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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

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#ifndef SHARE_VM_GC_IMPLEMENTATION_SHARED_PLAB_HPP

#define SHARE_VM_GC_IMPLEMENTATION_SHARED_PLAB_HPP

#include "gc_implementation/shared/gcUtil.hpp"

#include "memory/allocation.hpp"

#include "runtime/atomic.hpp"

#include "utilities/globalDefinitions.hpp"

// Forward declarations.

class PLABStats;

// A per-thread allocation buffer used during GC.

class PLAB: public CHeapObj<mtGC> {

protected:

  char      head[32];

  size_t    _word_sz;          // In HeapWord units

  HeapWord* _bottom;

  HeapWord* _top;

  HeapWord* _end;           // Last allocatable address + 1

  HeapWord* _hard_end;      // _end + AlignmentReserve

  // In support of ergonomic sizing of PLAB's

  size_t    _allocated;     // in HeapWord units

  size_t    _wasted;        // in HeapWord units

  char      tail[32];

  static size_t AlignmentReserve;

  // Force future allocations to fail and queries for contains()

  // to return false. Returns the amount of unused space in this PLAB.

  size_t invalidate() {

    _end    = _hard_end;

    size_t remaining = pointer_delta(_end, _top);  // Calculate remaining space.

    _top    = _end;      // Force future allocations to fail.

    _bottom = _end;      // Force future contains() queries to return false.

    return remaining;

  }

  // Fill in remaining space with a dummy object and invalidate the PLAB. Returns

  // the amount of remaining space.

  size_t retire_internal();

public:

  // Initializes the buffer to be empty, but with the given "word_sz".

  // Must get initialized with "set_buf" for an allocation to succeed.

  PLAB(size_t word_sz);

  virtual ~PLAB() {}

  // Minimum PLAB size.

  static size_t min_size();

  // Maximum PLAB size.

  static size_t max_size();

  // If an allocation of the given "word_sz" can be satisfied within the

  // buffer, do the allocation, returning a pointer to the start of the

  // allocated block.  If the allocation request cannot be satisfied,

  // return NULL.

  HeapWord* allocate(size_t word_sz) {

    HeapWord* res = _top;

    if (pointer_delta(_end, _top) >= word_sz) {

      _top = _top + word_sz;

      return res;

    } else {

      return NULL;

    }

  }

  // Allocate the object aligned to "alignment_in_bytes".

  HeapWord* allocate_aligned(size_t word_sz, unsigned short alignment_in_bytes);

  // Undo the last allocation in the buffer, which is required to be of the

  // "obj" of the given "word_sz".

  void undo_allocation(HeapWord* obj, size_t word_sz) {

    assert(pointer_delta(_top, _bottom) >= word_sz, "Bad undo");

    assert(pointer_delta(_top, obj)     == word_sz, "Bad undo");

    _top = obj;

  }

  // The total (word) size of the buffer, including both allocated and

  // unallocated space.

  size_t word_sz() { return _word_sz; }

  // Should only be done if we are about to reset with a new buffer of the

  // given size.

  void set_word_size(size_t new_word_sz) {

    assert(new_word_sz > AlignmentReserve, "Too small");

    _word_sz = new_word_sz;

  }

  // The number of words of unallocated space remaining in the buffer.

  size_t words_remaining() {

    assert(_end >= _top, "Negative buffer");

    return pointer_delta(_end, _top, HeapWordSize);

  }

  bool contains(void* addr) {

    return (void*)_bottom <= addr && addr < (void*)_hard_end;

  }

  // Sets the space of the buffer to be [buf, space+word_sz()).

  virtual void set_buf(HeapWord* buf) {

    _bottom   = buf;

    _top      = _bottom;

    _hard_end = _bottom + word_sz();

    _end      = _hard_end - AlignmentReserve;

    assert(_end >= _top, "Negative buffer");

    // In support of ergonomic sizing

    _allocated += word_sz();

  }

  // Flush allocation statistics into the given PLABStats supporting ergonomic

  // sizing of PLAB's and retire the current buffer. To be called at the end of

  // GC.

  void flush_and_retire_stats(PLABStats* stats);

  // Fills in the unallocated portion of the buffer with a garbage object and updates

  // statistics. To be called during GC.

  virtual void retire();

  void print() PRODUCT_RETURN;

};

// PLAB book-keeping.

class PLABStats VALUE_OBJ_CLASS_SPEC {

  size_t _allocated;      // Total allocated

  size_t _wasted;         // of which wasted (internal fragmentation)

  size_t _unused;         // Unused in last buffer

  size_t _desired_plab_sz;// Output of filter (below), suitably trimmed and quantized

  AdaptiveWeightedAverage

         _filter;         // Integrator with decay

  void reset() {

    _allocated = 0;

    _wasted    = 0;

    _unused    = 0;

  }

 public:

  PLABStats(size_t desired_plab_sz_, unsigned wt) :

    _allocated(0),

    _wasted(0),

    _unused(0),

    _desired_plab_sz(desired_plab_sz_),

    _filter(wt)

  { }

  static const size_t min_size() {

    return PLAB::min_size();

  }

  static const size_t max_size() {

    return PLAB::max_size();

  }

  size_t desired_plab_sz() {

    return _desired_plab_sz;

  }

  // Updates the current desired PLAB size. Computes the new desired PLAB size,

  // updates _desired_plab_sz and clears sensor accumulators.

  void adjust_desired_plab_sz(uint no_of_gc_workers);

  void add_allocated(size_t v) {

    Atomic::add_ptr(v, &_allocated);

  }

  void add_unused(size_t v) {

    Atomic::add_ptr(v, &_unused);

  }

  void add_wasted(size_t v) {

    Atomic::add_ptr(v, &_wasted);

  }

};

#endif // SHARE_VM_GC_IMPLEMENTATION_SHARED_PLAB_HPP