Cracking the coding interview--Q18.4

题目

原文：

Design a class which provides a lock only if there are no possible deadlocks.

译文：

设计一个提供锁但不可能发生死锁的类。

解答

原书解答：

class MyThread extends Thread {long time;ArrayList<Resource> res = new ArrayList<Resource>();public ArrayList<Resource> getRes() { return res; }public void run() {/* Run infinitely */time = System.currentTimeMillis();int count = 0;while (true) {if (count < 4) {if (Question.canAcquireResource(this,Question.r[count])) {res.add(Question.r[count]);count++;System.out.println(“Resource: [“ +Question.r[count - 1].getId() + “] acquired bythread: [“ + this.getName() + “]”);try {sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}}}else {this.stop();}}}public long getTime() { return time; }public void setRes(ArrayList<Resource> res) { this.res = res; MyThread(String name) {super(name);}}

死锁例子：

/*死锁同步中嵌套同步，而锁不同*/class Ticket implements Runnable{private int tick=100;   Object obj=new Object();boolean flag=true;public void run(){if(flag){while(true){synchronized(Ticket.class){ //若是obj，会出现0号票if(tick>0){System.out.println(currentThread().getName()+"sale:"+tick--);}}}}else{while(true) show();}}public static synchronized void show(){synchronized(obj){if(tick>0){try{Thread.sleep(10);}catch(Exception e){System.out.println(currentThread().getName()+"sale:"+tick--);}}}}class DeadLockDemo{public static void main(String[] args){Ticket t=new Ticket();Thread t1=new Thread(t);Thread t2=new Thread(t);Thread t3=new Thread(t);Thread t4=new Thread(t);t1.start();t2.start();t3.start();t4.start();}}

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