Java多線程系列七——ExecutorService
阿新 • • 發佈：2017-07-08
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java.util.concurrent.ExecutorService接口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，若需要阻塞可借助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，若需要阻塞可借助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，便可以基於此接口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 | 創建新線程的工廠 |
| 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 | 線程池中僅含一個工作線程 |
| newCachedThreadPool | 按需創建線程，若線程池中無可用線程，則創建新的線程並加入，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