1、从JAVA5.0开始,提供了新的选择:ReentrantLock。
2、可定时和可轮询的锁获取模式由tryLock方法实现。
3、使用tryLock试图获得的锁如果不能同时获得，就回退，并重新尝试。休眠时间由一个特定组件管理。（下面的代码完成转帐）
public boolean transferMoney(Account fromAcct,AccounttoAcct,DollarAmonunt amount,long timeout,TimeUnit unit)
throwsInsufficientFundsException,InterruptedException{
longfixedDelay=getFixedDelayComponentNanos(timeout,unit);
longrandMod=getRandomDelayModulusNanos(timeout,unit);
longstopTime=System.nanoTime()+unit.toNanos(timeout);
while (true){
if (fromAcct.lock.tryLock()){
try{
if(toAcct.lock.tryLock()){
try {
if (fromAcct.getBalance().compareTo(amount)<0)
thrownew InsufficientFundsException();
else {
fromAcct.debit(amount);
toAcct.credit(amount);
returntrue;
}
}finally{toAcct.lock.unlock();}
}
}finally{fromAcct.lock.unlock();}
}
}
if(System.nanoTime()<stopTime) return false;
NANOSECONDS.sleep(fixedDelay+rnd.nextLong()%randMod);
}
4、具有时间限制的活动,定时锁同样有用.超时后程序提前返回.
public boolean trySendOnSharedLine(String message,longtimeout,TimeUnit unit)
throwsInterruptedException{
longnanosToLock=unit.toNanos(timeout)-estimatedNanosToSend(message);
if (!lock.tryLock(nanosToLock,NANOSECONDS)) return false;
try{
return sendOnSharedLine(message);
}finally{lock.unlock();}
}
5、一个可中断的锁可以响应中断，能取消。
public boolean sendOnSharedLine(Stringmessage)
throws InterruptedException{
lock.lockInterruptibly();
try{
return cancellableSendOnSharedLine(message);
}finally{
lock.unlock();
}
}
private boolean cancellableSendOnSharedLine(String message)
throwsInterruptedException{…}
}
