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Commit f18ac21

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author
Rajeev Kumar Singh
committed
Callables and Futures Examples
1 parent 4e1324f commit f18ac21

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5 files changed

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import java.util.concurrent.*;
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/**
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* Created by rajeevkumarsingh on 11/05/17.
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*/
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public class FutureAndCallableExample {
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public static void main(String[] args) throws InterruptedException, ExecutionException {
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ExecutorService executorService = Executors.newSingleThreadExecutor();
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Callable<String> callable = () -> {
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// Perform some computation
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Thread.sleep(2000);
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return "Hello from Callable";
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};
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Future<String> future = executorService.submit(callable);
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// This line executes immediately
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System.out.println("Do something else while callable is getting executed");
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System.out.println("Retrieve the result of the future");
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// Future.get() blocks until the result is available
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String result = future.get();
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System.out.println(result);
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executorService.shutdown();
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}
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}
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import java.util.concurrent.*;
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/**
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* Created by rajeevkumarsingh on 10/05/17.
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*/
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public class FutureCancelExample {
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public static void main(String[] args) throws InterruptedException, ExecutionException {
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ExecutorService executorService = Executors.newSingleThreadExecutor();
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Callable<String> callable = () -> {
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// Perform some computation
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Thread.sleep(2000);
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return "Hello from Callable";
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};
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long startTime = System.nanoTime();
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Future<String> future = executorService.submit(callable);
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while(!future.isDone()) {
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System.out.println("Task is still not done...");
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Thread.sleep(200);
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double elapsedTimeInSec = (System.nanoTime() - startTime)/1000000000.0;
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if(elapsedTimeInSec > 1) {
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// cancel future if the elapsed time is more than one second
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future.cancel(true);
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}
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}
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// Check if future is cancelled before retrieving the result
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if(!future.isCancelled()) {
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System.out.println("Task completed! Retrieving the result");
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// Future.get() blocks until the result is available
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String result = future.get();
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System.out.println(result);
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} else {
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System.out.println("Task was cancelled");
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}
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executorService.shutdown();
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}
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}
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import java.util.concurrent.*;
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/**
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* Created by rajeevkumarsingh on 11/05/17.
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*/
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public class FutureIsDoneExample {
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public static void main(String[] args) throws InterruptedException, ExecutionException {
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ExecutorService executorService = Executors.newSingleThreadExecutor();
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Future<String> future = executorService.submit(() -> {
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Thread.sleep(2000);
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return "Hello from Callable";
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});
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while(!future.isDone()) {
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System.out.println("Task is still not done...");
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Thread.sleep(200);
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}
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System.out.println("Task completed! Retrieving the result");
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String result = future.get();
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System.out.println(result);
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executorService.shutdown();
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}
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}
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import java.util.Arrays;
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import java.util.List;
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import java.util.concurrent.*;
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/**
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* Created by rajeevkumarsingh on 10/05/17.
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*/
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public class InvokeAllExample {
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public static void main(String[] args) throws InterruptedException, ExecutionException {
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ExecutorService executorService = Executors.newFixedThreadPool(5);
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Callable<String> task1 = () -> {
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Thread.sleep(2000);
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return "Result of Task1";
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};
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Callable<String> task2 = () -> {
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Thread.sleep(1000);
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return "Result of Task2";
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};
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Callable<String> task3 = () -> {
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Thread.sleep(5000);
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return "Result of Task3";
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};
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List<Callable<String>> taskList = Arrays.asList(task1, task2, task3);
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List<Future<String>> futures = executorService.invokeAll(taskList);
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for(Future<String> future: futures) {
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// The result is printed only after all the futures are complete. (i.e. after 5 seconds)
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System.out.println(future.get());
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}
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}
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}
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import java.util.Arrays;
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import java.util.List;
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import java.util.concurrent.*;
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/**
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* Created by rajeevkumarsingh on 10/05/17.
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*/
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public class InvokeAnyExample {
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public static void main(String[] args) throws InterruptedException, ExecutionException {
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ExecutorService executorService = Executors.newFixedThreadPool(5);
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Callable<String> task1 = () -> {
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Thread.sleep(2000);
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return "Result of Task1";
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};
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Callable<String> task2 = () -> {
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Thread.sleep(1000);
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return "Result of Task2";
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};
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Callable<String> task3 = () -> {
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Thread.sleep(5000);
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return "Result of Task3";
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};
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// Returns the result of the fastest callable. (task2 in this case)
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String result = executorService.invokeAny(Arrays.asList(task1, task2, task3));
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System.out.println(result);
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}
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}

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