gc_implementation/g1/g1BiasedArray.hpp

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#ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1BIASEDARRAY_HPP
#define SHARE_VM_GC_IMPLEMENTATION_G1_G1BIASEDARRAY_HPP

#include "memory/allocation.hpp"
#include "utilities/debug.hpp"

// Implements the common base functionality for arrays that contain provisions
// for accessing its elements using a biased index.
// The element type is defined by the instantiating the template.
class G1BiasedMappedArrayBase VALUE_OBJ_CLASS_SPEC {
  friend class VMStructs;
public:
  typedef size_t idx_t;
protected:
  address _base;          // the real base address
  size_t _length;         // the length of the array
  address _biased_base;   // base address biased by "bias" elements
  size_t _bias;           // the bias, i.e. the offset biased_base is located to the right in elements
  uint _shift_by;         // the amount of bits to shift right when mapping to an index of the array.

protected:

  G1BiasedMappedArrayBase() : _base(NULL), _length(0), _biased_base(NULL),
    _bias(0), _shift_by(0) { }

  // Allocate a new array, generic version.
  static address create_new_base_array(size_t length, size_t elem_size);

  // Initialize the members of this class. The biased start address of this array
  // is the bias (in elements) multiplied by the element size.
  void initialize_base(address base, size_t length, size_t bias, size_t elem_size, uint shift_by) {
    assert(base != NULL, "just checking");
    assert(length > 0, "just checking");
    assert(shift_by < sizeof(uintptr_t) * 8, err_msg("Shifting by " SSIZE_FORMAT ", larger than word size?", (size_t) shift_by));
    _base = base;
    _length = length;
    _biased_base = base - (bias * elem_size);
    _bias = bias;
    _shift_by = shift_by;
  }

  // Allocate and initialize this array to cover the heap addresses in the range
  // of [bottom, end).
  void initialize(HeapWord* bottom, HeapWord* end, size_t target_elem_size_in_bytes, size_t mapping_granularity_in_bytes) {
    assert(mapping_granularity_in_bytes > 0, "just checking");
    assert(is_power_of_2(mapping_granularity_in_bytes),
      err_msg("mapping granularity must be power of 2, is %zd", mapping_granularity_in_bytes));
    assert((uintptr_t)bottom % mapping_granularity_in_bytes == 0,
      err_msg("bottom mapping area address must be a multiple of mapping granularity %zd, is " PTR_FORMAT,
        mapping_granularity_in_bytes, p2i(bottom)));
    assert((uintptr_t)end % mapping_granularity_in_bytes == 0,
      err_msg("end mapping area address must be a multiple of mapping granularity %zd, is " PTR_FORMAT,
        mapping_granularity_in_bytes, p2i(end)));
    size_t num_target_elems = pointer_delta(end, bottom, mapping_granularity_in_bytes);
    idx_t bias = (uintptr_t)bottom / mapping_granularity_in_bytes;
    address base = create_new_base_array(num_target_elems, target_elem_size_in_bytes);
    initialize_base(base, num_target_elems, bias, target_elem_size_in_bytes, log2_intptr(mapping_granularity_in_bytes));
  }

  size_t bias() const { return _bias; }
  uint shift_by() const { return _shift_by; }

  void verify_index(idx_t index) const PRODUCT_RETURN;
  void verify_biased_index(idx_t biased_index) const PRODUCT_RETURN;
  void verify_biased_index_inclusive_end(idx_t biased_index) const PRODUCT_RETURN;

public:
   // Return the length of the array in elements.
   size_t length() const { return _length; }
};

// Array that provides biased access and mapping from (valid) addresses in the
// heap into this array.
template<class T>
class G1BiasedMappedArray : public G1BiasedMappedArrayBase {
public:
  typedef G1BiasedMappedArrayBase::idx_t idx_t;

  T* base() const { return (T*)G1BiasedMappedArrayBase::_base; }
  // Return the element of the given array at the given index. Assume
  // the index is valid. This is a convenience method that does sanity
  // checking on the index.
  T get_by_index(idx_t index) const {
    verify_index(index);
    return this->base()[index];
  }

  // Set the element of the given array at the given index to the
  // given value. Assume the index is valid. This is a convenience
  // method that does sanity checking on the index.
  void set_by_index(idx_t index, T value) {
    verify_index(index);
    this->base()[index] = value;
  }

  // The raw biased base pointer.
  T* biased_base() const { return (T*)G1BiasedMappedArrayBase::_biased_base; }

  // Return the element of the given array that covers the given word in the
  // heap. Assumes the index is valid.
  T get_by_address(HeapWord* value) const {
    idx_t biased_index = ((uintptr_t)value) >> this->shift_by();
    this->verify_biased_index(biased_index);
    return biased_base()[biased_index];
  }

  // Set the value of the array entry that corresponds to the given array.
  void set_by_address(HeapWord * address, T value) {
    idx_t biased_index = ((uintptr_t)address) >> this->shift_by();
    this->verify_biased_index(biased_index);
    biased_base()[biased_index] = value;
  }

protected:
  // Returns the address of the element the given address maps to
  T* address_mapped_to(HeapWord* address) {
    idx_t biased_index = ((uintptr_t)address) >> this->shift_by();
    this->verify_biased_index_inclusive_end(biased_index);
    return biased_base() + biased_index;
  }

public:
  // Return the smallest address (inclusive) in the heap that this array covers.
  HeapWord* bottom_address_mapped() const {
    return (HeapWord*) ((uintptr_t)this->bias() << this->shift_by());
  }

  // Return the highest address (exclusive) in the heap that this array covers.
  HeapWord* end_address_mapped() const {
    return (HeapWord*) ((uintptr_t)(this->bias() + this->length()) << this->shift_by());
  }

protected:
  virtual T default_value() const = 0;
  // Set all elements of the given array to the given value.
  void clear() {
    T value = default_value();
    for (idx_t i = 0; i < length(); i++) {
      set_by_index(i, value);
    }
  }
public:
  G1BiasedMappedArray() {}

  // Allocate and initialize this array to cover the heap addresses in the range
  // of [bottom, end).
  void initialize(HeapWord* bottom, HeapWord* end, size_t mapping_granularity) {
    G1BiasedMappedArrayBase::initialize(bottom, end, sizeof(T), mapping_granularity);
    this->clear();
  }
};

#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BIASEDARRAY_HPP