is invoked when an allocation of an object covering

   // "start" to "end occurs crosses the threshold; returns the next

   // threshold.  (The default implementation does nothing.)

   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* the_end) {

     return end();

   }

   // Requires "allowed_deadspace_words > 0", that "q" is the start of a

   // free block of the given "word_len", and that "q", were it an object,

   // would not move if forwared.  If the size allows, fill the free

   // block with an object, to prevent excessive compaction.  Returns "true"

   // iff the free region was made deadspace, and modifies

   // "allowed_deadspace_words" to reflect the number of available deadspace

   // words remaining after this operation.

   bool insert_deadspace(size_t& allowed_deadspace_words, HeapWord* q,

                         size_t word_len);

 };

 #define SCAN_AND_FORWARD(cp,scan_limit,block_is_obj,block_size) {            \

   /* Compute the new addresses for the live objects and store it in the mark \

    * Used by universe::mark_sweep_phase2()                                   \

    */                                                                        \

   HeapWord* compact_top; /* This is where we are currently compacting to. */ \

                                                                              \

   /* We're sure to be here before any objects are compacted into this        \

    * space, so this is a good time to initialize this:                       \

    */                                                                        \

   set_compaction_top(bottom());                                              \

                                                                              \

   if (cp->space == NULL) {                                                   \

     assert(cp->gen != NULL, "need a generation");                            \

     assert(cp->threshold == NULL, "just checking");                          \

     assert(cp->gen->first_compaction_space() == this, "just checking");      \

     cp->space = cp->gen->first_compaction_space();                           \

     compact_top = cp->space->bottom();                                       \

     cp->space->set_compaction_top(compact_top);                              \

     cp->threshold = cp->space->initialize_threshold();                       \

   } else {                                                                   \

     compact_top = cp->space->compaction_top();                               \

   }                                                                          \

                                                                              \

   /* We allow some amount of garbage towards the bottom of the space, so     \

    * we don't start compacting before there is a significant gain to be made.\

    * Occasionally, we want to ensure a full compaction, which is determined  \

    * by the MarkSweepAlwaysCompactCount parameter.                           \

    */                                                                        \

   int invocations = SharedHeap::heap()->perm_gen()->stat_record()->invocations;\

   bool skip_dead = ((invocations % MarkSweepAlwaysCompactCount) != 0);       \

                                                                              \

   size_t allowed_deadspace = 0;                                              \

   if (skip_dead) {                                                           \

     const size_t ratio = allowed_dead_ratio();                               \

     allowed_deadspace = (capacity() * ratio / 100) / HeapWordSize;           \

   }                                                                          \

                                                                              \

   HeapWord* q = bottom();                                                    \

   HeapWord* t = scan_limit();                                                \

                                                                              \

   HeapWord*  end_of_live= q;    /* One byte beyond the last byte of the last \

                                    live object. */                           \

   HeapWord*  first_dead = end();/* The first dead object. */                 \

   LiveRange* liveRange  = NULL; /* The current live range, recorded in the   \

                                    first header of preceding free area. */   \

   _first_dead = first_dead;                                                  \

                                                                              \

   const intx interval = PrefetchScanIntervalInBytes;                         \

                                                                              \

   while (q < t) {                                                            \

     assert(!block_is_obj(q) ||                                               \

            oop(q)->mark()->is_marked() || oop(q)->mark()->is_unlocked() ||   \

            oop(q)->mark()->has_bias_pattern(),                               \

            "these are the only valid states during a mark sweep");           \

     if (block_is_obj(q) && oop(q)->is_gc_marked()) {                         \

       /* prefetch beyond q */                                                \

       Prefetch::write(q, interval);                                          \

       /* size_t size = oop(q)->size();  changing this for cms for perm gen */\

       size_t size = block_size(q);                                           \

       compact_top = cp->space->forward(oop(q), size, cp, compact_top);       \

       q += size;                                                             \

       end_of_live = q;                                                       \

     } else {                                                                 \

       /* run over all the contiguous dead objects */                         \

       HeapWord* end = q;                                                     \

       do {                                                                   \

         /* prefetch beyond end */                                            \

         Prefetch::write(end, interval);                                      \

         end += block_size(end);                                              \

       } while (end < t && (!block_is_obj(end) || !oop(end)->is_gc_marked()));\

                                                                              \

       /* see if we might want to pretend this object is alive so that        \

        * we don't have to compact quite as often.                            \

        */                                                                    \

       if (allowed_deadspace > 0 && q == compact_top) {                       \

         size_t sz = pointer_delta(end, q);                                   \

         if (insert_deadspace(allowed_deadspace, q, sz)) {                    \

           compact_top = cp->space->forward(oop(q), sz, cp, compact_top);     \

           q = end;                                                           \

           end_of_live = end;                                                 \

           continue;                                                          \

         }                                                                    \

       }                                                                      \

                                                                              \

       /* otherwise, it really is a free region. */                           \

                                                                              \

       /* for the previous LiveRange, record the end of the live objects. */  \

       if (liveRange) {                                                       \

         liveRange->set_end(q);                                               \

       }                                                                      \

                                                                              \

       /* record the current LiveRange object.                                \

        * liveRange->start() is overlaid on the mark word.                    \

        */                                                                    \

       liveRange = (LiveRange*)q;                                             \

       liveRange->set_start(end);                                             \

       liveRange->set_end(end);                                               \

                                                                              \

       /* see if this is the first dead region. */                            \

       if (q < first_dead) {                                                  \

         first_dead = q;                                                      \

       }                                                                      \

                                                                              \

       /* move on to the next object */                                       \

       q = end;                                                               \

     }                                                                        \

   }                                                                          \

                                                                              \

   assert(q == t, "just checking");                                           \

   if (liveRange != NULL) {                                                   \

     liveRange->set_end(q);                                                   \

   }                                                                          \

   _end_of_live = end_of_live;                                                \

   if (end_of_live < first_dead) {                                            \

     first_dead = end_of_live;                                                \

   }                                                                          \

   _first_dead = first_dead;                                                  \

                                                                              \

   /* save the compaction_top of the compaction space. */                     \

   cp->space->set_compaction_top(compact_top);                                \

 }

 #define SCAN_AND_ADJUST_POINTERS(adjust_obj_size) {                             \

   /* adjust all the interior pointers to point at the new locations of objects  \

    * Used by MarkSweep::mark_sweep_phase3() */                                  \

                                                                                 \

   HeapWord* q = bottom();                                                       \

   HeapWord* t = _end_of_live;  /* Established by "prepare_for_compaction". */   \

                                                                                 \

   assert(_first_dead <= _end_of_live, "Stands to reason, no?");                 \

                                                                                 \

   if (q < t && _first_dead > q &&                                               \

       !oop(q)->is_gc_marked()) {                                                \

     /* we have a chunk of the space which hasn't moved and we've                \

      * reinitialized the mark word during the previous pass, so we can't        \

      * use is_gc_marked for the traversal. */                                   \

     HeapWord* end = _first_dead;                                                \

                                                                                 \

     while (q < end) {                                                           \

       /* I originally tried to conjoin "block_start(q) == q" to the             \

        * assertion below, but that doesn't work, because you can't              \

        * accurately traverse previous objects to get to the current one         \

        * after their pointers (including pointers into permGen) have been       \

        * updated, until the actual compaction is done.  dld, 4/00 */            \

       assert(block_is_obj(q),                                                   \

              "should be at block boundaries, and should be looking at objs");   \

                                                                                 \

       VALIDATE_MARK_SWEEP_ONLY(MarkSweep::track_interior_pointers(oop(q)));     \

                                                                                 \

       /* point all the oops to the new location */                              \

       size_t size = oop(q)->adjust_pointers();                                  \

       size = adjust_obj_size(size);                                             \

                                                                                 \

       VALIDATE_MARK_SWEEP_ONLY(MarkSweep::check_interior_pointers());           \

                                                                                 \

       VALIDATE_MARK_SWEEP_ONLY(MarkSweep::validate_live_oop(oop(q), size));     \

                                                                                 \

       q += size;                                                                \

     }                                                                           \

                                                                                 \

     if (_first_dead == t) {                                                     \

       q = t;                                                                    \

     } else {                                                                    \

       /* $$$ This is funky.  Using this to read the previously written          \

        * LiveRange.  See also use below. */                                     \

       q = (HeapWord*)oop(_first_dead)->mark()->decode_pointer();                \

     }                                                                           \

   }                                                                             \

                                                                                 \

   const intx interval = PrefetchScanIntervalInBytes;                            \

                                                                                 \

   debug_only(HeapWord* prev_q = NULL);                                          \

   while (q < t) {                                                               \

     /* prefetch beyond q */                                                     \

     Prefetch::write(q, interval);                                               \

     if (oop(q)->is_gc_marked()) {                                               \

       /* q is alive */                                                          \

       VALIDATE_MARK_SWEEP_ONLY(MarkSweep::track_interior_pointers(oop(q)));     \

       /* point all the oops to the new location */                              \

       size_t size = oop(q)->adjust_pointers();                                  \

       size = adjust_obj_size(size);                                             \

       VALIDATE_MARK_SWEEP_ONLY(MarkSweep::check_interior_pointers());           \

       VALIDATE_MARK_SWEEP_ONLY(MarkSweep::validate_live_oop(oop(q), size));     \

       debug_only(prev_q = q);                                                   \

       q += size;                                                                \

     } else {                                                                    \

       /* q is not a live object, so its mark should point at the next           \

        * live object */                                                         \

       debug_only(prev_q = q);                                                   \

       q = (HeapWord*) oop(q)->mark()->decode_pointer();                         \

       assert(q > prev_q, "we should be moving forward through memory");         \

     }                                                                           \

   }                                                                             \

                                                                                 \

   assert(q == t, "just checking");                                              \

 }

 #define SCAN_AND_COMPACT(obj_size) {                                            \

   /* Copy all live objects to their new location                                \

    * Used by MarkSweep::mark_sweep_phase4() */                                  \

                                                                                 \

   HeapWord*       q = bottom();                                                 \

   HeapWord* const t = _end_of_live;                                             \

   debug_only(HeapWord* prev_q = NULL);                                          \

                                                                                 \

   if (q < t && _first_dead > q &&                                               \

       !oop(q)->is_gc_marked()) {                                                \

     debug_only(                                                                 \

     /* we have a chunk of the space which hasn't moved and we've reinitialized  \

      * the mark word during the previous pass, so we can't use is_gc_marked for \

      * the traversal. */                                                        \

     HeapWord* const end = _first_dead;                                          \

                                                                                 \

     while (q < end) {                                                           \

       size_t size = obj_size(q);                                                \

       assert(!oop(q)->is_gc_marked(),                                           \

              "should be unmarked (special dense prefix handling)");             \

       VALIDATE_MARK_SWEEP_ONLY(MarkSweep::live_oop_moved_to(q, size, q));       \

       debug_only(prev_q = q);                                                   \

       q += size;                                                                \

     }                                                                           \

     )  /* debug_only */                                                         \

                                                                                 \

     if (_first_dead == t) {                                                     \

       q = t;                                                                    \

     } else {                                                                    \

       /* $$$ Funky */                                                           \

       q = (HeapWord*) oop(_first_dead)->mark()->decode_pointer();               \

     }                                                                           \

   }                                                                             \

                                                                                 \

   const intx scan_interval = PrefetchScanIntervalInBytes;                       \

   const intx copy_interval = PrefetchCopyIntervalInBytes;                       \

   while (q < t) {                                                               \

     if (!oop(q)->is_gc_marked()) {                                              \

       /* mark is pointer to next marked oop */                                  \

       debug_only(prev_q = q);                                                   \

       q = (HeapWord*) oop(q)->mark()->decode_pointer();                         \

       assert(q > prev_q, "we should be moving forward through memory");         \

     } else {                                                                    \

       /* prefetch beyond q */                                                   \

       Prefetch::read(q, scan_interval);                                         \

                                                                                 \

       /* size and destination */                                                \

       size_t size = obj_size(q);                                                \

       HeapWord* compaction_top = (HeapWord*)oop(q)->forwardee();                \

                                                                                 \

       /* prefetch beyond compaction_top */                                      \

       Prefetch::write(compaction_top, copy_interval);                           \

                                                                                 \

       /* copy object and reinit its mark */                                     \

       VALIDATE_MARK_SWEEP_ONLY(MarkSweep::live_oop_moved_to(q, size,            \

                                                             compaction_top));   \

       assert(q != compaction_top, "everything in this pass should be moving");  \

       Copy::aligned_conjoint_words(q, compaction_top, size);                    \

       oop(compaction_top)->init_mark();                                         \

       assert(oop(compaction_top)->klass() != NULL, "should have a class");      \

                                                                                 \

       debug_only(prev_q = q);                                                   \

       q += size;                                                                \

     }                                                                           \

   }                                                                             \

                                                                                 \

   /* Let's remember if we were empty before we did the compaction. */           \

   bool was_empty = used_region().is_empty();                                    \

   /* Reset space after compaction is complete */                                \

   reset_after_compaction();                                                     \

   /* We do this clear, below, since it has overloaded meanings for some */      \

   /* space subtypes.  For example, OffsetTableContigSpace's that were   */      \

   /* compacted into will have had their offset table thresholds updated */      \

   /* continuously, but those that weren't need to have their thresholds */      \

   /* re-initialized.  Also mangles unused area for debugging.           */      \

   if (used_region().is_empty()) {                                               \

     if (!was_empty) clear(SpaceDecorator::Mangle);                              \

   } else {                                                                      \

     if (ZapUnusedHeapArea) mangle_unused_area();                                \

   }                                                                             \

 }

 class GenSpaceMangler;

 // A space in which the free area is contiguous.  It therefore supports

 // faster allocation, and compaction.

 class ContiguousSpace: public CompactibleSpace {

   friend class OneContigSpaceCardGeneration;

   friend class VMStructs;

  protected:

   HeapWord* _top;

   HeapWord* _concurrent_iteration_safe_limit;

   // A helper for mangling the unused area of the space in debug builds.

   GenSpaceMangler* _mangler;

   GenSpaceMangler* mangler() { return _mangler; }

   // Allocation helpers (return NULL if full).

   inline HeapWord* allocate_impl(size_t word_size, HeapWord* end_value);

   inline HeapWord* par_allocate_impl(size_t word_size, HeapWord* end_value);

  public:

   ContiguousSpace();

   ~ContiguousSpace();

   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);

   virtual void clear(bool mangle_space);

   // Accessors

   HeapWord* top() const            { return _top;    }

   void set_top(HeapWord* value)    { _top = value; }

   virtual void set_saved_mark()    { _saved_mark_word = top();    }

   void reset_saved_mark()          { _saved_mark_word = bottom(); }

   WaterMark bottom_mark()     { return WaterMark(this, bottom()); }

   WaterMark top_mark()        { return WaterMark(this, top()); }

   WaterMark saved_mark()      { return WaterMark(this, saved_mark_word()); }

   bool saved_mark_at_top() const { return saved_mark_word() == top(); }

   // In debug mode mangle (write it with a particular bit

   // pattern) the unused part of a space.

   // Used to save the an address in a space for later use during mangling.

   void set_top_for_allocations(HeapWord* v) PRODUCT_RETURN;

   // Used to save the space's current top for later use during mangling.

   void set_top_for_allocations() PRODUCT_RETURN;

   // Mangle regions in the space from the current top up to the

   // previously mangled part of the space.

   void mangle_unused_area() PRODUCT_RETURN;

   // Mangle [top, end)

   void mangle_unused_area_complete() PRODUCT_RETURN;

   // Mangle the given MemRegion.

   void mangle_region(MemRegion mr) PRODUCT_RETURN;

   // Do some sparse checking on the area that should have been mangled.

   void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;

   // Check the complete area that should have been mangled.

   // This code may be NULL depending on the macro DEBUG_MANGLING.

   void check_mangled_unused_area_complete() PRODUCT_RETURN;

   // Size computations: sizes in bytes.

   size_t capacity() const        { return byte_size(bottom(), end()); }

   size_t used() const            { return byte_size(bottom(), top()); }

   size_t free() const            { return byte_size(top(),    end()); }

   // Override from space.

   bool is_in(const void* p) const;

   virtual bool is_free_block(const HeapWord* p) const;

   // In a contiguous space we have a more obvious bound on what parts

   // contain objects.

   MemRegion used_region() const { return MemRegion(bottom(), top()); }

   MemRegion used_region_at_save_marks() const {

     return MemRegion(bottom(), saved_mark_word());

   }

   // Allocation (return NULL if full)

   virtual HeapWord* allocate(size_t word_size);

   virtual HeapWord* par_allocate(size_t word_size);

   virtual bool obj_allocated_since_save_marks(const oop obj) const {

     return (HeapWord*)obj >= saved_mark_word();

   }

   // Iteration

   void oop_iterate(OopClosure* cl);

   void oop_iterate(MemRegion mr, OopClosure* cl);

   void object_iterate(ObjectClosure* blk);

   void object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl);

   // iterates on objects up to the safe limit

   HeapWord* object_iterate_careful(ObjectClosureCareful* cl);

   inline HeapWord* concurrent_iteration_safe_limit();

   // changes the safe limit, all objects from bottom() to the new

   // limit should be properly initialized

   inline void set_concurrent_iteration_safe_limit(HeapWord* new_limit);

 #ifndef SERIALGC

   // In support of parallel oop_iterate.

   #define ContigSpace_PAR_OOP_ITERATE_DECL(OopClosureType, nv_suffix)  \

     void par_oop_iterate(MemRegion mr, OopClosureType* blk);

     ALL_PAR_OOP_ITERATE_CLOSURES(ContigSpace_PAR_OOP_ITERATE_DECL)

   #undef ContigSpace_PAR_OOP_ITERATE_DECL

 #endif // SERIALGC

   // Compaction support

   virtual void reset_after_compaction() {

     assert(compaction_top() >= bottom() && compaction_top() <= end(), "should point inside space");

     set_top(compaction_top());

     // set new iteration safe limit

     set_concurrent_iteration_safe_limit(compaction_top());

   }

   virtual size_t minimum_free_block_size() const { return 0; }

   // Override.

   DirtyCardToOopClosure* new_dcto_cl(OopClosure* cl,

                                      CardTableModRefBS::PrecisionStyle precision,

                                      HeapWord* boundary = NULL);

   // Apply "blk->do_oop" to the addresses of all reference fields in objects

   // starting with the _saved_mark_word, which was noted during a generation's

   // save_marks and is required to denote the head of an object.

   // Fields in objects allocated by applications of the closure

   // *are* included in the iteration.

   // Updates _saved_mark_word to point to just after the last object

   // iterated over.

 #define ContigSpace_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)  \

   void oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk);

   ALL_SINCE_SAVE_MARKS_CLOSURES(ContigSpace_OOP_SINCE_SAVE_MARKS_DECL)

 #undef ContigSpace_OOP_SINCE_SAVE_MARKS_DECL

   // Same as object_iterate, but starting from "mark", which is required

   // to denote the start of an object.  Objects allocated by

   // applications of the closure *are* included in the iteration.

   virtual void object_iterate_from(WaterMark mark, ObjectClosure* blk);

   // Very inefficient implementation.

   virtual HeapWord* block_start_const(const void* p) const;

   size_t block_size(const HeapWord* p) const;

   // If a block is in the allocated area, it is an object.

   bool block_is_obj(const HeapWord* p) const { return p < top(); }

   // Addresses for inlined allocation

   HeapWord** top_addr() { return &_top; }

   HeapWord** end_addr() { return &_end; }

   // Overrides for more efficient compaction support.

   void prepare_for_compaction(CompactPoint* cp);

   // PrintHeapAtGC support.

   virtual void print_on(outputStream* st) const;

   // Checked dynamic downcasts.

   virtual ContiguousSpace* toContiguousSpace() {

     return this;

   }

   // Debugging

   virtual void verify(bool allow_dirty) const;

   // Used to increase collection frequency.  "factor" of 0 means entire

   // space.

   void allocate_temporary_filler(int factor);

 };

 // A dirty card to oop closure that does filtering.

 // It knows how to filter out objects that are outside of the _boundary.

 class Filtering_DCTOC : public DirtyCardToOopClosure {

 protected:

   // Override.

   void walk_mem_region(MemRegion mr,

                        HeapWord* bottom, HeapWord* top);

   // Walk the given memory region, from bottom to top, applying

   // the given oop closure to (possibly) all objects found. The

   // given oop closure may or may not be the same as the oop

   // closure with which this closure was created, as it may

   // be a filtering closure which makes use of the _boundary.

   // We offer two signatures, so the FilteringClosure static type is

   // apparent.

   virtual void walk_mem_region_with_cl(MemRegion mr,

                                        HeapWord* bottom, HeapWord* top,

                                        OopClosure* cl) = 0;

   virtual void walk_mem_region_with_cl(MemRegion mr,

                                        HeapWord* bottom, HeapWord* top,

                                        FilteringClosure* cl) = 0;

 public:

   Filtering_DCTOC(Space* sp, OopClosure* cl,

                   CardTableModRefBS::PrecisionStyle precision,

                   HeapWord* boundary) :

     DirtyCardToOopClosure(sp, cl, precision, boundary) {}

 };

 // A dirty card to oop closure for contiguous spaces

 // (ContiguousSpace and sub-classes).

 // It is a FilteringClosure, as defined above, and it knows:

 //

 // 1. That the actual top of any area in a memory region

 //    contained by the space is bounded by the end of the contiguous

 //    region of the space.

 // 2. That the space is really made up of objects and not just

 //    blocks.

 class ContiguousSpaceDCTOC : public Filtering_DCTOC {

 protected:

   // Overrides.

   HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);

   virtual void walk_mem_region_with_cl(MemRegion mr,

                                        HeapWord* bottom, HeapWord* top,

                                        OopClosure* cl);

   virtual void walk_mem_region_with_cl(MemRegion mr,

                                        HeapWord* bottom, HeapWord* top,

                                        FilteringClosure* cl);

 public:

   ContiguousSpaceDCTOC(ContiguousSpace* sp, OopClosure* cl,

                        CardTableModRefBS::PrecisionStyle precision,

                        HeapWord* boundary) :

     Filtering_DCTOC(sp, cl, precision, boundary)

   {}

 };

 // Class EdenSpace describes eden-space in new generation.

 class DefNewGeneration;

 class EdenSpace : public ContiguousSpace {

   friend class VMStructs;

  private:

   DefNewGeneration* _gen;

   // _soft_end is used as a soft limit on allocation.  As soft limits are

   // reached, the slow-path allocation code can invoke other actions and then

   // adjust _soft_end up to a new soft limit or to end().

   HeapWord* _soft_end;

  public:

   EdenSpace(DefNewGeneration* gen) :

    _gen(gen), _soft_end(NULL) {}

   // Get/set just the 'soft' limit.

   HeapWord* soft_end()               { return _soft_end; }

   HeapWord** soft_end_addr()         { return &_soft_end; }

   void set_soft_end(HeapWord* value) { _soft_end = value; }

   // Override.

   void clear(bool mangle_space);

   // Set both the 'hard' and 'soft' limits (_end and _soft_end).

   void set_end(HeapWord* value) {

     set_soft_end(value);

     ContiguousSpace::set_end(value);

   }

   // Allocation (return NULL if full)

   HeapWord* allocate(size_t word_size);

   HeapWord* par_allocate(size_t word_size);

 };

 // Class ConcEdenSpace extends EdenSpace for the sake of safe

 // allocation while soft-end is being modified concurrently

 class ConcEdenSpace : public EdenSpace {

  public:

   ConcEdenSpace(DefNewGeneration* gen) : EdenSpace(gen) { }

   // Allocation (return NULL if full)

   HeapWord* par_allocate(size_t word_size);

 };

 // A ContigSpace that Supports an efficient "block_start" operation via

 // a BlockOffsetArray (whose BlockOffsetSharedArray may be shared with

 // other spaces.)  This is the abstract base class for old generation

 // (tenured, perm) spaces.

 class OffsetTableContigSpace: public ContiguousSpace {

   friend class VMStructs;

  protected:

   BlockOffsetArrayContigSpace _offsets;

   Mutex _par_alloc_lock;

  public:

   // Constructor

   OffsetTableContigSpace(BlockOffsetSharedArray* sharedOffsetArray,

                          MemRegion mr);

   void set_bottom(HeapWord* value);

   void set_end(HeapWord* value);

   void clear(bool mangle_space);

   inline HeapWord* block_start_const(const void* p) const;

   // Add offset table update.

   virtual inline HeapWord* allocate(size_t word_size);

   inline HeapWord* par_allocate(size_t word_size);

   // MarkSweep support phase3

   virtual HeapWord* initialize_threshold();

   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* end);

   virtual void print_on(outputStream* st) const;

   // Debugging

   void verify(bool allow_dirty) const;

   // Shared space support

   void serialize_block_offset_array_offsets(SerializeOopClosure* soc);

 };

 // Class TenuredSpace is used by TenuredGeneration

 class TenuredSpace: public OffsetTableContigSpace {

   friend class VMStructs;

  protected:

   // Mark sweep support

   size_t allowed_dead_ratio() const;

  public:

   // Constructor

   TenuredSpace(BlockOffsetSharedArray* sharedOffsetArray,

                MemRegion mr) :

     OffsetTableContigSpace(sharedOffsetArray, mr) {}

 };

 // Class ContigPermSpace is used by CompactingPermGen

 class ContigPermSpace: public OffsetTableContigSpace {

   friend class VMStructs;

  protected:

   // Mark sweep support

   size_t allowed_dead_ratio() const;

  public:

   // Constructor

   ContigPermSpace(BlockOffsetSharedArray* sharedOffsetArray, MemRegion mr) :

     OffsetTableContigSpace(sharedOffsetArray, mr) {}

 };