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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，
st=>start: MyCat接受客户端连接并为之建立唯一绑定的Session e=>end: 将请求发送给对应连接,处理完之后归还连接 op1=>operation: MyCat接受客户端的请求，计算路由 op2=>operation: 根据请求和路由创建合适的handler，这里为SingleNodeHandler op3=>operation: 从PhysicalDBNode中获取后端连接 cond=>condition: 尝试获取连接，连接够用？ op4=>operation: 尝试异步创建新的连接 op5=>operation: 通过DelegateResponseHandler将连接与之前的Handler，这里是SingleNodeHandler绑定 st->op1->op2->op3->condcond(yes)->econd(no)->op4->op5->e
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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