从Java Condition Docs
class BoundedBuffer<E> {
final Lock lock = new ReentrantLock();
final Condition notFull = lock.newCondition();
final Condition notEmpty = lock.newCondition();
final Object[] items = new Object[100];
int putptr, takeptr, count;
public void put(E x) throws InterruptedException {
lock.lock();
try {
while (count == items.length)
notFull.await();
items[putptr] = x;
if (++putptr == items.length) putptr = 0;
++count;
notEmpty.signal();
} finally {
lock.unlock();
}
}
public E take() throws InterruptedException {
lock.lock();
try {
while (count == 0)
notEmpty.await();
E x = (E) items[takeptr];
if (++takeptr == items.length) takeptr = 0;
--count;
notFull.signal();
return x;
} finally {
lock.unlock();
}
}
}
假设线程Produce
调用put
,因此Produce
现在拥有锁lock
。但是while
条件成立,因此Produce
确实notFull.await()
。我的问题是,如果一个线程Consume
调用take
,在显示lock.lock()
的那一行上,究竟会发生什么?
我有点困惑,因为我们让旧的lock
进入了关键部分,现在需要从另一个线程中获取它。
答案 0 :(得分:1)
如果您仔细查看Condition.await()的Javadoc,您会发现await()方法以原子方式释放了锁并使其自身挂起:
“与此条件相关联的锁被自动释放,并且出于线程调度目的,当前线程被禁用,并且处于休眠状态,直到发生四件事之一...”