wait 和notify 在 synchronized 包含的范围中 必须与synchronized 使用同一个对象
可以在一个锁中设定 多个 condition 来执行等待的方法，这样的好处就是能实现多个
方法之间的等待执行。例如下面例子 的两个condition
class BoundedBuffer {
final Lock lock = new ReentrantLock();
final Condition notFull = lock.newCondition(); //使用condition 来代替 wait 和 notify
final Condition notEmpty = lock.newCondition();
final Object[] items = new Object[100];
int putptr, takeptr, count;
public void put(Object x) throws InterruptedException {
lock.lock();
try {
while (count == items.length)
notFull.await();//这里要使用await 只是condition的专用方法
items[putptr] = x;
if (++putptr == items.length) putptr = 0;
++count;
notEmpty.signal();//这也是condition的专用方法
} finally {
lock.unlock();
}
}
public Object take() throws InterruptedException {
lock.lock();
try {
while (count == 0)
notEmpty.await();
Object x = items[takeptr];
if (++takeptr == items.length) takeptr = 0;
--count;
notFull.signal();
return x;
} finally {
lock.unlock();
}
}