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Add multiple stage demo (#162)
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‎concurrency/src/main/java/io/mincong/concurrency/completablefuture/MultipleStageDemo.java‎

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

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