一、定义
Work Thread模式和Thread-Per-Message模式类似，Thread-Per-Message每次都创建一个新的线程处理请求，而Work Thread模式预先会创建一个线程池（Thread Pool），每次从线程池中取出线程处理请求。
二、模式案例
Request请求类：
public class Request {
private final String name;
private final int number;
private static final Random random = new Random();
public Request(String name, int number) {
this.name = name;
this.number = number;
}
public void execute() {
System.out.println(Thread.currentThread().getName() + " executes " + this);
try {
Thread.sleep(random.nextInt(1000));
} catch (InterruptedException e) {
}
}
public String toString() {
return "[ Request from " + name + " No." + number + " ]";
}
}
Client线程类：
Client线程类用来送出请求：
- 创建Request实例
- 将这个实例传送给Channel类的putRequest方法
public class ClientThread extends Thread {
private final Channel channel;
private static final Random random = new Random();
public ClientThread(String name, Channel channel) {
super(name);
this.channel = channel;
}
public void run() {
try {
for (int i = 0; true; i++) {
Request request = new Request(getName(), i);
channel.putRequest(request);
Thread.sleep(random.nextInt(1000));
}
} catch (InterruptedException e) {
}
}
}
Worker线程类：
WorkerThread类表示工人线程，工人线程可以执行以下动作：
- 从Channel实例取出Request实例
- 调用Request实例的execute方法
public class WorkerThread extends Thread {
private final Channel channel;
public WorkerThread(String name, Channel channel) {
super(name);
this.channel = channel;
}
public void run() {
while (true) {
Request request = channel.takeRequest();
request.execute();
}
}
}
Channel类：
//Channel类可用来接受、传送工作请求，并保存工人线程。
public class Channel {
private static final int MAX_REQUEST = 100; // 最大请求数
private final Request[] requestQueue; // 请求队列
private int tail;
private int head;
private int count;
private final WorkerThread[] threadPool;
public Channel(int threads) {
this.requestQueue = new Request[MAX_REQUEST];
this.head = 0;
this.tail = 0;
this.count = 0;
threadPool = new WorkerThread[threads];
for (int i = 0; i < threadPool.length; i++) {
threadPool[i] = new WorkerThread("Worker-" + i, this);
}
}
public void startWorkers() {
for (int i = 0; i < threadPool.length; i++) {
threadPool[i].start();
}
}
public synchronized void putRequest(Request request) {
while (count >= requestQueue.length) {
try {
wait();
} catch (InterruptedException e) {
}
}
requestQueue[tail] = request;
tail = (tail + 1) % requestQueue.length;
count++;
notifyAll();
}
public synchronized Request takeRequest() {
while (count <= 0) {
try {
wait();
} catch (InterruptedException e) {
}
}
Request request = requestQueue[head];
head = (head + 1) % requestQueue.length;
count--;
notifyAll();
return request;
}
}
执行：
public class Main {
public static void main(String[] args) {
Channel channel = new Channel(5);
channel.startWorkers();
new ClientThread("Alice", channel).start();
new ClientThread("Bobby", channel).start();
new ClientThread("Chris", channel).start();
}
}
三、模式讲解
Work Thread模式的角色如下：
- Client（委托人）参与者
Client参与者会创建请求(Request)，然后传送给Channel参与者。 - Channel（通道）参与者
Channel参与者保存Request请求队列，同时会预创建Worker线程。 - Worker（工人）参与者
Worker参与者会从Channel获取Request。 - Request（请求）参与者
Worker参与者会从Channel获取Request。
注：启动线程是一项繁重的工作，Worker Thread模式预先创建一批线程，可以重复使用线程，达到资源再利用、提升性能的目的。
