[Java] Thread Pool Example

1. Thread Pool

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import java.time.LocalDateTime; import java.util.List; import java.util.concurrent.Callable; import java.util.concurrent.CompletionService; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorCompletionService; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; import java.util.concurrent.TimeUnit; public class ThreadPool<T> { ExecutorService executorService; CompletionService<T> completionService; public void createFixedThreadPool(int nThreads) { createService(nThreads); } public void createFixedThreadPool() { createService(Runtime.getRuntime().availableProcessors()); } private void createService(int nThreads) { executorService = Executors.newFixedThreadPool(nThreads); completionService = new ExecutorCompletionService<T>(executorService); } public void shutdown() { executorService.shutdown(); } public List<Runnable> shutdownNow() { return executorService.shutdownNow(); } public Boolean awaitTermination( long timeout, TimeUnit unit ) throws InterruptedException { return executorService.awaitTermination(timeout, unit); } public void execute(Runnable task) { executorService.execute(task); } public Future<Result> submit(Runnable task, Result result) { return executorService.submit(task, result); } public Future<T> submit(Callable<T> task) { return executorService.submit(task); } public Future<T> submitCompletion(Callable<T> task) { return completionService.submit(task); } //---------------------------------------------------------------------- // Test Code - Start //---------------------------------------------------------------------- public static Runnable newRunnable(int id) { Runnable task = new Runnable() { @Override public void run() { String threadName = Thread.currentThread().getName(); for( int i=0; i < 10; i++ ) { try { Thread.sleep(1000); System.out.println( "[" + threadName + "] Runnable_" + id + ": " + i); } catch (InterruptedException e) { e.printStackTrace(); } } } }; return task; } public static Callable<Integer> newCallable(int id) { Callable<Integer> task = new Callable<Integer>() { @Override public Integer call() throws Exception { String threadName = Thread.currentThread().getName(); for( int i=0; i < 10; i++ ) { try { Thread.sleep(1000); System.out.println( "[" + threadName + "] Callable_" + id + ": " + i); } catch (InterruptedException e) { e.printStackTrace(); } } return id*100; } }; return task; } public static void sleep(int sec) { try { Thread.sleep(sec*1000); } catch (InterruptedException e) { e.printStackTrace(); } } public static void println(String s) { System.out.println( "[" + LocalDateTime.now() + "] " + s); } public static void runnableTest() { println("runnableTest() start !"); ThreadPool<Integer> threads = new ThreadPool<Integer>(); threads.createFixedThreadPool(); for( int i=0; i < 10; i++ ) { threads.execute(newRunnable(i)); } println("runnableTest() shutdown !"); threads.shutdown(); println("runnableTest() end !"); } @SuppressWarnings("unchecked") public static void callableTest() { println("callableTest() start !"); ThreadPool<Integer> threads = new ThreadPool<Integer>(); threads.createFixedThreadPool(); Future<Integer>[] future = new Future[10]; for( int i=0; i < 10; i++ ) { future[i] = threads.submit(newCallable(i)); } println("callableTest() shutdown !"); threads.shutdown(); Integer[] result = new Integer[10]; for( int i=0; i < 10; i++ ) { try { result[i] = (Integer)future[i].get(); println("callableTest() result[" + i + "] = " + result[i]); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } println("callableTest() end !"); } public static void callableWithCompletionServiceTest() { println("callableWithCompletionServiceTest() start !"); ThreadPool<Integer> threads = new ThreadPool<Integer>(); threads.createFixedThreadPool(); for( int i=0; i < 10; i++ ) { threads.submitCompletion(newCallable(i)); } println("callableWithCompletionServiceTest() shutdown !"); threads.shutdown(); for( int i=0; i < 10; i++ ) { try { Future<Integer> future = threads.completionService.take(); Integer result = (Integer)future.get(); println("callableWithCompletionServiceTest() result[" + i + "] = " + result); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } println("callableWithCompletionServiceTest() end !"); } public static void main(String[] args) { runnableTest(); callableTest(); callableWithCompletionServiceTest(); } }