src/hotspot/share/gc/shared/space.hpp

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#ifndef SHARE_GC_SHARED_SPACE_HPP
#define SHARE_GC_SHARED_SPACE_HPP

#include "gc/shared/blockOffsetTable.hpp"
#include "gc/shared/cardTable.hpp"
#include "gc/shared/workerThread.hpp"
#include "memory/allocation.hpp"
#include "memory/iterator.hpp"
#include "memory/memRegion.hpp"
#include "oops/markWord.hpp"
#include "runtime/mutexLocker.hpp"
#include "utilities/align.hpp"
#include "utilities/macros.hpp"
#if INCLUDE_SERIALGC
#include "gc/serial/serialBlockOffsetTable.hpp"
#endif

// 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.

// Forward decls.
class Space;
class ContiguousSpace;
#if INCLUDE_SERIALGC
class BlockOffsetArray;
class BlockOffsetArrayContigSpace;
class BlockOffsetTable;
#endif
class Generation;
class ContiguousSpace;
class CardTableRS;
class DirtyCardToOopClosure;
class FilteringClosure;

// 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<mtGC> {
  friend class VMStructs;
 protected:
  HeapWord* _bottom;
  HeapWord* _end;

  // Used in support of save_marks()
  HeapWord* _saved_mark_word;

  Space():
    _bottom(nullptr), _end(nullptr) { }

 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; }

  // 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 {
    return cast_from_oop<HeapWord*>(obj) >= saved_mark_word();
  }

  // Returns a subregion of the space containing only the allocated objects in
  // the space.
  virtual MemRegion used_region() const = 0;

  // 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 distinguish between objects in the region allocated before
  // and after the call to save marks.
  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.
  // We also call this when expanding a space to satisfy an allocation
  // request. See bug #4668531
  virtual void mangle_unused_area() = 0;
  virtual void mangle_unused_area_complete() = 0;

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

  // Returns true iff the given the space contains the
  // given address as part of an allocated object. For
  // certain 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.
  bool is_in(const void* p) const {
    return used_region().contains(p);
  }
  bool is_in(oop obj) const {
    return is_in((void*)obj);
  }

  // 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 ::is_aligned(p, sizeof(double));
  }

  // 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(OopIterateClosure* cl);

  // 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;

  // 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.
  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;

#if INCLUDE_SERIALGC
  // Mark-sweep-compact support: all spaces can update pointers to objects
  // moving as a part of compaction.
  virtual void adjust_pointers() = 0;
#endif

  virtual void print() const;
  virtual void print_on(outputStream* st) const;
  virtual void print_short() const;
  virtual void print_short_on(outputStream* st) const;


  // IF "this" is a ContiguousSpace, return it, else return null.
  virtual ContiguousSpace* toContiguousSpace() {
    return nullptr;
  }

  // Debugging
  virtual void verify() const = 0;
};

// A dirty card to oop closure for contiguous spaces (ContiguousSpace and
// sub-classes). It knows how to filter out objects that are outside of the
// _boundary.
// (Note that because of the imprecise nature of the write barrier, this may
// iterate over oops beyond the region.)
//
// Assumptions:
// 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 DirtyCardToOopClosure: public MemRegionClosure {
protected:
  OopIterateClosure* _cl;
  Space* _sp;
  HeapWord* _min_done;          // Need a downwards traversal to compensate
                                // imprecise write barrier; 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.
  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.
  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.
  void walk_mem_region_with_cl(MemRegion mr,
                               HeapWord* bottom, HeapWord* top,
                               OopIterateClosure* cl);
public:
  DirtyCardToOopClosure(Space* sp, OopIterateClosure* cl) :
    _cl(cl), _sp(sp), _min_done(nullptr) {
    NOT_PRODUCT(_last_bottom = nullptr);
  }

  void do_MemRegion(MemRegion mr) override;
};

// A structure to represent a point at which objects are being copied
// during compaction.
class CompactPoint : public StackObj {
public:
  Generation* gen;
  ContiguousSpace* space;

  CompactPoint(Generation* g = nullptr) :
    gen(g), space(nullptr) {}
};

class GenSpaceMangler;

// A space in which the free area is contiguous.  It therefore supports
// faster allocation, and compaction.
class ContiguousSpace: public Space {
  friend class VMStructs;

private:
  HeapWord* _compaction_top;
  ContiguousSpace* _next_compaction_space;

  static inline void verify_up_to_first_dead(ContiguousSpace* space) NOT_DEBUG_RETURN;

  static inline void clear_empty_region(ContiguousSpace* space);

 protected:
  HeapWord* _top;
  // A helper for mangling the unused area of the space in debug builds.
  GenSpaceMangler* _mangler;

  // Used during compaction.
  HeapWord* _first_dead;
  HeapWord* _end_of_live;

  // This the function to invoke when an allocation of an object covering
  // "start" to "end" occurs to update other internal data structures.
  virtual void alloc_block(HeapWord* start, HeapWord* the_end) { }

  GenSpaceMangler* mangler() { return _mangler; }

  // Allocation helpers (return null if full).
  inline HeapWord* allocate_impl(size_t word_size);
  inline HeapWord* par_allocate_impl(size_t word_size);

 public:
  ContiguousSpace();
  ~ContiguousSpace();

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

  void clear(bool mangle_space) override;

  // 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 == nullptr || (value >= bottom() && value <= end()),
      "should point inside space");
    _compaction_top = value;
  }

  // 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 ContiguousSpace* next_compaction_space() const {
    return _next_compaction_space;
  }

  void set_next_compaction_space(ContiguousSpace* csp) {
    _next_compaction_space = csp;
  }

#if INCLUDE_SERIALGC
  // 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.
  void prepare_for_compaction(CompactPoint* cp);
  // MarkSweep support phase3
  void adjust_pointers() override;
  // MarkSweep support phase4
  virtual void compact();
#endif // INCLUDE_SERIALGC

  // 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
  // initializes these data structures for further updates.
  virtual void initialize_threshold() { }

  // "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".
  // Invokes the "alloc_block" function of the then-current compaction
  // space.
  virtual HeapWord* forward(oop q, size_t size, CompactPoint* cp,
                    HeapWord* compact_top);

  // Accessors
  HeapWord* top() const            { return _top;    }
  void set_top(HeapWord* value)    { _top = value; }

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

  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 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() override PRODUCT_RETURN;
  // Mangle [top, end)
  void mangle_unused_area_complete() override 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 used() const override   { return byte_size(bottom(), top()); }
  size_t free() const override   { return byte_size(top(),    end()); }

  bool is_free_block(const HeapWord* p) const override;

  // In a contiguous space we have a more obvious bound on what parts
  // contain objects.
  MemRegion used_region() const override { return MemRegion(bottom(), top()); }

  // Allocation (return null if full)
  HeapWord* allocate(size_t word_size) override;
  HeapWord* par_allocate(size_t word_size) override;

  // Iteration
  void oop_iterate(OopIterateClosure* cl) override;
  void object_iterate(ObjectClosure* blk) override;

  // Compaction support
  void reset_after_compaction() {
    assert(compaction_top() >= bottom() && compaction_top() <= end(), "should point inside space");
    set_top(compaction_top());
  }

  // 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.
  template <typename OopClosureType>
  void oop_since_save_marks_iterate(OopClosureType* blk);

  // 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(HeapWord* mark, ObjectClosure* blk);

  // Very inefficient implementation.
  HeapWord* block_start_const(const void* p) const override;
  size_t block_size(const HeapWord* p) const override;
  // If a block is in the allocated area, it is an object.
  bool block_is_obj(const HeapWord* p) const override { return p < top(); }

  // Addresses for inlined allocation
  HeapWord** top_addr() { return &_top; }
  HeapWord** end_addr() { return &_end; }

  void print_on(outputStream* st) const override;

  // Checked dynamic downcasts.
  ContiguousSpace* toContiguousSpace() override {
    return this;
  }

  // Debugging
  void verify() const override;
};

#if INCLUDE_SERIALGC

// Class TenuredSpace is used by TenuredGeneration; it supports an efficient
// "block_start" operation via a BlockOffsetArray (whose BlockOffsetSharedArray
// may be shared with other spaces.)

class TenuredSpace: public ContiguousSpace {
  friend class VMStructs;
 protected:
  BlockOffsetArrayContigSpace _offsets;
  Mutex _par_alloc_lock;

  // Mark sweep support
  size_t allowed_dead_ratio() const override;
 public:
  // Constructor
  TenuredSpace(BlockOffsetSharedArray* sharedOffsetArray,
               MemRegion mr);

  void set_bottom(HeapWord* value) override;
  void set_end(HeapWord* value) override;

  void clear(bool mangle_space) override;

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

  // Add offset table update.
  inline HeapWord* allocate(size_t word_size) override;
  inline HeapWord* par_allocate(size_t word_size) override;

  // MarkSweep support phase3
  void initialize_threshold() override;
  void alloc_block(HeapWord* start, HeapWord* end) override;

  void print_on(outputStream* st) const override;

  // Debugging
  void verify() const override;
};
#endif //INCLUDE_SERIALGC

#endif // SHARE_GC_SHARED_SPACE_HPP