一、描述线程池执行任务的流程，直到什么时候会启动拒绝策略
- 情况一：
- 每过来一个任务会启动一个线程去执行
- 当核心线程数用完后，会把新来的任务存入阻塞队列中
- 阻塞队列存满后，会再启动超过核心线程数量到最大线程数量之间的线程
- 当线程的数量达到最大线程数量，再来任务就启动拒绝策略
- 情况二：
当我们调用 shutdown 等方法关闭线程池的时候，如果此时继续向线程池提交任务，就会被拒绝
二、 线程池的几种拒绝策略
策略 |
处理方式 |
| AbortPolicy | 直接抛出异常 |
| DiscardPolicy | 丢弃当前被拒绝的任务(不抛出异常) |
| DiscardOldestPolicy | 将工作队列中最早的任务丢弃，去执行新的任务 |
| CallerRunsPolicy | 交给调用线程池的线程处理 |
三、 简述线程池的拒绝策略：
1.AbortPolicy:ThreadPoolExecutor中默认的拒绝策略就是AbortPolicy。直接抛出异常也不处理。
package com.apesource.demo1;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.ThreadPoolExecutor.AbortPolicy;
import java.util.concurrent.TimeUnit;
public class Test7 {
public static void main(String[] args) throws InterruptedException {
//第一个任务
Runnable r1 = new Runnable() {
@Override
public void run() {
System.out.println("1"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第二个任务
Runnable r2 = new Runnable() {
@Override
public void run() {
System.out.println("2"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第三个任务
Runnable r3 = new Runnable() {
@Override
public void run() {
System.out.println("3"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第四个任务
Runnable r4 = new Runnable() {
@Override
public void run() {
System.out.println("4"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
/*
* 创建线程池：
* 1：核心线程数是 1
* 2：最大线程数是 2
* 10：最大存活时间
* TimeUnit.SECONDS：最大存活时间的单位
* new ArrayBlockingQueue<Runnable>(1)：阻塞队列，队列中只能存放一个任务
* Executors.defaultThreadFactory()：线程工厂
* new AbortPolicy())：拒绝策略（第一种：直接抛出异常）
*/
ThreadPoolExecutor pool = new ThreadPoolExecutor(1,2,10,TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(1),
Executors.defaultThreadFactory(),
new AbortPolicy());
//new DiscardPolicy());
//new DiscardOldestPolicy());
pool.execute(r1);
pool.execute(r2);
pool.execute(r3);
pool.execute(r4);
}
}
2.DiscardPolicy:采用这个拒绝策略，会让被线程池拒绝的任务直接抛弃，不会抛异常也不会执行。
package com.apesource.demo1;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.ThreadPoolExecutor.DiscardPolicy;
import java.util.concurrent.TimeUnit;
public class Test7 {
public static void main(String[] args) throws InterruptedException {
//第一个任务
Runnable r1 = new Runnable() {
@Override
public void run() {
System.out.println("1"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第二个任务
Runnable r2 = new Runnable() {
@Override
public void run() {
System.out.println("2"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第三个任务
Runnable r3 = new Runnable() {
@Override
public void run() {
System.out.println("3"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第四个任务
Runnable r4 = new Runnable() {
@Override
public void run() {
System.out.println("4"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
/*
* 创建线程池：
* 1：核心线程数是 1
* 2：最大线程数是 2
* 10：最大存活时间
* TimeUnit.SECONDS：最大存活时间的单位
* new ArrayBlockingQueue<Runnable>(1)：阻塞队列，队列中只能存放一个任务
* Executors.defaultThreadFactory()：线程工厂
* new AbortPolicy())：拒绝策略（第一种：直接抛出异常）
*/
ThreadPoolExecutor pool = new ThreadPoolExecutor(1,2,10,TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(1),
Executors.defaultThreadFactory(),
//new AbortPolicy());
new DiscardPolicy());
//new DiscardOldestPolicy());
pool.execute(r1);
pool.execute(r2);
pool.execute(r3);
pool.execute(r4);
}
}
3.DiscardOldestPolicy:DiscardOldestPolicy策略的作用是，当任务被拒绝添加时，会抛弃任务队列中最旧的任务也就是最先加入队列的，再把这个新任务添加进去。
package com.apesource.demo1;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.ThreadPoolExecutor.DiscardOldestPolicy;
import java.util.concurrent.TimeUnit;
public class Test7 {
public static void main(String[] args) throws InterruptedException {
//第一个任务
Runnable r1 = new Runnable() {
@Override
public void run() {
System.out.println("1"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第二个任务
Runnable r2 = new Runnable() {
@Override
public void run() {
System.out.println("2"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第三个任务
Runnable r3 = new Runnable() {
@Override
public void run() {
System.out.println("3"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第四个任务
Runnable r4 = new Runnable() {
@Override
public void run() {
System.out.println("4"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
/*
* 创建线程池：
* 1：核心线程数是 1
* 2：最大线程数是 2
* 10：最大存活时间
* TimeUnit.SECONDS：最大存活时间的单位
* new ArrayBlockingQueue<Runnable>(1)：阻塞队列，队列中只能存放一个任务
* Executors.defaultThreadFactory()：线程工厂
* new AbortPolicy())：拒绝策略（第一种：直接抛出异常）
*/
ThreadPoolExecutor pool = new ThreadPoolExecutor(1,2,10,TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(1),
Executors.defaultThreadFactory(),
//new AbortPolicy());
//new DiscardPolicy());
new DiscardOldestPolicy());
pool.execute(r1);
pool.execute(r2);
pool.execute(r3);
pool.execute(r4);
}
}
4.CallerRunsPolicy:CallerRunsPolicy在任务被拒绝添加后，会调用当前线程池的所在的线程去执行被拒绝的任务。
package com.apesource.demo1;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.ThreadPoolExecutor.CallerRunsPolicy;
import java.util.concurrent.TimeUnit;
public class Test7 {
public static void main(String[] args) throws InterruptedException {
//第一个任务
Runnable r1 = new Runnable() {
@Override
public void run() {
System.out.println("1"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第二个任务
Runnable r2 = new Runnable() {
@Override
public void run() {
System.out.println("2"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第三个任务
Runnable r3 = new Runnable() {
@Override
public void run() {
System.out.println("3"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
//第四个任务
Runnable r4 = new Runnable() {
@Override
public void run() {
System.out.println("4"+Thread.currentThread().getName());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
/*
* 创建线程池：
* 1：核心线程数是 1
* 2：最大线程数是 2
* 10：最大存活时间
* TimeUnit.SECONDS：最大存活时间的单位
* new ArrayBlockingQueue<Runnable>(1)：阻塞队列，队列中只能存放一个任务
* Executors.defaultThreadFactory()：线程工厂
* new AbortPolicy())：拒绝策略（第一种：直接抛出异常）
*/
ThreadPoolExecutor pool = new ThreadPoolExecutor(1,2,10,TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(1),
Executors.defaultThreadFactory(),
//new AbortPolicy());
//new DiscardPolicy());
//new DiscardOldestPolicy());
new CallerRunsPolicy());
pool.execute(r1);
pool.execute(r2);
pool.execute(r3);
pool.execute(r4);
}
}
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