刚才在看CSDN的问答时。发现这个问题。
原问题的作者是在观察jstack的输出时提出的疑问。那么BLOCKED和WAITING有什么差别呢？
答复在JDK源代码中能够找到，例如以下是java.lang.Thread.State类的一部分凝视。
/**
* Thread state for a thread blocked waiting for a monitor lock.
* A thread in the blocked state is waiting for a monitor lock
* to enter a synchronized block/method or
* reenter a synchronized block/method after calling
* {@link Object#wait() Object.wait}.
*/
BLOCKED,
/**
* Thread state for a waiting thread.
* A thread is in the waiting state due to calling one of the
* following methods:
* {@link Object#wait() Object.wait} with no timeout
* {@link #join() Thread.join} with no timeout
* {@link LockSupport#park() LockSupport.park}
*
*
* A thread in the waiting state is waiting for another thread to
* perform a particular action.
*
* For example, a thread that has called Object.wait()
* on an object is waiting for another thread to call
* Object.notify() or Object.notifyAll() on
* that object. A thread that has called Thread.join()
* is waiting for a specified thread to terminate.
*/
WAITING,
从中能够清晰的得到线程处于BLOCKED和WAITING状态的场景。
BLOCKED状态
线程处于BLOCKED状态的场景。
- 当前线程在等待一个monitor lock，比方等待运行synchronized代码块或者使用synchronized标记的方法。
- 在synchronized块中循环调用Object类型的wait方法，例如以下是例子
synchronized(this)
{
while (flag)
{
obj.wait();
}
// some other code
}
WAITING状态
线程处于WAITING状态的场景。
- 调用Object对象的wait方法，但没有指定超时值。
- 调用Thread对象的join方法，但没有指定超时值。
- 调用LockSupport对象的park方法。
提到WAITING状态，顺便提一下TIMED_WAITING状态的场景。
TIMED_WAITING状态
线程处于TIMED_WAITING状态的场景。
- 调用Thread.sleep方法。
- 调用Object对象的wait方法，指定超时值。
- 调用Thread对象的join方法，指定超时值。
- 调用LockSupport对象的parkNanos方法。
- 调用LockSupport对象的parkUntil方法。