- 正确答案：自定义线程池应包含核心参数（corePoolSize、maxPoolSize、keepAliveTime、workQueue、threadFactory、handler）、状态控制（RUNNING/SHUTDOWN/STOP/TIDYING/TERMINATED）、任务提交与执行机制、线程创建与复用逻辑、空闲线程回收策略、拒绝策略可插拔设计，以及线程安全的状态变更和任务队列操作。典型实现需基于AQS或显式锁（如ReentrantLock）保障并发安全性，并通过Worker内部类封装线程生命周期。 - 解答思路：首先明确线程池的本质——资源复用+任务调度+流量控制。设计分五层展开：1）定义可控的运行参数；2）建立线程生命周期管理模型（Worker继承AbstractQueuedSynchronizer实现中断隔离与状态同步）；3）实现任务提交流程（execute()方法遵循“先试加核心线程→再入队→最后扩容至max→最终触发拒绝”四步策略）；4）构建阻塞队列与线程空闲超时回收机制（利用ScheduledThreadPoolExecutor中DelayQueue或Worker自身wait/notify配合keepAliveTime实现）；5）提供扩展点（ThreadFactory定制线程命名与属性，RejectedExecutionHandler实现不同拒绝语义）。整个过程需严格保证可见性（volatile修饰状态）、原子性（CAS更新ctl字段）、互斥性（锁保护workers集合和workQueue）。 - 深度知识讲解： 1）状态字段ctl的位运算设计：JDK中ThreadPoolExecutor用一个int型ctl同时存储运行状态（高3位）和工作线程数（低29位），通过COUNT_BITS = 29、RUNNING = -1< workQueue; private final ReentrantLock mainLock = new ReentrantLock(); private final HashSet workers = new HashSet<>(); private volatile ThreadFactory threadFactory; private volatile RejectedExecutionHandler handler; public void execute(Runnable task) { if (task == null) throw new NullPointerException(); int c = ctl.get(); // 1. 若当前线程数 < corePoolSize，直接添加新线程 if (workerCountOf(c) < corePoolSize) { if (addWorker(task, true)) return; c = ctl.get(); } // 2. 否则尝试入队 if (isRunning(c) && workQueue.offer(task)) { int recheck = ctl.get(); if (!isRunning(recheck) && remove(task)) reject(task); else if (workerCountOf(recheck) == 0) addWorker(null, false); } // 3. 入队失败且线程数未达max，扩容 else if (!addWorker(task, false)) reject(task); // 4. 最终拒绝 } private boolean addWorker(Runnable firstTask, boolean core) { retry: for (;;) { int c = ctl.get(); int rs = runStateOf(c); if (rs >= SHUTDOWN && ! (rs == SHUTDOWN && firstTask == null && ! workQueue.isEmpty())) return false; for (;;) { int wc = workerCountOf(c); if (wc >= (core ? corePoolSize : maxPoolSize)) return false; if (compareAndIncrementWorkerCount(c)) break retry; c = ctl.get(); if (runStateOf(c) != rs) continue retry; } } Worker w = new Worker(firstTask); Thread t = threadFactory.newThread(w); if (t != null) { final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { int c = ctl.get(); if (isRunning(c)) { workers.add(w); t.start(); // 真正启动线程 } } finally { mainLock.unlock(); } return true; } return false; } private final class Worker extends AbstractQueuedSynchronizer implements Runnable { final Thread thread; Runnable firstTask; long completedTasks; Worker(Runnable firstTask) { setState(-1); // 防止在runWorker前被中断 this.firstTask = firstTask; this.thread = getThreadFactory().newThread(this); } public void run() { runWorker(this); } final void runWorker(Worker w) { Thread wt = Thread.currentThread(); Runnable task = w.firstTask; w.firstTask = null; w.setState(0); // 允许中断 boolean completedAbruptly = true; try { while (task != null || (task = getTask()) != null) { w.lock(); if ((runStateAtLeast(ctl.get(), STOP) || (Thread.interrupted() && runStateAtLeast(ctl.get(), STOP))) && !wt.isInterrupted()) wt.interrupt(); try { beforeExecute(wt, task); task.run(); afterExecute(task, null); } finally { task = null; w.completedTasks++; w.unlock(); } } completedAbruptly = false; } finally { processWorkerExit(w, completedAbruptly); } } private Runnable getTask() { boolean timedOut = false; for (;;) { int c = ctl.get(); int rs = runStateOf(c); if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) { decrementWorkerCount(); return null; } int wc = workerCountOf(c); boolean timed = wc > corePoolSize || allowCoreThreadTimeOut; if ((wc > maximumPoolSize || (timed && timedOut)) && (wc > 1 || workQueue.isEmpty())) { if (compareAndDecrementWorkerCount(c)) return null; continue; } try { Runnable r = timed ? workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) : workQueue.take(); if (r != null) return r; timedOut = true; } catch (InterruptedException retry) { timedOut = false; } } } } } ```

快手ai后台开发日常实习一面

全站热榜

创作者周榜