java使用单独的锁对象的代码展示
private Lock bankLock = new ReentrantLock();
//因为sufficientFunds是锁创建的条件所以称其为条件对象也叫条件变量。
private Condition sufficientFunds = bankLock.newCondition();
public void transfer(int from, int to, double amount) throws InterruptedException
{
bankLock.lock();
try
{
while (accounts[from] < amount)
sufficientFunds.await();
System.out.print(Thread.currentThread());
accounts[from] -= amount;
System.out.printf(" %10.2f from %d to %d", amount, from, to);
accounts[to] += amount;
System.out.printf(" Total Balance: %10.2f%n", getTotalBalance());
sufficientFunds.signalAll();
}
finally
{
bankLock.unlock();
}
}
假如线程1已经走到bankLock.lock(),就获得了这把锁，别的线程再来就会被阻塞。
然后假如线程1满足while (accounts[from] < amount)条件就会进入这把锁的等待集，此时线程1的状态就是等待状态，并且释放这把锁。
如果此时别的线程获得这把锁并且走到了sufficientFunds.signalAll();,那么处于等待状态的线程将全部转为阻塞状态,而不是在原来的位置接着执行。也就是说将重新争夺这把锁。
使用内部锁
内部对象锁只有一个相关条件。
wait方法添加一个线程到等待集中,notifyAll,notify方法解除等待线程的阻塞状态(也就是从锁的等待集释放).
换句话说,调用 wait 或 notityAll等价于
intrinsicCondition.await();intrinsicCondition.signalAll();
此时代码简化为:
public synchronized void transfer(int from, int to, double amount) throws InterruptedException
{
while (accounts[from] < amount)
wait();
System.out.print(Thread.currentThread());
accounts[from] -= amount;
System.out.printf(" %10.2f from %d to %d", amount, from, to);
accounts[to] += amount;
System.out.printf(" Total Balance: %10.2f%n", getTotalBalance());
notifyAll();
}