您如何确定线程是否正在运行？
Answers:
您可以使用以下方法：
boolean isAlive()
如果线程仍处于活动状态，则返回true；如果线程已终止，则返回false。这不是静态的。您需要对Thread类的对象的引用。
另一个提示：如果要检查其状态以使主线程在新线程仍在运行时等待，则可以使用join（）方法。更方便。
我认为您可以使用GetState（） ; 它可以返回线程的确切状态。
提供了Thread.State枚举类和新的getState（） API，用于查询线程的执行状态。
在给定的时间点，线程只能处于一种状态。这些状态是虚拟机状态，不反映任何操作系统线程状态[ NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, TERMINATED]。
枚举Thread.State扩展枚举实现Serializable，Comparable
getState（）jdk5 - public State getState() {...} « 返回this线程状态。此方法设计用于监视系统状态，而不用于同步控制。
的IsAlive（） - public final native boolean isAlive(); « 返回真，如果在调用它的线程还活着，否则返回假。如果线程已经启动但尚未死亡，则该线程是活动的。
类java.lang.Thread和的示例源代码sun.misc.VM。
package java.lang;
public class Thread implements Runnable {
public final native boolean isAlive();
// Java thread status value zero corresponds to state "NEW" - 'not yet started'.
private volatile int threadStatus = 0;
public enum State {
NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, TERMINATED;
}
public State getState() {
return sun.misc.VM.toThreadState(threadStatus);
}
}
package sun.misc;
public class VM {
// ...
public static Thread.State toThreadState(int threadStatus) {
if ((threadStatus & JVMTI_THREAD_STATE_RUNNABLE) != 0) {
return Thread.State.RUNNABLE;
} else if ((threadStatus & JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER) != 0) {
return Thread.State.BLOCKED;
} else if ((threadStatus & JVMTI_THREAD_STATE_WAITING_INDEFINITELY) != 0) {
return Thread.State.WAITING;
} else if ((threadStatus & JVMTI_THREAD_STATE_WAITING_WITH_TIMEOUT) != 0) {
return Thread.State.TIMED_WAITING;
} else if ((threadStatus & JVMTI_THREAD_STATE_TERMINATED) != 0) {
return Thread.State.TERMINATED;
} else if ((threadStatus & JVMTI_THREAD_STATE_ALIVE) == 0) {
return Thread.State.NEW;
} else {
return Thread.State.RUNNABLE;
}
}
}
与java.util.concurrent.CountDownLatch并行执行多个线程的示例，在完成所有线程后，主线程执行。（直到并行线程完成其任务，主线程才会被阻塞。）
public class MainThread_Wait_TillWorkerThreadsComplete {
public static void main(String[] args) throws InterruptedException {
System.out.println("Main Thread Started...");
// countDown() should be called 4 time to make count 0. So, that await() will release the blocking threads.
int latchGroupCount = 4;
CountDownLatch latch = new CountDownLatch(latchGroupCount);
new Thread(new Task(2, latch), "T1").start();
new Thread(new Task(7, latch), "T2").start();
new Thread(new Task(5, latch), "T3").start();
new Thread(new Task(4, latch), "T4").start();
//latch.countDown(); // Decrements the count of the latch group.
// await() method block until the current count reaches to zero
latch.await(); // block until latchGroupCount is 0
System.out.println("Main Thread completed.");
}
}
class Task extends Thread {
CountDownLatch latch;
int iterations = 10;
public Task(int iterations, CountDownLatch latch) {
this.iterations = iterations;
this.latch = latch;
}
@Override
public void run() {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + " : Started Task...");
for (int i = 0; i < iterations; i++) {
System.out.println(threadName + " : "+ i);
sleep(1);
}
System.out.println(threadName + " : Completed Task");
latch.countDown(); // Decrements the count of the latch,
}
public void sleep(int sec) {
try {
Thread.sleep(1000 * sec);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
@也可以看看
A thread is alive if it has been started and has not yet died。什么意思死了？状态是TERMINATED？
想到编写代码来演示isAlive（）和getState（）方法，此示例监视线程仍终止（死）。
package Threads;
import java.util.concurrent.TimeUnit;
public class ThreadRunning {
static class MyRunnable implements Runnable {
private void method1() {
for(int i=0;i<3;i++){
try{
TimeUnit.SECONDS.sleep(1);
}catch(InterruptedException ex){}
method2();
}
System.out.println("Existing Method1");
}
private void method2() {
for(int i=0;i<2;i++){
try{
TimeUnit.SECONDS.sleep(1);
}catch(InterruptedException ex){}
method3();
}
System.out.println("Existing Method2");
}
private void method3() {
for(int i=0;i<1;i++){
try{
TimeUnit.SECONDS.sleep(1);
}catch(InterruptedException ex){}
}
System.out.println("Existing Method3");
}
public void run(){
method1();
}
}
public static void main(String[] args) {
MyRunnable runMe=new MyRunnable();
Thread aThread=new Thread(runMe,"Thread A");
aThread.start();
monitorThread(aThread);
}
public static void monitorThread(Thread monitorMe) {
while(monitorMe.isAlive())
{
try{
StackTraceElement[] threadStacktrace=monitorMe.getStackTrace();
System.out.println(monitorMe.getName() +" is Alive and it's state ="+monitorMe.getState()+" || Execution is in method : ("+threadStacktrace[0].getClassName()+"::"+threadStacktrace[0].getMethodName()+") @line"+threadStacktrace[0].getLineNumber());
TimeUnit.MILLISECONDS.sleep(700);
}catch(Exception ex){}
/* since threadStacktrace may be empty upon reference since Thread A may be terminated after the monitorMe.getStackTrace(); call*/
}
System.out.println(monitorMe.getName()+" is dead and its state ="+monitorMe.getState());
}
}
使用Thread.currentThread（）。isAlive（）来查看线程是否处于活动状态[输出应为true]，这意味着线程仍在运行run（）方法内的代码，或使用Thread.currentThread.getState（）方法来获取线程。线程的确切状态。
Thread.State.RUNNABLE（最后一个似乎更可靠）有所不同