jdk源码解析五之Executor框架

Executor基于生产者消费者模式,提交任务操作相当于生产者,执行任务的线程相当于消费者

线程不能不停创建,所以复用线程衍生出了线程池的概念,而不停的复用线程,假如有10个线程去跑100请求,还有90请求怎么办？引入了阻塞队列.而如果10个线程最多只能处理100线程,那101线程怎么办?这里就引入new ThreadPoolExecutor.CallerRunsPolicy()4种处理的概念

开启多少线程,最大多少线程,?
线程的任务使FIFO,LIFO还是按照优先级执行?
多余的任务,是否阻塞队列缓存?
队列撑爆了,使用何种策略处理?
取消的时候,平滑过渡,还是强制终止所有任务?
出现异常,可定义异常处理器setDefaultUncaughtExceptionHandler/setUncaughtExceptionHandler

设置线程池大小
线程池过大,造成大量线程在相对很小的cpu和内存资源上发生竞争，会导致内存过高
线程池过小,许多空闲处理器无法工作,降低吞吐
需要考虑,cpu，内存,任务是计算密集类型还是io密集还是2者,
如果需要执行不同类别任务,并且之间行为相差很大,考虑使用多个线程池，从而使每个线程池可以根据各自的工作负载来调整
计算密集型,线程大小为N+1(多一个备份)
包含I/O或者其他阻塞任务
N=cpu个数 Runtime.availableProcessors
U=CPU利用率 0<=U<=1
W/C=任务等待时间/计算时间
线程池最优大小=NU(1+W/C)
资源:该资源的可用总量/每个任务对该资源的需求量

	N *(W+C)/C

美团给出的解决方案

Executor

ExecutorService

提供了管理终止的方法，以及可为跟踪一个或多个异步任务执行状况而生成 Future 的方法。

ScheduledExecutorService

对可调度的支持

AbstractExecutorService

    protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
        //底层封装FutureTask
        return new FutureTask<T>(runnable, value);
    }

  public Future<?> submit(Runnable task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<Void> ftask = newTaskFor(task, null);
        //子类实现
        execute(ftask);
        return ftask;
    }

  //返回最快的结果
    public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
        throws InterruptedException, ExecutionException {
        try {
            return doInvokeAny(tasks, false, 0);
        } catch (TimeoutException cannotHappen) {
            assert false;
            return null;
        }
    }

 private <T> T doInvokeAny(Collection<? extends Callable<T>> tasks,
                              boolean timed, long nanos)
        throws InterruptedException, ExecutionException, TimeoutException {
        //任务为空校验
        if (tasks == null)
            throw new NullPointerException();
        int ntasks = tasks.size();
        if (ntasks == 0)
            throw new IllegalArgumentException();

        ArrayList<Future<T>> futures = new ArrayList<Future<T>>(ntasks);
        //使用ExecutorCompletionService,获取结果前阻塞.内部维护一个阻塞队列,继承Future保存结果
        ExecutorCompletionService<T> ecs =
            new ExecutorCompletionService<T>(this);


        try {

            ExecutionException ee = null;
            final long deadline = timed ? System.nanoTime() + nanos : 0L;
            //获取回调方法的迭代器
            Iterator<? extends Callable<T>> it = tasks.iterator();
            //结果封装到集合
            futures.add(
                    //执行回调函数
                    ecs.submit(it.next())
            );
            --ntasks;
            //记录执行的回调函数个数
            int active = 1;

            for (;;) {
                //获取结果,非阻塞
                Future<T> f = ecs.poll();
                //尚未获取结果
                if (f == null) {
                    //回调任务>1,则继续执行下一个回调任务
                    if (ntasks > 0) {
                        --ntasks;
                        futures.add(ecs.submit(it.next()));
                        //记录正在执行个数
                        ++active;
                    }
                    else if (active == 0)
                        //正在执行个数为0，则说明获取结果阶段抛出异常,直接结束
                        break;
                    else if (timed) {
                        //如果阻塞,则设置超时获取结果
                        f = ecs.poll(nanos, TimeUnit.NANOSECONDS);
                        if (f == null)
                            throw new TimeoutException();
                        //超时时间减少
                        nanos = deadline - System.nanoTime();
                    }
                    else
                        //阻塞,获取并移除表示下一个已完成任务的 Future
                        f = ecs.take();
                }
                //阻塞队列如果有结果
                if (f != null) {
                    --active;
                    try {
                        //返回结果
                        return f.get();
                    } catch (ExecutionException eex) {
                        ee = eex;
                    } catch (RuntimeException rex) {
                        ee = new ExecutionException(rex);
                    }
                }
            }

            if (ee == null)
                ee = new ExecutionException();
            throw ee;

        } finally {
            for (int i = 0, size = futures.size(); i < size; i++)
                //取消所有结果
                futures.get(i).cancel(true);
        }
    }

 public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
        throws InterruptedException {
        if (tasks == null)
            throw new NullPointerException();
        ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
        boolean done = false;
        try {
            for (Callable<T> t : tasks) {
                //FutureTask底层封装
                RunnableFuture<T> f = newTaskFor(t);
                //结果存储集合
                futures.add(f);
                //子类实现
                execute(f);
            }
            for (int i = 0, size = futures.size(); i < size; i++) {
                //获取结果
                Future<T> f = futures.get(i);
                //如果还在执行
                if (!f.isDone()) {
                    try {
                        //阻塞获取结果
                        f.get();
                    } catch (CancellationException ignore) {
                    } catch (ExecutionException ignore) {
                    }
                }
            }
            done = true;
            //返回结果集
            return futures;
        } finally {
            //如果中途抛出异常
            if (!done)
                for (int i = 0, size = futures.size(); i < size; i++)
                    //取消所有任务
                    futures.get(i).cancel(true);
        }
    }

 public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
                                         long timeout, TimeUnit unit)
        throws InterruptedException {
        if (tasks == null)
            throw new NullPointerException();
        long nanos = unit.toNanos(timeout);
        ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
        boolean done = false;
        try {
            //所有回调任务封装成Task,且保存到集合
            for (Callable<T> t : tasks)
                futures.add(newTaskFor(t));

            //记录超时时间
            final long deadline = System.nanoTime() + nanos;
            final int size = futures.size();

            // Interleave time checks and calls to execute in case
            // executor doesn't have any/much parallelism.
            for (int i = 0; i < size; i++) {
                //执行任务
                execute((Runnable)futures.get(i));
                nanos = deadline - System.nanoTime();
                //如果超时,则直接返回结果
                if (nanos <= 0L)
                    return futures;
            }

            for (int i = 0; i < size; i++) {
                Future<T> f = futures.get(i);
                //如果任务还在执行
                if (!f.isDone()) {
                    if (nanos <= 0L)
                        return futures;
                    try {
                        //超时获取结果
                        f.get(nanos, TimeUnit.NANOSECONDS);
                    } catch (CancellationException ignore) {
                    } catch (ExecutionException ignore) {
                    } catch (TimeoutException toe) {
                        return futures;
                    }
                    nanos = deadline - System.nanoTime();
                }
            }
            done = true;
            return futures;
        } finally {
            if (!done)
                for (int i = 0, size = futures.size(); i < size; i++)
                    futures.get(i).cancel(true);
        }
    }

总结

底层使用FutureTask
invokeAny使用ExecutorCompletionService阻塞队列获取结果

ThreadPoolExecutor

成员变量以及方法

 //保存线程数量和线程池的状态,初始CTL=111 0(32-3个0)
    private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
    private static final int COUNT_BITS = Integer.SIZE - 3;
    //线程池最大1^29-1
    private static final int CAPACITY   = (1 << COUNT_BITS) - 1;

    // runState is stored in the high-order bits
    //5种运行状态,分别用高3位保存运行状态
    // 接收新任务,并执行队列中的任务
    private static final int RUNNING    = -1 << COUNT_BITS;
    // 不接收新任务,但是执行队列中的任务
    private static final int SHUTDOWN   =  0 << COUNT_BITS;
    // 不接收新任务,不执行队列中的任务,中断正在执行中的任务
    private static final int STOP       =  1 << COUNT_BITS;
    //所有的任务都已结束,线程数量为 0,处于该状态的线程池即将调用 terminated()方法
    private static final int TIDYING    =  2 << COUNT_BITS;
    // terminated()方法执行完成
    private static final int TERMINATED =  3 << COUNT_BITS;

    // Packing and unpacking ctl
    //获取高3位
    private static int runStateOf(int c)     { return c & ~CAPACITY; }
    //获取低29位
    private static int workerCountOf(int c)  { return c & CAPACITY; }
    private static int ctlOf(int rs, int wc) { return rs | wc; }

构造

 public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            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();
        //设置核心大小
        this.corePoolSize = corePoolSize;
        //设置最大线程大小
        //当添加新的执行任务,如果运行的线程少于 corePoolSize，则创建新线程来处理请求
        this.maximumPoolSize = maximumPoolSize;
        //设置工作队列
        this.workQueue = workQueue;
        //空闲时间
        //如果池中当前有多于 corePoolSize 的线程，则这些多出的线程在空闲时间超过 keepAliveTime 时将会终止
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        //创建线程的工厂,默认Executors.defaultThreadFactory()
        this.threadFactory = threadFactory;
        //饱和策略,默认AbortPolicy()
        /*
    AbortPolicy(终止策略):默认策略,抛出RejectExecutionException
    DisCardPolicy:新提交的任务无法保存到队列中等待执行时,抛弃该任务
    DisCardOldestPolicy:抛弃下一个将被执行的任务,尝试重新提交新的任务(如果工作队列是一个优先队列,此策略会导致抛弃优先级最高的任务)
    CallerRunsPolicy:将任务回退到调用者执行,主线程在一段时间内不能提交任务,使工作者线程有时间处理完正在执行的任务,在此期间主线程不会accept,到达的请求会保存在TCP层队列，持续过载,TCP会抛弃请求
                路径为：线程池-工作队列-应用程序-TCP-客户端
         */
        this.handler = handler;
    }

execute

 public void execute(Runnable command) {
        //空校验
        if (command == null)
            throw new NullPointerException();

        int c = ctl.get();
        //当前工作线程个数<核心大小
        if (workerCountOf(c) < corePoolSize) {
            //添加新的工作线程,并执行
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        //核心池都在运行状态，添加到队列中
        if (isRunning(c) && workQueue.offer(command)) {
            //再次获取控制状态
            int recheck = ctl.get();
            //如果任务不处于Run状态,则删除任务,并拒绝任务.
            if (! isRunning(recheck) && remove(command))
                //拒绝任务
                reject(command);
            else if (workerCountOf(recheck) == 0)
                //处于运行状态,但可使用线程为0,则试着创建线程最大线程数新开一个新线程
                addWorker(null, false);
        }
        else if
            //核心池没处于运行状态或者队列已满，试着创建线程最大线程数新开一个新线程处理
        (!addWorker(command, false))
            //如果创建新线程失败了，说明线程池被关闭或者线程池完全满了，拒绝任务
            reject(command);
    }

    private boolean addWorker(Runnable firstTask, boolean core) {
        retry://goto 语句,避免死循环
        for (;;) {
            //获取线程数量和线程池的状态
            int c = ctl.get();
            //获取运行状态
            int rs = runStateOf(c);

            // Check if queue empty only if necessary.
            /*
            1:线程池已经最少关闭
            2:状态没关闭,任务不为空,且工作线程为空
            同时满足以上2条件,则直接返回false

            2种情况下允许添加新线程
            线程池处于运行状态
            线程池处于关闭状态,且任务为null,且工作线程不为空
             */
            //状态至少SHUTDOWN,
            if (rs >= SHUTDOWN &&
                    //状态不为shutDown
                ! (rs == SHUTDOWN &&
                        //任务不为空
                   firstTask == null &&
                        //工作线程为空
                   ! workQueue.isEmpty()))
                return false;

            //自旋
            for (;;) {
                //获取当前工作线程个数
                int wc = workerCountOf(c);
                //当前工作线程>最大上限 或根据是否开启最大线程判断,则返回
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize))
                    return false;
                //当前工作线程+1,成功则结束
                if (compareAndIncrementWorkerCount(c))
                    break retry;
                //cas操作失败
                //获取最新ctl值
                c = ctl.get();  // Re-read ctl
                //说明更改了线程池的状态,继续重试
                if (runStateOf(c) != rs)
                    continue retry;
                //CAS由于更改workerCount而失败，继续内层循环
                // else CAS failed due to workerCount change; retry inner loop
            }
        }

        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
            //创建工作线程
            w = new Worker(firstTask);
            //获取线程
            final Thread t = w.thread;
            //线程不为空
            if (t != null) {
                //获取main锁
                final ReentrantLock mainLock = this.mainLock;
                //锁
                mainLock.lock();
                try {
                    // Recheck while holding lock.
                    // Back out on ThreadFactory failure or if
                    // shut down before lock acquired.
                    //获取最新运行状态
                    int rs = runStateOf(ctl.get());

                    //如果处于运行状态,或者处于关闭状态且任务为null
                    if (rs < SHUTDOWN ||
                        (rs == SHUTDOWN && firstTask == null)) {
                        //线程存活
                        if (t.isAlive()) // precheck that t is startable
                            //线程尚未启动,就处于存活状态,则异常
                            throw new IllegalThreadStateException();
                        //添加到workers集合
                        workers.add(w);
                        //获取当前工作线程大小
                        int s = workers.size();
                        //超过largestPoolSize
                        if (s > largestPoolSize)
                            //重新设置largestPoolSize
                            largestPoolSize = s;
                        //标记正常处理
                        workerAdded = true;
                    }
                } finally {
                    //释放锁
                    mainLock.unlock();
                }
                //正常添加
                if (workerAdded) {
                    //执行
                    t.start();
                    //标记正常启动
                    workerStarted = true;
                }
            }
        } finally {
            //如果没正常启动
            if (! workerStarted)
                //异常处理,包括删除添加的工作线程,工作线程个数-1等
                addWorkerFailed(w);
        }
        return workerStarted;
    }

  private void addWorkerFailed(Worker w) {
        //获取重入锁
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            if (w != null)
                //移除当前工作线程
                workers.remove(w);
            //CAS当前工作线程数量-1
            decrementWorkerCount();
            //终止线程池
            tryTerminate();
        } finally {
            mainLock.unlock();
        }
    }

    private void decrementWorkerCount() {
        do {} while (! compareAndDecrementWorkerCount(ctl.get()));
    }

tryTerminate

final void tryTerminate() {
        for (;;) {
            int c = ctl.get();
            /*处于运行状态,或者
             *线程池状态>=TIDYING
             *线程池=SHUTDOWN并且workQueue不为空
             *直接return，不能终止
             */
            if (isRunning(c) ||
                runStateAtLeast(c, TIDYING) ||
                (runStateOf(c) == SHUTDOWN && ! workQueue.isEmpty()))
                return;
            //工作线程个数>0
            if (workerCountOf(c) != 0) { // Eligible to terminate
                //中断工作线程
                interruptIdleWorkers(ONLY_ONE);
                return;
            }

            final ReentrantLock mainLock = this.mainLock;
            mainLock.lock();
            try {
                //CAS设置线程池状态为TIDYING
                if (ctl.compareAndSet(c, ctlOf(TIDYING, 0))) {
                    try {
                        terminated();
                    } finally {
                        //设置线程池的状态为TERMINATED
                        ctl.set(ctlOf(TERMINATED, 0));
                        //发送释放信号给在termination条件上等待的线程
                        termination.signalAll();
                    }
                    return;
                }
            } finally {
                //释放锁
                mainLock.unlock();
            }
            // else retry on failed CAS
        }
    }

interruptIdleWorkers

 private void interruptIdleWorkers(boolean onlyOne) {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            //遍历工作线程
            for (Worker w : workers) {
                Thread t = w.thread;
                //当前线程没有中断,且尝试获取锁成功
                if (!t.isInterrupted() && w.tryLock()) {
                    try {
                        //中断
                        t.interrupt();
                    } catch (SecurityException ignore) {
                    } finally {
                        w.unlock();
                    }
                }
                //最多中断一个线程
                if (onlyOne)
                    break;
            }
        } finally {
            mainLock.unlock();
        }
    }

run

  private boolean addWorker(Runnable firstTask, boolean core) {
//  ...
            w = new Worker(firstTask);
//...
//这里调用的Worker.run
                    t.start();
//...
}

  Worker(Runnable firstTask) {
            setState(-1); // inhibit interrupts until runWorker
            this.firstTask = firstTask;
            this.thread = getThreadFactory().newThread(this);
        }

        /** Delegates main run loop to outer runWorker  */
        public void run() {
            runWorker(this);
        }

 final void runWorker(Worker w) {
        //获取当前线程
        Thread wt = Thread.currentThread();
        //获取任务
        Runnable task = w.firstTask;
        //提前释放
        w.firstTask = null;
        /*
         *unlock方法会调用AQS的release方法
         *release方法会调用具体实现类也就是Worker的tryRelease方法
         *也就是将AQS状态置为0，允许中断
         * interruptIfStarted()中只有 state>=0 才允许调用中断A
         */
        w.unlock(); // allow interrupts
        //标记是否正常执行完
        boolean completedAbruptly = true;
        try {
            //如果task不为null,或者获取任务不为null,则进入循环
            //线程复用
            while (task != null || (task = getTask()) != null) {
                //不是为了防止并发执行任务，为了在 shutdown()时不终止正在运行的 worker
                w.lock();
                // If pool is stopping, ensure thread is interrupted;
                // if not, ensure thread is not interrupted.  This
                // requires a recheck in second case to deal with
                // shutdownNow race while clearing interrupt
                //如果当前线程池状态>=stop或者
                if ((runStateAtLeast(ctl.get(), STOP) ||
                // 当前线程是否被中断（检查中断标志），返回一个boolean并清除中断状态，第二次再调用时中断状态已经被清除，将返回一个false。
                     (Thread.interrupted() &&
                             //且当前线程池>=stop状态
                      runStateAtLeast(ctl.get(), STOP))) &&
                        //测试此线程是否被中断 ，不清除中断状态。
                    !wt.isInterrupted())
                    //中断当前线程
                    wt.interrupt();
                try {
                    //钩子方法,子类实现
                    beforeExecute(wt, task);
                    Throwable thrown = null;
                    try {
                        //执行
                        task.run();
                    } catch (RuntimeException x) {
                        thrown = x; throw x;
                    } catch (Error x) {
                        thrown = x; throw x;
                    } catch (Throwable x) {
                        thrown = x; throw new Error(x);
                    } finally {
                        //钩子方法,子类实现
                        afterExecute(task, thrown);
                    }
                } finally {
                    //清除当前任务,下次则执行getTask获取最新任务
                    task = null;
                    //记录当前线程完成任务个数
                    w.completedTasks++;
                    w.unlock();
                }
            }
            //标记正常完成
            completedAbruptly = false;
        } finally {
            //后置处理
            processWorkerExit(w, completedAbruptly);
        }
    }

    private Runnable getTask() {
        //标志是否获取任务超时
        boolean timedOut = false; // Did the last poll() time out?

        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);

            // Check if queue empty only if necessary.
            //如果线程池状态>=SHUTDOWN,且workQueue为空
            // >=STOP,shutdownNow()会导致变成 STOP（此时不用考虑 workQueue的情况）
            if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
                //CAS 当前线程数-1
                decrementWorkerCount();
                //当前线程会退出执行
                return null;
            }

            int wc = workerCountOf(c);

            // Are workers subject to culling?
            //判断核心线程是否允许进行超时,默认不允许
            //当前线程数是否>核心线程数,对于超过核心线程的线程进行超时控制
            boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;

            //超过最大线程数,只有2种设置最大线程数,构造+setMaximumPoolSize.
            // 当构造设置大小后,按照正常的顺序,不会超过线程数,也就是说,这里可能执行了setMaximumPoolSize,在CPU时钟周期时,获取的时之前的旧值
            // 或超时
            if ((wc > maximumPoolSize || (timed && timedOut))
                    //当前线程个数>1,且工作队列为空
                && (wc > 1 || workQueue.isEmpty())) {
                //当前线程数-1,成功返回null,结束当前线程执行任务
                if (compareAndDecrementWorkerCount(c))
                    return null;
                continue;
            }

            try {
                //如果设置了超时,则阻塞获取,否则直接获取
                Runnable r = timed ?
                    workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
                    workQueue.take();
                if (r != null)
                    return r;
                //r为null,说明超时,下次自旋回收
                timedOut = true;
            } catch (InterruptedException retry) {
                //出现中断,设置超时为false,并循环重试
                timedOut = false;
            }
        }
    }

 private void processWorkerExit(Worker w, boolean completedAbruptly) {
        //没正常执行成功,正常执行成功,则不需要因为getTask执行了-1操作
        if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted
            //CAS 当前线程数量-1
            decrementWorkerCount();

        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            //统计所有线程执行成功次数
            completedTaskCount += w.completedTasks;
            //删除当前工作线程
            workers.remove(w);
        } finally {
            mainLock.unlock();
        }

        //终止线程池
        tryTerminate();

        int c = ctl.get();
        //如果是否
        if (runStateLessThan(c, STOP)) {
            //是否正常执行成功
            if (!completedAbruptly) {
                //是否允许核心线程超时
                int min = allowCoreThreadTimeOut ? 0 : corePoolSize;
                //允许核心线程超时,且队列不为空，设置最少存活一个线程处理任务
                if (min == 0 && ! workQueue.isEmpty())
                    min = 1;
                //当前线程个数>1,则直接返回
                if (workerCountOf(c) >= min)
                    return; // replacement not needed
            }
            //试着创建线程最大线程数新开一个新线程
            addWorker(null, false);
        }
    }

shutdown

  public void shutdown() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            checkShutdownAccess();
            //设置线程池状态
            advanceRunState(SHUTDOWN);
            //中断所有线程
            interruptIdleWorkers();
            //钩子方法,子类实现
            onShutdown(); // hook for ScheduledThreadPoolExecutor
        } finally {
            mainLock.unlock();
        }
        //终止线程池
        tryTerminate();
    }
    private void advanceRunState(int targetState) {
        for (;;) {
            int c = ctl.get();
            //c是否>=targetState状态
            if (runStateAtLeast(c, targetState) ||
                    //设置成目标状态
                ctl.compareAndSet(c, ctlOf(targetState, workerCountOf(c))))
                break;
        }
    }

    private void interruptIdleWorkers() {
        //中断所有线程
        //onlyOne
        //true表示只中断一个
        //false:中断所有
        interruptIdleWorkers(false);
    }

shutdownNow

 public List<Runnable> shutdownNow() {
        List<Runnable> tasks;
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            checkShutdownAccess();
            //设置状态为stop
            advanceRunState(STOP);
            //中断所有线程
            interruptWorkers();
            //获取所有尚未执行任务
            tasks = drainQueue();
        } finally {
            mainLock.unlock();
        }
        tryTerminate();
        return tasks;
    }


    private void interruptWorkers() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            for (Worker w : workers)
                w.interruptIfStarted();
        } finally {
            mainLock.unlock();
        }
    }

 void interruptIfStarted() {
            Thread t;
            //允许中断且当前线程不为null,且测试是否已经中断
            if (getState() >= 0 && (t = thread) != null && !t.isInterrupted()) {
                try {
                    //中断
                    t.interrupt();
                } catch (SecurityException ignore) {
                }
            }
        }

    private List<Runnable> drainQueue() {
        BlockingQueue<Runnable> q = workQueue;
        ArrayList<Runnable> taskList = new ArrayList<Runnable>();
        //移除此队列中所有可用的元素，并将它们添加到给定 collection 中。
        q.drainTo(taskList);
        if (!q.isEmpty()) {
            for (Runnable r : q.toArray(new Runnable[0])) {
                if (q.remove(r))
                    //添加
                    taskList.add(r);
            }
        }
        return taskList;
    }

总结

使用Worker#lock和unlock分别控制是否能够中断.


执行shutdown的时候,会中断所有空闲线程,繁忙的线程则不处理
shutdownNow中断所有可以标记了unlock的线程,且返回尚未执行的所有任务
每个线程和任务绑定使用,当任务执行完成后,线程复用.

ScheduledThreadPoolExecutor

//todo

Thread

构造

  private void init(ThreadGroup g, Runnable target, String name,
                      long stackSize, AccessControlContext acc,
                      boolean inheritThreadLocals) {
        if (name == null) {
            throw new NullPointerException("name cannot be null");
        }

        //线程名,默认"Thread-" + nextThreadNum()
        this.name = name;

        //获取当前线程
        Thread parent = currentThread();
        SecurityManager security = System.getSecurityManager();
        //线程组为空
        if (g == null) {
            /* Determine if it's an applet or not */

            /* If there is a security manager, ask the security manager
               what to do. */
            if (security != null) {
                g = security.getThreadGroup();
            }

            /* If the security doesn't have a strong opinion of the matter
               use the parent thread group. */
            if (g == null) {
                //默认继承父线程线程组
                g = parent.getThreadGroup();
            }
        }

        /* checkAccess regardless of whether or not threadgroup is
           explicitly passed in. */
        g.checkAccess();

        /*
         * Do we have the required permissions?
         */
        if (security != null) {
            if (isCCLOverridden(getClass())) {
                security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
            }
        }

        g.addUnstarted();

        this.group = g;
        //设置是否为守护线程,继承调用线程的主线程,main默认是false
        this.daemon = parent.isDaemon();
        //默认5
        this.priority = parent.getPriority();
        if (security == null || isCCLOverridden(parent.getClass()))
            this.contextClassLoader = parent.getContextClassLoader();
        else
            this.contextClassLoader = parent.contextClassLoader;
        this.inheritedAccessControlContext =
                acc != null ? acc : AccessController.getContext();
        this.target = target;
        setPriority(priority);
        if (inheritThreadLocals && parent.inheritableThreadLocals != null)
            //创建线程共享变量副本
            this.inheritableThreadLocals =
                ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
        /* Stash the specified stack size in case the VM cares */
        //设置栈大小，如果未指定大小，将在jvm 初始化参数中声明：Xss参数进行指定*/
        this.stackSize = stackSize;

        /* Set thread ID */
        //设置线程id
        tid = nextThreadID();
    }

start

  public synchronized void start() {
        /**
         * This method is not invoked for the main method thread or "system"
         * group threads created/set up by the VM. Any new functionality added
         * to this method in the future may have to also be added to the VM.
         *
         * A zero status value corresponds to state "NEW".
         */
        //当前线程状态
        if (threadStatus != 0)
            throw new IllegalThreadStateException();

        /* Notify the group that this thread is about to be started
         * so that it can be added to the group's list of threads
         * and the group's unstarted count can be decremented. */
        //当前线程加入线程组
        group.add(this);

        boolean started = false;
        try {
            //启动
            start0();
            //标记正常结束
            started = true;
        } finally {
            try {
                if (!started) {
                   //线程启动失败，从线程组里面移除该线程
                    group.threadStartFailed(this);
                }
            } catch (Throwable ignore) {
                /* do nothing. If start0 threw a Throwable then
                  it will be passed up the call stack */
            }
        }
    }

interrupt

    public void interrupt() {
        //如果不是当前线程
        if (this != Thread.currentThread())
            //判断当前线程是否允许修改其他线程
            checkAccess();

        //中断
        synchronized (blockerLock) {
            Interruptible b = blocker;
            if (b != null) {
                //设置中断标识位
                interrupt0();           // Just to set the interrupt flag
                b.interrupt(this);
                return;
            }
        }
        interrupt0();
    }

join

 public final synchronized void join(long millis)
    throws InterruptedException {
        long base = System.currentTimeMillis();
        long now = 0;

        if (millis < 0) {
            throw new IllegalArgumentException("timeout value is negative");
        }

        //等待该线程终止的时间最长为 millis 毫秒。
        if (millis == 0) {
            //测试线程是否处于活动状态。如果线程已经启动且尚未终止，则为活动状态。
            while (isAlive()) {
                wait(0);
            }
        } else {
            //指定了超时时间
            while (isAlive()) {
                long delay = millis - now;
                //超时,结束
                if (delay <= 0) {
                    break;
                }
                //等待阻塞
                wait(delay);
                now = System.currentTimeMillis() - base;
            }
        }
    }

State

/* NEW：初始状态，线程被构建，还未调用start()方法；
    RUNNABLE：运行状态，在java多线程模型中，就绪和运行都是运行状态；
    BLOCKED：阻塞状态；
    WAITING：等待状态，比如中断，需要其他的线程来唤醒；
    TIME_WAITING：超时等待，可以在指定的时间内自行返回；
    TERMINATED：终止状态，线程执行完毕。*/
    public enum State {}

run

    public void run() {
        if (target != null) {
            target.run();
        }
    }

总结

thread很多方法算是底层调用的了,
设置优先级调用,取决于操作系统

ThreadFactory

基本上都是当做内部类使用,随便看一个实现即可
java.util.concurrent.Executors.DefaultThreadFactory

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();
            //默认继承父类线程组
            group = (s != null) ? s.getThreadGroup() :
                                  Thread.currentThread().getThreadGroup();

            //pool-自增1开始-thread-
            namePrefix = "pool-" +
                          poolNumber.getAndIncrement() +
                         "-thread-";
        }

        public Thread newThread(Runnable r) {
            //pool-1-thread-1
            Thread t = new Thread(group, r,
                                  namePrefix + threadNumber.getAndIncrement(),
                                  0);
            //是否是守护线程
            if (t.isDaemon())
                //如果是守护线程,则设置成普通线程
                t.setDaemon(false);
            //
            //设置优先级,默认5
            if (t.getPriority() != Thread.NORM_PRIORITY)
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
    }

Executors

 public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
        //线程最大设置Integer.MAX,基本大小=0,超时设置1分钟
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>(),
                                      threadFactory);
    }

    public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
  //创建一个可重用固定线程数的线程池，以共享的无界队列方式来运行这些线程
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>(),
                                      threadFactory);
    }

    public static ScheduledExecutorService newScheduledThreadPool(
            int corePoolSize, ThreadFactory threadFactory) {
        //创建一个线程池，它可安排在给定延迟后运行命令或者定期地执行。
        return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
    }

   public static ExecutorService newSingleThreadExecutor() {
        //创建一个使用单个 worker 线程的 Executor，以无界队列方式来运行该线程。
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }

ExecutorCompletionService

阻塞获取结果

构造

    public ExecutorCompletionService(Executor executor) {
        if (executor == null)
            throw new NullPointerException();
        this.executor = executor;
        this.aes = (executor instanceof AbstractExecutorService) ?
            (AbstractExecutorService) executor : null;
        //使用LinkedBlockingQueue保存结果
        this.completionQueue = new LinkedBlockingQueue<Future<V>>();
    }


    public ExecutorCompletionService(Executor executor,
                                     BlockingQueue<Future<V>> completionQueue) {
        if (executor == null || completionQueue == null)
            throw new NullPointerException();
        this.executor = executor;
        this.aes = (executor instanceof AbstractExecutorService) ?
            (AbstractExecutorService) executor : null;
        //自定义阻塞队列
        this.completionQueue = completionQueue;
    }

submit

    public Future<V> submit(Callable<V> task) {
        if (task == null) throw new NullPointerException();
        //封装成FutureTask
        RunnableFuture<V> f = newTaskFor(task);
        //封装成阻塞结果的FutureTask,执行
        executor.execute(new QueueingFuture(f));
        return f;
    }

   private class QueueingFuture extends FutureTask<Void> {
        QueueingFuture(RunnableFuture<V> task) {
            super(task, null);
            this.task = task;
        }
        protected void done() {
            //实现父类,完成后添加到阻塞队列
            completionQueue.add(task); }
        private final Future<V> task;
    }

take

    public Future<V> take() throws InterruptedException {
        //阻塞获取结果
        return completionQueue.take();
    }

poll

    public Future<V> poll() {
        //直接获取结果,没有返回null
        return completionQueue.poll();
    }

总结

底层封装阻塞队列,且封装了FutureTask,当执行结束,把Future存储到阻塞队列中.