这段java并发代码为啥经常不能正常运行？

Question

//本来我是想比较一下Synchronized和Lock的性能的
public class SynchronizedVSLock {
    static final Lock lock = new ReentrantLock();
    static final int loopTime = 10;
    static final int numOfThread = 6;
    static final Random random = new Random();
    static final Semaphore runningThreadsNum = new Semaphore(numOfThread);
    //这个代码会产生不同的运行结果，但是我不知道原因
    public static void main(String[] args) throws InterruptedException {
        long startTime = System.currentTimeMillis();
        for (int i = 0; i < numOfThread - 1; i++) {
            new Thread(new Test1()).start();
        }
        new Thread(new Test1()).join();
        runningThreadsNum.acquire(numOfThread);
        long endTime = System.currentTimeMillis();
        System.out.println(endTime - startTime);
    }

    static class Test1 implements Runnable {
        @Override
        public void run() {
            try {
                runningThreadsNum.acquire();
            } catch (InterruptedException e) {
                throw new RuntimeException();
            }
            for (int i = 0; i < SynchronizedVSLock.loopTime; i++) {
                SynchronizedVSLock.lock.lock();
                System.out.println(SynchronizedVSLock.random.nextDouble());
                SynchronizedVSLock.lock.unlock();
            }
            runningThreadsNum.release();
        }
    }

    static class Test2 implements Runnable {
        @Override
        public void run() {
            try {
                runningThreadsNum.acquire();
            } catch (InterruptedException e) {
                throw new RuntimeException();
            }
            for (int i = 0; i < SynchronizedVSLock.loopTime; i++) {
                synchronized (SynchronizedVSLock.lock) {
                    System.out.println(SynchronizedVSLock.random.nextDouble());
                }
            }
            runningThreadsNum.release();
        }
    }
}

Answer 1

我看你代码你是想主线程通过调用其它线程的join()方法等其它线程执行完后再执行主线程，那你可以这样写：

        for (int i = 0; i < numOfThread; i++) {
            Thread thread = new Thread(new Test1());
            thread.start();
            thread.join();
        }