ReentrantReadWriteLockExample.java

static class ReentrantReadWriteLockExample {
    private int loopNum = 30000;
    private int slotNum = 10;
    private int writeThreadNum = 5;
    private int readThreadNum = 5;

    public void examinReentrantReadWriteLock() throws InterruptedException {

        final HashMap<Integer, Pair<Integer, Integer>> tbl = new HashMap<>();
        for (int slot = 0; slot < slotNum; slot++) {
            tbl.put(slot, new Pair<Integer, Integer>(0, 0));
        }

        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
        ExecutorService executorService = Executors.newFixedThreadPool(writeThreadNum + readThreadNum);
        final CountDownLatch countDownLatch = new CountDownLatch(writeThreadNum + readThreadNum);
        Runnable writeTask = new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < loopNum; i++) {
                    for (int slot = 0; slot < slotNum; slot++) {
                        ReentrantReadWriteLock.WriteLock writeLock = lock.writeLock();
                        writeLock.lock();
                        Pair<Integer, Integer> pair = tbl.get(slot);
                        pair.first++;
                        pair.second++;
                        tbl.put(slot, pair);
                        writeLock.unlock();
                    }
                }
                System.out.println("writeTask: finished");
                countDownLatch.countDown();
            }
        };
        Runnable readTask = new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < loopNum; i++) {
                    for (int slot = 0; slot < slotNum; slot++) {
                        ReentrantReadWriteLock.ReadLock readLock = lock.readLock();
                        readLock.lock();
                        Pair<Integer, Integer> pair = tbl.get(slot);
                        int first = pair.first;
                        int second = pair.second;
                        if (first != second) {
                            System.out.println("values didn't match: slot=" + slot + ", first=" + first + ", second=" + second);
                        }
                        readLock.unlock();
                    }
                }
                System.out.println("readTask: finished");
                countDownLatch.countDown();
            }
        };

        for (int i = 0; i < writeThreadNum; i++) {
            executorService.execute(writeTask);
        }

        for (int i = 0; i < readThreadNum; i++) {
            executorService.execute(readTask);
        }

        long start = System.currentTimeMillis();
        countDownLatch.await(30, TimeUnit.SECONDS);
        System.out.println("elapsed time: " + (System.currentTimeMillis() - start));

        for (int slot = 0; slot < slotNum; slot++) {
            Pair<Integer, Integer> pair = tbl.get(slot);
            System.out.println("slot=" + slot + ", expected=" + loopNum * writeThreadNum + ", first=" + pair.first + ", second=" + pair.second);
        }
    }

    public void setLoopNum(int loopNum) {
        this.loopNum = loopNum;
    }

    public void setSlotNum(int slotNum) {
        this.slotNum = slotNum;
    }

    public void setWriteThreadNum(int writeThreadNum) {
        this.writeThreadNum = writeThreadNum;
    }

    public void setReadThreadNum(int readThreadNum) {
        this.readThreadNum = readThreadNum;
    }
}