一、概述
在java doc中,并不提倡我们直接使用ThreadPoolExecutor,而是使用Executors类中提供的几个静态方法来创建线程池:
以下方法是Executors下的静态方法,Executors中所定义的 Executor、ExecutorService、ScheduledExecutorService、ThreadFactory 和 Callable 类的工厂和实用方法。
Executors只是一个工厂类,它所有的方法返回的都是ThreadPoolExecutor
、ScheduledThreadPoolExecutor
这两个类的实例。一共可以创建四种线程池。
1.1、基础类
import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.TimeUnit; public class TestThread implements Runnable { // 线程私有属性,创建线程时创建 private Integer num = 0; public TestThread(Integer num) { this.num = num; } @Override public void run() { SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"); System.out.println("thread:" + Thread.currentThread().getName() + ",time:" + sdf1.format(new Date()) + ",num:" + num); try { //使线程睡眠,模拟线程阻塞情况 TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("task "+num+"执行完毕"); } }
0、使用ThreadPoolExecutor 创建使用【不推荐】
public static void testThreadPoolExecutor() { ThreadPoolExecutor executor = new ThreadPoolExecutor(5, 10, 200, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<Runnable>(5)); for (int i = 0; i < 15; i++) { TestThread myTask = new TestThread(i); executor.execute(myTask); System.out.println("线程池中线程数目:" + executor.getPoolSize() + ",队列中等待执行的任务数目:" + executor.getQueue().size() + ",已执行玩别的任务数目:" + executor.getCompletedTaskCount()); } executor.shutdown(); }
输出:
/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/bin/java "-javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=54880:/Applications/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/tools.jar:/Users/lihongxu6/IdeaProjects/java-data-structure-algorithm/data-005-jdkstruct/target/classes:/Users/lihongxu6/.m2/repository/junit/junit/4.11/junit-4.11.jar com.github.bjlhx15.datastructure.algorithm.thread.ThreadPoolDemo2 线程池中线程数目:1,队列中等待执行的任务数目:0,已执行完的任务数目:0 线程池中线程数目:2,队列中等待执行的任务数目:0,已执行完的任务数目:0 线程池中线程数目:3,队列中等待执行的任务数目:0,已执行完的任务数目:0 线程池中线程数目:4,队列中等待执行的任务数目:0,已执行完的任务数目:0 线程池中线程数目:5,队列中等待执行的任务数目:0,已执行完的任务数目:0 线程池中线程数目:5,队列中等待执行的任务数目:1,已执行完的任务数目:0 线程池中线程数目:5,队列中等待执行的任务数目:2,已执行完的任务数目:0 线程池中线程数目:5,队列中等待执行的任务数目:3,已执行完的任务数目:0 线程池中线程数目:5,队列中等待执行的任务数目:4,已执行完的任务数目:0 线程池中线程数目:5,队列中等待执行的任务数目:5,已执行完的任务数目:0 线程池中线程数目:6,队列中等待执行的任务数目:5,已执行完的任务数目:0 线程池中线程数目:7,队列中等待执行的任务数目:5,已执行完的任务数目:0 线程池中线程数目:8,队列中等待执行的任务数目:5,已执行完的任务数目:0 线程池中线程数目:9,队列中等待执行的任务数目:5,已执行完的任务数目:0 线程池中线程数目:10,队列中等待执行的任务数目:5,已执行完的任务数目:0 thread:pool-1-thread-6,time:2019-06-19 06:10:53,num:10 thread:pool-1-thread-2,time:2019-06-19 06:10:53,num:1 thread:pool-1-thread-7,time:2019-06-19 06:10:53,num:11 thread:pool-1-thread-5,time:2019-06-19 06:10:53,num:4 thread:pool-1-thread-9,time:2019-06-19 06:10:53,num:13 thread:pool-1-thread-8,time:2019-06-19 06:10:53,num:12 thread:pool-1-thread-4,time:2019-06-19 06:10:53,num:3 thread:pool-1-thread-10,time:2019-06-19 06:10:53,num:14 thread:pool-1-thread-1,time:2019-06-19 06:10:53,num:0 thread:pool-1-thread-3,time:2019-06-19 06:10:53,num:2 task 11执行完毕 task 14执行完毕 task 12执行完毕 task 0执行完毕 task 2执行完毕 task 3执行完毕 task 13执行完毕 task 1执行完毕 task 10执行完毕 task 4执行完毕 thread:pool-1-thread-3,time:2019-06-19 06:10:56,num:9 thread:pool-1-thread-1,time:2019-06-19 06:10:56,num:8 thread:pool-1-thread-10,time:2019-06-19 06:10:56,num:7 thread:pool-1-thread-8,time:2019-06-19 06:10:56,num:6 thread:pool-1-thread-7,time:2019-06-19 06:10:56,num:5 task 8执行完毕 task 5执行完毕 task 7执行完毕 task 9执行完毕 task 6执行完毕 Process finished with exit code 0
1、newFixedThreadPool //创建固定容量大小的缓冲池
public static ExecutorService newFixedThreadPool(int nThreads) { return new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>()); }
newFixedThreadPool返回一个包含指定数目【固定大小】线程的线程池ThreadPool,如果任务数量多于线程数目,那么没有没有执行的任务必须等待,直到有任务完成为止。
newFixedThreadPool创建的线程池corePoolSize和maximumPoolSize值是相等的,它使用的LinkedBlockingQueue;
示例:
public static void main(String[] args) { ExecutorService fixedThreadPool = Executors.newFixedThreadPool(5); for (int i = 0; i < 50; i++) { fixedThreadPool.submit(new TestThread((i + 1))); } fixedThreadPool.shutdown(); }
2、newCachedThreadPool //创建一个缓冲池,缓冲池容量大小为Integer.MAX_VALUE,空闲60s销毁
public static ExecutorService newCachedThreadPool() { return new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>()); }
newCachedThreadPool比较适合没有固定大小并且比较快速就能完成的小任务,没必要维持一个Pool,这比直接new Thread来处理的好处是能在60秒内重用已创建的线程。
其他类型的ThreadPool看看构建参数再结合上面所说的特性就大致知道它的特性。该线程池不会对线程数目加以限制,完全依赖于JVM能创建线程的数量,可能引起内存不足。
newCachedThreadPool将corePoolSize设置为0,将maximumPoolSize设置为Integer.MAX_VALUE,使用的SynchronousQueue,也就是说来了任务就创建线程运行,当线程空闲超过60秒,就销毁线程。
public static void main(String[] args) { ExecutorService cachedThreadPool = Executors.newCachedThreadPool(); for (int i = 0; i < 50; i++) { cachedThreadPool.submit(new TestThread((i + 1))); } cachedThreadPool.shutdown(); }
3、newSingleThreadExecutor //创建容量为1的缓冲池
public static ExecutorService newSingleThreadExecutor() { return new FinalizableDelegatedExecutorService (new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>())); }
newSingleThreadExecutor返回以个包含单线程的Executor,将多个任务交给此Exector时,这个线程处理完一个任务后接着处理下一个任务,若该线程出现异常,将会有一个新的线程来替代。它只会用唯一的工作线程来执行任务,保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。
newSingleThreadExecutor将corePoolSize和maximumPoolSize都设置为1,也使用的LinkedBlockingQueue;
从它们的具体实现来看,它们实际上也是调用了ThreadPoolExecutor,只不过参数都已配置好了。
实际中,如果Executors提供的三个静态方法能满足要求,就尽量使用它提供的三个方法,因为自己去手动配置ThreadPoolExecutor的参数有点麻烦,要根据实际任务的类型和数量来进行配置。
另外,如果ThreadPoolExecutor达不到要求,可以自己继承ThreadPoolExecutor类进行重写。
public static void main(String[] args) { ExecutorService singleThreadPool = Executors.newSingleThreadExecutor(); for (int i = 0; i < 50; i++) { singleThreadPool.submit(new TestThread((i + 1))); } singleThreadPool.shutdown(); }
4、newScheduledThreadPool
可调度线程池
public static void main(String[] args) { ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5); //定时 // scheduledThreadPool.schedule(new Runnable() { // @Override // public void run() { // SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"); // System.out.println("thread:" + Thread.currentThread().getName() + ",time:" + sdf1.format(new Date())); // } // }, 3, TimeUnit.SECONDS); //循环周期执行 scheduledThreadPool.scheduleAtFixedRate(new Runnable() { @Override public void run() { System.out.println("delay 1 seconds, and excute every 3 seconds"); } }, 1, 3, TimeUnit.SECONDS); }
原文地址:https://www.cnblogs.com/bjlhx/p/11053077.html