encoder/buffer_pool.h

// Copyright (c) 2012 The WebM project authors. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS.  All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
#ifndef WEBMLIVE_ENCODER_BUFFER_POOL_H_
#define WEBMLIVE_ENCODER_BUFFER_POOL_H_

#include <mutex>
#include <queue>

#include "encoder/basictypes.h"
#include "encoder/encoder_base.h"

namespace webmlive {

// Buffer pooling object used to pass data between threads. In order to be
// managed by this class Buffer objects must implement the following methods:
//   uint8* buffer() const;
//   int64 timestamp() const;
//   int Clone(Type*);
//   int Swap(Type*);
template <class Type>
class BufferPool {
 public:
  enum {
    // |Init()| called more than once.
    kAlreadyInitialized = -4,
    // |Push| called before |Init|.
    kNoBuffers = -3,
    kNoMemory = -2,
    kInvalidArg = -1,
    kSuccess = 0,

    // No buffer objects waiting in |active_buffers_|.
    kEmpty = 1,

    // No buffer objects available in |inactive_buffers_|.
    kFull = 2,
  };

  static const int32 kDefaultBufferCount = 4;
  BufferPool() : allow_growth_(false) {}
  ~BufferPool();

  // Allocates |num_buffers| buffer objects, pushes them into
  // |inactive_buffers_|, and returns |kSuccess|. Returns |kInvalidArg| when
  // |num_buffers| is <= 0. Returns |kAlreadyInitialized| when |Init()| has
  // already been called.
  int Init(bool allow_growth, int num_buffers);

  // Grabs a buffer object pointer from |inactive_buffers_|, copies the data
  // from |ptr_buffer|, and pushes it into |active_buffers_|. Returns |kSuccess|
  // when able to store the data. Returns |kFull| when |inactive_buffers_| is
  // empty AND |allow_growth_| is false. Avoids copy using |Type::Swap| whenever
  // possible.
  int Commit(Type* ptr_buffer);

  // Grabs a buffer object from |active_buffers_| and copies it to |ptr_buffer|.
  // Returns |kSuccess| when able to copy the buffer. Returns |kEmpty| when
  // |active_buffers_| contains no buffer objects.
  int Decommit(Type* ptr_buffer);

  // Drops all queued buffer objects by moving them all from |active_buffers_|
  // to |inactive_buffers_|.
  void Flush();

  // Writes timestamp of buffer available in next call to |Decommit()| to
  // |ptr_timestamp| and returns |kSuccess|. Returns |kEmpty| when there are no
  // buffers to read in |active_buffers_|. Returns |kInvalidArg| when
  // |ptr_timestamp| is NULL.
  int ActiveBufferTimestamp(int64* ptr_timestamp);

  // Drops front buffer from |active_buffers_| by moving it back into
  // |inactive_buffers_|.
  void DropActiveBuffer();

  // Returns true when |active_buffers_| is empty.
  bool IsEmpty() const;

 private:
  // Moves or copies |ptr_source| to |ptr_target| using |Type::Swap| or
  // |Type::Clone| based on presence of non-NULL buffer pointer in
  // |ptr_target|.
  int Exchange(Type* ptr_source, Type* ptr_target);

  bool allow_growth_;
  mutable std::mutex mutex_;
  std::queue<Type*> inactive_buffers_;
  std::queue<Type*> active_buffers_;
  WEBMLIVE_DISALLOW_COPY_AND_ASSIGN(BufferPool);
};

}  // namespace webmlive

#endif  // WEBMLIVE_ENCODER_BUFFER_POOL_H_