java - run 方法内部的线程状态冲突；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权并处于 "RUNNABLE" 状态，当 run() 被 start() 内部调用时，它被称为处于运行状态。

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

但是在执行下面的代码时观察到，即使在 run 方法中进行测试，线程状态也永远不会显示为 "RUNNING"。

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() 方法，我们在其中测试线程的状态，它再次显示为“RUNNABLE”而不是“RUNNING”

Answer 1

因为状态 RUNNING 不存在。如果您查看 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);
}

如果你分析什么是State，你会发现它是下面的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;
    }

或来自 API Thread.State :

public static enum Thread.State extends Enum<Thread.State> A threadstate. A thread can be in one of the following states:

NEW A thread that has not yet started is in this state.

RUNNABLE A thread executing in the Java virtual machine is in this state.

BLOCKED A thread that is blocked waiting for a monitor lock is in this state.

WAITING A thread that is waiting indefinitely for another thread to perform a particular action is in this state.

TIMED_WAITING A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.

TERMINATED A thread that has exited is in this state. A thread can be in only one state at a given point intime. These states are virtual machine states which do not reflect anyoperating system thread states.