线程停止的原理
使用interrupt来通知，而不是强制
java提供了interrrupt让一个线程来通知另一个线程停止
如果想中断一个线程，但是那个线程不想去中断，那就无能为力，我们没有强制去中断线程的手段，因为线程停止前需要做一定的收尾工作
所以正确停止线程，是如何用interrupt来通知那个线程，以及被停止的线程如何进行配合
如何正确停止线程
在普通情况下停止线程
代码展示
- 调用interrupt没有作用
- 下面这段代码，执行interrupt之后，线程并没有被中断
- 因为被执行的线程并没有相应中断的方式
public class stopThreadWithoutSleep implements Runnable{
public static void main(String[] args) throws InterruptedException {
Thread thread = new Thread(new stopThreadWithoutSleep());
thread.start();
Thread.sleep(1000);
thread.interrupt();
}
@Override
public void run() {
int num = 0;
while(num <= Integer.MAX_VALUE / 2) {
if (num % 10000 == 0) {
System.out.println(num + "是10000的倍数");
}
num++;
}
System.out.println("结束");
}
}
- 被执行线程加上相应中断的操作之后
- 结果可知，被执行线程相应一秒之后就结束了
public class stopThreadWithoutSleep implements Runnable{
public static void main(String[] args) throws InterruptedException {
Thread thread = new Thread(new stopThreadWithoutSleep());
thread.start();
Thread.sleep(1000);
thread.interrupt();
}
@Override
public void run() {
int num = 0;
while(!Thread.currentThread().isInterrupted() && num <= Integer.MAX_VALUE / 2) {
if (num % 10000 == 0) {
System.out.println(num + "是10000的倍数");
}
num++;
}
System.out.println("结束");
}
}
在阻塞情况下停止线程
代码展示
- 中断之后，抛出异常
- 线程在sleep的过程中，会catch到InterruptedException这个异常，从而相应中断
public class stopThreadWithSleep {
public static void main(String[] args) {
Runnable runnable = () -> {
int num = 0;
while (num <= 300 && !Thread.currentThread().isInterrupted()) {
if (num % 100 == 0) {
System.out.println(num + "是100的倍数");
}
num++;
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
};
Thread thread = new Thread(runnable);
thread.start();
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
thread.interrupt();
}
}
线程在每次迭代后都阻塞
- 代码展示 即使不在while判断是否中断，sleep也能中断异常
public class stopThreadWithSleepEveryLoop {
public static void main(String[] args) {
Runnable runnable = () -> {
int num = 0;
try {
while (num <= 10000) {
if (num % 100 == 0) {
System.out.println(num + "是100的倍数");
}
num++;
Thread.sleep(10);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
};
Thread thread = new Thread(runnable);
thread.start();
try {
Thread.sleep(5000);
} catch (
InterruptedException e) {
e.printStackTrace();
}
thread.interrupt();
}
}
当catch写到while内，则不能正常中断
public class CantInterrupt {
public static void main(String[] args) {
Runnable runnable = () -> {
int num = 0;
while (num <= 10000) {
if (num % 100 == 0) {
System.out.println(num + "是100的倍数");
}
num ++;
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Thread thread = new Thread(runnable);
thread.start();
try {
Thread.sleep(5000);
} catch (
InterruptedException e) {
e.printStackTrace();
}
thread.interrupt();
}
}
- 即使在while的判断条件中，加上检测中断的机制，也不能正常中断
- 因为java的sleep函数，一旦相应中断，就会将中断的标志位删除
public class CantInterrupt {
public static void main(String[] args) {
Runnable runnable = () -> {
int num = 0;
while (num <= 10000 && !Thread.currentThread().isInterrupted()) {
if (num % 100 == 0) {
System.out.println(num + "是100的倍数");
}
num++;
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Thread thread = new Thread(runnable);
thread.start();
try {
Thread.sleep(5000);
} catch (
InterruptedException e) {
e.printStackTrace();
}
thread.interrupt();
}
}
停止线程的最佳实践
- 在方法签名中抛出异常，在run方法中强制进行try catch
public class StopThreadInProd implements Runnable{
public static void main(String[] args) throws InterruptedException {
Thread thread = new Thread(new StopThreadInProd());
thread.start();
Thread.sleep(1000);
thread.interrupt();
}
@Override
public void run() {
while (true) {
System.out.println("start");
try {
throwInMethod();
} catch (InterruptedException e) {
System.out.println("保存日志/关闭程序");
e.printStackTrace();
}
}
}
private void throwInMethod() throws InterruptedException {
Thread.sleep(2000);
}
}
- 在catch语句中调用Thread.currentThread().interrupt恢复中断状态
- 结果：抛出异常，程序结束
public class StopThreadInProd2 implements Runnable{
public static void main(String[] args) throws InterruptedException {
Thread thread = new Thread(new StopThreadInProd2());
thread.start();
Thread.sleep(1000);
thread.interrupt();
}
@Override
public void run() {
while (true) {
if (Thread.currentThread().isInterrupted()) {
System.out.println("Interrupt");
break;
}
reInterrupt();
}
}
private void reInterrupt() {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
e.printStackTrace();
}
}
}
- 依照上面的代码，如果方法没有没有重新抛出异常
- 结果：程序抛出异常，但是程序没有停止运行
public class StopThreadInProd2 implements Runnable{
public static void main(String[] args) throws InterruptedException {
Thread thread = new Thread(new StopThreadInProd2());
thread.start();
Thread.sleep(1000);
thread.interrupt();
}
@Override
public void run() {
while (true) {
if (Thread.currentThread().isInterrupted()) {
System.out.println("Interrupt");
break;
}
reInterrupt();
}
}
private void reInterrupt() {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
// Thread.currentThread().interrupt();
e.printStackTrace();
}
}
}
错误停止的方法
被弃用的stop,suspend和resume方法
- 使用stop停止线程，会导致线程运行一半突然停止，没办法完成最基本的操作，会造成脏数据
- 下面这段代码的结果会造成一个连队只有部分人领取到了装备
- stop是不安全的，会直接停止监视器
- suspend和resume不会破坏对象，但是会让线程挂起，不释放锁，容易造成死锁
public class StopThread implements Runnable{
@Override
public void run() {
// 模拟指挥军队,一共五个连队,每个连队一百人
// 以连队为单位发放武器
for (int i = 0; i < 5; i++) {
System.out.println("连队" + i + "领取武器");
for (int j = 0; j < 10; j++) {
System.out.println(j);
try {
Thread.sleep(50);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("连队" + i + "领取完毕");
}
}
public static void main(String[] args) {
Thread thread = new Thread(new StopThread());
thread.start();
try {
thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
thread.stop();
}
}
用volatile设置boolean标记位
- 下面这段代码，通过改变标志位的值会成功终止线程
public class Volatile implements Runnable {
private volatile boolean canceled = false;
@Override
public void run() {
int num = 0;
try {
while (num <= 10000 && !canceled) {
if (num % 100 == 0) {
System.out.println(num + " 是100的倍数");
}
num++;
Thread.sleep(1);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws InterruptedException {
Volatile v = new Volatile();
Thread thread = new Thread(v);
thread.start();
Thread.sleep(1000);
v.canceled = true;
}
}
- 当陷入阻塞的时候，是无法停止线程的
- 下面这段代码的运行结果，并没有打印生产者停止运行，说明根本没有执行生产者的finally那部分代码
- 同时程序也没停止
- 原因见生产者代码 while循环中的注释
// 模拟生产者和消费者
public class cantStop {
public static void main(String[] args) throws InterruptedException {
// 阻塞队列
// 满了之后,放不进去
// 空的时候取数据,也会堵塞
ArrayBlockingQueue storage = new ArrayBlockingQueue(10);
Producer producer = new Producer(storage);
Thread producerThread = new Thread(producer);
producerThread.start();
Thread.sleep(1000);
Consumer consumer = new Consumer(storage);
while (consumer.needMore()) {
System.out.println(consumer.storage.take() + "被消费");
Thread.sleep(100);
}
System.out.println("消费者不需要更多数据");
// 消费者不需要数据,让生产者停下来
producer.canceled = true;
}
}
// 生产者
class Producer implements Runnable {
public volatile boolean canceled = false;
BlockingQueue storage;
public Producer(BlockingQueue storage) {
this.storage = storage;
}
@Override
public void run() {
int num = 0;
try {
while (num <= 10000 && !canceled) {
if (num % 100 == 0) {
// 当堵塞队列满了之后，会堵塞在这里，而这段代码没有判断机制
storage.put(num);
System.out.println("num" + "生产");
}
num++;
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
System.out.println("生产者停止运行");
}
}
}
// 消费者
class Consumer {
BlockingQueue storage;
public Consumer(BlockingQueue storage) {
this.storage = storage;
}
public boolean needMore() {
if (Math.random() > 0.9) {
return false;
}
return true;
}
}
- 将上面代码用interrupt进行中断
- 程序成功停止
public class finxed {
public static void main(String[] args) throws InterruptedException {
finxed finxed = new finxed();
// 阻塞队列
// 满了之后,放不进去
// 空的时候取数据,也会堵塞
ArrayBlockingQueue storage = new ArrayBlockingQueue(10);
Producer producer = finxed.new Producer(storage);
Thread producerThread = new Thread(producer);
producerThread.start();
Thread.sleep(1000);
Consumer consumer = finxed.new Consumer(storage);
while (consumer.needMore()) {
System.out.println(consumer.storage.take() + "被消费");
Thread.sleep(100);
}
System.out.println("消费者不需要更多数据");
// 消费者不需要数据,让生产者停下来
producerThread.interrupt();
}
class Producer implements Runnable {
public volatile boolean canceled = false;
BlockingQueue storage;
public Producer(BlockingQueue storage) {
this.storage = storage;
}
@Override
public void run() {
int num = 0;
try {
while (num <= 10000 && !Thread.currentThread().isInterrupted()) {
if (num % 100 == 0) {
storage.put(num);
System.out.println("num" + "生产");
}
num++;
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
System.out.println("生产者停止运行");
}
}
}
class Consumer {
BlockingQueue storage;
public Consumer(BlockingQueue storage) {
this.storage = storage;
}
public boolean needMore() {
if (Math.random() > 0.9) {
return false;
}
return true;
}
}
}
interrupt源码查看
- 这段代码做的都是一些判断，真正执行中断的代码时interrupt0
- interrupt0是native代码
public void interrupt() {
if (this != Thread.currentThread())
checkAccess();
synchronized (blockerLock) {
Interruptible b = blocker;
if (b != null) {
interrupt0(); // Just to set the interrupt flag
b.interrupt(this);
return;
}
}
interrupt0();
}
private native void interrupt0();
interrupt相关函数练习
- isInterrupted获取中断标志，获取的是前面的线程
- interrupted获取中断标志并重置，只关心执行的线程，所以下面代码执行的是main线程
public class InterruptedTest {
public static void main(String[] args) throws InterruptedException {
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
while (true) {
}
}
});
thread.start();
thread.interrupt();
// 获取中断标志
System.out.println(thread.isInterrupted()); // true
// 获取中断标志并重置
System.out.println(thread.interrupted()); //false
System.out.println(Thread.interrupted()); // false
System.out.println(thread.isInterrupted()); //true
thread.join();
System.out.println("over");
}
}
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