--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/memory/space.hpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,1046 @@
+/*
+ * Copyright 1997-2007 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 virtual OopClosure {
+  OopClosure* cl;
+  MemRegion mr;
+public:
+  void do_oop(oop* p) {
+    if (mr.contains(p)) {
+      cl->do_oop(p);
+    }
+  }
+  SpaceMemRegionOopsIterClosure(OopClosure* _cl, MemRegion _mr): cl(_cl), mr(_mr) {}
+};
+
+
+// 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; }
+
+  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
+  virtual void initialize(MemRegion mr, bool clear_space);
+  virtual void clear();
+
+  // 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_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 void* p) const = 0;
+
+  // 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;)
+
+  // 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;)
+  }
+
+  void do_MemRegion(MemRegion mr);
+
+  void set_min_done(HeapWord* min_done) {
+    _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:
+  virtual void initialize(MemRegion mr, bool clear_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 int 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) {                                                           \
+    int 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");   \
+                                                                                \
+      debug_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);                                             \
+                                                                                \
+      debug_only(MarkSweep::check_interior_pointers());                         \
+                                                                                \
+      debug_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 */                                                          \
+      debug_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);                                             \
+      debug_only(MarkSweep::check_interior_pointers());                         \
+      debug_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)"); \
+      debug_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 */                                     \
+      debug_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;                                                                \
+    }                                                                           \
+  }                                                                             \
+                                                                                \
+  /* 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 (is_empty()) {                                                             \
+    clear();                                                                    \
+  } else {                                                                      \
+    if (ZapUnusedHeapArea) mangle_unused_area();                                \
+  }                                                                             \
+}
+
+// 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;
+
+  // 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:
+  virtual void initialize(MemRegion mr, bool clear_space);
+
+  // Accessors
+  HeapWord* top() const            { return _top;    }
+  void set_top(HeapWord* value)    { _top = value; }
+
+  void set_saved_mark()       { _saved_mark_word = top();    }
+  void reset_saved_mark()     { _saved_mark_word = bottom(); }
+
+  virtual void clear();
+
+  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(); }
+
+  void mangle_unused_area();
+  void mangle_region(MemRegion mr);
+
+  // 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 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();
+
+  // 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();
+
+  inline HeapWord* block_start(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
+  int 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
+  int allowed_dead_ratio() const;
+ public:
+  // Constructor
+  ContigPermSpace(BlockOffsetSharedArray* sharedOffsetArray, MemRegion mr) :
+    OffsetTableContigSpace(sharedOffsetArray, mr) {}
+};