leveldb::Arena Class Reference

#include <arena.h>

Public Member Functions
	Arena ()
	~Arena ()
char *	Allocate (size_t bytes)
char *	AllocateAligned (size_t bytes)
size_t	MemoryUsage () const

Private Member Functions
char *	AllocateFallback (size_t bytes)
char *	AllocateNewBlock (size_t block_bytes)
	Arena (const Arena &)
void	operator= (const Arena &)

Private Attributes
char *	alloc_ptr_
size_t	alloc_bytes_remaining_
std::vector< char * >	blocks_
port::AtomicPointer	memory_usage_

Detailed Description

Definition at line 16 of file arena.h.

Constructor & Destructor Documentation

Arena() [1/2]

leveldb::Arena::Arena

(

)

Definition at line 12 of file arena.cc.

             : memory_usage_(0) {
  alloc_ptr_ = NULL;  // First allocation will allocate a block
  alloc_bytes_remaining_ = 0;
}

~Arena()

leveldb::Arena::~Arena

(

)

Definition at line 17 of file arena.cc.

              {
  for (size_t i = 0; i < blocks_.size(); i++) {
    delete[] blocks_[i];
  }
}

Arena() [2/2]

leveldb::Arena::Arena ( const Arena &  )

private

Member Function Documentation

Allocate()

char * leveldb::Arena::Allocate ( size_t  bytes )

inline

Definition at line 52 of file arena.h.

                                         {
  // The semantics of what to return are a bit messy if we allow
  // 0-byte allocations, so we disallow them here (we don't need
  // them for our internal use).
  assert(bytes > 0);
  if (bytes <= alloc_bytes_remaining_) {
    char* result = alloc_ptr_;
    alloc_ptr_ += bytes;
    alloc_bytes_remaining_ -= bytes;
    return result;
  }
  return AllocateFallback(bytes);
}

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AllocateAligned()

char * leveldb::Arena::AllocateAligned

(

size_t

bytes

)

Definition at line 41 of file arena.cc.

                                         {
  const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
  assert((align & (align-1)) == 0);   // Pointer size should be a power of 2
  size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align-1);
  size_t slop = (current_mod == 0 ? 0 : align - current_mod);
  size_t needed = bytes + slop;
  char* result;
  if (needed <= alloc_bytes_remaining_) {
    result = alloc_ptr_ + slop;
    alloc_ptr_ += needed;
    alloc_bytes_remaining_ -= needed;
  } else {
    // AllocateFallback always returned aligned memory
    result = AllocateFallback(bytes);
  }
  assert((reinterpret_cast<uintptr_t>(result) & (align-1)) == 0);
  return result;
}

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AllocateFallback()

char * leveldb::Arena::AllocateFallback ( size_t  bytes )

private

Definition at line 23 of file arena.cc.

                                          {
  if (bytes > kBlockSize / 4) {
    // Object is more than a quarter of our block size.  Allocate it separately
    // to avoid wasting too much space in leftover bytes.
    char* result = AllocateNewBlock(bytes);
    return result;
  }

  // We waste the remaining space in the current block.
  alloc_ptr_ = AllocateNewBlock(kBlockSize);
  alloc_bytes_remaining_ = kBlockSize;

  char* result = alloc_ptr_;
  alloc_ptr_ += bytes;
  alloc_bytes_remaining_ -= bytes;
  return result;
}

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AllocateNewBlock()

char * leveldb::Arena::AllocateNewBlock ( size_t  block_bytes )

private

Definition at line 60 of file arena.cc.

                                                {
  char* result = new char[block_bytes];
  blocks_.push_back(result);
  memory_usage_.NoBarrier_Store(
      reinterpret_cast<void*>(MemoryUsage() + block_bytes + sizeof(char*)));
  return result;
}

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MemoryUsage()

size_t leveldb::Arena::MemoryUsage ( ) const

inline

Definition at line 29 of file arena.h.

                             {
    return reinterpret_cast<uintptr_t>(memory_usage_.NoBarrier_Load());
  }

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operator=()

void leveldb::Arena::operator= ( const Arena &  )

private

Member Data Documentation

alloc_bytes_remaining_

size_t leveldb::Arena::alloc_bytes_remaining_

private

Definition at line 39 of file arena.h.

alloc_ptr_

char* leveldb::Arena::alloc_ptr_

private

Definition at line 38 of file arena.h.

blocks_

std::vector<char*> leveldb::Arena::blocks_

private

Definition at line 42 of file arena.h.

memory_usage_

port::AtomicPointer leveldb::Arena::memory_usage_

private

Definition at line 45 of file arena.h.

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The documentation for this class was generated from the following files:

• util/arena.h
• util/arena.cc