JDK线程池实践

来源：互联网发布：javascript常用函数编辑：程序博客网时间：2024/06/06 03:11

JDK线程池，网上很多代码和示例，自己就实践一下，看看运行结果，加深理解。

public class Test {    public static int getCoreSize() {        int core = Runtime.getRuntime().availableProcessors();        System.out.println("core : " + core);        return core;    }    /**     * SinglePool。     * 预期结果：顺序执行     * @throws InterruptedException      */    public static void singlePool() throws InterruptedException {        ExecutorService es = Executors.newSingleThreadExecutor();        Runnable r1 =  SimpleRunnable.getInstance(5);        Runnable r2 =  SimpleRunnable.getInstance(4);        Runnable r3 =  SimpleRunnable.getInstance(3);        Runnable r4 =  SimpleRunnable.getInstance(2);        Runnable r5 =  SimpleRunnable.getInstance(1);        es.submit(r1);        es.submit(r2);        es.submit(r3);        es.submit(r4);        es.submit(r5);        Thread.sleep(1000l);        es.shutdown();    }    /**     * 线程不会终止，SinglePool。     * 预期结果：1个线程运行     * @throws InterruptedException      */    public static void endlessSinglePool() throws InterruptedException {        ExecutorService es = Executors.newSingleThreadExecutor();        Runnable r1 =  EndlessRunnable.getInstance();        Runnable r2 =  EndlessRunnable.getInstance();        Runnable r3 =  EndlessRunnable.getInstance();        Runnable r4 =  EndlessRunnable.getInstance();        Runnable r5 =  EndlessRunnable.getInstance();        es.submit(r1);        es.submit(r2);        es.submit(r3);        es.submit(r4);        es.submit(r5);        Thread.sleep(1000l);    }    /**     * 线程不会终止，CachedPool。     * 预期结果：随机执行，所有线程执行     * @throws InterruptedException      */    public static void endlessCachedPool() throws InterruptedException {        ExecutorService es = Executors.newCachedThreadPool();        Runnable r1 =  EndlessRunnable.getInstance();        Runnable r2 =  EndlessRunnable.getInstance();        Runnable r3 =  EndlessRunnable.getInstance();        Runnable r4 =  EndlessRunnable.getInstance();        Runnable r5 =  EndlessRunnable.getInstance();        es.submit(r1);        es.submit(r2);        es.submit(r3);        es.submit(r4);        es.submit(r5);        Thread.sleep(1000l);        // 结果：程序并不会终止，无任何信息执行。意味着shutdown无用。        // 代码分析： interruptIdleWorkers();终止空闲线程。通过thread.interrupt()。        // es.shutdown();        // 结果：程序并不会终止，报sleep被中断异常。shutdownNow会试图终止掉阻塞的线程，但因为while循环，并不会杀死线程。        // 代码分析： interruptWorkers();终止工作线程。通过thread.interrupt()。        //es.shutdownNow();    }    /**     * 线程不会终止，FixedPool。     * 预期结果：3个线程运行     * @throws InterruptedException      */    public static void endlessFixedPool() throws InterruptedException {        ExecutorService es = Executors.newFixedThreadPool(3);        Runnable r1 =  EndlessRunnable.getInstance();        Runnable r2 =  EndlessRunnable.getInstance();        Runnable r3 =  EndlessRunnable.getInstance();        Runnable r4 =  EndlessRunnable.getInstance();        Runnable r5 =  EndlessRunnable.getInstance();        es.submit(r1);        es.submit(r2);        es.submit(r3);        es.submit(r4);        es.submit(r5);        Thread.sleep(1000l);    }    /**     * 前置条件：core:2, max:4, queue:2。EndlessRunanble。     * 预期结果：加入2个任务，2个线程运行。加入4个线程，2个线程运行。     *              加入6个线程，4个线程运行，且运行的是1，2，5，6。加入8个线程，报拒绝异常。     * 关于线程生成策略思考：小于core，每个任务都新建线程：哥有的是线程资源，随便用，不用等；     *                    大于core小于core+queueSize，排队不生成新线程：虽然任务有点多，但还是可以负担得起。不增加新线程，节约开销；     *                    大于core+queueSize小于max，创建新线程处理新任务，旧的排队线程依然排队（不讲先来后到）：扛不住了，找外援；     *                    大于max，根据策略处理新加的任务，默认拒绝：我处理不了了，拒绝新任务。     * @throws InterruptedException      */    public static void threadPool() throws InterruptedException {        ExecutorService es = new ThreadPoolExecutor(2, 4, 1000, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(2));        EndlessRunnableWithState r1 = EndlessRunnableWithState.getInstance(1);        EndlessRunnableWithState r2 = EndlessRunnableWithState.getInstance(2);        EndlessRunnableWithState r3 = EndlessRunnableWithState.getInstance(3);        EndlessRunnableWithState r4 = EndlessRunnableWithState.getInstance(4);        EndlessRunnableWithState r5 = EndlessRunnableWithState.getInstance(5);        EndlessRunnableWithState r6 = EndlessRunnableWithState.getInstance(6);        EndlessRunnableWithState r7 = EndlessRunnableWithState.getInstance(7);        EndlessRunnableWithState r8 = EndlessRunnableWithState.getInstance(8);        es.submit(r1);        es.submit(r2);        Thread.sleep(3000l);        System.out.println("sleep 1 over.");        es.submit(r3);        es.submit(r4);        Thread.sleep(3000l);        System.out.println("sleep 2 over.");        es.submit(r5);        es.submit(r6);        Thread.sleep(3000l);        System.out.println("sleep 3 over.");        es.submit(r7);        es.submit(r8);    }    /**     * 预期结果：4个线程执行同一个任务。     * 结果分析：每次commit，将任务包装为RunnableFuture对象，然后进行后续操作。不会判断任务是否已存在。同一个任务多个线程执行，得注意线程安全。     * @throws InterruptedException     */    public static void taskRunMultiTime() throws InterruptedException {        ExecutorService es = Executors.newFixedThreadPool(4);        EndlessRunnableWithState r1 = EndlessRunnableWithState.getInstance(1);        es.submit(r1);        es.submit(r1);        es.submit(r1);        es.submit(r1);        Thread.sleep(3000l);    }    public static void main(String[] args) throws InterruptedException {                //singlePool();        //endlessSinglePool();        //endlessCachedPool();        //endlessFixedPool();        //  threadPool();        taskRunMultiTime();    }}

public class SimpleRunnable implements Runnable {    private int count;    private SimpleRunnable(int count) {        this.count = count;    }    public static SimpleRunnable getInstance(int count) {        return new SimpleRunnable(count);    }    @Override    public void run() {        System.out.println(Thread.currentThread().getName() + " running ... with count : " + count);    }}

public class EndlessRunnable implements Runnable {    public static EndlessRunnable getInstance() {        return new EndlessRunnable();    }    @Override    public void run() {        System.out.println(Thread.currentThread().getName() + " running ...");        while (true) {            try {                Thread.sleep(10000l);            } catch (InterruptedException e) {                e.printStackTrace();            }        }    }}

public class EndlessRunnableWithState implements Runnable {    private int count;    private EndlessRunnableWithState(int count) {        this.count = count;    }    public static EndlessRunnableWithState getInstance(int count) {        return new EndlessRunnableWithState(count);    }    @Override    public void run() {        System.out.println("thread " + count + " running ...");        while (true) {            try {                Thread.sleep(10000l);            } catch (InterruptedException e) {                e.printStackTrace();            }        }    }}

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