• 线程池中的饱和策略

    ThreadPoolExecutor允许提供一个BlockingQueue来保存等待执行的任务。

    查看结构图

     

       我们需要关注的方法是offer(E),put(E),take()

    newFixedThreadPool和newSingleThreadExecutor在默认情况下将使用一个无界的队列(LinkedBlockingQueue),如果所有线程都在执行任务，那么任务将在队列中等待，如果任务到达的速度大于线程执行的速度，造成的后果将是队列无限期增加。

    更稳妥的管理策略是使用有界队列，如：ArrayBlockingQueue,有界的LinkedBlockingQueue,PriorityBlockingQueue.有界队列避免了资源耗尽的情况，但出现一个问题，队列填满后，新的任务该怎么办？使用拒绝策略。

       JDK提供了几种不同的RejectedExecutionHandler实现，每种都是不同的饱和策略：AbortPolicy,CallerRunsPolicy,DiscardPolicy和DiscardOldestPolicy.

    AbortPolicy 当任务添加到线程池中被拒绝时，它将抛出 RejectedExecutionException 异常。
    如下代码：
     1 package cn.concurrent.executor;
 2 
 3 import java.util.concurrent.*;
 4 
 5 /**
 6  * Created by spark on 17-9-24.
 7  */
 8 public class AbortPolicyDemo {
 9 
10     public static void main(String[] args) {
11         //初始化一个初始化容量大小为1，阻塞队列容量为1，maxmumPoolSize大小为1的线程池
12         ThreadPoolExecutor pool = new ThreadPoolExecutor(1, 1,
13                 0, TimeUnit.SECONDS, new LinkedBlockingQueue<>(1));
14         //设置饱和策略为AbortPolicy---拒绝策略/**/,用户可以捕获这个异常
15         pool.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
16         //创建线程执行
17         for (int i = 0; i < 5; i++) {
18             MyRunnable myRunnable = new MyRunnable();
19             pool.execute(myRunnable);
20         }
21         pool.shutdown();
22     }
23 
24 
25     static class MyRunnable implements Runnable {
26         @Override
27         public void run() {
28             System.err.println(Thread.currentThread().getId() + ":正在执行");
29             try {
30                 Thread.sleep(300);
31             } catch (InterruptedException e) {
32                 e.printStackTrace();
33             }
34         }
35     }
36 }
    

    结果如下：
    

    

    Exception in thread "main" java.util.concurrent.RejectedExecutionException: Task cn.concurrent.executor.AbortPolicyDemo$MyRunnable@1d44bcfa rejected from java.util.concurrent.ThreadPoolExecutor@266474c2[Running, pool size = 1, active threads = 1, queued tasks = 1, completed tasks = 0]
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2066)
    at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
    at cn.concurrent.executor.AbortPolicyDemo.main(AbortPolicyDemo.java:19)
10:正在执行
10:正在执行
    

    

    抛出了RejectedExecutionException，由于饱和策略引起的。
    

    如果修改代码如下：
    

    

     1 package cn.concurrent.executor;
 2 
 3 import java.util.concurrent.*;
 4 
 5 /**
 6  * Created by spark on 17-9-24.
 7  */
 8 public class AbortPolicyDemo {
 9 
10     public static void main(String[] args) {
11         //初始化一个初始化容量大小为1，阻塞队列容量为1，maxmumPoolSize大小为1的线程池
12         ThreadPoolExecutor pool = new ThreadPoolExecutor(1, 1,
13                 0, TimeUnit.SECONDS, new LinkedBlockingQueue<>(1));
14         //设置饱和策略为AbortPolicy---拒绝策略/**/,用户可以捕获这个异常
15         pool.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
16         //创建线程执行
17         for (int i = 0; i < 5; i++) {
18             try {
19                 Thread.sleep(500);
20             } catch (InterruptedException e) {
21                 e.printStackTrace();
22             }
23             MyRunnable myRunnable = new MyRunnable();
24             pool.execute(myRunnable);
25         }
26         pool.shutdown();
27     }
28 
29 
30     static class MyRunnable implements Runnable {
31         @Override
32         public void run() {
33             System.err.println(Thread.currentThread().getId() + ":正在执行");
34             try {
35                 Thread.sleep(300);
36             } catch (InterruptedException e) {
37                 e.printStackTrace();
38             }
39         }
40     }
41 }
    

    

    

    执行结果为：
    

    

    1 /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=43205:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.AbortPolicyDemo
2 10:正在执行
3 10:正在执行
4 10:正在执行
5 10:正在执行
6 10:正在执行
7 
8 Process finished with exit code 0
    

    

    原因是：正好每一个线程都有足够的时间执行，因此有界阻塞队列不会填满，程序能够正常运行。
    

    

    DiscardOldestPolicy  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(抛弃下一个将被执行的任务)，然后将被拒绝的任务添加到等待队列中，如果队列是一个优先队列，那么抛弃
    最旧的策略就会抛弃优先级最高的任务，因此不要将两者在一起使用。
    如下代码：
    

    

     1 package cn.concurrent.executor;
 2 
 3 import java.util.concurrent.ArrayBlockingQueue;
 4 import java.util.concurrent.ThreadPoolExecutor;
 5 import java.util.concurrent.TimeUnit;
 6 
 7 /**
 8  * Created by spark on 17-9-24.
 9  */
10 public class DiscardOledesrPolicy {
11 
12     public static void main(String[] args) {
13 
14         ThreadPoolExecutor pool = new ThreadPoolExecutor(1, 1, 0, TimeUnit.SECONDS,
15                 new ArrayBlockingQueue<Runnable>(1));
16         //设置饱和策略为DiscardOledestPolicy
17         pool.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardOldestPolicy());
18 
19 
20         for (int i = 0; i < 6; i++) {
21             MyRunnable myRunnable = new MyRunnable("this is " + i + " task");
22             pool.submit(myRunnable);
23         }
24         pool.shutdown();
25     }
26 
27     static class MyRunnable implements Runnable {
28 
29         private String name;
30 
31         public MyRunnable(String name) {
32             this.name = name;
33         }
34 
35         @Override
36         public void run() {
37             System.err.println(this.name + ": is running.");
38             try {
39                 Thread.sleep(300);
40             } catch (InterruptedException e) {
41                 e.printStackTrace();
42             }
43         }
44     }
45 }
    

    

    

    结果如下：
    

    

    /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=33258:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.DiscardOledesrPolicy
this is 0 task: is running.
this is 5 task: is running.

Process finished with exit code 0
    

    

    从结果中可以看到，1,2,3,4都被丢弃了。
    

    

    DiscardPolicy       该策略默默地丢弃无法处理的任务，不予任何处理。
    

    代码如下：
    

    

     1 package cn.concurrent.executor;
 2 
 3 import java.util.concurrent.ArrayBlockingQueue;
 4 import java.util.concurrent.PriorityBlockingQueue;
 5 import java.util.concurrent.ThreadPoolExecutor;
 6 import java.util.concurrent.TimeUnit;
 7 
 8 /**
 9  * Created by spark on 17-9-24.
10  */
11 public class DiscardPolicy {
12 
13     public static void main(String[] args) {
14         ThreadPoolExecutor pool=new ThreadPoolExecutor(1,1,0, TimeUnit.SECONDS,
15                 new ArrayBlockingQueue<Runnable>(1));
16         //添加饱和策略为丢弃策略
17         pool.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());
18         for (int i = 0; i < 6; i++) {
19             MyRunnable myRunnable = new MyRunnable("this is " + i + " task");
20             pool.submit(myRunnable);
21         }
22         pool.shutdown();
23     }
24     static class MyRunnable implements Runnable {
25 
26         private String name;
27 
28         public MyRunnable(String name) {
29             this.name = name;
30         }
31 
32         @Override
33         public void run() {
34             System.err.println(this.name + ": is running.");
35             try {
36                 Thread.sleep(300);
37             } catch (InterruptedException e) {
38                 e.printStackTrace();
39             }
40         }
41     }
42 }
    

    

    

     结果如下：
    

    

    1 /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=41981:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.DiscardPolicy
2 this is 0 task: is running.
3 this is 1 task: is running.
4 
5 Process finished with exit code 0
    

    

     从结果可以看出，2,3,4,5任务都被丢弃了。
    

    线程池pool的"最大池大小"和"核心池大小"都为1(THREADS_SIZE)，这意味着"线程池能同时运行的任务数量最大只能是1"。
    线程池pool的阻塞队列是ArrayBlockingQueue，ArrayBlockingQueue是一个有界的阻塞队列，ArrayBlockingQueue的容量为1。这也意味着线程池的阻塞队列只能有一个线程池阻塞等待。根据""中分析的execute()代码可知：线程池中共运行了2个任务。第1个任务直接放到Worker中，通过线程去执行；第2个任务放到阻塞队列中等待。其他的任务都被丢弃了！
    

    修改线程池中的队列为PriorityBlockingQueue看看结果
    

    

    

     1 package cn.concurrent.executor;
 2 
 3 import java.util.concurrent.ArrayBlockingQueue;
 4 import java.util.concurrent.PriorityBlockingQueue;
 5 import java.util.concurrent.ThreadPoolExecutor;
 6 import java.util.concurrent.TimeUnit;
 7 
 8 /**
 9  * Created by spark on 17-9-24.
10  * 13  */
14 public class DiscardPolicy2 {
15 
16     public static void main(String[] args) {
17         ThreadPoolExecutor pool=new ThreadPoolExecutor(1,1,0, TimeUnit.SECONDS,
18                 new PriorityBlockingQueue<>(1));
19         //添加饱和策略为丢弃策略
20         pool.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());
21         for (int i = 0; i < 6; i++) {
22             MyRunnable myRunnable = new MyRunnable("this is " + i + " task");
23             pool.submit(myRunnable);
24         }
25         pool.shutdown();
26     }
27     static class MyRunnable implements Runnable {
28 
29         private String name;
30 
31         public MyRunnable(String name) {
32             this.name = name;
33         }
34 
35         @Override
36         public void run() {
37             System.err.println(this.name + ": is running.");
38             try {
39                 Thread.sleep(300);
40             } catch (InterruptedException e) {
41                 e.printStackTrace();
42             }
43         }
44     }
45 }
    

    


    结果如下：
    

    

    /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=42797:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.DiscardPolicy2
Exception in thread "main" java.lang.ClassCastException: java.util.concurrent.FutureTask cannot be cast to java.lang.Comparable
    at java.util.concurrent.PriorityBlockingQueue.siftUpComparable(PriorityBlockingQueue.java:357)
    at java.util.concurrent.PriorityBlockingQueue.offer(PriorityBlockingQueue.java:489)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1371)
    at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:112)
    at cn.concurrent.executor.DiscardPolicy2.main(DiscardPolicy2.java:23)
this is 0 task: is running.
    

    

    

    报错的原因是因为我们的任务没有优先级，因此应该实现Comparaable接口再看看
    

    

     1 package cn.concurrent.executor;
 2 
 3 import java.util.concurrent.ArrayBlockingQueue;
 4 import java.util.concurrent.PriorityBlockingQueue;
 5 import java.util.concurrent.ThreadPoolExecutor;
 6 import java.util.concurrent.TimeUnit;
 7 
 8 /**
 9  * Created by spark on 17-9-24.
10  * 线程池pool的"最大池大小"和"核心池大小"都为1(THREADS_SIZE)，这意味着"线程池能同时运行的任务数量最大只能是1"。
11  * 线程池pool的阻塞队列是ArrayBlockingQueue，ArrayBlockingQueue是一个有界的阻塞队列，ArrayBlockingQueue的容量为1。这也意味着线程池的阻塞队列只能有一个线程池阻塞等待。
12  * 根据""中分析的execute()代码可知：线程池中共运行了2个任务。第1个任务直接放到Worker中，通过线程去执行；第2个任务放到阻塞队列中等待。其他的任务都被丢弃了！
13  */
14 public class DiscardPolicy2 {
15 
16     public static void main(String[] args) {
17         ThreadPoolExecutor pool = new ThreadPoolExecutor(1, 1, 0, TimeUnit.SECONDS,
18                 new PriorityBlockingQueue<>(1));
19         //添加饱和策略为丢弃策略
20         pool.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());
21         for (int i = 0; i < 6; i++) {
22             MyRunnable myRunnable = new MyRunnable("this is " + i + " task", i);
23             pool.execute(myRunnable);
24         }
25         pool.shutdown();
26     }
27 
28     static class MyRunnable implements Runnable, Comparable {
29 
30         private String name;
31         private int num;
32 
33         public MyRunnable(String name, int num) {
34             this.name = name;
35             this.num = num;
36         }
37 
38         public MyRunnable(String name) {
39             this.name = name;
40         }
41 
42         @Override
43         public void run() {
44             System.err.println(this.name + ": is running.");
45             try {
46                 Thread.sleep(300);
47             } catch (InterruptedException e) {
48                 e.printStackTrace();
49             }
50         }
51 
52         @Override
53         public int compareTo(Object o) {
54             return 0;
55         }
56     }
57 }
    

    

    结果：
    

    

    /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:41534,suspend=y,server=n -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar:/usr/local/idea/lib/idea_rt.jar cn.concurrent.executor.DiscardPolicy2
Connected to the target VM, address: '127.0.0.1:41534', transport: 'socket'
this is 0 task: is running.
this is 1 task: is running.
this is 5 task: is running.
this is 4 task: is running.
this is 3 task: is running.
this is 2 task: is running.
Disconnected from the target VM, address: '127.0.0.1:41534', transport: 'socket'

Process finished with exit code 0
    

    

     这里使用execute没有使用submit是因为submit返回的结果为FutureTask，这个类没有实现Comparable
    

    

    CallerRunsPolicy       该策略只要线程池未关闭，该策略直接在调用者线程中，运行当前被丢弃的任务（白话就是不会抛弃线程，也不抛出异常，而是将任务回退到调用者，
                           从而降低新任务的流量），这样会影响QPS。
    

    代码如下：
    

    

     1 package cn.concurrent.executor;
 2 
 3 import java.util.concurrent.ArrayBlockingQueue;
 4 import java.util.concurrent.ThreadPoolExecutor;
 5 import java.util.concurrent.TimeUnit;
 6 
 7 /**
 8  * Created by spark on 17-9-24.
 9  */
10 public class CallerRunsPolicyDemo {
11     public static void main(String[] args) {
12         ThreadPoolExecutor pool=new ThreadPoolExecutor(1,1,0, TimeUnit.SECONDS,
13                 new ArrayBlockingQueue<Runnable>(1));
14         //添加饱和策略为丢弃策略
15         pool.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
16         for (int i = 0; i < 6; i++) {
17             MyRunnable myRunnable = new MyRunnable("this is " + i + " task");
18             pool.submit(myRunnable);
19         }
20         pool.shutdown();
21     }
22     static class MyRunnable implements Runnable {
23 
24         private String name;
25 
26         public MyRunnable(String name) {
27             this.name = name;
28         }
29 
30         @Override
31         public void run() {
32             System.err.println(this.name + ": is running.");
33             try {
34                 Thread.sleep(300);
35             } catch (InterruptedException e) {
36                 e.printStackTrace();
37             }
38         }
39     }
40 }
    

    

    

    结果如下：
    

    

    /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=40487:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.CallerRunsPolicyDemo
this is 2 task: is running.
this is 0 task: is running.
this is 3 task: is running.
this is 1 task: is running.
this is 5 task: is running.
this is 4 task: is running.

Process finished with exit code 0
    

    


    我们还可以自定义饱和策略：如下：
    

    

     1 package cn.concurrent;
 2 
 3 import java.util.concurrent.*;
 4 
 5 /**
 6  * Created by spark on 17-9-3.
 7  * 主要演示线程池的拒绝策略实现的接口RejectedExecutionHandler
 8  */
 9 public class RejectThreadPoolDemo {
10 
11     public static class MyTask implements Runnable {
12         @Override
13         public void run() {
14             System.out.println(System.currentTimeMillis() + ":Thread ID:" + Thread.currentThread().getId());
15             try {
16                 Thread.sleep(100);
17             } catch (InterruptedException e) {
18                 e.printStackTrace();
19             }
20         }
21     }
22 
23     //实现RejectExecutionHandler
24     public static void main(String[] args) throws InterruptedException {
25         MyTask myTask = new MyTask();
26         //创建一个线程池
27         ExecutorService es = new ThreadPoolExecutor(5, 5, 0L, TimeUnit.MILLISECONDS,
28                 new LinkedBlockingDeque<Runnable>(10),
29                 Executors.defaultThreadFactory(),
30                 new RejectedExecutionHandler() {
31                     //自定义拒绝策略的处理
32                     @Override
33                     public void rejectedExecution(Runnable runnable, ThreadPoolExecutor threadPoolExecutor) {
34                         System.out.println(runnable.toString() + " is discard");
35                     }
36                 });
37         for(int i=0;i<Integer.MAX_VALUE;i++){
38             es.submit(myTask);
39             Thread.sleep(10);
40         }
41     }
42 }
    

    

    

    结果如下：
    

      
    

    

    /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=35478:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.RejectThreadPoolDemo
1506244149620:Thread ID:10
1506244149630:Thread ID:11
1506244149640:Thread ID:12
1506244149651:Thread ID:13
1506244149661:Thread ID:14
1506244149720:Thread ID:10
1506244149730:Thread ID:11
1506244149740:Thread ID:12
1506244149751:Thread ID:13
1506244149761:Thread ID:14
1506244149821:Thread ID:10
1506244149830:Thread ID:11
1506244149841:Thread ID:12
1506244149851:Thread ID:13
1506244149862:Thread ID:14
java.util.concurrent.FutureTask@63947c6b is discard
java.util.concurrent.FutureTask@2b193f2d is discard
java.util.concurrent.FutureTask@355da254 is discard
java.util.concurrent.FutureTask@4dc63996 is discard
java.util.concurrent.FutureTask@d716361 is discard
1506244149921:Thread ID:10
1506244149930:Thread ID:11
1506244149941:Thread ID:12
1506244149951:Thread ID:13
1506244149962:Thread ID:14
java.util.concurrent.FutureTask@6ff3c5b5 is discard
java.util.concurrent.FutureTask@3764951d is discard
java.util.concurrent.FutureTask@4b1210ee is discard
java.util.concurrent.FutureTask@4d7e1886 is discard
java.util.concurrent.FutureTask@3cd1a2f1 is discard
1506244150023:Thread ID:10
1506244150031:Thread ID:11
    

    

     可以看到，饱和策略生效了，在实际应用中，我们可以记录日志，分析系统的负载和任务丢失的情况。
    

    记录点点滴滴，有很多要学习，望大家指点。
    

     
    


    
    
          
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            原文地址：https://www.cnblogs.com/lwy19998273333/p/7587686.html
          
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