ThreadPoolExecutor参数含义及源码执行流程详解

public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue,
                          ThreadFactory threadFactory,
                          RejectedExecutionHandler handler) {
    if (corePoolSize < 0 ||
        // maximumPoolSize 必须大于 0，且必须大于 corePoolSize
        maximumPoolSize <= 0 ||
        maximumPoolSize < corePoolSize ||
        keepAliveTime < 0)
        throw new IllegalArgumentException();
    if (workQueue == null || threadFactory == null || handler == null)
        throw new NullPointerException();
    this.acc = System.getSecurityManager() == null ?
            null :
            AccessController.getContext();
    this.corePoolSize = corePoolSize;
    this.maximumPoolSize = maximumPoolSize;
    this.workQueue = workQueue;
    this.keepAliveTime = unit.toNanos(keepAliveTime);
    this.threadFactory = threadFactory;
    this.handler = handler;
}

public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue) {
    // Executors.defaultThreadFactory() 为默认的线程创建工厂
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
         Executors.defaultThreadFactory(), defaultHandler);
}
public static ThreadFactory defaultThreadFactory() {
    return new DefaultThreadFactory();
}
// 默认的线程创建工厂，需要实现 ThreadFactory 接口
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-";
    }
    // 创建线程
    public Thread newThread(Runnable r) {
        Thread t = new Thread(group, r,
                              namePrefix + threadNumber.getAndIncrement(),
                              0);
        if (t.isDaemon()) 
            t.setDaemon(false); // 创建一个非守护线程
        if (t.getPriority() != Thread.NORM_PRIORITY)
            t.setPriority(Thread.NORM_PRIORITY); // 线程优先级设置为默认值
        return t;
    }
}

public void execute(Runnable command) {
    if (command == null)
        throw new NullPointerException();
    int c = ctl.get();
    // 当前工作的线程数小于核心线程数
    if (workerCountOf(c) < corePoolSize) {
        // 创建新的线程执行此任务
        if (addWorker(command, true))
            return;
        c = ctl.get();
    }
    // 检查线程池是否处于运行状态，如果是则把任务添加到队列
    if (isRunning(c) && workQueue.offer(command)) {
        int recheck = ctl.get();
        // 再出检查线程池是否处于运行状态，防止在第一次校验通过后线程池关闭
        // 如果是非运行状态，则将刚加入队列的任务移除
        if (! isRunning(recheck) && remove(command))
            reject(command);
        // 如果线程池的线程数为 0 时（当 corePoolSize 设置为 0 时会发生）
        else if (workerCountOf(recheck) == 0)
            addWorker(null, false); // 新建线程执行任务
    }
    // 核心线程都在忙且队列都已爆满，尝试新启动一个线程执行失败
    else if (!addWorker(command, false)) 
        // 执行拒绝策略
        reject(command);
}

ThreadPoolExecutor executor = new ThreadPoolExecutor(2, 10, 10L,
        TimeUnit.SECONDS, new LinkedBlockingQueue(20));
// execute 使用
executor.execute(new Runnable() {
    @Override
    public void run() {
        System.out.println("Hello, execute.");
    }
});
// submit 使用
Future<String> future = executor.submit(new Callable<String>() {
    @Override
    public String call() throws Exception {
        System.out.println("Hello, submit.");
        return "Success";
    }
});
System.out.println(future.get());

ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 3, 10,
        TimeUnit.SECONDS, new LinkedBlockingQueue<>(2),
        new ThreadPoolExecutor.AbortPolicy()); // 添加 AbortPolicy 拒绝策略
for (int i = 0; i < 6; i++) {
    executor.execute(() -> {
        System.out.println(Thread.currentThread().getName());
    });
}

ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 3, 10,
        TimeUnit.SECONDS, new LinkedBlockingQueue<>(2),
        new RejectedExecutionHandler() {  // 添加自定义拒绝策略
            @Override
            public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
                // 业务处理方法
                System.out.println("执行自定义拒绝策略");
            }
        });
for (int i = 0; i < 6; i++) {
    executor.execute(() -> {
        System.out.println(Thread.currentThread().getName());
    });
}

public class ThreadPoolExtend {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        // 线程池扩展调用
        MyThreadPoolExecutor executor = new MyThreadPoolExecutor(2, 4, 10,
                TimeUnit.SECONDS, new LinkedBlockingQueue());
        for (int i = 0; i < 3; i++) {
            executor.execute(() -> {
                Thread.currentThread().getName();
            });
        }
    }
   
    static class MyThreadPoolExecutor extends ThreadPoolExecutor {
        // 保存线程执行开始时间
        private final ThreadLocal<Long> localTime = new ThreadLocal<>();
        public MyThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime,
                            TimeUnit unit, BlockingQueue<Runnable> workQueue) {
    super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
        
        @Override
        protected void beforeExecute(Thread t, Runnable r) {
            Long sTime = System.nanoTime(); // 开始时间 (单位：纳秒)
            localTime.set(sTime);
            System.out.println(String.format("%s | before | time=%s",
                    t.getName(), sTime));
            super.beforeExecute(t, r);
        }
        
        @Override
        protected void afterExecute(Runnable r, Throwable t) {
            Long eTime = System.nanoTime(); // 结束时间 (单位：纳秒)
            Long totalTime = eTime - localTime.get(); // 执行总时间
            System.out.println(String.format("%s | after | time=%s | 耗时：%s 毫秒",
                    Thread.currentThread().getName(), eTime, (totalTime / 1000000.0)));
            super.afterExecute(r, t);
        }
    }
}