java8使用记录

记录以下Java8 使用IntStream和 synchronized， executor的问题

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代码

public class LockDemo {
    volatile int count = 0;

    synchronized void increment() {
        count = count + 1;
    }

    void incrementSync() {
        synchronized (this) {
            count = count + 1;
        }
    }

    private void testIncrement() throws Exception {
        ExecutorService executor = Executors.newFixedThreadPool(2);

        IntStream.range(0, 10000)
                .forEach(i -> {
                    executor.submit(this::incrementSync);
                });
//        executor.awaitTermination(2L, TimeUnit.SECONDS);
        executor.shutdown();
        System.out.println(count);  // 4238
    }

    public static void main(String[] args) throws Exception {
        LockDemo lockDemo = new LockDemo();
        lockDemo.testIncrement();
    }
}

输出的结果是 4461

解答

是因为线程池任务执行中，主线程里shutdown了，所以没执行完。就打印到一部分

executor.shutdown() 不会阻塞 ，等待所有的完成
可以通过executor.isTerminated()来判断

解答一： 成功 √
executor.awaitTermination(2L, TimeUnit.SECONDS);

/**
     * Blocks until all tasks have completed execution after a shutdown
     * request, or the timeout occurs, or the current thread is
     * interrupted, whichever happens first.
     *
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @return {@code true} if this executor terminated and
     *         {@code false} if the timeout elapsed before termination
     * @throws InterruptedException if interrupted while waiting
     */
    boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException;

解答二： 失败， ×
使用原子类 AtomcInteger,

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