读ScheduledThreadPoolExecutor源码
//一个可以延迟执行的定时任务 //先看构造函数 构造函数最重要的区别是传入了DelayedWorkQueue一个延迟的queue /** 总结:该线程池继承了ThreadPoolExecutor。同时内部封装了一个DelayedWorkQueue和 ScheduledFutureTask。DelayedWorkQueue用于管理任务的新增和获取。ScheduledFutureTask 用于管理任务的执行。 */ public ScheduledThreadPoolExecutor(int corePoolSize) { super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, new DelayedWorkQueue()); } public ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory) { super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, new DelayedWorkQueue(), threadFactory); } public ScheduledThreadPoolExecutor(int corePoolSize, RejectedExecutionHandler handler) { super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, new DelayedWorkQueue(), handler); } public ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory, RejectedExecutionHandler handler) { super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS, new DelayedWorkQueue(), threadFactory, handler); } //创建并执行任务 public void execute(Runnable command) { schedule(command, 0, TimeUnit.NANOSECONDS); } //延迟执行Runnable任务 public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) { if (command == null || unit == null) throw new NullPointerException(); //装饰Task,相当于将任务转化为RunnableScheduledFuture RunnableScheduledFuture<?> t = decorateTask(command, new ScheduledFutureTask<Void>(command, null, triggerTime(delay, unit))); delayedExecute(t); return t; } private void delayedExecute(RunnableScheduledFuture<?> task) { //线程关闭不再处理任务 if (isShutdown()) reject(task); else { //将任务加入到队列中 super.getQueue().add(task); if (isShutdown() && !canRunInCurrentRunState(task.isPeriodic()) && remove(task)) task.cancel(false); else ensurePrestart(); } } //创建线程 void ensurePrestart() { int wc = workerCountOf(ctl.get()); if (wc < corePoolSize) //以corePoolSize来决定是否创建线程 addWorker(null, true); else if (wc == 0) //以maximumPoolSize来决定是否创建线程 addWorker(null, false); } //看线程执行方法 public void run() { boolean periodic = isPeriodic(); if (!canRunInCurrentRunState(periodic)) cancel(false); //不需要延迟直接执行 else if (!periodic) ScheduledFutureTask.super.run(); //先执行 else if (ScheduledFutureTask.super.runAndReset()) { //设置下一次需要执行的时间 setNextRunTime(); reExecutePeriodic(outerTask); } } void reExecutePeriodic(RunnableScheduledFuture<?> task) { if (canRunInCurrentRunState(true)) { super.getQueue().add(task); if (!canRunInCurrentRunState(true) && remove(task)) task.cancel(false); else ensurePrestart(); } } //延迟执行Callable任务 public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) { if (callable == null || unit == null) throw new NullPointerException(); RunnableScheduledFuture<V> t = decorateTask(callable, new ScheduledFutureTask<V>(callable, triggerTime(delay, unit))); delayedExecute(t); return t; } //立即执行任务 public Future<?> submit(Runnable task) { return schedule(task, 0, TimeUnit.NANOSECONDS); } //立即执行任务 public <T> Future<T> submit(Runnable task, T result) { return schedule(Executors.callable(task, result), 0, TimeUnit.NANOSECONDS); } //立即执行任务 public <T> Future<T> submit(Callable<T> task) { return schedule(task, 0, TimeUnit.NANOSECONDS); } //每隔initialDelay+period后执行。下一次则是initialDelay+period*2以此类推 public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) { if (command == null || unit == null) throw new NullPointerException(); if (period <= 0) throw new IllegalArgumentException(); ScheduledFutureTask<Void> sft = new ScheduledFutureTask<Void>(command, null, triggerTime(initialDelay, unit), unit.toNanos(period)); RunnableScheduledFuture<Void> t = decorateTask(command, sft); sft.outerTask = t; delayedExecute(t); return t; } //相当于时间递减 public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) { if (command == null || unit == null) throw new NullPointerException(); if (delay <= 0) throw new IllegalArgumentException(); ScheduledFutureTask<Void> sft = new ScheduledFutureTask<Void>(command, null, triggerTime(initialDelay, unit), unit.toNanos(-delay)); RunnableScheduledFuture<Void> t = decorateTask(command, sft); sft.outerTask = t; delayedExecute(t); return t; }
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