如何确定线程是否在运行?
Thread.isAlive()
你可以使用这种方法:
boolean isAlive()
如果线程仍然存活,则返回true,如果线程已死则返回false。 这不是静态的。您需要对Thread类的对象进行引用。
再提醒一点: 如果您正在检查它的状态以使主线程在新线程仍在运行时等待,可以使用join()方法。它更加方便。
通过调用Thread.isAlive
检查线程状态。
确切地说,
Thread.isAlive()
返回 true,如果线程已经启动(可能还没有运行)但还没有完成其运行方法。
Thread.getState()
返回线程的确切状态。
一个线程在任何时刻只能处于一种状态。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
]。
枚举类 Thread.State 扩展自 Enum 类并实现了 Serializable 和 Comparable
getState()jdk5
- public State getState() {...}
« 返回 this
线程的状态。此方法设计用于监视系统状态,而不是同步控制。
isAlive() - public final native boolean isAlive();
« 如果调用它的线程仍然存活,则返回 true,否则返回 false。如果线程已启动但尚未结束,则线程是存活的。
类 java.lang.Thread
和 sun.misc.VM
的示例源代码。
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;
}
}
}
示例使用java.util.concurrent.CountDownLatch
来并行执行多个线程,当所有线程都完成后,主线程执行。(在并行线程完成任务之前,主线程将被阻塞。)
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();
}
}
}
@参见
当线程完成时,让它通知其他线程。这样你就始终知道正在发生什么。
Thread.currentThread().isAlive();
。如果此线程仍活着则返回true,否则返回false。Thread.currentThread().isAlive()
吗?因此总是返回true? - Matthew使用 Thread.currentThread().isAlive() 来查看线程是否存活[输出应该为true],这意味着线程仍在运行 run() 方法中的代码,或者使用 Thread.currentThread.getState() 方法来获取线程的确切状态。
本文旨在编写一段代码,演示 isAlive() , getState() 方法的使用。该示例会监控一个线程,直到它终止(死亡)。
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());
}
}
Thread.State.RUNNABLE
有一些不同(后者似乎更可靠). - user924