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。
