https://*.com/questions/8517121/java-what-is-the-difference-between-init-and-clinit#
<init> is the (or one of the) constructor(s) for the instance, and non-static field initialization.
<clinit> are the static initialization blocks for the class, and static field initialization.
以DefaultFuture为例，分析java类中各变量的初始化顺序。
首次执行代码：DefaultFuture future = new DefaultFuture(channel, req, timeout);
1. 首先加载class文件（Launcher$AppClassLoader(ClassLoader).loadClass(String) line: 358）
2. 进DefaultFuture.<clinit>()，顺序执行static语句
为static变量赋值
private static final Logger logger = LoggerFactory.getLogger(DefaultFuture.class);
private static final Map<Long, Channel> CHANNELS = new ConcurrentHashMap<Long, Channel>();
private static final Map<Long, DefaultFuture> FUTURES = new ConcurrentHashMap<Long, DefaultFuture>();
执行后面的static语句
static {
Thread th = new Thread(new RemotingInvocationTimeoutScan(), "DubboResponseTimeoutScanTimer");
th.setDaemon(true);
th.start();
}
3. 进构造函数（DefaultFuture.<init>(Channel, Request, int) line: 73）
4. 执行实例变量赋值语句（构造函数外部的赋值语句先执行）
private final Lock lock = new ReentrantLock();
private final Condition done = lock.newCondition();
private final long start = System.currentTimeMillis();
5. 执行构造函数
public DefaultFuture(Channel channel, Request request, int timeout){
this.channel = channel;
this.request = request;
this.id = request.getId();
this.timeout = timeout > 0 ? timeout : channel.getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
// put into waiting map.
FUTURES.put(id, this);
CHANNELS.put(id, channel);
}
DefaultFuture源码如下：
package com.alibaba.dubbo.remoting.exchange.support; import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.logger.Logger;
import com.alibaba.dubbo.common.logger.LoggerFactory;
import com.alibaba.dubbo.remoting.Channel;
import com.alibaba.dubbo.remoting.RemotingException;
import com.alibaba.dubbo.remoting.TimeoutException;
import com.alibaba.dubbo.remoting.exchange.Request;
import com.alibaba.dubbo.remoting.exchange.Response;
import com.alibaba.dubbo.remoting.exchange.ResponseCallback;
import com.alibaba.dubbo.remoting.exchange.ResponseFuture; /**
* DefaultFuture.
*
* @author qian.lei
* @author chao.liuc
*/
public class DefaultFuture implements ResponseFuture {
private static final Logger logger = LoggerFactory.getLogger(DefaultFuture.class);
private static final Map<Long, Channel> CHANNELS = new ConcurrentHashMap<Long, Channel>();
private static final Map<Long, DefaultFuture> FUTURES = new ConcurrentHashMap<Long, DefaultFuture>();
// invoke id.
private final long id;
private final Channel channel;
private final Request request;
private final int timeout;
private final Lock lock = new ReentrantLock();
private final Condition done = lock.newCondition();
private final long start = System.currentTimeMillis();
private volatile long sent;
private volatile Response response;
private volatile ResponseCallback callback;
public DefaultFuture(Channel channel, Request request, int timeout){
this.channel = channel;
this.request = request;
this.id = request.getId();
this.timeout = timeout > 0 ? timeout : channel.getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
// put into waiting map.
FUTURES.put(id, this);
CHANNELS.put(id, channel);
}
public Object get() throws RemotingException {
return get(timeout);
}
public Object get(int timeout) throws RemotingException {
if (timeout <= 0) {
timeout = Constants.DEFAULT_TIMEOUT;
}
if (! isDone()) {
long start = System.currentTimeMillis();
lock.lock();
try {
while (! isDone()) {
done.await(timeout, TimeUnit.MILLISECONDS);
if (isDone() || System.currentTimeMillis() - start > timeout) {
break;
}
}
} catch (InterruptedException e) {
throw new RuntimeException(e);
} finally {
lock.unlock();
}
if (! isDone()) {
throw new TimeoutException(sent > 0, channel, getTimeoutMessage(false));
}
}
return returnFromResponse();
} public void cancel(){
Response errorResult = new Response(id);
errorResult.setErrorMessage("request future has been canceled.");
response = errorResult ;
FUTURES.remove(id);
CHANNELS.remove(id);
} public boolean isDone() {
return response != null;
} public void setCallback(ResponseCallback callback) {
if (isDone()) {
invokeCallback(callback);
} else {
boolean isdone = false;
lock.lock();
try{
if (!isDone()) {
this.callback = callback;
} else {
isdone = true;
}
}finally {
lock.unlock();
}
if (isdone){
invokeCallback(callback);
}
}
}
private void invokeCallback(ResponseCallback c){
ResponseCallback callbackCopy = c;
if (callbackCopy == null){
throw new NullPointerException("callback cannot be null.");
}
c = null;
Response res = response;
if (res == null) {
throw new IllegalStateException("response cannot be null. url:"+channel.getUrl());
} if (res.getStatus() == Response.OK) {
try {
callbackCopy.done(res.getResult());
} catch (Exception e) {
logger.error("callback invoke error .reasult:" + res.getResult() + ",url:" + channel.getUrl(), e);
}
} else if (res.getStatus() == Response.CLIENT_TIMEOUT || res.getStatus() == Response.SERVER_TIMEOUT) {
try {
TimeoutException te = new TimeoutException(res.getStatus() == Response.SERVER_TIMEOUT, channel, res.getErrorMessage());
callbackCopy.caught(te);
} catch (Exception e) {
logger.error("callback invoke error ,url:" + channel.getUrl(), e);
}
} else {
try {
RuntimeException re = new RuntimeException(res.getErrorMessage());
callbackCopy.caught(re);
} catch (Exception e) {
logger.error("callback invoke error ,url:" + channel.getUrl(), e);
}
}
} private Object returnFromResponse() throws RemotingException {
Response res = response;
if (res == null) {
throw new IllegalStateException("response cannot be null");
}
if (res.getStatus() == Response.OK) {
return res.getResult();
}
if (res.getStatus() == Response.CLIENT_TIMEOUT || res.getStatus() == Response.SERVER_TIMEOUT) {
throw new TimeoutException(res.getStatus() == Response.SERVER_TIMEOUT, channel, res.getErrorMessage());
}
throw new RemotingException(channel, res.getErrorMessage());
} private long getId() {
return id;
} private Channel getChannel() {
return channel;
} private boolean isSent() {
return sent > 0;
} public Request getRequest() {
return request;
} private int getTimeout() {
return timeout;
} private long getStartTimestamp() {
return start;
} public static DefaultFuture getFuture(long id) {
return FUTURES.get(id);
} public static boolean hasFuture(Channel channel) {
return CHANNELS.containsValue(channel);
} public static void sent(Channel channel, Request request) {
DefaultFuture future = FUTURES.get(request.getId());
if (future != null) {
future.doSent();
}
} private void doSent() {
sent = System.currentTimeMillis();
} public static void received(Channel channel, Response response) {
try {
DefaultFuture future = FUTURES.remove(response.getId());
if (future != null) {
future.doReceived(response);
} else {
logger.warn("The timeout response finally returned at "
+ (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date()))
+ ", response " + response
+ (channel == null ? "" : ", channel: " + channel.getLocalAddress()
+ " -> " + channel.getRemoteAddress()));
}
} finally {
CHANNELS.remove(response.getId());
}
} private void doReceived(Response res) {
lock.lock();
try {
response = res;
if (done != null) {
done.signal();
}
} finally {
lock.unlock();
}
if (callback != null) {
invokeCallback(callback);
}
} private String getTimeoutMessage(boolean scan) {
long nowTimestamp = System.currentTimeMillis();
return (sent > 0 ? "Waiting server-side response timeout" : "Sending request timeout in client-side")
+ (scan ? " by scan timer" : "") + ". start time: "
+ (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date(start))) + ", end time: "
+ (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date())) + ","
+ (sent > 0 ? " client elapsed: " + (sent - start)
+ " ms, server elapsed: " + (nowTimestamp - sent)
: " elapsed: " + (nowTimestamp - start)) + " ms, timeout: "
+ timeout + " ms, request: " + request + ", channel: " + channel.getLocalAddress()
+ " -> " + channel.getRemoteAddress();
} private static class RemotingInvocationTimeoutScan implements Runnable { public void run() {
while (true) {
try {
for (DefaultFuture future : FUTURES.values()) {
if (future == null || future.isDone()) {
continue;
}
if (System.currentTimeMillis() - future.getStartTimestamp() > future.getTimeout()) {
// create exception response.
Response timeoutResponse = new Response(future.getId());
// set timeout status.
timeoutResponse.setStatus(future.isSent() ? Response.SERVER_TIMEOUT : Response.CLIENT_TIMEOUT);
timeoutResponse.setErrorMessage(future.getTimeoutMessage(true));
// handle response.
DefaultFuture.received(future.getChannel(), timeoutResponse);
}
}
Thread.sleep(30);
} catch (Throwable e) {
logger.error("Exception when scan the timeout invocation of remoting.", e);
}
}
}
} static {
Thread th = new Thread(new RemotingInvocationTimeoutScan(), "DubboResponseTimeoutScanTimer");
th.setDaemon(true);
th.start();
} }