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  • 【图灵学院10】高并发之java线程池源码分析

    1. 提纲

    1)线程池的模块结构

    2)示例&原理解析

    2. 问题

    1)线程池包含哪些东西

    2)线程池的运作原理

    3)调度线程池的运作原理

    4)线程池怎么实现FixRate,FixDelay,他们之间的区别

    5)任务怎么取消

    3. 源码解析

    3.1 线程池框架

    接口简介:

    java.util.concurrent.Executor:执行器,执行方法

    java.util.concurrent.ExecutorService:(执行服务)包含服务的生命周期

    java.util.concurrent.ScheduledExecutorService:(调度相关的服务)

    辅助类:

    java.util.concurrent.Executors:

    核心实现类:

    java.util.concurrent.ThreadPoolExecutor:(普通的线程池实现类)

    java.util.concurrent.ScheduledThreadPoolExecutor:(调度的核心实现类)

    java.util.concurrent.ForkJoinPool

    完成服务:

    java.util.concurrent.CompletionService:

    java.util.concurrent.ExecutorCompletionService:

    3.2 ThreadPoolExecutor源码剖析

    1)构造器

    核心数量,任务队列容器,存活时间,线程工厂,处理器

    ThreadPoolExecutor.execute()方法源码

        public void execute(Runnable command) {
            if (command == null)
                throw new NullPointerException();
            /*
             * Proceed in 3 steps:
             *
             * 1. If fewer than corePoolSize threads are running, try to
             * start a new thread with the given command as its first
             * task.  The call to addWorker atomically checks runState and
             * workerCount, and so prevents false alarms that would add
             * threads when it shouldn't, by returning false.
             *
             * 2. If a task can be successfully queued, then we still need
             * to double-check whether we should have added a thread
             * (because existing ones died since last checking) or that
             * the pool shut down since entry into this method. So we
             * recheck state and if necessary roll back the enqueuing if
             * stopped, or start a new thread if there are none.
             *
             * 3. If we cannot queue task, then we try to add a new
             * thread.  If it fails, we know we are shut down or saturated
             * and so reject the task.
             */
            int c = ctl.get();
            if (workerCountOf(c) < corePoolSize) {
                if (addWorker(command, true))
                    return;
                c = ctl.get();
            }
            if (isRunning(c) && workQueue.offer(command)) {
                int recheck = ctl.get();
                if (! isRunning(recheck) && remove(command))
                    reject(command);
                else if (workerCountOf(recheck) == 0)
                    addWorker(null, false);
            }
            else if (!addWorker(command, false))
                reject(command);
        }

    ThreadPoolExecutor.runWorker()方法源码

        final void runWorker(Worker w) {
            Thread wt = Thread.currentThread();
            Runnable task = w.firstTask;
            w.firstTask = null;
            w.unlock(); // allow interrupts
            boolean completedAbruptly = true;
            try {
                while (task != null || (task = getTask()) != null) {
                    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
                    if ((runStateAtLeast(ctl.get(), STOP) ||
                         (Thread.interrupted() &&
                          runStateAtLeast(ctl.get(), STOP))) &&
                        !wt.isInterrupted())
                        wt.interrupt();
                    try {
                        beforeExecute(wt, task);
                        Throwable thrown = null;
                        try {
                            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 {
                            afterExecute(task, thrown);
                        }
                    } finally {
                        task = null;
                        w.completedTasks++;
                        w.unlock();
                    }
                }
                completedAbruptly = false;
            } finally {
                processWorkerExit(w, completedAbruptly);
            }
        }

    3.3 ScheduledThreadPoolExecutor

     1)

    2)FixRate和FixDelay的区别

            /**
             * Sets the next time to run for a periodic task.
             */
            private void setNextRunTime() {
                long p = period;
                if (p > 0)
                    time += p;
                else
                    time = triggerTime(-p);
            }

    FixRate严格按照设定的时间

    FixDelay按照上一个线程执行完成的时间间隔

    FixRate: 21:40,21:41,21:42

    FixDelay:21:40,21:43

        void reExecutePeriodic(RunnableScheduledFuture<?> task) {
            if (canRunInCurrentRunState(true)) {
           //此处没有捕获异常,如果单个任务发生异常,会导致后续任务无法继续执行
    super.getQueue().add(task); if (!canRunInCurrentRunState(true) && remove(task)) task.cancel(false); else ensurePrestart(); } }
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  • 原文地址:https://www.cnblogs.com/yeahwell/p/7625564.html
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