Java多線程系列七——ExecutorService

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java.util.concurrent.ExecutorService介面提供了許多線程管理的方法

Method	說明
shutdown	拒絕接收新的任務，待已提交的任務執行後關閉，且宿主線程不阻塞，若需要阻塞可藉助awaitTermination實現
shutdownNow	停止所有正在執行的任務，掛起未執行的任務並關閉，且宿主線程不阻塞，若需要阻塞可藉助awaitTermination實現
awaitTermination	當發生shutdown時，阻塞宿主線程直到約定的時間已過或者所有任務完成
submit	提交任務Callable/Runnable，可利用Future的get()方法使宿主線程阻塞直到任務結束後返回結果

有了以上方法，便可以基於此介面實現線程池的各種功能(例如java.util.concurrent.ThreadPoolExecutor/java.util.concurrent.ScheduledThreadPoolExecutor)，以java.util.concurrent.ThreadPoolExecutor為例，其參數的詳解

Name	Type	說明
corePoolSize	int	線程池中最小的線程數
maximumPoolSize	int	線程池中最大的線程數
keepAliveTime	long	線程空閑時間，若線程數大於corePoolSize，空閑時間超過該值的線程將被終止回收
unit	TimeUnit	keepAliveTime的時間單位
workQueue	BlockingQueue<Runnable>	已提交但未執行的任務隊列
threadFactory	ThreadFactory	建立新線程的工廠
handler	RejectedExecutionHandler	當線程池或隊列達到上限拒絕新任務拋出異常時的處理類

同時，java.util.concurrent.Executors類提供了基於java.util.concurrent.ThreadPoolExecutor類的工具方法，常用方法有

Method	說明
newFixedThreadPool	線程池中含固定數量的線程
newSingleThreadExecutor	線程池中僅含一個背景工作執行緒
newCachedThreadPool	按需建立線程，若線程池中無可用線程，則建立新的線程並加入，直到線程數達到上限值(Integer.MAX_VALUE)

測試代碼如下

import java.util.Date;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;import java.util.concurrent.TimeUnit;import org.junit.Assert;import org.junit.Test;/** * @Description: 測試ExecutorService */public class ThreadExecutorServiceTest {    private static final String THIS_IS_SHUTDOWN_WITH_AWAIT_TERMINATION = "This is shutdownWithAwaitTermination";    private static final int RESULT = 111;    private static boolean submitRunnable() throws InterruptedException, ExecutionException {        ExecutorService executorService = Executors.newSingleThreadExecutor();        Future<?> future = executorService.submit(new Runnable() {            @Override            public void run() {                System.out.println("This is submitRunnable");            }        });        return future.get() == null;    }    private static Integer submitRunnableWithResult() throws InterruptedException, ExecutionException {        ExecutorService executorService = Executors.newSingleThreadExecutor();        Future<Integer> future = executorService.submit(new Runnable() {            @Override            public void run() {                System.out.println("This is submitRunnableWithResult");            }        }, RESULT);        return future.get();    }    private static Integer submitBlockCallable() throws InterruptedException, ExecutionException {        ExecutorService executorService = Executors.newFixedThreadPool(1);        Future<Integer> future = executorService.submit(new Callable<Integer>() {            @Override            public Integer call() throws Exception {                System.out.println("This is submitBlockCallable");                return RESULT;            }        });        return future.get();// 阻塞    }    private static boolean submitNonBlockCallable() throws InterruptedException, ExecutionException {        ExecutorService executorService = Executors.newFixedThreadPool(1);        Future<Integer> future = executorService.submit(new Callable<Integer>() {            @Override            public Integer call() throws Exception {                System.out.println("This is submitNonBlockCallable");                return RESULT;            }        });        while (!future.isDone()) {// 非阻塞            System.out.println(new Date());        }        return future.isDone();    }    private static String shutdown() throws InterruptedException, ExecutionException {        ExecutorService executorService = Executors.newFixedThreadPool(1);        final StringBuilder sb = new StringBuilder();        executorService.submit(new Callable<Integer>() {            @Override            public Integer call() throws Exception {                Thread.sleep(10000);                sb.append("This is shutdown");                return RESULT;            }        });        executorService.shutdown();        return sb.toString();    }    private static String shutdownWithAwaitTermination() throws InterruptedException, ExecutionException {        ExecutorService executorService = Executors.newFixedThreadPool(1);        final StringBuilder sb = new StringBuilder();        executorService.submit(new Callable<Integer>() {            @Override            public Integer call() throws Exception {                Thread.sleep(10000);                sb.append(THIS_IS_SHUTDOWN_WITH_AWAIT_TERMINATION);                return RESULT;            }        });        executorService.shutdown();        executorService.awaitTermination(Integer.MAX_VALUE, TimeUnit.DAYS);        return sb.toString();    }    @Test    public void test() throws InterruptedException, ExecutionException {        Assert.assertTrue(submitRunnable());        Assert.assertEquals(RESULT, submitRunnableWithResult().intValue());        Assert.assertEquals(RESULT, submitBlockCallable().intValue());        Assert.assertTrue(submitNonBlockCallable());        Assert.assertTrue(shutdown().isEmpty());        Assert.assertEquals(THIS_IS_SHUTDOWN_WITH_AWAIT_TERMINATION, shutdownWithAwaitTermination());    }}

 

Java多線程系列七——ExecutorService