import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class TaskExecutor {
    private List<Integer> list = new ArrayList<>();
    private AtomicInteger count = new AtomicInteger();
    private ReentrantLock lock = new ReentrantLock();
    /**
     * 积压消息容量
     */
    private int capacity;
    private Condition c1 = lock.newCondition();
    private Condition c2 = lock.newCondition();

    /**
     * 可读索引
     */
    private int read;

    public TaskExecutor(int capacity) {
        this.capacity = capacity;
    }

    public Integer product() {
        Integer value = null;
        lock.lock();
        try {
            while (list.size() >= capacity) {
                c1.await();
            }
            value = count.incrementAndGet();
            list.add(value);
            read++;
            c2.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

        return value;
    }

    public Integer consume() {
        Integer value = null;
        lock.lock();
        try {
            while (list.size() <= 0) {
                c2.await();
            }
            read--;
            value = list.remove(read);

            c1.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

        return value;
    }

    private Integer getSize() {
        lock.lock();
        try {
            return list.size();
        } finally {
            lock.unlock();
        }
    }

    public static void main(String[] args) {
        TaskExecutor taskExecutor = new TaskExecutor(20);
        new Thread(()-> {
            for (;;) {
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + " 生产: " + taskExecutor.product() + " 积压: " + taskExecutor.getSize());
            }
        }, "producer").start();
        new Thread(()-> {
            for (;;) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + " 消费: " + taskExecutor.consume() + " 积压: " + taskExecutor.getSize());
            }
        }, "consumer").start();

    }
}