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| 1 | +package multithread.completablefutureexamples; |
| 2 | + |
| 3 | +import java.util.ArrayList; |
| 4 | +import java.util.List; |
| 5 | +import java.util.concurrent.CompletableFuture; |
| 6 | +import java.util.concurrent.ExecutionException; |
| 7 | +import java.util.concurrent.ExecutorService; |
| 8 | +import java.util.concurrent.Executors; |
| 9 | +import java.util.concurrent.Future; |
| 10 | + |
| 11 | +import static multithread.completablefutureexamples.CompletableFutureDemo2.WorkerPool.TIME_FOR_A_COMPUTATION_JOB_IN_MS; |
| 12 | + |
| 13 | +public class CompletableFutureDemo2 { |
| 14 | + |
| 15 | + private static final int POOL_SIZE = 10; |
| 16 | + private static final int NUMBER_OF_COMPUTATION_JOBS = 20; |
| 17 | + |
| 18 | + public static void main(String... args) throws ExecutionException, InterruptedException { |
| 19 | + System.out.println("Program started."); |
| 20 | + long start = System.currentTimeMillis(); |
| 21 | + WorkerPool workerPool = new WorkerPool(POOL_SIZE); |
| 22 | + int finalResult = 0; |
| 23 | + List<Future<String>> futureList = new ArrayList<>(); |
| 24 | + for (int i = 1; i <= NUMBER_OF_COMPUTATION_JOBS; i++) { |
| 25 | + Future<String> completableFuture = workerPool.executeAsync(i); |
| 26 | + futureList.add(completableFuture); |
| 27 | + } |
| 28 | + for (Future<String> future : futureList) { |
| 29 | + String result = future.get(); |
| 30 | + finalResult += Integer.parseInt(result); |
| 31 | + } |
| 32 | + long end = System.currentTimeMillis(); |
| 33 | + System.out.println("It took " + (end - start) / 1000 |
| 34 | + + " seconds to complete computation, final result: " + finalResult |
| 35 | + + ", a total of " + NUMBER_OF_COMPUTATION_JOBS + " computation jobs " |
| 36 | + + "have been completed, total pool worker size is: " + POOL_SIZE |
| 37 | + + ", and each job took " + TIME_FOR_A_COMPUTATION_JOB_IN_MS / 1000 + " second(s)." |
| 38 | + ); |
| 39 | + System.out.println("Program ended."); |
| 40 | + } |
| 41 | + |
| 42 | + static class WorkerPool { |
| 43 | + static final long TIME_FOR_A_COMPUTATION_JOB_IN_MS = 1000l; |
| 44 | + int poolSize; |
| 45 | + ExecutorService executorService; |
| 46 | + |
| 47 | + public WorkerPool(int poolSize) { |
| 48 | + this.poolSize = poolSize; |
| 49 | + this.executorService = Executors.newFixedThreadPool(poolSize); |
| 50 | + } |
| 51 | + |
| 52 | + public Future<String> executeAsync(int input) { |
| 53 | + final CompletableFuture completableFuture = new CompletableFuture<>(); |
| 54 | + this.executorService.submit(() -> doWork(completableFuture, input)); |
| 55 | + return completableFuture; |
| 56 | + } |
| 57 | + |
| 58 | + private void doWork(CompletableFuture completableFuture, int input) { |
| 59 | + int result = 0; |
| 60 | + try { |
| 61 | + System.out.println(Thread.currentThread().getName() + " is doing some real work now that'll take 1 second to complete."); |
| 62 | + Thread.sleep(TIME_FOR_A_COMPUTATION_JOB_IN_MS); |
| 63 | + result += input * 2; |
| 64 | + } catch (InterruptedException e) { |
| 65 | + throw new RuntimeException(e); |
| 66 | + } |
| 67 | + completableFuture.complete("" + result); |
| 68 | + } |
| 69 | + } |
| 70 | + |
| 71 | +} |
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