run方法内部线程状态冲突；为什么线程状态不是“RUNNING”

Question

我正在做一些测试以了解 Java 中的不同线程状态，并且遇到了一些查询。

通常，当一个线程被实例化时，它被称为处于"NEW"状态，然后当调用它的start() 方法时，操作系统调度程序获得控制并处于"RUNNABLE"状态，进一步当run()被start()它内部调用时被称为处于运行状态。

Thread.currentThread().getState() // Returns the state of the thread

但是在执行以下代码时观察到，"RUNNING"即使在run方法内部进行测试时，线程状态也永远不会显示。

谁能帮我理解为什么它会这样？

public static void main(String[] args) {
        System.out.println("Hello World");
        Thread t=new Thread(()->{
            System.out.println("Hi");
            System.out.println(Thread.currentThread().getState());  //// STATE DISPLAYED AS "RUNNABLE" AGAIN
        });
        System.out.println(t.getState());  // STATE DISPLAYED AS "NEW"
        t.start();
        System.out.println(t.getState());  // STATE DISPLAYED AS "RUNNABLE"
}

lambda 表达式用于实现run()我们测试线程状态的方法，该方法再次显示为“RUNNABLE”而不是“RUNNING”

Answer 1

因为状态RUNNING不存在。如果您查看该getState方法的定义，您会看到以下内容：

public State getState() {
    // get current thread state
    return jdk.internal.misc.VM.toThreadState(threadStatus);
}

如果您分析是什么State，您可以看到它是以下 ENUM：

   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 {@code Object.wait()}
         * on an object is waiting for another thread to call
         * {@code Object.notify()} or {@code Object.notifyAll()} on
         * that object. A thread that has called {@code Thread.join()}
         * 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;
    }

或者从 API Thread.State：

public static enum Thread.State extends Enum<Thread.State> 线程状态。线程可以处于以下状态之一：

NEW尚未启动的线程处于此状态。

RUNNABLE在 Java 虚拟机中执行的线程处于此状态。

BLOCKED被阻塞等待监视器锁的线程处于这种状态。

WAITING无限期等待另一个线程执行特定操作的线程处于此状态。

TIMED_WAITING一个线程正在等待另一个线程执行操作达指定的等待时间时处于此状态。

TERMINATED已退出的线程处于此状态。一个线程在给定的时间点只能处于一种状态。这些状态是不反映任何操作系统线程状态的虚拟机状态。