Storm-源码分析- Messaging (backtype.storm.messaging)

先定义两个接口和一个类
TaskMessage类本身比较好理解, 抽象storm的message格式
对于IContext, 注释也说了, 定义messaging plugin, 通过什么渠道去发送message, storm这里设计成可替换的
默认定义storm实现了local和ZMQ两种plugin, 当然你可以实现更多的
local应该是用于local mode, 而ZMQ用于distributed mode

IContext接口主要是用于创建IConnection, 体现对socket的管理, 分别通过bind和connect定义服务器端和客户端的connection 
IConnection接口主要用于定义, 真正收发message的逻辑

最终通过TransportFactory, 根据Config.STORM_MESSAGING_TRANSPORT的配置, 利用Java的reflection动态的创建不同类型的context

IContext接口

/**
* This interface needs to be implemented for messaging plugin.
*
* Messaging plugin is specified via Storm config parameter, storm.messaging.transport.
*
* A messaging plugin should have a default constructor and implements IContext interface.
* Upon construction, we will invoke IContext::prepare(storm_conf) to enable context to be configured
* according to storm configuration.
*/
public interface IContext {
/**
* This method is invoked at the startup of messaging plugin
* @param storm_conf storm configuration
*/
public void prepare(Map storm_conf);

/**
* This method is invoked when a worker is unload a messaging plugin
*/
public void term();

/**
* This method establishes a server side connection
* @param storm_id topology ID
* @param port port #
* @return server side connection
*/
public IConnection bind(String storm_id, int port);

/**
* This method establish a client side connection to a remote server
* @param storm_id topology ID
* @param host remote host
* @param port remote port
* @return client side connection
*/
public IConnection connect(String storm_id, String host, int port);
};

IConnection接口

public interface IConnection {
/**
* receive a message (consists taskId and payload)
* @param flags 0: block, 1: non-block
* @return
*/
public TaskMessage recv(int flags);
/**
* send a message with taskId and payload
* @param taskId task ID
* @param payload
*/
public void send(int taskId,  byte[] payload);

/**
* close this connection
*/
public void close();
}

TaskMessage

TaskMessage如其名, 包含task和message字段, 以说明发送给哪个task的message

并且定义了序列化和反序列化的函数

public class TaskMessage {
private int _task;
private byte[] _message;

public TaskMessage(int task, byte[] message) {
_task = task;
_message = message;
}

public int task() {
return _task;
}

public byte[] message() {
return _message;
}

public ByteBuffer serialize() {
ByteBuffer bb = ByteBuffer.allocate(_message.length+2);
bb.putShort((short)_task);
bb.put(_message);
return bb;
}

public void deserialize(ByteBuffer packet) {
if (packet==null) return;
_task = packet.getShort();
_message = new byte[packet.limit()-2];
packet.get(_message);
}
}

TransportFactory

public class TransportFactory {
public static IContext makeContext(Map storm_conf) {
//get factory class name
String transport_plugin_klassName = (String)storm_conf.get(Config.STORM_MESSAGING_TRANSPORT);
LOG.info("Storm peer transport plugin:"+transport_plugin_klassName);

IContext transport = null;
try {
//create a factory class
Class klass = Class.forName(transport_plugin_klassName);
//obtain a context object
Object obj = klass.newInstance();
if (obj instanceof IContext) {
//case 1: plugin is a IContext class
transport = (IContext)obj;
//initialize with storm configuration
transport.prepare(storm_conf);
} else {
//case 2: Non-IContext plugin must have a makeContext(storm_conf) method that returns IContext object
Method method = klass.getMethod("makeContext", Map.class);
LOG.debug("object:"+obj+" method:"+method);
transport = (IContext) method.invoke(obj, storm_conf);
}
} catch(Exception e) {
throw new RuntimeException("Fail to construct messaging plugin from plugin "+transport_plugin_klassName, e);
}
return transport;
}
}

 

可以详细看看local和ZMQ的plugin的实现

Local

在local模式下使用的message plugin

实现比较简单, 所有都基于queues-map来实现, 这里的queue直接使用LinkedBlockingQueue, 因为local用于测试, 不用考虑高效性

所有的接收队列或发送队列都通过add-queue!加到queues-map里面(stormid+port作为key)

那么所有的recv和send, 都是基于queue的操作

(defn add-queue! [queues-map lock storm-id port]
(let [id (str storm-id "-" port)]
(locking lock
(when-not (contains? @queues-map id)
(swap! queues-map assoc id (LinkedBlockingQueue.))))
(@queues-map id)))

(deftype LocalConnection [storm-id port queues-map lock queue]
IConnection
(^TaskMessage recv [this ^int flags]
(when-not queue
(throw (IllegalArgumentException. "Cannot receive on this socket")))
(if (= flags 1)
(.poll queue)
(.take queue)))
(^void send [this ^int taskId ^bytes payload]
(let [send-queue (add-queue! queues-map lock storm-id port)]
(.put send-queue (TaskMessage. taskId payload))
))
(^void close [this]
))

(deftype LocalContext [^{:unsynchronized-mutable true} queues-map
^{:unsynchronized-mutable true} lock]
IContext
(^void prepare [this ^Map storm-conf]
(set! queues-map (atom {}))
(set! lock (Object.)))
(^IConnection bind [this ^String storm-id ^int port]
(LocalConnection. storm-id port queues-map lock (add-queue! queues-map lock storm-id port)))
(^IConnection connect [this ^String storm-id ^String host ^int port]
(LocalConnection. storm-id port queues-map lock nil))
(^void term [this]
))

这里使用Deftype, 而不是Defrecord, 即connection和context本身不需要对字典的支持

并且在IContext的实现中, 使用到了可变field, 据说是比较难用对的高级特性

我个人的理解, 是因为deftype和defrecord一样, 没有闭包的效果, 而只有field(对象成员)可以随时被接口函数访问, 所以有些场景下需要field的mutable, 比如这里的queues-map

之前类似的场景都是用reify实现的, 这里给出用deftype实现的版本

ZMQ

号称最快的消息队列, 接近socket API 的性能, 参考/article/4687432.html

在distributed mode时, storm使用ZMQ作为进程间和instrance间通信

(deftype ZMQConnection [socket]
IConnection
(^TaskMessage recv [this ^int flags]
(require 'backtype.storm.messaging.zmq)
(if-let [packet (mq/recv socket flags)]
(parse-packet packet)))
(^void send [this ^int taskId ^bytes payload]
(require 'backtype.storm.messaging.zmq)
(mq/send socket (mk-packet taskId payload) ZMQ/NOBLOCK)) ;; TODO: how to do backpressure if doing noblock?... need to only unblock if the target disappears
(^void close [this]
(.close socket)))

(deftype ZMQContext [^{:unsynchronized-mutable true} context
^{:unsynchronized-mutable true} linger-ms
^{:unsynchronized-mutable true} hwm
^{:unsynchronized-mutable true} local?]
IContext
(^void prepare [this ^Map storm-conf]
(let [num-threads (storm-conf ZMQ-THREADS)]
(set! context (mq/context num-threads))
(set! linger-ms (storm-conf ZMQ-LINGER-MILLIS))
(set! hwm (storm-conf ZMQ-HWM))
(set! local? (= (storm-conf STORM-CLUSTER-MODE) "local"))))
(^IConnection bind [this ^String storm-id ^int port]
(require 'backtype.storm.messaging.zmq)
(-> context
(mq/socket mq/pull)
(mq/set-hwm hwm)
(mq/bind (get-bind-zmq-url local? port))
mk-connection
))
(^IConnection connect [this ^String storm-id ^String host ^int port]
(require 'backtype.storm.messaging.zmq)
(-> context
(mq/socket mq/push)
(mq/set-hwm hwm)
(mq/set-linger linger-ms)
(mq/connect (get-connect-zmq-url local? host port))
mk-connection))
(^void term [this]
(.term context))

ZMQContextQuery
(zmq-context [this]
context))