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DiscardOldestPolicy策略
DiscardOldestPolicy策略是当任务添加到线程池中被拒绝时，线程池会放弃等待队列中最旧的未处理任务，将被拒绝的任务添加到等待队列中。
线程执行代码如下：
public class TheRunnable implements Runnable {
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
private String username;
public TheRunnable(String username){
super();
this.username=username;
}
@Override
public void run() {
try {
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("HH:mm:ss");
System.out.println("线程名："+username+" 开始时间："+simpleDateFormat.format(new Date()));
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
复制代码运行类代码如下：
@Slf4j
public class DiscardOldestPolicyRun {
public static void main(String[] args) {
ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue(2);
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2, 3, 10, TimeUnit.SECONDS, arrayBlockingQueue, new ThreadPoolExecutor.DiscardOldestPolicy());
for (int i = 0; i < 5 ; i++) {
TheRunnable runnable = new TheRunnable("Runnable " + i );
threadPoolExecutor.execute(runnable);
}
try {
Thread.sleep(500);
Iterator iterator = arrayBlockingQueue.iterator();
while (iterator.hasNext()){
Object object = iterator.next();
log.info("线程名:{}",((TheRunnable)object).getUsername());
}
threadPoolExecutor.execute(new TheRunnable("Runnable 6"));
threadPoolExecutor.execute(new TheRunnable("Runnable 7"));
iterator = arrayBlockingQueue.iterator();
while(iterator.hasNext()){
Object object = iterator.next();
log.info("线程名：{}",((TheRunnable)object).getUsername());
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
复制代码运行结果如下：
线程名：Runnable 4 开始时间：16:47:54
线程名：Runnable 1 开始时间：16:47:54
线程名：Runnable 0 开始时间：16:47:54
16:47:55.509 [main] INFO com.ozx.concurrentprogram.executor.controller.DiscardOldestPolicyRun - 线程名:Runnable 2
16:47:55.516 [main] INFO com.ozx.concurrentprogram.executor.controller.DiscardOldestPolicyRun - 线程名:Runnable 3
16:47:55.517 [main] INFO com.ozx.concurrentprogram.executor.controller.DiscardOldestPolicyRun - 线程名：Runnable 6
16:47:55.517 [main] INFO com.ozx.concurrentprogram.executor.controller.DiscardOldestPolicyRun - 线程名：Runnable 7
线程名：Runnable 7 开始时间：16:47:56
线程名：Runnable 6 开始时间：16:47:56
从运行结果看出早期放入队列中两个任务被取消了，执行了后来添加的两个任务。
DiscardPolicy策略
DiscardPolicy策略是当任务添加到线程池中被拒绝时，线程池将丢弃被拒绝的任务。
运行类代码如下：
@Slf4j
public class DiscardPolicyRun {
public static void main(String[] args) throws InterruptedException {
Runnable runnable = new Runnable() {
@Override
public void run() {
try {
Thread.sleep(5000);
log.info(Thread.currentThread().getName()+"执行结束");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue(2);
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2, 3, 10, TimeUnit.SECONDS, arrayBlockingQueue, new ThreadPoolExecutor.DiscardPolicy());
for (int i = 0; i < 8 ; i++) {
threadPoolExecutor.execute(runnable);
}
Thread.sleep(8000);
log.info("线程池中最大线程数：{},队列数：{}",threadPoolExecutor.getPoolSize(),arrayBlockingQueue.size());
}
}
复制代码运行结果如下：
17:40:14.301 [pool-1-thread-1] INFO com.ozx.concurrentprogram.executor.controller.DiscardPolicyRun - pool-1-thread-1执行结束
17:40:14.301 [pool-1-thread-2] INFO com.ozx.concurrentprogram.executor.controller.DiscardPolicyRun - pool-1-thread-2执行结束
17:40:14.301 [pool-1-thread-3] INFO com.ozx.concurrentprogram.executor.controller.DiscardPolicyRun - pool-1-thread-3执行结束
17:40:17.278 [main] INFO com.ozx.concurrentprogram.executor.controller.DiscardPolicyRun - 线程池中最大线程数：3,队列数：0
17:40:19.326 [pool-1-thread-1] INFO com.ozx.concurrentprogram.executor.controller.DiscardPolicyRun - pool-1-thread-1执行结束
17:40:19.326 [pool-1-thread-2] INFO com.ozx.concurrentprogram.executor.controller.DiscardPolicyRun - pool-1-thread-2执行结束
从运行结果看出多余的任务直接被取消执行。