root/gpu/command_buffer/client/transfer_buffer.cc

DEFINITIONS

1. usable_
2. Initialize
3. Free
4. HaveBuffer
5. GetOffset
6. FreePendingToken
7. AllocateRingBuffer
8. Log2Floor
9. Log2Ceiling
10. ComputePOTSize
11. ReallocateRingBuffer
12. AllocUpTo
13. Alloc
14. GetResultBuffer
15. GetResultOffset
16. GetShmId
17. GetCurrentMaxAllocationWithoutRealloc
18. GetMaxAllocation
19. Release
20. Reset

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// A class to Manage a growing transfer buffer.

#include "gpu/command_buffer/client/transfer_buffer.h"

#include "base/debug/trace_event.h"
#include "base/logging.h"
#include "gpu/command_buffer/client/cmd_buffer_helper.h"

namespace gpu {

AlignedRingBuffer::~AlignedRingBuffer() {
}

TransferBuffer::TransferBuffer(
    CommandBufferHelper* helper)
    : helper_(helper),
      result_size_(0),
      default_buffer_size_(0),
      min_buffer_size_(0),
      max_buffer_size_(0),
      alignment_(0),
      size_to_flush_(0),
      bytes_since_last_flush_(0),
      buffer_id_(-1),
      result_buffer_(NULL),
      result_shm_offset_(0),
      usable_(true) {
}

TransferBuffer::~TransferBuffer() {
  Free();
}

bool TransferBuffer::Initialize(
    unsigned int default_buffer_size,
    unsigned int result_size,
    unsigned int min_buffer_size,
    unsigned int max_buffer_size,
    unsigned int alignment,
    unsigned int size_to_flush) {
  result_size_ = result_size;
  default_buffer_size_ = default_buffer_size;
  min_buffer_size_ = min_buffer_size;
  max_buffer_size_ = max_buffer_size;
  alignment_ = alignment;
  size_to_flush_ = size_to_flush;
  ReallocateRingBuffer(default_buffer_size_ - result_size);
  return HaveBuffer();
}

void TransferBuffer::Free() {
  if (HaveBuffer()) {
    TRACE_EVENT0("gpu", "TransferBuffer::Free");
    helper_->Finish();
    helper_->command_buffer()->DestroyTransferBuffer(buffer_id_);
    buffer_id_ = -1;
    buffer_ = NULL;
    result_buffer_ = NULL;
    result_shm_offset_ = 0;
    ring_buffer_.reset();
    bytes_since_last_flush_ = 0;
  }
}

bool TransferBuffer::HaveBuffer() const {
  DCHECK(buffer_id_ == -1 || buffer_);
  return buffer_id_ != -1;
}

RingBuffer::Offset TransferBuffer::GetOffset(void* pointer) const {
  return ring_buffer_->GetOffset(pointer);
}

void TransferBuffer::FreePendingToken(void* p, unsigned int token) {
  ring_buffer_->FreePendingToken(p, token);
  if (bytes_since_last_flush_ >= size_to_flush_ && size_to_flush_ > 0) {
    helper_->Flush();
    bytes_since_last_flush_ = 0;
  }
}

void TransferBuffer::AllocateRingBuffer(unsigned int size) {
  for (;size >= min_buffer_size_; size /= 2) {
    int32 id = -1;
    scoped_refptr<gpu::Buffer> buffer =
        helper_->command_buffer()->CreateTransferBuffer(size, &id);
    if (id != -1) {
      DCHECK(buffer);
      buffer_ = buffer;
      ring_buffer_.reset(new AlignedRingBuffer(
          alignment_,
          id,
          result_size_,
          buffer_->size() - result_size_,
          helper_,
          static_cast<char*>(buffer_->memory()) + result_size_));
      buffer_id_ = id;
      result_buffer_ = buffer_->memory();
      result_shm_offset_ = 0;
      return;
    }
    // we failed so don't try larger than this.
    max_buffer_size_ = size / 2;
  }
  usable_ = false;
}

// Returns the integer i such as 2^i <= n < 2^(i+1)
static int Log2Floor(uint32 n) {
  if (n == 0)
    return -1;
  int log = 0;
  uint32 value = n;
  for (int i = 4; i >= 0; --i) {
    int shift = (1 << i);
    uint32 x = value >> shift;
    if (x != 0) {
      value = x;
      log += shift;
    }
  }
  DCHECK_EQ(value, 1u);
  return log;
}

// Returns the integer i such as 2^(i-1) < n <= 2^i
static int Log2Ceiling(uint32 n) {
  if (n == 0) {
    return -1;
  } else {
    // Log2Floor returns -1 for 0, so the following works correctly for n=1.
    return 1 + Log2Floor(n - 1);
  }
}

static unsigned int ComputePOTSize(unsigned int dimension) {
  return (dimension == 0) ? 0 : 1 << Log2Ceiling(dimension);
}

void TransferBuffer::ReallocateRingBuffer(unsigned int size) {
  // What size buffer would we ask for if we needed a new one?
  unsigned int needed_buffer_size = ComputePOTSize(size + result_size_);
  needed_buffer_size = std::max(needed_buffer_size, min_buffer_size_);
  needed_buffer_size = std::max(needed_buffer_size, default_buffer_size_);
  needed_buffer_size = std::min(needed_buffer_size, max_buffer_size_);

  if (usable_ && (!HaveBuffer() || needed_buffer_size > buffer_->size())) {
    if (HaveBuffer()) {
      Free();
    }
    AllocateRingBuffer(needed_buffer_size);
  }
}

void* TransferBuffer::AllocUpTo(
    unsigned int size, unsigned int* size_allocated) {
  DCHECK(size_allocated);

  ReallocateRingBuffer(size);

  if (!HaveBuffer()) {
    return NULL;
  }

  unsigned int max_size = ring_buffer_->GetLargestFreeOrPendingSize();
  *size_allocated = std::min(max_size, size);
  bytes_since_last_flush_ += *size_allocated;
  return ring_buffer_->Alloc(*size_allocated);
}

void* TransferBuffer::Alloc(unsigned int size) {
  ReallocateRingBuffer(size);

  if (!HaveBuffer()) {
    return NULL;
  }

  unsigned int max_size = ring_buffer_->GetLargestFreeOrPendingSize();
  if (size > max_size) {
    return NULL;
  }

  bytes_since_last_flush_ += size;
  return ring_buffer_->Alloc(size);
}

void* TransferBuffer::GetResultBuffer() {
  ReallocateRingBuffer(result_size_);
  return result_buffer_;
}

int TransferBuffer::GetResultOffset() {
  ReallocateRingBuffer(result_size_);
  return result_shm_offset_;
}

int TransferBuffer::GetShmId() {
  ReallocateRingBuffer(result_size_);
  return buffer_id_;
}

unsigned int TransferBuffer::GetCurrentMaxAllocationWithoutRealloc() const {
  return HaveBuffer() ? ring_buffer_->GetLargestFreeOrPendingSize() : 0;
}

unsigned int TransferBuffer::GetMaxAllocation() const {
  return HaveBuffer() ? max_buffer_size_ - result_size_ : 0;
}

void ScopedTransferBufferPtr::Release() {
  if (buffer_) {
    transfer_buffer_->FreePendingToken(buffer_, helper_->InsertToken());
    buffer_ = NULL;
    size_ = 0;
  }
}

void ScopedTransferBufferPtr::Reset(unsigned int new_size) {
  Release();
  // NOTE: we allocate buffers of size 0 so that HaveBuffer will be true, so
  // that address will return a pointer just like malloc, and so that GetShmId
  // will be valid. That has the side effect that we'll insert a token on free.
  // We could add code skip the token for a zero size buffer but it doesn't seem
  // worth the complication.
  buffer_ = transfer_buffer_->AllocUpTo(new_size, &size_);
}

}  // namespace gpu