线程的动态死锁

package com.thread.deadlock;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import javax.naming.InsufficientResourcesException;

/**
* 动态加锁顺序产生的死锁
*
* 使用模拟转账的例子来说明：
*
* 这个转账操作看起来都是同样的顺序获得锁的，但是事实上锁的顺序取决于传递给transferMoney的参数的顺序，
* 这个参数的顺序实际上又取决外部输入的顺序。
*
* 如果两个线程同时调用transferMoney,一个从X向Y转账，另一个从Y向X转账，那么就会发生死锁：
* A:  transferMoney(myAccount,yourAccount,10)
* B:  transferMoney(yourAccount,myAccount,20)
*
* 为了解决这个问题，我们必须制定锁的执行顺序，使得在整个应用程序中，获得锁都必须始终遵守这个既定的顺序。
*
* 改进方法：
* 1、通过System.identityHashCode来定义锁的顺序
*
* 2、如果Account对象中有唯一的账号编码信息，可以直接通过账号编码排定对象顺序
*
* @author hadoop
*
*/
public class DynamicDeadlock {

class Account{
private String accountCode;//账户编码
private int balance;//账户余额

public Account(String accountCode, int balance) {
this.accountCode = accountCode;
this.balance = balance;
}

public int getBalance() {
return balance;
}

//汇出
public  void debit(int dollarAmount){//这里犹豫每次都是对整个对象加锁，所以可以不用使用synchronized来同步
this.balance  = this.balance - dollarAmount;
}

//汇入
public void credit(int dollarAmount){
this.balance  = this.balance + dollarAmount;
}
}
/**
* 转账(安全)
* @param fromAccount   转出账户
* @param toAccount     转入账户
* @param dollarAmount  金额
* @throws InsufficientResourcesException
*/
public void transferMoney(Account fromAccount,Account toAccount,int dollarAmount) throws InsufficientResourcesException{
synchronized(fromAccount){
synchronized(toAccount){
if(fromAccount.getBalance() - dollarAmount < 0){//余额不足
throw new InsufficientResourcesException();
}else{
System.out.println("开始转账");
try {
Thread.sleep(2*1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
fromAccount.debit(dollarAmount);//汇出
toAccount.credit(dollarAmount);//转入
System.out.println("转出金额为："+dollarAmount+",转出账户"+fromAccount.accountCode+"余额：" + fromAccount.getBalance()+",转入账户"+toAccount.accountCode+"余额：" + toAccount.getBalance());
}
}
}
}

/**
* 转账(安全)
* @param fromAccount   转出账户
* @param toAccount     转入账户
* @param dollarAmount  金额
* @throws InsufficientResourcesException
*/
public void transferMoneyForSafe(Account fromAccount,Account toAccount,int dollarAmount) throws InsufficientResourcesException{
if(Integer.valueOf(fromAccount.accountCode) > Integer.valueOf(toAccount.accountCode)){//根据账号编号指定执行顺序，让多个线程调用的时候，始终是先获取编号大的账号的锁，然后获取编号小的账号的锁
synchronized(fromAccount){
synchronized(toAccount){
if(fromAccount.getBalance() - dollarAmount < 0){//余额不足
throw new InsufficientResourcesException();
}else{
try {
Thread.sleep(2*1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
fromAccount.debit(dollarAmount);//汇出
toAccount.credit(dollarAmount);//转入
System.out.println("转出金额为："+dollarAmount+",转出账户"+fromAccount.accountCode+"余额：" + fromAccount.getBalance()+",转入账户"+toAccount.accountCode+"余额：" + toAccount.getBalance());
}
}
}
}else if(Integer.valueOf(fromAccount.accountCode) < Integer.valueOf(toAccount.accountCode)){
synchronized(toAccount){
synchronized(fromAccount){
if(fromAccount.getBalance() - dollarAmount < 0){//余额不足
throw new InsufficientResourcesException();
}else{
try {
Thread.sleep(2*1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
fromAccount.debit(dollarAmount);//汇出
toAccount.credit(dollarAmount);//转入
System.out.println("转出金额为："+dollarAmount+",转出账户"+fromAccount.accountCode+"余额：" + fromAccount.getBalance()+",转入账户"+toAccount.accountCode+"余额：" + toAccount.getBalance());
}
}
}
}else{//如果相等，提示不能转账
System.out.println("不能向自己转账");
}

}

public static void main(String[] args) {
final DynamicDeadlock dynamicDeadlock =new DynamicDeadlock();
//这里是模拟，使用共享域作为账户对象，能够让多个线程访问账户数据
final Account fromAccount = dynamicDeadlock.new Account("666666", 80000);
final Account toAccount  = dynamicDeadlock.new Account("888888", 5000);
//模拟多个线程执行对这2个账户进行转账操作
ExecutorService executorService = Executors.newCachedThreadPool();
for (int i = 0; i < 100; i++) {
executorService.execute(new Runnable() {
@Override
public void run() {
try {
System.out.println("借钱：");
dynamicDeadlock.transferMoney(fromAccount,toAccount,100);
//dynamicDeadlock.transferMoneyForSafe(fromAccount,toAccount,100);
} catch (InsufficientResourcesException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});

executorService.execute(new Runnable() {
@Override
public void run() {
try {
System.out.println("还钱：");
dynamicDeadlock.transferMoney(toAccount,fromAccount,50);
} catch (InsufficientResourcesException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
}

}

}