Posts Tagged ‘threads’
Java CompletionService example
Friday, December 4th, 2020
Main.java
package com.lstierneyltd;
public class Main {
public static void main(String[] args) throws Exception {
final CompletionServiceExample completionServiceExample = new CompletionServiceExample();
completionServiceExample.runDemo();
}
}
CompletionServiceExample.java
package com.lstierneyltd;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
public class CompletionServiceExample {
private static final int NUMBER_OF_THREADS = 3;
private final List<Callable<String>> callables = new ArrayList<>();
private final ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor) Executors.newFixedThreadPool(NUMBER_OF_THREADS);
public CompletionServiceExample() {
initCallables();
}
public void runDemo() throws Exception {
final long startTime = System.currentTimeMillis();
processCallableTasks();
System.out.println("That took " + (System.currentTimeMillis() - startTime)/1000 + " seconds");
shutdownThreadPoolExecutor();
}
private Callable<String> getCallable(int id) {
final Callable<String> callable = () -> {
System.out.println("Starting Callable " + id);
final long taskStartTime = System.currentTimeMillis();
TimeUnit.MILLISECONDS.sleep(10000);
System.out.println("CallableTask " + id + " took " + (System.currentTimeMillis() - taskStartTime)/1000 + " seconds");
return "Callable completed";
};
return callable;
}
private void initCallables() {
callables.add(getCallable(1));
callables.add(getCallable(2));
callables.add(getCallable(3));
}
private void processCallableTasks() throws InterruptedException, ExecutionException {
final CompletionService<String> completionService = new ExecutorCompletionService<String>(threadPoolExecutor);
for(Callable<String> callable : callables) {
completionService.submit(callable);
}
int received = 0;
while(received < NUMBER_OF_THREADS) {
Future<String> resultFuture = completionService.take(); // blocks if none available
String result = resultFuture.get();
System.out.println("Future done " + result);
received++;
}
}
private void shutdownThreadPoolExecutor() {
threadPoolExecutor.shutdown();
try {
if (!threadPoolExecutor.awaitTermination(800, TimeUnit.MILLISECONDS)) {
threadPoolExecutor.shutdownNow();
}
} catch (InterruptedException e) {
threadPoolExecutor.shutdownNow();
}
}
}
Output
Starting Callable 1 Starting Callable 2 Starting Callable 3 CallableTask 3 took 10 seconds CallableTask 1 took 10 seconds CallableTask 2 took 10 seconds Future done Callable completed Future done Callable completed Future done Callable completed That took 10 seconds
Tags: java, threads
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