Concurrency: Add multiple stage demo

concurrency/src/main/java/io/mincong/concurrency/completablefuture/MultipleStageDemo.java

@@ -0,0 +1,205 @@
+package io.mincong.concurrency.completablefuture;
+
+import java.time.LocalTime;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Executors;
+import java.util.stream.IntStream;
+
+public class MultipleStageDemo {
+
+  public static void main(String[] args) {
+    var demo = new MultipleStageDemo();
+    demo.scenario1();
+    demo.scenario2();
+  }
+
+  /**
+   * In scenario 1, resource creation and deletion are done in the same completion stage. Given a
+   * fixed thread pool executor with 2 threads, the executor will complete the tasks of two
+   * resources (e.g. 0 and 1) before starting the next stages. Its behavior can be illustrated as
+   * follows:
+   *
+   * <pre>
+   *          +-----------------------------------------------------------------> Time
+   *          | +------------------------+ +------------------------+
+   * Thread 1 | | Creation 0, Deletion 0 | | Creation 2, Deletion 2 |
+   *          | +------------------------+ +------------------------+
+   * Thread 2 | | Creation 1, Deletion 1 | | Creation 3, Deletion 3 |
+   *          | +------------------------+ +------------------------+
+   *          |
+   * </pre>
+   *
+   * This is because these stages are queued in the following way:
+   *
+   * <pre>
+   * 0. +------------------------+
+   *    | Creation 0, Deletion 0 |
+   *    +------------------------+
+   * 1. +------------------------+
+   *    | Creation 1, Deletion 1 |
+   *    +------------------------+
+   * 2. +------------------------+
+   *    | Creation 2, Deletion 2 |
+   *    +------------------------+
+   * 3. +------------------------+
+   *    | Creation 3, Deletion 3 |
+   *    +------------------------+
+   * </pre>
+   *
+   * Console output:
+   *
+   * <pre>
+   * [15:41:18.010681][main] - Scenario 1 started
+   * [15:41:18.103478][pool-1-thread-1] - [id=0] New resource: creating
+   * [15:41:18.103482][pool-1-thread-2] - [id=1] New resource: creating
+   * [15:41:19.107141][pool-1-thread-1] - [id=0] New resource: created
+   * [15:41:19.107472][pool-1-thread-1] - [id=0] Old resource: creating
+   * [15:41:19.108780][pool-1-thread-2] - [id=1] New resource: created
+   * [15:41:19.108929][pool-1-thread-2] - [id=1] Old resource: creating
+   * [15:41:20.112909][pool-1-thread-2] - [id=1] Old resource: created
+   * [15:41:20.112909][pool-1-thread-1] - [id=0] Old resource: created
+   * [15:41:20.113265][pool-1-thread-1] - [id=2] New resource: creating
+   * [15:41:20.113452][pool-1-thread-2] - [id=3] New resource: creating
+   * [15:41:21.114555][pool-1-thread-1] - [id=2] New resource: created
+   * [15:41:21.114555][pool-1-thread-2] - [id=3] New resource: created
+   * [15:41:21.114914][pool-1-thread-1] - [id=2] Old resource: creating
+   * [15:41:21.115019][pool-1-thread-2] - [id=3] Old resource: creating
+   * [15:41:22.119584][pool-1-thread-2] - [id=3] Old resource: created
+   * [15:41:22.119584][pool-1-thread-1] - [id=2] Old resource: created
+   * [15:41:22.120209][main] - Scenario 1 finished
+   * </pre>
+   */
+  private void scenario1() {
+    print("Scenario 1 started");
+    var executor = Executors.newFixedThreadPool(2);
+    var futures =
+        IntStream.range(0, 4)
+            .mapToObj(
+                i ->
+                    CompletableFuture.runAsync(
+                        () -> {
+                          createNewResource(i);
+                          deleteOldResource(i);
+                        },
+                        executor))
+            .toArray(CompletableFuture[]::new);
+    try {
+      CompletableFuture.allOf(futures).join();
+    } finally {
+      executor.shutdownNow();
+    }
+    print("Scenario 1 finished");
+  }
+
+  /**
+   * In scenario 2, resource creation and deletion are done separately in two completion stages.
+   * Given a fixed thread pool executor with 2 threads, the executor will complete the creation of
+   * two resources (e.g. 0 and 1) then continue the creation of two other resources (e.g. 2 and 3).
+   * Once done, it will start the deletions in the same way.
+   *
+   * <pre>
+   *          +-----------------------------------------------------------------> Time
+   *          | +------------+ +------------+ +------------+ +------------+
+   * Thread 1 | | Creation 0 | | Creation 2 | | Deletion 0 | | Deletion 2 |
+   *          | +------------+ +------------+ +------------+ +------------+
+   * Thread 2 | | Creation 1 | | Creation 3 | | Deletion 1 | | Deletion 3 |
+   *          | +------------+ +------------+ +------------+ +------------+
+   *          |
+   * </pre>
+   *
+   * This is because these stages are queued in the following way:
+   *
+   * <pre>
+   * 0. +------------+
+   *    | Creation 0 |
+   *    +------------+
+   * 1. +------------+
+   *    | Creation 1 |
+   *    +------------+
+   * 2. +------------+
+   *    | Creation 2 |
+   *    +------------+
+   * 3. +------------+
+   *    | Creation 3 |
+   *    +------------+
+   * 4. +------------+
+   *    | Deletion 0 |
+   *    +------------+
+   * 5. +------------+
+   *    | Deletion 1 |
+   *    +------------+
+   * 6. +------------+
+   *    | Deletion 2 |
+   *    +------------+
+   * 7. +------------+
+   *    | Deletion 3 |
+   *    +-------------+
+   * </pre>
+   *
+   * Console output:
+   *
+   * <pre>
+   * [15:41:22.120374][main] - Scenario 2 started
+   * [15:41:22.123783][pool-2-thread-1] - [id=0] New resource: creating
+   * [15:41:22.124870][pool-2-thread-2] - [id=1] New resource: creating
+   * [15:41:23.126835][pool-2-thread-1] - [id=0] New resource: created
+   * [15:41:23.126927][pool-2-thread-2] - [id=1] New resource: created
+   * [15:41:23.127811][pool-2-thread-1] - [id=2] New resource: creating
+   * [15:41:23.127868][pool-2-thread-2] - [id=3] New resource: creating
+   * [15:41:24.132029][pool-2-thread-2] - [id=3] New resource: created
+   * [15:41:24.132044][pool-2-thread-1] - [id=2] New resource: created
+   * [15:41:24.132439][pool-2-thread-2] - [id=0] Old resource: creating
+   * [15:41:24.132452][pool-2-thread-1] - [id=1] Old resource: creating
+   * [15:41:25.137506][pool-2-thread-2] - [id=0] Old resource: created
+   * [15:41:25.137506][pool-2-thread-1] - [id=1] Old resource: created
+   * [15:41:25.137804][pool-2-thread-2] - [id=3] Old resource: creating
+   * [15:41:25.138011][pool-2-thread-1] - [id=2] Old resource: creating
+   * [15:41:26.138201][pool-2-thread-2] - [id=3] Old resource: created
+   * [15:41:26.138340][pool-2-thread-1] - [id=2] Old resource: created
+   * [15:41:26.139091][main] - Scenario 2 finished
+   * </pre>
+   */
+  private void scenario2() {
+    print("Scenario 2 started");
+    var executor = Executors.newFixedThreadPool(2);
+    var futures =
+        IntStream.range(0, 4)
+            .mapToObj(
+                i ->
+                    CompletableFuture.runAsync(() -> createNewResource(i), executor)
+                        .thenRunAsync(() -> deleteOldResource(i), executor))
+            .toArray(CompletableFuture[]::new);
+    try {
+      CompletableFuture.allOf(futures).join();
+    } finally {
+      executor.shutdownNow();
+    }
+    print("Scenario 2 finished");
+  }
+
+  private void createNewResource(int i) {
+    print("[id=" + i + "] New resource: creating");
+    try {
+      Thread.sleep(1000);
+    } catch (InterruptedException e) {
+      // ignore
+    }
+    print("[id=" + i + "] New resource: created");
+  }
+
+  private void deleteOldResource(int i) {
+    print("[id=" + i + "] Old resource: creating");
+    try {
+      Thread.sleep(1000);
+    } catch (InterruptedException e) {
+      // ignore
+    }
+    print("[id=" + i + "] Old resource: created");
+  }
+
+  private static void print(String message) {
+    var thread = Thread.currentThread().getName();
+    var time = LocalTime.now();
+    System.out.println("[" + time + "][" + thread + "] - " + message);
+  }
+}