这个例子来自java编程思想，模拟了银行出纳的多线程场景

package com.igoso.learning;

import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Random;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * created by igoso at 2017/12/20
 * 模仿银行出纳的多线程服务场景，java编程思想
 **/
public class BankTellerSimulation {
    static final int MAX_LINE_SIZE = 50;
    static final int ADJUSTMENT_PERIOD = 1000;

    public static void main(String[] args) throws InterruptedException {
        ExecutorService exec = Executors.newCachedThreadPool();
        //if customer line is too line , customer will leave
        CustomerLine customers = new CustomerLine(MAX_LINE_SIZE);
        exec.execute(new CustomerGenerator(customers));
        //manager add and remove tellers as necessary
        exec.execute(new TellerManager(exec,customers,ADJUSTMENT_PERIOD));

//        exec.shutdownNow();
    }

}


class Customer{
    private final int serviceTime;
    public Customer(int tm){
        serviceTime = tm;
    }

    public int getServiceTime() {
        return serviceTime;
    }

    @Override
    public String toString() {
        return "[" + serviceTime + "]";
    }
}

class CustomerLine extends ArrayBlockingQueue<Customer>{
    public CustomerLine(int capacity) {
        super(capacity);
    }

    @Override
    public String toString() {
        if(this.size()==0){
            return "[empty]";
        }
        StringBuilder sb = new StringBuilder();
        for(Customer customer: this){
            sb.append(customer);
        }
        return sb.toString();
    }

}

class CustomerGenerator implements Runnable{
    private CustomerLine customers;
    private static Random random = new Random(47);
    public CustomerGenerator(CustomerLine customerLine) {
        this.customers = customerLine;
    }

    public void run() {
        try {
            while (!Thread.interrupted()){
                TimeUnit.MILLISECONDS.sleep(random.nextInt(300));
                customers.put(new Customer(random.nextInt(8000)));
            }
        }catch (InterruptedException e){
            System.out.println("Customer generator interrupted");
        }
        System.out.println("Customer generator terminating");
    }
}

class Teller implements Runnable , Comparable<Teller>{
    private static int counter = 0;
    private final int id = counter++;
    private int customerServed = 0;
    private CustomerLine customers;
    private boolean servingCustomerLine = true;

    public Teller(CustomerLine customers){
        this.customers = customers;
    }

    public synchronized int compareTo(Teller o) {
        return customerServed < o.customerServed?-1:(customerServed == o.customerServed?0:1);
    }

    public void run() {
        try {
            while (!Thread.interrupted()) {
                Customer customer = customers.take();
                TimeUnit.MILLISECONDS.sleep(customer.getServiceTime());
                synchronized (this) {
                    customerServed++;
                    while (!servingCustomerLine) {
                        wait();
                    }
                }
            }
        } catch (InterruptedException e) {
            System.out.println(this + "interrupted");
        }
        System.out.println(this + "terminating");
    }

    public synchronized void doSomethingElse() {
        customerServed=0;
        servingCustomerLine=false;
    }

    public synchronized void serveCustomerLine(){
        assert !servingCustomerLine:"already serving:"+ this;
        servingCustomerLine=true;
        notifyAll();
    }

    @Override
    public String toString() {
        return "Teller " + id + " ";
    }

    public String shortString() {
        return "T" + id;
    }

}

class TellerManager implements Runnable{
    private ExecutorService exec;
    private CustomerLine customers;
    private PriorityQueue<Teller> workingTellers= new PriorityQueue<Teller>();
    private Queue<Teller> tellerDoingOtherThings = new LinkedList<Teller>();
    private int adjustmentPeriod;
    private static Random random = new Random(47);
    public TellerManager(ExecutorService exec, CustomerLine customers, int adjustmentPeriod){
        this.exec = exec;
        this.customers = customers;
        this.adjustmentPeriod = adjustmentPeriod;

        //start with a new single teller
        Teller teller = new Teller(customers);
        exec.execute(teller);
        workingTellers.add(teller);
    }

    //空闲分配任务
    public void adjustTellerNumber(){
        if(customers.size()/ workingTellers.size()>2){
            //if tellers are on break or doing
            // another job, bring one back
            if(tellerDoingOtherThings.size()>0){
                Teller teller = tellerDoingOtherThings.remove();
                teller.serveCustomerLine();
                workingTellers.offer(teller);
                return;
            }
            //hire a new teller
            Teller teller = new Teller(customers);
            exec.execute(teller);
            workingTellers.add(teller);
            return;
        }

        //if line is short enough, remove a teller
        if(workingTellers.size()>1 && customers.size()/workingTellers.size()<2){
            reassignOneTeller();
        }

        if(customers.size() == 0){
            while (workingTellers.size()>1){
                reassignOneTeller();
            }
        }

    }

    private void reassignOneTeller(){
        Teller teller = workingTellers.poll();
        teller.doSomethingElse();
        tellerDoingOtherThings.offer(teller);
    }


    public void run() {
        try {
            while (!Thread.interrupted()){
                TimeUnit.MILLISECONDS.sleep(adjustmentPeriod);
                adjustTellerNumber();
                System.out.print(customers + "{");
                for(Teller teller : workingTellers){
                    System.out.print(teller.shortString() + " ");
                }
                System.out.println("}");
            }
        }catch (InterruptedException e){
            System.out.println(this + " interrupted");
        }
        System.out.println(this + "terminating");
    }
}