java.lang.IllegalMonitorStateException 从线程中运行的方法抛出

Question

I am trying to create basic producer/consuner class using:

public class ProducerConsumer {
    private final static int MAX_SIZE = 100;
    private Queue<String> data = new PriorityQueue<>();
    private Lock lock = new ReentrantLock();
    private Condition bufferFull = lock.newCondition();
    private Condition bufferEmpty = lock.newCondition();

    public void produce(){
        while(true) {
            try {
                lock.lock();
                while (data.size() >= MAX_SIZE) {
                    bufferFull.await();
                }
                addData();
                bufferEmpty.notifyAll();
            } catch (InterruptedException e) {
                System.out.println("error produce");
            } finally {
                lock.unlock();
            }
        }
    }
    public void consume(){
        while(true) {
            try {
                lock.lock();
                while (data.isEmpty()) {
                    bufferEmpty.await();
                }
                String value = data.poll();
                System.out.println("Thread " + Thread.currentThread().getName() + " processing value " + value);
                bufferFull.notifyAll();
            } catch (InterruptedException e) {
                System.out.println("error consume");
            } finally {
                lock.unlock();
            }
        }
    }

    private void addData(){
        IntStream.range(0,10).forEach( i ->
                data.add(new Date().toString())
        );
    }

    public void start(int consumerNumber){
        IntStream.range(0,consumerNumber)
                .mapToObj(i -> new Thread(this::consume))
                .collect(Collectors.toList())
                .forEach(Thread::start);

        Thread t = new Thread(this::produce);
        t.start();
    }

} 

However it keeps throwing error: java.lang.IllegalMonitorStateException. My question is, why does it throw this error? method of this intance are running in threads, so they should own condition lock thus i dont understand meaning behind this error.

Thanks for help!

Answer 1

bufferEmpty.notifyAll() is the wrong method to call. That method requires you hold the monitor on the "bufferEmpty" object itself, which is unrelated to the lock instance you're using.

The right method to call is

bufferEmpty.signalAll();