Simplify and fix bugs in StreamUtil (#551)

* Simplify and fix bugs in StreamUtil

* Fix checkstyle

---------

Co-authored-by: Karthik Ramgopal <kramgopa@linkedin.com>

avro-builder/builder-spi/build.gradle

@@ -17,7 +17,9 @@ dependencies {
     implementation "org.apache.logging.log4j:log4j-api:2.17.1"
     implementation "commons-io:commons-io:2.11.0"
     implementation "jakarta.json:jakarta.json-api:2.0.1"
+    implementation "com.pivovarit:parallel-collectors:2.5.0"
 
+    testImplementation project(":test-common")
     testImplementation "org.apache.avro:avro:1.9.2"
 }
 

avro-builder/builder-spi/src/main/java/com/linkedin/avroutil1/builder/util/StreamUtil.java

@@ -6,11 +6,10 @@
 
 package com.linkedin.avroutil1.builder.util;
 
-import java.util.Collection;
-import java.util.concurrent.CompletableFuture;
+import com.pivovarit.collectors.ParallelCollectors;
+import java.util.List;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Semaphore;
 import java.util.concurrent.SynchronousQueue;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
@@ -52,7 +51,7 @@ private StreamUtil() {
    * @return a {@code Collector} which collects all processed elements into a {@code Stream} in parallel.
    */
   public static <T, R> Collector<T, ?, Stream<R>> toParallelStream(Function<T, R> mapper, int parallelism) {
-    return toParallelStream(mapper, parallelism, 1);
+    return ParallelCollectors.parallelToStream(mapper, WORK_EXECUTOR, parallelism);
   }
 
   /**
@@ -72,8 +71,9 @@ private StreamUtil() {
    */
   public static <T, R> Collector<T, ?, Stream<R>> toParallelStream(Function<T, R> mapper, int parallelism,
       int batchSize) {
-    if (parallelism <= 0 || batchSize <= 0) {
-      throw new IllegalArgumentException("Parallelism and batch size must be >= 1");
+    // When batch size is 1, fallback to toParallelStream
+    if (batchSize == 1) {
+      return toParallelStream(mapper, parallelism);
     }
 
     return Collectors.collectingAndThen(Collectors.toList(), list -> {
@@ -85,39 +85,16 @@ private StreamUtil() {
         return list.stream().map(mapper);
       }
 
-      final Executor limitingExecutor = new LimitingExecutor(parallelism);
       final int batchCount = (list.size() - 1) / batchSize;
-      return IntStream.rangeClosed(0, batchCount)
-          .mapToObj(batch -> {
-            int startIndex = batch * batchSize;
-            int endIndex = (batch == batchCount) ? list.size() : (batch + 1) * batchSize;
-            return list.subList(startIndex, endIndex);
-          })
-          .map(batch -> CompletableFuture.supplyAsync(() -> batch.stream().map(mapper).collect(Collectors.toList()),
-              limitingExecutor))
-          .map(CompletableFuture::join)
-          .flatMap(Collection::stream);
-    });
-  }
-
-  private final static class LimitingExecutor implements Executor {
+      final Function<List<T>, List<R>> batchingMapper =
+          batch -> batch.stream().map(mapper).collect(Collectors.toList());
+      List<List<T>> sublists = IntStream.rangeClosed(0, batchCount).mapToObj(batch -> {
+        int startIndex = batch * batchSize;
+        int endIndex = (batch == batchCount) ? list.size() : (batch + 1) * batchSize;
+        return list.subList(startIndex, endIndex);
+      }).collect(Collectors.toList());
 
-    private final Semaphore _limiter;
-
-    private LimitingExecutor(int maxParallelism) {
-      _limiter = new Semaphore(maxParallelism);
-    }
-
-    @Override
-    public void execute(Runnable command) {
-      try {
-        _limiter.acquire();
-        WORK_EXECUTOR.execute(command);
-      } catch (InterruptedException e) {
-        throw new RuntimeException(e);
-      } finally {
-        _limiter.release();
-      }
-    }
+      return sublists.stream().collect(toParallelStream(batchingMapper, parallelism)).flatMap(List::stream);
+    });
   }
 }

avro-builder/builder-spi/src/test/java/com/linkedin/avroutil1/builder/util/StreamUtilTest.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2024 LinkedIn Corp.
+ * Licensed under the BSD 2-Clause License (the "License").
+ * See License in the project root for license information.
+ */
+
+package com.linkedin.avroutil1.builder.util;
+
+import java.util.stream.IntStream;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+
+/**
+ * This is to test {@link StreamUtil}
+ */
+public class StreamUtilTest {
+
+  @Test
+  public void testParallelStreaming() {
+    int result = IntStream.rangeClosed(1, 100)
+        .boxed()
+        .collect(StreamUtil.toParallelStream(x -> x * x, 3, 4))
+        .reduce(0, Integer::sum);
+
+    int expected = IntStream.rangeClosed(1, 100).map(x -> x * x).sum();
+
+    Assert.assertEquals(result, expected);
+  }
+}