java執行緒池-工作佇列workQueue

執行緒池之工作佇列

ArrayBlockingQueue

採用陣列來實現,並採用可重入鎖ReentrantLock來做併發控制，無論是新增還是讀取，都先要獲得鎖才能進行操作 可看出進行讀寫操作都使用了ReentrantLock，ArrayBlockingQueue需要為其指定容量

    public boolean offer(E e) {
        checkNotNull(e);
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            if (count == items.length)
                return false;
            else {
                enqueue(e);
                return true;
            }
        } finally {
            lock.unlock();
        }
    }
    
    public void put(E e) throws InterruptedException {
        checkNotNull(e);
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            while (count == items.length)
                notFull.await();
            enqueue(e);
        } finally {
            lock.unlock();
        }
    }

SynchronousQueue

由於SynchronousQueue原始碼比較複雜，裡面大量的Cas操作，SynchronousQueue沒有容器，所以裡面是裝不了任務的，當一個生產者執行緒生產一個任務的 時候，如果沒有對應的消費者消費，那麼該生產者會一直阻塞，知道有消費者消費為止。
圖示：
 如下程式碼，如果我們將消費者執行緒註釋掉執行，那麼生產者哪裡將會一直阻塞

package thread.customthreadpool;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;

/**
 * 測試SynchronousQueue
 */
public class SynchronousQueueTest {

    private static final SynchronousQueue<String> synchronousQueue = new SynchronousQueue<>();

    private static final ExecutorService service = Executors.newCachedThreadPool();

    public static void main(String[] args) {
        /**
         * Provider
         */
        service.submit(() -> {
            try {
                synchronousQueue.put("liu");
            }catch (Exception e){
                e.printStackTrace();
            }
            System.out.println("Consumer finished spending");
        });

        /**
         * Consumer
         */
        service.submit(() ->{
            try {
                synchronousQueue.take();
            }catch (Exception e){
                e.printStackTrace();
            }
            System.out.println("take over");
        });
    }
}

LinkedBlockingDeque

LinkedBlockingDeque是一個雙向佇列，底層使用單連結串列實現，任何一段都可進行元素的讀寫操作，在初始化LinkedBlockingDeque的時候， 我們可以指定容量，也可不指定，如果不指定，則容量為Integer.MAX_VALUE，

注：Deque是雙端佇列，而Queue是單端佇列，雙端意思是兩端都可以進行讀寫操作，而單端則只能從一端進，一端出（FIFO）

public LinkedBlockingDeque() {
        this(Integer.MAX_VALUE);
}

package thread.customthreadpool;
import java.util.concurrent.LinkedBlockingDeque;
public class LinkedBlockingDequeTest {

    private static final LinkedBlockingDeque<Integer> deque = new LinkedBlockingDeque<>();

    public static void main(String[] args) throws InterruptedException {
        deque.put(1);
        deque.put(2);
        deque.put(3);
        deque.put(4);
        deque.put(5);
        System.out.println(deque);
        System.out.println("deque size  "+deque.size());
        deque.take();
        deque.take();
        deque.take();
        deque.take();
        deque.take();
        System.out.println(deque);
        System.out.println("deque size  "+deque.size());
    }
}

 

LinkedBlockingQueue

底層基於單向連表實現，是一個單向佇列，具有先進先出(FIFO)特點，使用了ReentrantLock來做併發控制,讀寫操作都上鎖

private final ReentrantLock putLock = new ReentrantLock();
    public void put(E e) throws InterruptedException {
        if (e == null) throw new NullPointerException();
        int c = -1;
        Node<E> node = new Node<E>(e);
        final ReentrantLock putLock = this.putLock;
        final AtomicInteger count = this.count;
        putLock.lockInterruptibly();
        try {
            while (count.get() == capacity) {
                notFull.await();
            }
            enqueue(node);
            c = count.getAndIncrement();
            if (c + 1 < capacity)
                notFull.signal();
        } finally {
            putLock.unlock();
        }
        if (c == 0)
            signalNotEmpty();
    }
    public E take() throws InterruptedException {
        E x;
        int c = -1;
        final AtomicInteger count = this.count;
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lockInterruptibly();
        try {
            while (count.get() == 0) {
                notEmpty.await();
            }
            x = dequeue();
            c = count.getAndDecrement();
            if (c > 1)
                notEmpty.signal();
        } finally {
            takeLock.unlock();
        }
        if (c == capacity)
            signalNotFull();
        return x;
    }

DelayDeque

DelayDeque是一個無界佇列，新增進DelayDeque的元素會經過compareTo方法計算，然後按照時間 進行排序，排在隊頭的元素是最早到期的，越往後到期時間越長，DelayDeque只能接受Delayed介面型別 如圖所示，佇列裡的元素並不是按照先進先出的規則，而是按照過期時間

示例

package thread.customthreadpool.delayDeque;

import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

public class MyDelayed implements Delayed {

    private final String taskName ;
    private final long nowTime = System.currentTimeMillis();
    private final long expireTime ;

    public MyDelayed(String taskName,long expireTime) {
        this.taskName = taskName;
        this.expireTime = expireTime;
    }

    @Override
    public long getDelay(TimeUnit unit) {
        return unit.convert((nowTime+expireTime) - System.currentTimeMillis(),TimeUnit.MILLISECONDS);
    }

    @Override
    public int compareTo(Delayed o) {
        MyDelayed myDelayed = (MyDelayed) o;
        return (int) (this.getDelay(TimeUnit.MILLISECONDS) - o.getDelay(TimeUnit.MILLISECONDS));
    }

    @Override
    public String toString() {
        return "MyDelayed{" +
                "taskName='" + taskName + '\'' +
                ", nowTime=" + nowTime +
                ", expireTime=" + expireTime +
                '}';
    }
}

package thread.customthreadpool.delayDeque;

import java.util.concurrent.*;

public class MyDelayQueue {

    private static final DelayQueue<MyDelayed> delayQueue = new DelayQueue<>();

    private static final ExecutorService service = Executors.newCachedThreadPool();

    public static void main(String[] args) throws InterruptedException {
        service.submit(() -> {
            delayQueue.put(new MyDelayed("A-Task",5000));
            delayQueue.put(new MyDelayed("B-Task",4000));
            delayQueue.put(new MyDelayed("C-Task",3000));
            delayQueue.put(new MyDelayed("D-Task",2000));
            delayQueue.put(new MyDelayed("E-Task",1000));
        });
        while (true){
            System.out.println(delayQueue.take());
        }
    }
}

 

result

應用場景

1.美團外賣訂單：當我們下單後沒付款 ，30分鐘後將自動取消訂單
2.快取，對於某些任務，需要在特定的時間清理；
and so on

LinkedTransferQueue

當消費執行緒從佇列中取元素時，如果佇列為空，那麼生成一個為null的節點，消費者執行緒就一直等待，此時如果生產者執行緒發現佇列中有一個null節點， 它就不入隊了，而是將元素填充到這個null節點並喚醒消費者執行緒，然後消費者執行緒取走元素。
LinkedTransferQueue是 SynchronousQueue 和 LinkedBlockingQueue 的整合，效能比較高，因為沒有鎖操作， SynchronousQueue不能儲存元素，而LinkedTransferQueue能儲存元素，

PriorityBlockingQueue

PriorityBlockingQueue是一個無界的阻塞佇列，同時是一個支援優先順序的佇列，讀寫操作都是基於ReentrantLock, 內部使用堆演算法保證每次出隊都是優先順序最高的元素

public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        E result;
        try {
            while ( (result = dequeue()) == null)
                notEmpty.await();
        } finally {
            lock.unlock();
        }
        return result;
}