frank1234 阅读(411) 评论(0)
Master-Worker模式的核心思想是,系统由两类进程协作工作:Master进程和Worker进程。Master进程负责接收和分配任务,Worker进程负责处理子任务。当Worker进程将各个子任务处理完成后,将结果返回给Master进程,由Master进程做归纳和汇总。
工作示意图如下图所示:




它的优势在于将一个大的任务分解成一个个的子任务并行执行,提高程序执行效率。
代码示例:

Master进程类:
public class Master {
    protected Queue<Object> workQueue = new ConcurrentLinkedQueue<Object>();//存放子任务
    protected Map<String,Thread> threadMap = new HashMap<String,Thread>();//存放Worker线程
    protected Map<String,Object> resultMap = new ConcurrentHashMap<String, Object>();//存放返回结果集
    public boolean isCompleted(){
        for(Map.Entry<String,Thread> entry:threadMap.entrySet()){
            if(entry.getValue().getState() != Thread.State.TERMINATED){
                return false;
            }
        }
        return true;
    }
    public Master(Worker worker,int countWorker){
        worker.setWorkQueue(workQueue);
        worker.setResultMap(resultMap);
        for(int i=0;i<countWorker;i++){//创建多个Worker线程
            threadMap.put(Integer.toString(i),new Thread(worker,Integer.toString(i)));
        }
    }
    public void submit(Object job){
        workQueue.add(job);//将任务加到子任务队列中
    }
    public Map<String,Object> getResultMap(){
        return resultMap;
    }
    public void execute(){
//循环启动Worker线程
        for(Map.Entry<String,Thread> entry:threadMap.entrySet()){
           entry.getValue().start();
        }
    }

}


Worker进程类:

public class Worker implements  Runnable{
    protected Queue<Object> workQueue;
    protected Map<String,Object> resultMap;
    public void setWorkQueue(Queue<Object> workQueue){
        this.workQueue = workQueue;
    }
    public void setResultMap( Map<String,Object> resultMap){
        this.resultMap = resultMap;
    }
    public Object handle(Object input){
        return input;
    }
    public void run(){
        while(true){
            Object input = workQueue.poll();//从子任务中取任务执行
            if(input == null) break;
            Object re = handle(input);//这是一个模板方法模式
            resultMap.put(Integer.toString(input.hashCode()),re);
        }
    }
}


PlusWorker进程类:
public class PlusWorker extends Worker {
    public Object handle(Object input){
        Integer i = (Integer)input;
        return i*i*i;
    }
}

测试类:
public class Main {
    public static void  main(String[] args){
        Master m = new Master(new PlusWorker(),5);
        for(int i=0;i<100;i++)
            m.submit(i);
        m.execute();
        int re = 0;
        Map<String,Object> resultMap = m.getResultMap();
        while(resultMap.size() >0 || !m.isCompleted()){
            Set<String> keys = resultMap.keySet();
            String key = null;
            for(String k:keys){
                key = k;
                break;
            }
            Integer i = null;
            if(key != null)
                i = (Integer)resultMap.get(key);
            if(i != null)
                re += i;
            if(key != null)
                resultMap.remove(key);

        }
        System.out.println("re:"+re);
    }
}


Main不用等所有的Worker线程都计算完以后再执行,只要有计算完成的,它就一直计算。



《Java性能优化》 -葛一鸣