Cat 跨线程之 ForkedTransaction 用法和原理分析

package com.dianping.cat.message.internal;

import com.dianping.cat.Cat;
import com.dianping.cat.message.ForkedTransaction;
import com.dianping.cat.message.Message;
import com.dianping.cat.message.Transaction;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.unidal.helper.Threads;

import java.io.File;
import java.util.concurrent.TimeUnit;

public class MultiThreadingTest {
    @After
    public void after() {
    }

    @Before
    public void before() {
        Cat.initialize(new File("/data/appdatas/cat/client.xml"));
    }

    @Test
    public void testForkedTransaction() throws Exception {
        Transaction t = Cat.newTransaction("ForkedRoot", "Root");
        ForkedTransaction t1 = Cat.newForkedTransaction("ForkedChild", "Child1"); //在当前消息树中埋点桥接节点
        Threads.forGroup().start(new TimedThread(t1, 100)); //与子线程共享这个对象
        TimeUnit.MILLISECONDS.sleep(200);
        t.setStatus(Message.SUCCESS);
        t.complete();
    }

    static class TimedThread extends Thread {
        private ForkedTransaction m_transaction;

        private int m_timeout;

        public TimedThread(ForkedTransaction t, int timeout) {
            m_transaction = t;
            m_timeout = timeout;
        }

        @Override
        public void run() {
            m_transaction.fork();
            try {
                TimeUnit.MILLISECONDS.sleep(m_timeout);
                Cat.logEvent("TimedThread", "Timeout." + m_timeout);
                m_transaction.setStatus(Message.SUCCESS);
            } catch (Exception e) {
                Cat.logError(e);
                m_transaction.setStatus(e);
            } finally {
                m_transaction.complete();
            }
        }
    }
}

模型图

代码和流程分析

new一个ForkT在干嘛？
1.初始化当前线程的消息树根节点消息Id
2.创建子线程中的事务，并设置自己的根节点和父节点的消息Id
3.在消息树的当前节点加入一个额外的event节点，并且把子线程的msgId记录下来

linkasRunAway的具体逻辑

子线程的fork在干嘛？

1.在子线程中初始化本线程的消息树

2. 把forkT的消息id作为子线程的根节点消息id，这样就可以通过runway event节点找到子线程的消息树