java多线程使用mdc追踪日志方式

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多线程使用mdc追踪日志

背景

多线程情况下，子线程的sl4j打印日志缺少traceId等信息，导致定位问题不方便

解决方案

打印日志时添加用户ID、trackId等信息，缺点是每个日志都要手动添加
使用mdc直接拷贝父线程值

实现


// 新建线程时：
Map<String, String> mdcContextMap = MDC.getCopyOfContextMap()
// 子线程运行时：
if(null != mdcContextMap){
    MDC.setContextMap(mdcContextMap);
}
// 销毁线程时
MDC.clear();

参考


import org.slf4j.MDC;
import java.util.Map;
import java.util.concurrent.*;
/**
 * A SLF4J MDC-compatible {@link ThreadPoolExecutor}.
 * <p/>
 * In general, MDC is used to store diagnostic information (e.g. a user"s session id) in per-thread variables, to facilitate
 * logging. However, although MDC data is passed to thread children, this doesn"t work when threads are reused in a
 * thread pool. This is a drop-in replacement for {@link ThreadPoolExecutor} sets MDC data before each task appropriately.
 * <p/>
 * Created by jlevy.
 * Date: 6/14/13
 */
public class MdcThreadPoolExecutor extends ThreadPoolExecutor {
    final private boolean useFixedContext;
    final private Map<String, Object> fixedContext;
    /**
     * Pool where task threads take MDC from the submitting thread.
     */
    public static MdcThreadPoolExecutor newWithInheritedMdc(int corePoolSize, int maximumPoolSize, long keepAliveTime,
                                                            TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        return new MdcThreadPoolExecutor(null, corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }
    /**
     * Pool where task threads take fixed MDC from the thread that creates the pool.
     */
    @SuppressWarnings("unchecked")
    public static MdcThreadPoolExecutor newWithCurrentMdc(int corePoolSize, int maximumPoolSize, long keepAliveTime,
                                                          TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        return new MdcThreadPoolExecutor(MDC.getCopyOfContextMap(), corePoolSize, maximumPoolSize, keepAliveTime, unit,
                workQueue);
    }
    /**
     * Pool where task threads always have a specified, fixed MDC.
     */
    public static MdcThreadPoolExecutor newWithFixedMdc(Map<String, Object> fixedContext, int corePoolSize,
                                                        int maximumPoolSize, long keepAliveTime, TimeUnit unit,
                                                        BlockingQueue<Runnable> workQueue) {
        return new MdcThreadPoolExecutor(fixedContext, corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }
    private MdcThreadPoolExecutor(Map<String, Object> fixedContext, int corePoolSize, int maximumPoolSize,
                                  long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
        this.fixedContext = fixedContext;
        useFixedContext = (fixedContext != null);
    }
    @SuppressWarnings("unchecked")
    private Map<String, Object> getContextForTask() {
        return useFixedContext ? fixedContext : MDC.getCopyOfContextMap();
    }
    /**
     * All executions will have MDC injected. {@code ThreadPoolExecutor}"s submission methods ({@code submit()} etc.)
     * all delegate to this.
     */
    @Override
    public void execute(Runnable command) {
        super.execute(wrap(command, getContextForTask()));
    }
    public static Runnable wrap(final Runnable runnable, final Map<String, Object> context) {
        return new Runnable() {
            @Override
            public void run() {
                Map previous = MDC.getCopyOfContextMap();
                if (context == null) {
                    MDC.clear();
                } else {
                    MDC.setContextMap(context);
                }
                try {
                    runnable.run();
                } finally {
                    if (previous == null) {
                        MDC.clear();
                    } else {
                        MDC.setContextMap(previous);
                    }
                }
            }
        };
    }
}

多线程日志追踪

主要目的是记录工作中的一些编程思想和细节，以便后来查阅。

1.问题描述

由于项目中设计高并发内容，涉及到一个线程创建多个子线程的情况。那么，如何跟踪日志，识别子线程是由哪个主线程创建的，属于哪个request请求。

例如，在现有项目中，一个设备信息上传的请求（包括基本数据和异常数据两种数据），然后主线程创建两个子线程，来处理基本数据和异常数据。

简化代码如下：


public class mainApp {
    public static void main(String[] args) {
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                //接收到一个request
                System.out.println("[Thread-"+ Thread.currentThread().getId() +"]开始发起请求");
                String[] data = {"异常数据","基本数据"};
                //创建子线程1，处理异常数据
                MThread mThread1 = new MThread(new Runnable() {
                    @Override
                    public void run() {
                        System.out.println("[Thread-"+ Thread.currentThread().getId() +"]处理了" + data[0]);
                    }
                });
                创建子线程2，处理普通数据
                MThread mThread2 = new MThread(new Runnable() {
                    @Override
                    public void run() {
                        System.out.println("[Thread-"+ Thread.currentThread().getId() +"]处理了"  + data[1]);
                    }
                });
                new Thread(mThread1).start();
                new Thread(mThread2).start(); 
            }
        });
        t.start();
    }
}
 
class MThread implements Runnable { 
    private Runnable r; 
    public MThread(Runnable r) {
        this.r = r;
    }
 
    @Override
    public void run() {
        r.run();
    }
}

运行结果如下：

java多线程使用mdc追踪日志方式

一个请求有三个线程，如果有多个请求，运行结果如下：

java多线程使用mdc追踪日志方式

从日志中无法看出他们之间的所属关系（判断不出来他们是否是处理同一个request请求的）。如果某一个线程出现问题，我们也很难快速定位是哪个请求的处理结果。

2. 代理实现日志追踪

因此，我们使用MDC来在日志中增加traceId（同一个请求的多个线程拥有同一个traceId）。

思路如下：

1. 在request进来的时候，利用AOP为每个request创建一个traceId（保证每个request的traceId不同，同一个request的traceId相同）

2. 创建子线程的时候，将traceId通过动态代理的方式，传递到子线程中


public class mainApp {
    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                //AOP 生成一个traceId
                MDC.put("traceId", UUID.randomUUID().toString().replace("-", ""));
                //接收到一个request
                System.out.println("[Thread-"+ Thread.currentThread().getId() +"]traceId["+ MDC.get("traceId") +"]开始发起请求");
                String[] data = {"异常数据","基本数据"};
 
                MThread mThread1 = new MThread(new Runnable() {
                    @Override
                    public void run() {
                        System.out.println("[Thread-"+ Thread.currentThread().getId() +"]traceId["+ MDC.get("traceId") +"]处理了" + data[0]);
                    }
                }, MDC.getCopyOfContextMap());
                MThread mThread2 = new MThread(new Runnable() {
                    @Override
                    public void run() {
                        System.out.println("[Thread-"+ Thread.currentThread().getId() +"]traceId["+ MDC.get("traceId") +"]处理了"  + data[1]);
                    }
                }, MDC.getCopyOfContextMap());
                new Thread(mThread1).start();
                new Thread(mThread2).start(); 
            }
        };
        new Thread(runnable).start();
        new Thread(runnable).start();
    }
}
 
class MThread implements Runnable { 
    private Runnable r; 
    public MThread(Runnable r, Map<String, String> parentThreadMap) {
        LogProxy logProxy = new LogProxy(r, parentThreadMap);
        Runnable rProxy = (Runnable) Proxy.newProxyInstance(r.getClass().getClassLoader(), r.getClass().getInterfaces(), logProxy);
        this.r = rProxy;
    }
 
    @Override
    public void run() {
        r.run();
    }
}
 
//日志代理
class LogProxy implements InvocationHandler {
    private Runnable r;
    private  Map<String, String> parentThreadMap;
    public LogProxy(Runnable r, Map<String, String> parentThreadMap) {
        this.r = r;
        this.parentThreadMap = parentThreadMap;
    }
 
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (method.getName().equals("run")) {
            MDC.setContextMap(parentThreadMap);
        }
        return method.invoke(r, args);
    }
}

运行结果如下：

java多线程使用mdc追踪日志方式