The following code can reproduce the problem, writing out of bounds causes JVM Crash

   StringBuilder buf = new StringBuilder();
    buf.append('中');

    final CountDownLatch latch = new CountDownLatch(10);
    Runnable r = () -> {
        for (int i = 0; i < 10000; i++) {
            buf.setLength(0);
            buf.trimToSize();
            buf.append(123456789);
        }
        latch.countDown();
    };
    Thread[] threads = new Thread[10];
    for (int i = 0; i < threads.length; i++) {
        threads[i] = new Thread(r);
    }
    for (Thread t : threads) {
        t.start();
    }
    latch.await();
}