标签：rate and extends tac void rgs 方案 rom str
一、需求描述：
将资金从一个账户转移到另一个账户。
二、程序实现：
（1）账户类：
public class Account {
private long account;
public Account(String user, long account) {
this.account = account;
}
public Account() {
super();
}
public long getAccount() {
return account;
}
public void setAccount(long account) {
this.account = account;
}
public void debit(long money){
this.account -= money;
}
public void credit(long money){
this.account += money;
}
}
（2）资产转移类：
public class TransMoney {
private static final Object tieLock = new Object();
public static void transferMoney(Account fromAccount,Account toAccount,long amount){
synchronized (fromAccount){
synchronized (toAccount){
fromAccount.debit(amount);
toAccount.credit(amount);
}
}
}
}
（3）测试类：
public class DemonstrateDeadLock {
private static final int NUM_THREADS = 20;
private static final int NUM_ACCOUNTS = 5;
private static final int NUM_ITERATIONS = 1000000;
public static void main(String[] args) {
final Random rdn = new Random();
final Account[] accounts = new Account[NUM_ACCOUNTS];
for(int i=0;i<accounts.length;i++){
accounts[i] = new Account();
}
class TransferThread extends Thread{
public void run(){
for(int i=0;i<NUM_ITERATIONS;i++){
int fromAccount = rdn.nextInt(NUM_ACCOUNTS);
int toAccount = rdn.nextInt(NUM_ACCOUNTS);
TransMoney.transferMoney(accounts[fromAccount],accounts[toAccount],rdn.nextInt(1000));
}
}
}
for(int i=0;i<NUM_THREADS;i++){
new TransferThread().start();
}
}
}
（4）解析：
上述程序容易形成死锁，原因在于多账户调用TransMoney.transferMoney时，存在锁顺序冲突，
解决方案是使用System.identityHashCode来定义锁的顺序，消除死锁的可能性，代码实现如下：
public static void transferMoney(final Account fromAccount,final Account toAccount,final long amount){
class Helper{
public void transfer(){
fromAccount.debit(amount);
toAccount.credit(amount);
}
}
int fromHash = System.identityHashCode(fromAccount);
int toHash = System.identityHashCode(toAccount);
if(fromHash < toHash){
synchronized (fromAccount){
synchronized (toAccount){
new Helper().transfer();
}
}
}else if(fromHash > toHash){
synchronized (toAccount){
synchronized (fromAccount){
new Helper().transfer();
}
}
}else{
synchronized (tieLock){
synchronized (fromAccount){
synchronized (toAccount){
new Helper().transfer();
}
}
}
}
}
标签：rate and extends tac void rgs 方案 rom str
原文地址：http://www.cnblogs.com/hunterCecil/p/6189171.html
