One 、 What is blocking queue

         From the name, we can see that blocking queue is a kind of queue , It's a kind of FIFO（ fifo ） Data structure of , Unlike ordinary queues , It supports blocking addition and blocking deletion

Block to add ： When the queue is full , Adding elements to the queue blocks the wait

Blocking the delete ： When the queue is empty , Deleting or getting elements into the queue will be blocked

Two 、 Four groups of blocking queues API

The way	Throw an exception	Does not throw an exception , There is a return value	Block waiting	Overtime waiting
add to	add()	offer()	put()	offer(e,timeout,TimeUnit)
remove	remove()	poll()	take()	poll(timeout,TimeUnit)
Get team leader elements	element()	peek()	-	-

1. Throw an exception

public static void test1(){
        // The size of the queue is filled in brackets , Look at the source code 
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
        for (int i = 0; i < 3; i++) {
            System.out.println(blockingQueue.add(String.valueOf(i)));
        }
        // Get team leader elements 
        System.out.println(blockingQueue.element());
        // The queue is full , Adding another element to the queue will throw an exception   :  Queue full -->   The queue is full 
        //blockingQueue.add("hhh");
        System.out.println("===================");
        // Pop up the elements in the queue 
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
        // The queue is empty , Taking elements from the queue will throw an exception  NoSuchElementException -->  There is no element 
        //blockingQueue.remove();
    }

 

 2. Don't throw exceptions , There is a return value

public static void test2(){
        // Similarly, fill in the size of the queue in parentheses 
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue(3);
        for (int i = 0; i < 3; i++) {
            System.out.println(blockingQueue.offer(String.valueOf(i)));
        }
        // Get team leader elements 
        System.out.println(blockingQueue.peek());
        // At this point the queue is full , Adding another element to the queue will return false
        System.out.println(blockingQueue.offer("hhh"));
        System.out.println("===========");
        // Pop up the elements in the queue 
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        // The queue is empty , Pop up the element again, and no exception will be thrown , return null
        System.out.println(blockingQueue.poll());
    }

 

3. Block waiting

public static void test3() throws InterruptedException {
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue(3);
        for (int i = 0; i < 3; i++) {
            blockingQueue.put(String.valueOf(i));
        }
        // The queue has no place , It will keep blocking 
        //blockingQueue.put("hhhh");
        System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.take());
        System.out.println(blockingQueue.take());
        // The queue is empty , It will keep blocking 
        //System.out.println(blockingQueue.take());
    }

 

 4. Overtime waiting

public static void test4() throws InterruptedException {
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue(3);
        for (int i = 0; i < 3; i++) {
            System.out.println(blockingQueue.offer(String.valueOf(i)));
        }
        // The queue is full , Set the wait time , If the waiting time is up, the element has no position to insert , Will timeout and exit 
        //blockingQueue.offer("hhh",2, TimeUnit.SECONDS);
        System.out.println("============");
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        System.out.println(blockingQueue.poll());
        // The queue is empty , Set the wait time , If the waiting time is up, there are no elements in the queue , Will time out and return null
        System.out.println(blockingQueue.poll(2,TimeUnit.SECONDS));
    }

 

  3、 ... and 、 Synchronous queue SynchronousQueue

And others BlockingQueue Different

Synchronization queues do not store elements

In line put An element Must wait for this element take Only after leaving the queue put The next element

public class SynchronousQueueTest {
    public static void main(String[] args) {
        SynchronousQueue<String> synchronousQueue = new SynchronousQueue<>();
        new Thread(()->{
            try {
                System.out.println(Thread.currentThread().getName()+" put  1");
                synchronousQueue.put("1");
                System.out.println(Thread.currentThread().getName()+" put  2");
                synchronousQueue.put("2");
                System.out.println(Thread.currentThread().getName()+" put  3");
                synchronousQueue.put("3");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"T1").start();

        new Thread(()->{
            try {
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+" get "+synchronousQueue.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+" get "+synchronousQueue.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+" get "+synchronousQueue.take());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        },"T2").start();
    }
}