一个refine/refactor的例子

我觉得refine比refactor的幅度大，refactor主要是等价替换，而refine有时候直接寻找更好的方案。

Server在管理Client的BufferTime，即决定什么时候应该发包的这部分逻辑，最初是这么写的：

u_int32_t Connection::PerformIO(){u_int32_t ret = PErrorCode::Success;ChunkPacketFarm* cfarm = rtmp.GetChunkFarm();MessagePacketFarm* mfarm = rtmp.GetMessageFarm();// buffer is full, async write will flush it.if(!cfarm->CanWrite()){return ret;}int client_buffer_time = 10 * 1000;// if stream farm is NULL, initialize it and do metadata.if(stream_farm == NULL){if((ret = EnQueueMetaData()) != PErrorCode::Success){return ret;}// enqueue the pre-load data ASAP.int64_t current_time = fire_time = client_start_time = Utility::GetCurrentTime();if((ret = EnQueueMessages(current_time, client_buffer_time)) != PErrorCode::Success){return ret;}// the abs time used to sync with client.fire_time = Utility::GetCurrentTime() + client_buffer_time;Singleton::Timer()->AddEvent(TimerEvent::EventIO, this, 0);}// if we are transfering audio/video, do itelse{// we have changed the original position of current time.int64_t current_time = Utility::GetCurrentTime() + client_buffer_time;if(fire_time <= current_time){// TODO: analysis the right queue size.int queue_interval_time = 10000;if((ret = EnQueueMessages(current_time, queue_interval_time)) != PErrorCode::Success){return ret;}}Singleton::Timer()->AddEvent(TimerEvent::EventIO, this, fire_time - client_buffer_time);}// when enqueue messages, send out all of them.bool all_sent_out = false;while(!all_sent_out){if((ret = mfarm->SendMessage(all_sent_out)) != PErrorCode::Success){return ret;}}return ret;
}u_int32_t Connection::EnQueueMessages(int64_t current_time, int buffer_time){u_int32_t ret = PErrorCode::Success;Message* msg = NULL;FLVTag* tag = NULL;fire_time = current_time + buffer_time;for(;;){if((ret = EnQueueTag(&tag, &msg)) != PErrorCode::Success){return ret;}if(tag != NULL && tag->tag_header.timestamp + client_start_time >= fire_time){break;}}return ret;
}

即第一次我们先发送10秒的包，让client能减少延迟。然后每隔10秒发送一次包。很不直观，而且很麻烦，refine如下：

u_int32_t Connection::PerformIO(){u_int32_t ret = PErrorCode::Success;ChunkPacketFarm* cfarm = rtmp.GetChunkFarm();MessagePacketFarm* mfarm = rtmp.GetMessageFarm();// buffer is full, wait for async write flush it.if(!cfarm->CanWrite()){return ret;}// if stream farm is NULL, initialize it and do metadata.if(stream_farm == NULL){if((ret = EnQueueMetaData()) != PErrorCode::Success){return ret;}// to notify the buffer time manager we begin stream.buffer_time.StreamBegin();}// enqueue the pakckets ASAP.if((ret = EnQueueMessages()) != PErrorCode::Success){return ret;}Singleton::Timer()->AddEvent(TimerEvent::EventIO, this, buffer_time.GetFireTime());// when enqueue messages, send out all of them.bool all_sent_out = false;while(!all_sent_out){if((ret = mfarm->SendMessage(all_sent_out)) != PErrorCode::Success){return ret;}}return ret;
}u_int32_t Connection::EnQueueMessages(){u_int32_t ret = PErrorCode::Success;Message* msg = NULL;FLVTag* tag = NULL;int64_t timestamp = buffer_time.GetTimesamp();if(timestamp == -1){return ret;}for(;;){if((ret = EnQueueTag(&tag, &msg)) != PErrorCode::Success){return ret;}if(tag != NULL && msg != NULL && tag->tag_header.timestamp > timestamp){break;}}return ret;
}void BufferTimeManager::StreamBegin(){client_start_time = Utility::GetCurrentTime();
}int64_t BufferTimeManager::GetFireTime(){return fire_time;
}int64_t BufferTimeManager::GetTimesamp(){int64_t current_time = Utility::GetCurrentTime();// we are not ready to enqueue more messages.if(current_time < fire_time){return -1;}// move fire time to next position.// the fire time and current time is used for timer_farm to calc the event active time.fire_time = current_time + pulse_time;// while the preload time is used to send the messages ASAP.    int preload_time = client_buffer_time + pulse_time;return current_time - client_start_time + preload_time;
}

我们extract出了一个新类BufferTimeManager，第一次发送流时告诉它记录当前时间，然后就EnQueueMessage（它从BufferTimeManager获取当前最大的时间戳GetTimestamp），发送完毕后下次发包的时间是GetFireTime。

Refine之前，很难理解在做什么；Refine之后，有点像自然语言，把buffertime聚集在一起，抽象出来时就会迫使我们去分析到底buffertime是什么，提供什么样的API，迫使代码接近逻辑上的本来抽象。

后来始终觉得这个缓冲区算法太复杂，随着功能增加，这个算法变成如下这样样子：

int64_t GetTimesamp(){int64_t current_time = Utility::GetCurrentTime();// we are not ready to enqueue more messages.if(current_time < fire_time){return -1;}// pause or low bandwidth delay.// only when event_abs_time is 0, that is the event is active by async write,// we think there exists a delay of socket buffer full.if((client_pauseraw || client_paused) || (fire_time > 0 && has_delay)){delay_time += current_time - fire_time;}// move fire time to next position.// the fire time and current time is used for timer_farm to calc the event active time.fire_time = current_time + pulse_time;// if paused, we return not-ready(-1) when we update the fire_time.if(client_paused){delay_time += pulse_time; // the pulse time is the message time, we consume it when pause.RtmpTrace("pulse time coming, client is paused. "\"pulse=%d, delay=%ld, buffer=%d, seek=%ld, current=%ld, fire=%ld", pulse_time, delay_time, client_buffer_time, seek_time, current_time, fire_time);return -1;}// main message timestamp algorithmint preload_time = client_buffer_time + pulse_time;int64_t absolute_auto_growth_time = current_time - client_start_time;int64_t preload_cache_time = absolute_auto_growth_time + preload_time;int64_t conti_delay_time = preload_cache_time - delay_time;int64_t message_time = seek_time + conti_delay_time;RtmpTrace("client=%d buffer time manager report. "\"message=%ld, seek=%ld, current=%ld, start=%ld, buffer=%d, pulse=%d, delay=%ld, fire=%ld", connection->GetFD(), message_time, seek_time, current_time, client_start_time, client_buffer_time, pulse_time, delay_time, fire_time);return message_time;
}

揪心啊，这么复杂的东西，别人实在很难看懂，我不能写这样的东西。以真实数据看看这个算法在做什么：

发现其实每次返回的值是一个序列！马上灵光一闪，简化算法如下：

int64_t GetTimesamp(){int64_t current_time = Utility::GetCurrentTime();// we are not ready to enqueue more messages.if(current_time < fire_time){return -1;}// move fire time to next position.// the fire time and current time is used for timer_farm to calc the event active time.fire_time = current_time + pulse_time;// only not paused, we consume a pulse time of messages.if(!client_paused){current_message_time += pulse_time;}RtmpTrace("client=%d buffer time manager report. "\"message=%ld, current=%ld, buffer=%d, pulse=%d, fire=%ld", connection->GetFD(), current_message_time, current_time, client_buffer_time, pulse_time, fire_time);return current_message_time;
}

恩，这个很简单，但和实际的场景一致。异步socket在没有发完数据之前都会继续发送，每次进到这个函数时，说明数据发完了，不管延迟还是什么的，都是发完了，然后再发一个pulse的包，其实就可以了。

再进一步，发觉if(paused)其实可以换算为speed，当paused时speed为0，正常时为1.0，pauseraw时加速为2.0，然后加速后需要一个衰减，改进如下：

#define FasterPulse 1000
#define NormalPulse 5000#define FasterSpeed 2.0
#define NormalSpeed 1.0
#define ZeroSpeed 0int64_t BufferTimeManager::GetCurrentTime(){int64_t current_time = Utility::GetCurrentTime();// we are not ready to enqueue more messages.if(current_time < fire_time){return -1;}// move fire time to next position.// the fire time and current time is used for timer_farm to calc the event active time.fire_time = current_time + pulse_time;// we can control the buffer by the speed. for example:// pauseraw: write faster, speed > 1// paused: write paused, speed = 0.message_time += pulse_time * speed;// if high speed, use attenuation to slow it down.if(speed > NormalSpeed){speed -= Attenuation;speed = RtmpMax(NormalSpeed, speed);}RtmpTrace("client=%d paused=%d buffer time manager report. "\"message=%ld, current=%ld, buffer=%d, pulse=%d, speed=%0.1f, fire=%ld delay=%ld", connection->GetFD(), client_paused, message_time, current_time, buffer_time, pulse_time, speed, fire_time, current_time - start_time - message_time + buffer_time + pulse_time);return message_time;
}

这样，控制speed就能控制发包（填充缓冲区）速度，控制pulse就能控制发包频率，控制attenuation能控制高速时的速度衰减。简化的原因是pulse和message的time没有关系，不应该关联到一起。简化过后这样的代码是可读的。

pulse：脉冲，发包的频率。
speed：速度，发包的速度。
attenuation：衰减，高速时的速度衰减。

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一个refine/refactor的例子

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