Thread线程有哪几种状态,这也是面试中很多小伙伴都会被问到的知识点。Thread线程状态是应该掌握的基础知识。但是很多小伙伴如果没有总结过的话,面试过程可能会懵圈,这里我稍作整理,希望小伙伴们可以查漏补缺。
Thread源码中有定义State的枚举类,State枚举类中有明确定义线程的状态。源码如下。
public enum State {
/**
* Thread state for a thread which has not yet started.
*/
NEW,
/**
* Thread state for a runnable thread. A thread in the runnable
* state is executing in the Java virtual machine but it may
* be waiting for other resources from the operating system
* such as processor.
*/
RUNNABLE,
/**
* 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:
* <ul>
* <li>{@link Object#wait() Object.wait} with no timeout</li>
* <li>{@link #join() Thread.join} with no timeout</li>
* <li>{@link LockSupport#park() LockSupport.park}</li>
* </ul>
*
* <p>A thread in the waiting state is waiting for another thread to
* perform a particular action.
*
* For example, a thread that has called <tt>Object.wait()</tt>
* on an object is waiting for another thread to call
* <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
* that object. A thread that has called <tt>Thread.join()</tt>
* is waiting for a specified thread to terminate.
*/
WAITING,
/**
* Thread state for a waiting thread with a specified waiting time.
* A thread is in the timed waiting state due to calling one of
* the following methods with a specified positive waiting time:
* <ul>
* <li>{@link #sleep Thread.sleep}</li>
* <li>{@link Object#wait(long) Object.wait} with timeout</li>
* <li>{@link #join(long) Thread.join} with timeout</li>
* <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
* <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
* </ul>
*/
TIMED_WAITING,
/**
* Thread state for a terminated thread.
* The thread has completed execution.
*/
TERMINATED;
}
通过源码阅读,我们可以知道线程的状态分别是NEW、RUNNABLE、BLOCKED、WAITING、TIMED_WAITING、TERMINATED。
我们分别对线程不同状态进行简单描述:
- NEW:尚未启动的线程的线程状态。
- RUNNABLE:可运行线程的线程状态。线程正在运行或者正在获取CPU时间片。
- BLOCKED:线程的线程状态被阻止,正在等待监视器锁。
- WAITING:等待线程的线程状态。调用某个线程的wait()、join()、 locksupport park()处于等待状态的线程。
- TIMED_WAITING:具有指定等待时间的等待线程的线程状态。调用某个线程的具有指定正等待时间的方法sleep(long)、wait(long)、join(long)、LockSupport Parknanos()、LockSupport ParkUntil()处于指定等待时间的等待线程的线程状态。
- TERMINATED:终止线程的线程状态。
我这边也整理了一份相关的线程状态转换图以供大家参考。
以上代供参考,如有不当之处,欢迎指出!!!
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