Java的每個Thread都希望擁有自己的名稱

一. 介紹

　　平時工作中可能會碰到排查多線程的bug，而在排查的時候，如果線程（單個線程或者是線程池的線程）沒有一個比較明確的名稱，那么在排查的時候就比較頭疼，因為排查問題首先需要找出“問題線程”，如果連“問題線程”都找不到，就很難找出問題原因，本文就針對多線程中涉及到的線程池、線程組、線程名稱，介紹如果對其進行設置名稱，方便排查問題時快速定位。

 

二. 設置線程名稱

2.1 使用Thread+Runnable接口形式

　　如果是使用實現Runnable接口，然后使用Thread構造器來直接創建線程時，有兩種方式設置線程名稱：

　　1.在調用Thread的構造器時，傳入第二個參數即可，構造器定義如下

Thread Thread(Runnable target, String threadName)

　　2.調用Thread對象的setName方法，設置線程名稱即可；

　　上面兩種方法的示例代碼如下：

package cn.ganlixin;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;

@Slf4j
public class DefineThreadName {

    /**
     * 不設置線程名稱，使用默認的線程名稱
     */
    @Test
    public void defaultThreadName() {
        new Thread(() -> {
            String threadName = Thread.currentThread().getName();
            String threadGroupName = Thread.currentThread().getThreadGroup().getName();
            long threadId = Thread.currentThread().getId();
            log.info("threadName:{}, threadGroupName:{}, threadId:{}", threadName, threadGroupName, threadId);
        }).start();
        // 輸出 threadName:Thread-1, threadGroupName:main, threadId:13
    }

    /**
     * 自定義線程的名稱
     */
    @Test
    public void customThreadName() {
        // 方式一：指定Thread構造方法的第二個參數，也就是線程的名稱
        new Thread(() -> {
            String threadName = Thread.currentThread().getName();
            String threadGroupName = Thread.currentThread().getThreadGroup().getName();
            long threadId = Thread.currentThread().getId();
            log.info("threadName:{}, threadGroupName:{}, threadId:{}", threadName, threadGroupName, threadId);
        }, "my-custom-thread-name-1").start();

        // 輸出 threadName:my-custom-thread-name-1, threadGroupName:main, threadId:13

        // 方式二：使用Thread對象的setName方法，設置線程名稱
        Thread thread = new Thread(() -> {
            String threadName = Thread.currentThread().getName();
            String threadGroupName = Thread.currentThread().getThreadGroup().getName();
            long threadId = Thread.currentThread().getId();
            log.info("threadName:{}, threadGroupName:{}, threadId:{}", threadName, threadGroupName, threadId);
        });
        thread.setName("my-custom-thread-name-2");
        thread.start();
        // 輸出 threadName:my-custom-thread-name-2, threadGroupName:main, threadId:14
    }
}

　　

2.2 繼承Thread類的形式

　　如果是繼承Thread類，那么可以在子類中調用Thread僅接受一個字符串作為線程名稱的構造器，像下面這么做：

package cn.ganlixin;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;

@Slf4j
public class DefineThreadName {

    /**
     * 自定義的繼承自Thread的線程類
     */
    private static class MyThread extends Thread {
        private MyThread(String threadName) {
            super(threadName); // Thread有一個構造器接收一個字符串類型的參數，作為線程名稱
        }

        @Override
        public void run() {
            // 因為繼承自Thread，所以下面可以直接調用這些方法，而不需要通過Thread.currentThread()獲取當前線程
            String threadName = getName();
            String threadGroupName = getThreadGroup().getName();
            long threadId = getId();
            log.info("threadName:{}, threadGroupName:{}, threadId:{}", threadName, threadGroupName, threadId);
        }
    }

    /**
     * 測試設置、更改線程名稱
     */
    @Test
    public void testInheritThread() {
        MyThread t1 = new MyThread("my-extends-thread-name-1");
        t1.start();
        // 輸出 threadName:my-extends-thread-name-1, threadGroupName:main, threadId:13

        MyThread t2 = new MyThread("my-extends-thread-name-2");
        t2.setName("changed-thread-name"); // 手動修改線程名稱
        t2.start();
        // 輸出 threadName:changed-thread-name, threadGroupName:main, threadId:14
    }
}

　　

三. 設置線程組的名稱

　　線程組名稱需要在創建線程組的時候進行指定，然后使用線程組的時候將線程組作為Thread類的構造器參數傳入即可，示例代碼如下：

package cn.ganlixin.name;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;

@Slf4j
public class ThreadGroupName {

    @Test
    public void defineThreadGroupName() {
        // 定義一個線程組，傳入線程組的名稱（自定義）
        ThreadGroup threadGroup = new ThreadGroup("my-thread-group-name");

        Runnable runnable = () -> {
            String threadGroupName = Thread.currentThread().getThreadGroup().getName();
            String threadName = Thread.currentThread().getName();
            long threadId = Thread.currentThread().getId();

            log.info("threadGroupName:{}, threadName:{}, threadId:{}", threadGroupName, threadName, threadId);
        };

        Thread t1 = new Thread(threadGroup, runnable);
        t1.start();
        // 輸出 threadGroupName:my-thread-group-name, threadName:Thread-1, threadId:13

        // 第三個參數是線程名稱
        Thread t2 = new Thread(threadGroup, runnable, "my-thread-name");
        t2.start();
        // threadGroupName:my-thread-group-name, threadName:my-thread-name, threadId:14
    }
}

　　

四. 設置線程池名稱

4.1 創建線程池的兩種途徑

　　創建線程池，有兩種方式：　

　　1.實例化ThreadPoolExecutor來創建線程池，可以指定相關的參數，方法定義如下：

　　

　　2.使用Executors的靜態方法創建線程池，實際是對ThreadPoolExecutor對象的創建過程進行了封裝，可用的方法定義如下：

　　

　　上面的諸多定義中，提到了一個ThreadFactory，“線程工廠”，這是一個接口，定義了創建線程的統一規范，實現類需要重寫newThread方法，定義如下：

package java.util.concurrent;

public interface ThreadFactory {
    Thread newThread(Runnable r);
}

　　當我們調用Executors或者使用ThreadPoolExecutor來創建線程池，如果沒有指定ThreadFactory，那么就會使用默認的Executors.DefaultThreadFactory：

static class DefaultThreadFactory implements ThreadFactory {
    private static final AtomicInteger poolNumber = new AtomicInteger(1);
    private final ThreadGroup group;
    private final AtomicInteger threadNumber = new AtomicInteger(1);
    private final String namePrefix;

    DefaultThreadFactory() {
        SecurityManager s = System.getSecurityManager();
        group = (s != null) ? s.getThreadGroup() :
                              Thread.currentThread().getThreadGroup();
        namePrefix = "pool-" +
                      poolNumber.getAndIncrement() +
                     "-thread-";
    }

    public Thread newThread(Runnable r) {
        Thread t = new Thread(group, r,
                              namePrefix + threadNumber.getAndIncrement(),
                              0);
        if (t.isDaemon())
            t.setDaemon(false);
        if (t.getPriority() != Thread.NORM_PRIORITY)
            t.setPriority(Thread.NORM_PRIORITY);
        return t;
    }
}

　　如果我們要對線程池中的線程創建進行擴展，那么實現ThreadFactory接口，加入自己的擴展即可，此處對於線程池中線程的名稱進行設置，也是可以在這里實現。

 　

4.2 自定義線程工廠（ThreadFactory)

　　自己實現ThreadFactory接口，可以參考Executors.DefaultThreadFactory，做一下細微的修改就行了，下面是我創建的NameableThreadFactory，意為“可命名的線程工廠”：

package cn.ganlixin.name;

import org.apache.commons.lang3.StringUtils;

import java.util.Objects;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 描述:
 * 參照Executors.DefaultThreadFactory，自定義ThreadFactory實現類
 *
 * @author ganlixin
 * @create 2020-05-23
 */
public class NameableThreadFactory implements ThreadFactory {
    /**
     * 對線程池的數量進行計數，注意是類屬性
     */
    private static final AtomicInteger poolNumber = new AtomicInteger(1);

    /**
     * 線程組名稱
     */
    private ThreadGroup group;

    /**
     * 對線程池中的線程數據進行計數，注意是實例屬性
     */
    private final AtomicInteger threadNumber = new AtomicInteger(1);

    /**
     * 線程名稱的前綴
     */
    private String namePrefix;

    /**
     * Executors.DefaultThreadFactory中默認的方式（設置線程組、線程名稱前綴）
     */
    public NameableThreadFactory() {
        SecurityManager s = System.getSecurityManager();
        group = (s != null) ? s.getThreadGroup() : Thread.currentThread().getThreadGroup();
        namePrefix = "pool-" + poolNumber.getAndIncrement() + "-thread-";
    }

    /**
     * 創建線程工廠，指定線程名稱前綴
     *
     * @param threadNamePrefix 線程名稱前綴
     */
    public NameableThreadFactory(String threadNamePrefix) {
        if (StringUtils.isBlank(threadNamePrefix)) {
            throw new IllegalArgumentException("線程名稱的前綴不能為空");
        }

        // 線程組，仍舊使用舊規則
        SecurityManager s = System.getSecurityManager();
        group = (s != null) ? s.getThreadGroup() : Thread.currentThread().getThreadGroup();

        // 指定線程的名稱前綴，設置為傳入的名稱前綴
        this.namePrefix = threadNamePrefix + "-";
    }

    /**
     * 創建線程工廠，指定線程組、以及線程名稱前綴
     *
     * @param threadGroup      線程組實例
     * @param threadNamePrefix 線程名稱前綴
     */
    public NameableThreadFactory(ThreadGroup threadGroup, String threadNamePrefix) {
        if (Objects.isNull(threadGroup)) {
            throw new IllegalArgumentException("線程組不能為空");
        }

        if (StringUtils.isBlank(threadNamePrefix)) {
            throw new IllegalArgumentException("線程名稱的前綴不能為空");
        }

        this.group = threadGroup;
        this.namePrefix = threadNamePrefix + "-";
    }

    public Thread newThread(Runnable r) {
        Thread t = new Thread(group, r, namePrefix + threadNumber.getAndIncrement(), 0);
        if (t.isDaemon()) {
            t.setDaemon(false);
        }
        if (t.getPriority() != Thread.NORM_PRIORITY) {
            t.setPriority(Thread.NORM_PRIORITY);
        }
        return t;
    }
}

　　進行測試，因為Executors和ThreadPoolExecutor的本質是一樣的，所以這里使用Executors進行測試，只需要在用到ThreadFactory的時候，引入自己的創建NameableThreadFactory即可：

package cn.ganlixin.name;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@Slf4j
public class TestNameableThreadFactory {

    @Test
    public void test() throws InterruptedException {
        ExecutorService executorService1 = Executors.newFixedThreadPool(3, new NameableThreadFactory("自定義線程池one"));

        Runnable runnable = () -> {
            String threadGroupName = Thread.currentThread().getThreadGroup().getName();
            String threadName = Thread.currentThread().getName();
            long threadId = Thread.currentThread().getId();
            log.info("threadGroupName:{}, threadName:{}, threadId:{}", threadGroupName, threadName, threadId);
        };

        for (int i = 0; i < 3; i++) {
            executorService1.submit(runnable);
        }
        // 輸出
        // threadGroupName:main, threadName:自定義線程池one-1, threadId:14
        // threadGroupName:main, threadName:自定義線程池one-2, threadId:15
        // threadGroupName:main, threadName:自定義線程池one-3, threadId:16
        Thread.sleep(100);

        // 創建線程組
        ThreadGroup threadGroup = new ThreadGroup("自定義線程組one");
        ExecutorService executorService2 = Executors.newFixedThreadPool(3, new NameableThreadFactory(threadGroup, "自定義線程池two"));
        for (int i = 0; i < 3; i++) {
            executorService2.submit(runnable);
        }
        // 輸出：
        // threadGroupName:自定義線程組one, threadName:自定義線程池two-1, threadId:16
        // threadGroupName:自定義線程組one, threadName:自定義線程池two-2, threadId:17
        // threadGroupName:自定義線程組one, threadName:自定義線程池two-3, threadId:18

        Thread.sleep(1000);
    }
}