view src/share/vm/memory/padded.hpp @ 5264:24e87613ee58

8009561: NPG: Metaspace fragmentation when retiring a Metachunk Summary: Use best-fit block-splitting freelist allocation from the block freelist. Reviewed-by: jmasa, stefank
author mgerdin
date Wed, 11 Sep 2013 09:37:14 +0200
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#include "memory/allocation.hpp"
#include "utilities/globalDefinitions.hpp"

// Bytes needed to pad type to avoid cache-line sharing; alignment should be the
// expected cache line size (a power of two).  The first addend avoids sharing
// when the start address is not a multiple of alignment; the second maintains
// alignment of starting addresses that happen to be a multiple.
#define PADDING_SIZE(type, alignment)                           \
  ((alignment) + align_size_up_(sizeof(type), alignment))

// Templates to create a subclass padded to avoid cache line sharing.  These are
// effective only when applied to derived-most (leaf) classes.

// When no args are passed to the base ctor.
template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
class Padded : public T {
  char _pad_buf_[PADDING_SIZE(T, alignment)];

// When either 0 or 1 args may be passed to the base ctor.
template <class T, typename Arg1T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
class Padded01 : public T {
  Padded01(): T() { }
  Padded01(Arg1T arg1): T(arg1) { }
  char _pad_buf_[PADDING_SIZE(T, alignment)];

// Super class of PaddedEnd when pad_size != 0.
template <class T, size_t pad_size>
class PaddedEndImpl : public T {
  char _pad_buf[pad_size];

// Super class of PaddedEnd when pad_size == 0.
template <class T>
class PaddedEndImpl<T, /*pad_size*/ 0> : public T {
  // No padding.

#define PADDED_END_SIZE(type, alignment) (align_size_up_(sizeof(type), alignment) - sizeof(type))

// More memory conservative implementation of Padded. The subclass adds the
// minimal amount of padding needed to make the size of the objects be aligned.
// This will help reducing false sharing,
// if the start address is a multiple of alignment.
template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
class PaddedEnd : public PaddedEndImpl<T, PADDED_END_SIZE(T, alignment)> {
  // C++ don't allow zero-length arrays. The padding is put in a
  // super class that is specialized for the pad_size == 0 case.

// Helper class to create an array of PaddedEnd<T> objects. All elements will
// start at a multiple of alignment and the size will be aligned to alignment.
template <class T, MEMFLAGS flags, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
class PaddedArray {
  // Creates an aligned padded array.
  // The memory can't be deleted since the raw memory chunk is not returned.
  static PaddedEnd<T>* create_unfreeable(uint length);