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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.util.concurrent.*;
  5. import java.util.concurrent.locks.*;
  6. import java.lang.*;
  7. import java.io.*;
  8.  
  9. /* Name of the class has to be "Main" only if the class is public. */
  10. class Ideone {
  11.   private final ConcurrentHashMap<String, Future<?>> pending = new ConcurrentHashMap<>();
  12.   private final ExecutorService executor;
  13.   private final long start;
  14.  
  15.   Ideone(ExecutorService executor) {
  16.     this.executor = executor;
  17.     this.start = System.nanoTime();
  18.   }
  19.  
  20.   void test(String hash) {
  21.   	System.out.println(Thread.currentThread().getName() + " started at: " + ((System.nanoTime() - start) / 1e9) + "s");
  22.  
  23.     Future<?> future =
  24.         pending.computeIfAbsent(hash, k -> executor.submit(() -> longRunningMethod()));
  25.     try {
  26.       future.get(); // Block until LRM has finished.
  27.       System.out.println(Thread.currentThread().getName() + " completed after: " + ((System.nanoTime() - start) / 1e9) + "s");
  28.     } catch (ExecutionException e) {
  29.       throw new RuntimeException(e);
  30.     } catch (InterruptedException e) {
  31.       Thread.currentThread().interrupt();
  32.       throw new RuntimeException(e);
  33.     } finally {
  34.       pending.values().remove(future);
  35.     }
  36.   }
  37.  
  38.   void longRunningMethod() {
  39.     System.out.println("Start: " + Thread.currentThread().getName());
  40.     try {
  41.       Thread.sleep(500);
  42.     } catch (InterruptedException e) {
  43.       Thread.currentThread().interrupt();
  44.       throw new RuntimeException(e);
  45.     }
  46.     System.out.println("End: " + Thread.currentThread().getName());
  47.   }
  48.  
  49.   static void startAndRun(Thread... ts) throws InterruptedException {
  50.   	for (Thread t : ts) t.start();
  51.   	for (Thread t : ts) t.join();
  52.   }
  53.  
  54.   public static void main(String[] args) throws java.lang.Exception {
  55.     ExecutorService executor = Executors.newCachedThreadPool();
  56.     try {
  57.       Ideone instance = new Ideone(executor);
  58.  
  59.       Runnable r = () -> instance.test("");
  60.  
  61.       // These threads all run concurrently, and basically finish at the same
  62.       // time.
  63.       startAndRun(new Thread(r), new Thread(r), new Thread(r));
  64.       // The LRM needs to be called again for these threads.
  65.       startAndRun(new Thread(r), new Thread(r));
  66.     } finally {
  67.       executor.shutdown();
  68.     }
  69.   }
  70. }
  71.  
Success #stdin #stdout 0.2s 322112KB
comments (?)
stdin 
Standard input is empty
stdout 
Thread-0 started at: 0.094508291s
Thread-1 started at: 0.099820226s
Thread-2 started at: 0.101491774s
Start: pool-1-thread-1
End: pool-1-thread-1
Thread-0 completed after: 0.602933698s
Thread-2 completed after: 0.603211042s
Thread-1 completed after: 0.60299587s
Thread-3 started at: 0.604279514s
Start: pool-1-thread-1
Thread-4 started at: 0.604574315s
End: pool-1-thread-1
Thread-3 completed after: 1.104799675s
Thread-4 completed after: 1.10501813s
https://ideone.com/axsKZl
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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