多线程实现阻塞队列

今天面试被问到了，多线程实现阻塞队列，记录一下。

import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class FixedSizeBlockingQueue<T> {
    private final int capacity;
    private final Queue<T> queue;
    private final ReentrantLock lock;
    private final Condition notFull;
    private final Condition notEmpty;
    private volatile boolean isClosed = false; // 用于标记队列是否已关闭

    public FixedSizeBlockingQueue(int capacity) {
        this.capacity = capacity;
        this.queue = new LinkedList<>();
        this.lock = new ReentrantLock();
        this.notFull = lock.newCondition();
        this.notEmpty = lock.newCondition();
    }

    public void put(T item) throws InterruptedException {
        lock.lock();
        try {
            while (queue.size() == capacity || isClosed) { // 检查队列是否已满或已关闭
                if (isClosed) {
                    throw new IllegalStateException("Queue is closed");
                }
                notFull.await();
            }
            queue.add(item);
            notEmpty.signal();
        } finally {
            lock.unlock();
        }
    }

    public T take() throws InterruptedException {
        lock.lock();
        try {
            while (queue.isEmpty()) {
                notEmpty.await();
            }
            T item = queue.poll();
            notFull.signal();
            return item;
        } finally {
            lock.unlock();
        }
    }

    // 返回队列中当前元素的数量
    public int size() {
        lock.lock();
        try {
            return queue.size();
        } finally {
            lock.unlock();
        }
    }

    // 关闭队列并返回所有剩余元素  
    public Collection<T> close() throws InterruptedException {  
        lock.lock();  
        try {  
            isClosed = true;  
            // 将队列中的剩余元素转移到remainingElements集合中  
            remainingElements.addAll(queue);  
            queue.clear(); // 清空队列（可选，取决于你是否还需要访问原始队列对象）  
  
            // 唤醒所有等待的put线程（它们将收到IllegalStateException）  
            notFull.signalAll();  
  
            // 返回剩余元素  
            return new ArrayList<>(remainingElements); // 返回一个新的列表副本，以避免外部修改  
        } finally {  
            lock.unlock();  
        }  
    }  
  
    // 一个可选的方法，用于在队列关闭后检查是否有剩余元素  
    public boolean hasRemainingElements() {  
        lock.lock();  
        try {  
            return !remainingElements.isEmpty();  
        } finally {  
            lock.unlock();  
        }  
    }  


}