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

/* vim:set ts=2 sw=2 sts=2 et cindent: */

/* 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/. */

#ifndef MEMORY_BLOCK_CACHE_H_

#define MEMORY_BLOCK_CACHE_H_

#include "MediaBlockCacheBase.h"

#include "mozilla/Mutex.h"

namespace mozilla {

// Manages block management for the media cache. Data comes in over the network

// via callbacks on the main thread, however we don't want to write the

// incoming data to the media cache on the main thread, as this could block

// causing UI jank.

//

// So MediaBlockCacheBase provides an abstraction for a temporary memory buffer

// as an array of blocks, which supports a block move operation, and

// allows synchronous reading and writing from any thread.

//

// Writes and cache block moves (which require reading) may be deferred to

// their own non-main thread. This object also ensures that data which has

// been scheduled to be written, but hasn't actually *been* written, is read

// as if it had, i.e. pending writes are cached in readable memory until

// they're flushed to file.

//

// To improve efficiency, writes can only be done at block granularity,

// whereas reads can be done with byte granularity.

class MemoryBlockCache : public MediaBlockCacheBase

{

public:

  explicit MemoryBlockCache(int64_t aContentLength);

protected:

  virtual ~MemoryBlockCache();

public:

  // Allocate initial buffer.

  // If re-initializing, clear buffer.

  virtual nsresult Init() override;

  void Flush() override;

  // Maximum number of blocks allowed in this block cache.

  // Based on initial content length, and minimum usable block cache.

  int32_t GetMaxBlocks() const override { return mMaxBlocks; }

  // Can be called on any thread.

  virtual nsresult WriteBlock(uint32_t aBlockIndex,

                              Span<const uint8_t> aData1,

                              Span<const uint8_t> aData2) override;

  // Synchronously reads data from buffer.

  virtual nsresult Read(int64_t aOffset,

                        uint8_t* aData,

                        int32_t aLength,

                        int32_t* aBytes) override;

  // Moves a block. Can be called on any thread.

  virtual nsresult MoveBlock(int32_t aSourceBlockIndex,

                             int32_t aDestBlockIndex) override;

private:

  static size_t BlockIndexToOffset(uint32_t aBlockIndex)

  {

    return static_cast<size_t>(aBlockIndex) * BLOCK_SIZE;

  }

  // Ensure the buffer has at least a multiple of BLOCK_SIZE that can contain

  // aContentLength bytes. Buffer size can only grow.

  // Returns false if allocation failed.

  bool EnsureBufferCanContain(size_t aContentLength);

  // Initial content length.

  const size_t mInitialContentLength;

  // Maximum number of blocks that this MemoryBlockCache expects.

  const int32_t mMaxBlocks;

  // Mutex which controls access to all members below.

  Mutex mMutex;

  nsTArray<uint8_t> mBuffer;

  bool mHasGrown = false;

};

} // End namespace mozilla.

#endif /* MEMORY_BLOCK_CACHE_H_ */