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说起BlockingQueue，大家最熟悉的就是生产者-消费者模式下的应用。但是如果在调用queue的上层代码加了同步块就会导致线程死锁。
例如：
static BlockingQueuequeue = new LinkedBlockingQueue(); /** * 同步锁 */ static Object lock = new Object(); static void producer(){ synchronized (lock){ queue.put("1"); } } static void cosumer(){ synchronized (lock){ //一旦阻塞，将挂起当前线程，lock锁永远等不到释放，生产者也就无法添加元素，take也就永远阻塞 String msg = queue.take(); } }
但是同步块必须使用的情况下，怎样改进queue的使用呢？见下面示例：
package com.hdwang;import com.alibaba.fastjson.JSON;import java.util.concurrent.BlockingQueue;import java.util.concurrent.LinkedBlockingQueue;/** * Created by hdwang on 2018/4/17. */public class MultiQueueSynTest { static BlockingQueue queue1 = new LinkedBlockingQueue(); static BlockingQueue queue2 = new LinkedBlockingQueue(); static int seq = 1; /** * 同步锁 */ static Object lock = new Object(); static void commit(String msg){ synchronized (lock) { Packet packet = new Packet(); packet.setSeq(seq++); packet.setMsg(msg); try { //queue1.put(packet); //阻塞式添加元素 while(queue1.size()== Integer.MAX_VALUE){ //队满，等待 lock.wait(); } queue1.offer(packet); //非阻塞式添加元素即可 System.out.println("commit msg:" + JSON.toJSONString(packet)); lock.notifyAll(); //通知等待线程 } catch (InterruptedException e) { e.printStackTrace(); } } } static void send(){ while(true) { synchronized (lock) { try { //Packet packet = queue1.take(); //阻塞式取元素 //queue2.put(packet); while(queue1.isEmpty()) { //队空，等待 lock.wait(); //等待，交出锁 } Packet packet = queue1.poll(); //非阻塞式取元素即可 System.out.println("send msg:" + JSON.toJSONString(packet)); lock.notifyAll(); //通知等待线程 while (queue2.size() == Integer.MAX_VALUE){ //队满，等待 lock.wait(); //等待，交出锁 } queue2.offer(packet); System.out.println("msg->queue2:"+JSON.toJSONString(packet)); lock.notifyAll(); //通知等待线程 } catch (InterruptedException e) { e.printStackTrace(); } } } } public static void main(String[] args) { //生产者1 new Thread(new Runnable() { @Override public void run() { while(true){ //不断产生消息 commit("hello1"); try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); //生产者2 new Thread(new Runnable() { @Override public void run() { while(true){ //不断产生消息 commit("hello2"); try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); //消费者 new Thread(new Runnable() { @Override public void run() { send(); } }).start(); } static class Packet{ int seq; String msg; public int getSeq() { return seq; } public void setSeq(int seq) { this.seq = seq; } public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; } }} 运行结果
commit msg:{"msg":"hello1","seq":1}send msg:{"msg":"hello1","seq":1}msg->queue2:{"msg":"hello1","seq":1}commit msg:{"msg":"hello2","seq":2}send msg:{"msg":"hello2","seq":2}msg->queue2:{"msg":"hello2","seq":2}commit msg:{"msg":"hello1","seq":3}send msg:{"msg":"hello1","seq":3}msg->queue2:{"msg":"hello1","seq":3}commit msg:{"msg":"hello2","seq":4}send msg:{"msg":"hello2","seq":4}msg->queue2:{"msg":"hello2","seq":4}commit msg:{"msg":"hello1","seq":5}send msg:{"msg":"hello1","seq":5}msg->queue2:{"msg":"hello1","seq":5}commit msg:{"msg":"hello2","seq":6}send msg:{"msg":"hello2","seq":6}msg->queue2:{"msg":"hello2","seq":6}
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