Parallel Collectors with Virtual Threads (#16313)

libraries-stream/src/test/java/com/baeldung/parallel_collectors/ParallelCollectorsVirtualThreadsManualTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.parallel_collectors;
+
+import com.pivovarit.collectors.ParallelCollectors;
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.concurrent.Executors;
+import java.util.function.Supplier;
+import java.util.stream.Stream;
+
+import static java.util.stream.Collectors.toList;
+
+public class ParallelCollectorsVirtualThreadsManualTest {
+
+    private static final Logger log = LoggerFactory.getLogger(ParallelCollectorsVirtualThreadsManualTest.class);
+
+    // increase the number of parallel processes to find the max number of threads on your machine
+    @Test
+    public void givenParallelism_whenUsingOSThreads_thenShouldRunOutOfThreads() {
+        int parallelProcesses = 50_000;
+
+        var e = Executors.newFixedThreadPool(parallelProcesses);
+
+        var result = timed(() -> Stream.iterate(0, i -> i + 1).limit(parallelProcesses)
+          .collect(ParallelCollectors.parallel(i -> fetchById(i), toList(), e, parallelProcesses))
+          .join());
+
+        log.info("{}", result);
+    }
+
+    @Test
+    public void givenParallelism_whenUsingVThreads_thenShouldProcessInParallel() {
+        int parallelProcesses = 1000_000;
+
+        var result = timed(() -> Stream.iterate(0, i -> i + 1).limit(parallelProcesses)
+          .collect(ParallelCollectors.parallel(i -> fetchById(i), toList()))
+          .join());
+
+        log.info("{}", result);
+    }
+
+    @Test
+    public void givenParallelismAndPCollectors2_whenUsingVThreads_thenShouldProcessInParallel() {
+        int parallelProcesses = 1000_000;
+
+        var result = timed(() -> Stream.iterate(0, i -> i + 1).limit(parallelProcesses)
+          .collect(ParallelCollectors.parallel(i -> fetchById(i), toList(), Executors.newVirtualThreadPerTaskExecutor(), Integer.MAX_VALUE))
+          .join());
+
+        log.info("{}", result);
+    }
+
+    private static String fetchById(int id) {
+        try {
+            Thread.sleep(1000);
+        } catch (InterruptedException e) {
+            // ignore shamelessly
+        }
+
+        return "user-" + id;
+    }
+
+    private static <T> T timed(Supplier<T> supplier) {
+        var before = Instant.now();
+        T result = supplier.get();
+        var after = Instant.now();
+        log.info("Execution time: {} ms", Duration.between(before, after).toMillis());
+        return result;
+    }
+}