文章目录
从源码看Thread中定义的六种线程状态
Thread类位于java.lang包下，在Thread类中有一个枚举类型State，State中定义了线程的六种状态。源码如下：
java.lang.Thread.State
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;
}
6中线程状态：
- 1、NEW
尚未启动的线程的线程状态。 - 2、RUNNABLE
可运行线程的线程状态。
可运行的线程状态正在Java虚拟机中执行，但它可能等待操作系统的其他资源如处理器。 - 3、BLOCKED
线程阻塞等待监视器锁定的线程状态。
处于synchronized同步代码块或方法中被阻塞。 - 4、WAITING
等待线程的线程状态。
处于等待状态的线程正在等待另一个线程执行特定的操作。 - 5、TIMED_WAITING
具有指定等待时间的等待线程的线程状态。 - 6、TERMINATED
终止线程的线程状态。
线程正常完成执行或者出现异常。
注：线程在给定时间点只能处于一种状态。这些状态是虚拟机状态，不反映任何操作系统线程状态。
调用getState方法可以得到当前线程的状态。
public class ThreadTest {
public static void main(String[] args) {
Thread thread1 = new MyThread();
System.out.println("thread1的线程状态：" + thread1.getState());
thread1.start();
System.out.println("thread1的线程状态：" + thread1.getState());
}
}
class MyThread extends Thread{
@Override
public void run() {
System.out.println(this.getName() + " is running。。。");
}
}
线程状态的变化
1.线程正常运行结束的状态变化
public class ThreadState {
public static void main(String[] args) throws InterruptedException {
Thread thread1 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("当前线程正在执行-------");
System.out.println("线程正在执行时的线程状态：" + Thread.currentThread().getState().toString());
}
});
System.out.println("创建线程后，调用start前的线程状态：" + thread1.getState().toString());
thread1.start();
Thread.sleep(2000L); // 等待thread1执行结束，再看状态
System.out.println("---等待两秒，线程执行结束后的状态：" + thread1.getState().toString());
//thread1.start(); //当线程终止之后，再进行调用，会抛出IllegalThreadStateException异常
}
}
程序运行结果显示：
- 当一个线程被创建时（还未调用start方法）处于NEW状态；
- 调用start方法后，线程开始执行，此时线程处于RUNNABLE状态；
- 线程继续执行，一段时间后，线程正常执行结束，此时线程处于TERMINATED状态。
（新建 -> 运行 -> 终止，NEW-> RUNNABLE-> TERMINATED）
注意：当线程执行结束之后，再进行调用，会抛出IllegalThreadStateException异常
2.线程执行过程中等待一段时间再继续执行结束的状态变化
public class ThreadState {
public static void main(String[] args) throws InterruptedException {
Thread thread2 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("当前线程正在执行-------,需要花费两秒时间------");
try {
// 将线程2移动到等待状态，2s后自动唤醒
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("线程正在执行时的线程状态：" + Thread.currentThread().getState().toString());
}
});
System.out.println("创建线程后，调用start前的线程状态：" + thread2.getState().toString());
thread2.start();
Thread.sleep(200L); // 等待200毫秒，再看状态
System.out.println("等待200毫秒（线程还没执行结束），线程的状态：" + thread2.getState().toString());
Thread.sleep(3000L); // 再等待3秒，让thread2执行完毕，再看状态
System.out.println("等待3秒（线程执行结束），线程的状态：" + thread2.getState().toString());
}
}
程序运行结果显示：
- 当一个线程被创建时（还未调用start方法）处于NEW状态；
- 调用start方法后，线程开始执行，此时线程处于RUNNABLE状态；
- 当线程运行过程中需要等待一段时间时，线程进入TIMED_WAITING状态
- 线程继续执行，一段时间后，线程正常执行结束，此时线程处于TERMINATED状态。
（新建 -> 运行 -> 等待 -> 运行 -> 终止，NEW-> RUNNABLE->TIMED_WAITING->RUNNABLE-> TERMINATED）
3.线程执行过程中等待其他线程被阻塞，然后继续执行到结束的状态变化
public class ThreadState {
public static void main(String[] args) throws InterruptedException {
Thread thread3 = new Thread(new Runnable() {
@Override
public void run() {
synchronized (ThreadState.class) {
System.out.println("当前线程正在执行-------");
System.out.println("线程正在执行时的线程状态：" + Thread.currentThread().getState().toString());
}
}
});
synchronized (ThreadState.class) {
System.out.println("没调用start方法，thread3当前状态：" + thread3.getState().toString());
thread3.start();
System.out.println("调用start方法，thread3当前状态：" + thread3.getState().toString());
Thread.sleep(200L);
System.out.println("等待200毫秒，线程遇到锁被堵塞时的状态：" + thread3.getState().toString());
}
Thread.sleep(3000L); // 再等待3秒，让thread3执行完毕，再看状态
System.out.println("等待3秒，线程抢到锁并执行结束时的状态：" + thread3.getState().toString());
}
}
程序运行结果显示：
- 当一个线程被创建时（还未调用start方法）处于NEW状态；
- 调用start方法后，线程开始执行，此时线程处于RUNNABLE状态；
- 当线程遇到锁被堵塞时线程进入BLOCKED状态
- 线程继续执行，一段时间后，线程正常执行结束，此时线程处于TERMINATED状态。
（新建 -> 运行 -> 阻塞 -> 运行 -> 终止，NEW-> RUNNABLE->BLOCKED->RUNNABLE-> TERMINATED）
