8000 add CompletionService demo · fishercoder1534/RandomJava@4d9dbe7 · GitHub
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add CompletionService demo
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‎src/main/java/multithread/CompletionServiceDemo.java

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package multithread;
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import java.util.concurrent.*;
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public class CompletionServiceDemo {
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/**
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* credit: https://stackoverflow.com/a/5580058/4117496
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*/
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class CalcResult {
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long result;
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CalcResult(long l) {
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result = l;
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}
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}
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class CallableTask implements Callable<CalcResult> {
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String taskName;
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long input1;
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int input2;
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CallableTask(String name, long v1, int v2) {
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taskName = name;
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input1 = v1;
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input2 = v2;
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}
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public CalcResult call() {
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System.out.println("Task " + taskName + " started -----");
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for (int i = 0; i < input2; i++) {
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try {
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Thread.sleep(200);
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} catch (InterruptedException e) {
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System.out.println("Task " + taskName + " interrupted !! ");
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e.printStackTrace();
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}
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input1 += i;
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}
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System.out.println("Task " + taskName + " completed.");
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return new CalcResult(input1);
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}
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}
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public void test() {
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ExecutorService executorService = Executors.newFixedThreadPool(3);
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CompletionService<CalcResult> completionService = new ExecutorCompletionService<>(executorService);
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int submittedTasks = 5;
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for (int i = 0; i < submittedTasks; i++) {
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completionService.submit(new CallableTask(
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String.valueOf(i),
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(i * 10),
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((i * 10) + 10)
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));
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System.out.println("Task " + i + " submitted");
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}
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for (int tasksHandled = 0; tasksHandled < submittedTasks; tasksHandled++) {
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try {
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System.out.println("trying to take from Completion service");
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Future<CalcResult> result = completionService.take();
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System.out.println("result for a task available in queue. Trying to get() now");
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// above call blocks till atleast one task is completed and results availble for it
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// but we don't have to worry which one
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// process the result here by doing result.get()
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CalcResult l = result.get();
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System.out.println("Task " + tasksHandled + " completed - results obtained : " + l.result);
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} catch (InterruptedException e) {
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// Something went wrong with a task submitted
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System.out.println("Error Interrupted exception");
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e.printStackTrace();
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} catch (ExecutionException e) {
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// Something went wrong with the result
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e.printStackTrace();
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System.out.println("Error get() threw exception");
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}
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}
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}
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public static void main(String... args) {
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CompletionServiceDemo demo = new CompletionServiceDemo();
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demo.test();
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System.out.println("\n\nProgram finished.\n");
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}
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}

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