等待多个异步任务执行完成的回答

朱晔 · 朱晔 · commit f91ce20afcd8 · 2020-04-07T09:33:41.000+08:00
diff --git a/src/main/java/org/geekbang/time/commonmistakes/concurrenttool/multiasynctasks/CommonMistakesApplication.java b/src/main/java/org/geekbang/time/commonmistakes/concurrenttool/multiasynctasks/CommonMistakesApplication.java
@@ -0,0 +1,71 @@
+package org.geekbang.time.commonmistakes.concurrenttool.multiasynctasks;
+
+import lombok.extern.slf4j.Slf4j;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.*;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+@Slf4j
+public class CommonMistakesApplication {
+
+    private static ExecutorService threadPool = Executors.newFixedThreadPool(10);
+
+    public static void main(String[] args) {
+        test1();
+    }
+
+    private static void test1() {
+        long begin = System.currentTimeMillis();
+        List<Future<Integer>> futures = IntStream.rangeClosed(1, 4)
+                .mapToObj(i -> threadPool.submit(getAsyncTask(i)))
+                .collect(Collectors.toList());
+        List<Integer> result = futures.stream().map(future -> {
+            try {
+                return future.get(2, TimeUnit.MILLISECONDS);
+            } catch (Exception e) {
+                e.printStackTrace();
+                return -1;
+            }
+        }).collect(Collectors.toList());
+        log.info("result {} took {} ms", result, System.currentTimeMillis() - begin);
+    }
+
+    private static Callable<Integer> getAsyncTask(int i) {
+        return () -> {
+            TimeUnit.SECONDS.sleep(i);
+            return i;
+        };
+    }
+
+    private static void test2() {
+        long begin = System.currentTimeMillis();
+        int count = 4;
+        List<Integer> result = new ArrayList<>(count);
+        CountDownLatch countDownLatch = new CountDownLatch(count);
+        IntStream.rangeClosed(1, count).forEach(i -> threadPool.execute(executeAsyncTask(i, countDownLatch, result)));
+        try {
+            countDownLatch.await(3, TimeUnit.SECONDS);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        log.info("result {} took {} ms", result, System.currentTimeMillis() - begin);
+    }
+
+    private static Runnable executeAsyncTask(int i, CountDownLatch countDownLatch, List<Integer> result) {
+        return () -> {
+            try {
+                TimeUnit.SECONDS.sleep(i);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+            synchronized (result) {
+                result.add(i);
+            }
+            countDownLatch.countDown();
+        };
+    }
+}
+
