MyCat - 源代码篇（10）

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数据库路由中间件MyCat - 源代码篇（10）

3. 连接模块

3.5 后端连接

3.5.2 后端连接获取与维护管理

还是那之前的流程，

现在我们到了尝试获取连接的阶段
PhysicalDataSource.java:

public void getConnection(String schema,boolean autocommit, final ResponseHandler handler,    final Object attachment) throws IOException {//从当前连接map中拿取已建立好的后端连接    BackendConnection con = this.conMap.tryTakeCon(schema,autocommit);    if (con != null) {//如果不为空，则绑定对应前端请求的handler        takeCon(con, handler, attachment, schema);        return;    } else {//如果为空，新建连接        int activeCons = this.getActiveCount();//当前最大活动连接        if(activeCons+1>size){//下一个连接大于最大连接数            LOGGER.error("the max activeConnnections size can not be max than maxconnections");            throw new IOException("the max activeConnnections size can not be max than maxconnections");        }else{            // create connection            LOGGER.info("not ilde connection in pool,create new connection for " + this.name                    + " of schema "+schema);            createNewConnection(handler, attachment, schema);        }    }}

private void createNewConnection(final ResponseHandler handler,        final Object attachment, final String schema) throws IOException {    //异步创建连接，将连接的handler绑定为DelegateResponseHandler    MycatServer.getInstance().getBusinessExecutor().execute(new Runnable() {        public void run() {            try {                createNewConnection(new DelegateResponseHandler(handler) {                    @Override                    public void connectionError(Throwable e,                            BackendConnection conn) {                        handler.connectionError(e, conn);                    }                    @Override                    public void connectionAcquired(BackendConnection conn) {                        takeCon(conn, handler, attachment, schema);                    }                }, schema);            } catch (IOException e) {                handler.connectionError(e, null);            }        }    });}

异步调用工厂方法创建后端连接，这里为MySQLConnection
MySQLDataSource.java:

@Override    public void createNewConnection(ResponseHandler handler,String schema) throws IOException {        factory.make(this, handler,schema);}

根据之前所述，MySQLConnection的工厂方法会先将NIOhandler设置为MySQLConnectionAuthenticator：
MySQLConnectionFactory.java:

public MySQLConnection make(MySQLDataSource pool, ResponseHandler handler,            String schema) throws IOException {        //DBHost配置        DBHostConfig dsc = pool.getConfig();        //根据是否为NIO返回SocketChannel或者AIO的AsynchronousSocketChannel        NetworkChannel channel = openSocketChannel(MycatServer.getInstance()                .isAIO());        //新建MySQLConnection        MySQLConnection c = new MySQLConnection(channel, pool.isReadNode());        //根据配置初始化MySQLConnection        MycatServer.getInstance().getConfig().setSocketParams(c, false);        c.setHost(dsc.getIp());        c.setPort(dsc.getPort());        c.setUser(dsc.getUser());        c.setPassword(dsc.getPassword());        c.setSchema(schema);        //目前实际连接还未建立，handler为MySQL连接认证MySQLConnectionAuthenticator，传入的handler为后端连接处理器ResponseHandler        c.setHandler(new MySQLConnectionAuthenticator(c, handler));        c.setPool(pool);        c.setIdleTimeout(pool.getConfig().getIdleTimeout());        //AIO和NIO连接方式建立实际的MySQL连接        if (channel instanceof AsynchronousSocketChannel) {            ((AsynchronousSocketChannel) channel).connect(                    new InetSocketAddress(dsc.getIp(), dsc.getPort()), c,                    (CompletionHandler) MycatServer.getInstance()                            .getConnector());        } else {            //通过NIOConnector建立连接            ((NIOConnector) MycatServer.getInstance().getConnector())                    .postConnect(c);        }        return c;    }

这里传入的ResponseHandler为DelegateResponseHandler，在连接建立验证之后，会调用：
MySQLConnectionAuthenticator.java:

public void handle(byte[] data) {    //省略                    //设置ResponseHandler    if (listener != null) {            listener.connectionAcquired(source);    }    //省略}

DelegateResponseHandler.java:

private final ResponseHandler target;@Override   public void connectionAcquired(BackendConnection conn) {   //将后端连接的ResponseHandler设置为target   target.connectionAcquired(conn);}

这样，原来没获取到连接的ResponseHandler就获得需要的连接，之后进行处理。处理完后，归还到连接池中。

private void returnCon(BackendConnection c) {    //清空连接的Attachment    c.setAttachment(null);    //设置为未使用    c.setBorrowed(false);    //更新上次使用时间，用于清理空闲连接    c.setLastTime(TimeUtil.currentTimeMillis());    //获取连接池对应的队列    ConQueue queue = this.conMap.getSchemaConQueue(c.getSchema());    //按照是否Autocommit分类归还连接    boolean ok = false;    if (c.isAutocommit()) {        ok = queue.getAutoCommitCons().offer(c);    } else {        ok = queue.getManCommitCons().offer(c);    }    //归还失败，关闭连接，记录    if (!ok) {        LOGGER.warn("can't return to pool ,so close con " + c);        c.close("can't return to pool ");    }}

4.配置模块

MyCat实例初始化时究竟会有什么操作呢？看下MyCat程序入口：
MycatStartup.java:

public static void main(String[] args) {    //是否启用zk配置，/myid.properties中的loadZk属性决定，默认不启用，从本地xml文件中读取配置    ZkConfig.instance().initZk();    try {        String home = SystemConfig.getHomePath();        if (home == null) {            System.out.println(SystemConfig.SYS_HOME + "  is not set.");            System.exit(-1);        }        // init        MycatServer server = MycatServer.getInstance();        server.beforeStart();        // startup        server.startup();        System.out.println("MyCAT Server startup successfully. see logs in logs/mycat.log");        while (true) {            Thread.sleep(300 * 1000);        }    } catch (Exception e) {        SimpleDateFormat sdf = new SimpleDateFormat(dateFormat);        LogLog.error(sdf.format(new Date()) + " startup error", e);        System.exit(-1);    }}

从代码中，可以简单的分为三步：

MycatServer.getInstance()：获取MyCat实例，其实就是读取配置文件，并验证正确性等
server.beforeStart()：获取环境变量，日志配置
server.startup()：启动MyCat，启动线程，初始化线程池和连接池等。

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