Dubbo support project loom

[AlbumenJ]

• I have searched the issues of this repository and believe that this is not a duplicate.

Describe the proposal

[robberphex]

随着JDK 19和 JEP 425的发布，是时候调研下dubbo如何支持project loom了。

loom对于上层的要求和建议，主要有几点（难度由低到高）：

1. 不应该缓存虚拟线程，即不应该像原来使用线程池那样池化。当然，这儿为了兼容性，可以使用ThreadPerTaskExecutor
2. 目前synchronized和native method，会导致虚拟线程无法卸载（即完全占用了一个物理线程）。
   • 预计在将来的版本中，synchronized的限制可以取消，但是native method这一块，需要loom提供新的接口，然后现有的native代码做适配。
   • 我看了目前DubboServerHandler的调用栈，目前是没有上述两种情况的。
3. loom最终的目标是"Code like sync, works like async"，而dubbo内核依赖了netty这样的，基于回调的编程范式。不论是基于老版本dubbo兼容性考虑，还是基于老版本java兼容性考虑，都没法做大的修改。

所以，这一块，我们至少可以分2步走：
第一步，在现有的基础上，逐步通过VirtualThread替换掉原有的Thread（DubboServerHandler、NettyServerWorker），并观察性能、异步编程难易度。在这一步，我们期望Dubbo的性能会有略微提升，用户的编程难度下降（尤其是流式、异步模式）。
第二步，根据第一步结果，如果大家都接受"Code like sync, works like async"，那么我们可以逐步改造dubo内核，实现更加容易的异步、高性能编程。

---

目前进展
在本地跑了简单Demo，需要做出如下改造，即可体验VirtualThread：

1. 添加VirtualThreadPool,

import org.apache.dubbo.common.URL;
import org.apache.dubbo.common.threadpool.ThreadPool;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import static org.apache.dubbo.common.constants.CommonConstants.DEFAULT_THREAD_NAME;
import static org.apache.dubbo.common.constants.CommonConstants.THREAD_NAME_KEY;

public class VirtualThreadPool implements ThreadPool {
  @Override
  public Executor getExecutor(URL url) {
    String name = url.getParameter(THREAD_NAME_KEY, 
      (String) url.getAttribute(THREAD_NAME_KEY, DEFAULT_THREAD_NAME)
    );
    ThreadFactory factory = Thread.ofVirtual().name(name).factory();
    return Executors.newThreadPerTaskExecutor(factory);
  }
}

2. 添加SPI src/main/resources/META-INF/dubbo/internal/org.apache.dubbo.common.threadpool.ThreadPool

virtual-thread=VirtualThreadPool

3. 使用SPI，添加配置：dubbo.provider.parameters.threadpool=virtual-thread

最终的stack：

at com.alibaba.edas.boot.EchoServiceImpl.echo(EchoServiceImpl.java:16)
	at com.alibaba.edas.boot.EchoServiceImplDubboWrap0.invokeMethod(EchoServiceImplDubboWrap0.java)
	at org.apache.dubbo.rpc.proxy.javassist.JavassistProxyFactory$1.doInvoke(JavassistProxyFactory.java:73)
	at org.apache.dubbo.rpc.proxy.AbstractProxyInvoker.invoke(AbstractProxyInvoker.java:100)
	at org.apache.dubbo.config.invoker.DelegateProviderMetaDataInvoker.invoke(DelegateProviderMetaDataInvoker.java:55)
	at org.apache.dubbo.rpc.protocol.InvokerWrapper.invoke(InvokerWrapper.java:56)
	at org.apache.dubbo.rpc.filter.ClassLoaderCallbackFilter.invoke(ClassLoaderCallbackFilter.java:38)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.protocol.dubbo.filter.TraceFilter.invoke(TraceFilter.java:79)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.filter.TimeoutFilter.invoke(TimeoutFilter.java:45)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.monitor.support.MonitorFilter.invoke(MonitorFilter.java:100)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.filter.ExceptionFilter.invoke(ExceptionFilter.java:54)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.filter.GenericFilter.invoke(GenericFilter.java:192)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.filter.ClassLoaderFilter.invoke(ClassLoaderFilter.java:54)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.filter.EchoFilter.invoke(EchoFilter.java:41)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.filter.ProfilerServerFilter.invoke(ProfilerServerFilter.java:57)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.filter.ContextFilter.invoke(ContextFilter.java:133)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CopyOfFilterChainNode.invoke(FilterChainBuilder.java:327)
	at org.apache.dubbo.rpc.cluster.filter.FilterChainBuilder$CallbackRegistrationInvoker.invoke(FilterChainBuilder.java:194)
	at org.apache.dubbo.rpc.protocol.dubbo.DubboProtocol$1.reply(DubboProtocol.java:156)
	at org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeHandler.handleRequest(HeaderExchangeHandler.java:102)
	at org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeHandler.received(HeaderExchangeHandler.java:177)
	at org.apache.dubbo.remoting.transport.DecodeHandler.received(DecodeHandler.java:53)
	at org.apache.dubbo.remoting.transport.dispatcher.ChannelEventRunnable.run(ChannelEventRunnable.java:61)
	at java.base/java.util.concurrent.ThreadPerTaskExecutor$TaskRunner.run(ThreadPerTaskExecutor.java:314)
	at java.base/java.lang.VirtualThread.run(VirtualThread.java:287)
	at java.base/java.lang.VirtualThread$VThreadContinuation.lambda$new$0(VirtualThread.java:174)
	at java.base/jdk.internal.vm.Continuation.enter0(Continuation.java:327)
	at java.base/jdk.internal.vm.Continuation.enter(Continuation.java:320)

[khatchad]

Is this issue closed by #13111?

[AlbumenJ]

Is this issue closed by #13111?

Yep