/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "BufferCache.h"

#include "MLGDevice.h"

#include "ShaderDefinitionsMLGPU.h"

#include "mozilla/MathAlgorithms.h"

namespace mozilla {

namespace layers {

using namespace mlg;

BufferCache::BufferCache(MLGDevice* aDevice)

 : mDevice(aDevice),

   mFirstSizeClass(CeilingLog2(kConstantBufferElementSize)),

   mFrameNumber(0),

   mNextSizeClassToShrink(0)

{

  // Create a cache of buffers for each size class, where each size class is a

  // power of 2 between the minimum and maximum size of a constant buffer.

  size_t maxBindSize = mDevice->GetMaxConstantBufferBindSize();

  MOZ_ASSERT(IsPowerOfTwo(maxBindSize));

  size_t lastSizeClass = CeilingLog2(maxBindSize);

  MOZ_ASSERT(lastSizeClass >= mFirstSizeClass);

  mCaches.resize(lastSizeClass - mFirstSizeClass + 1);

}

BufferCache::~BufferCache()

{

}

RefPtr<MLGBuffer>

BufferCache::GetOrCreateBuffer(size_t aBytes)

{

  size_t sizeClass = CeilingLog2(aBytes);

  size_t sizeClassIndex = sizeClass - mFirstSizeClass;

  if (sizeClassIndex >= mCaches.size()) {

    return mDevice->CreateBuffer(MLGBufferType::Constant, aBytes, MLGUsage::Dynamic, nullptr);

  }

  CachePool& pool = mCaches[sizeClassIndex];

  // See if we've cached a buffer that wasn't used in the past 2 frames. A buffer

  // used this frame could have already been mapped and written to, and a buffer

  // used the previous frame might still be in-use by the GPU. While the latter

  // case is okay, it causes aliasing in the driver. Since content is double

  // buffered we do not let the compositor get more than 1 frames ahead, and a

  // count of 2 frames should ensure the buffer is unused.

  if (!pool.empty() && mFrameNumber >= pool.front().mLastUsedFrame + 2) {

    RefPtr<MLGBuffer> buffer = pool.front().mBuffer;

    pool.pop_front();

    pool.push_back(CacheEntry(mFrameNumber, buffer));

    MOZ_RELEASE_ASSERT(buffer->GetSize() >= aBytes);

    return buffer;

  }

  // Allocate a new buffer and cache it.

  size_t bytes = (size_t(1) << sizeClass);

  MOZ_ASSERT(bytes >= aBytes);

  RefPtr<MLGBuffer> buffer =

    mDevice->CreateBuffer(MLGBufferType::Constant, bytes, MLGUsage::Dynamic, nullptr);

  if (!buffer) {

    return nullptr;

  }

  pool.push_back(CacheEntry(mFrameNumber, buffer));

  return buffer;

}

void

BufferCache::EndFrame()

{

  // Consider a buffer dead after ~5 seconds assuming 60 fps.

  static size_t kMaxUnusedFrameCount = 60 * 5;

  // At the end of each frame we pick one size class and see if it has any

  // buffers that haven't been used for many frames. If so we clear them.

  // The next frame we'll search the next size class. (This is just to spread

  // work over more than one frame.)

  CachePool& pool = mCaches[mNextSizeClassToShrink];

  while (!pool.empty()) {

    // Since the deque is sorted oldest-to-newest, front-to-back, we can stop

    // searching as soon as a buffer is active.

    if (mFrameNumber - pool.front().mLastUsedFrame < kMaxUnusedFrameCount) {

      break;

    }

    pool.pop_front();

  }

  mNextSizeClassToShrink = (mNextSizeClassToShrink + 1) % mCaches.size();

  mFrameNumber++;

}

} // namespace layers

} // namespace mozilla