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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.  
  12.   private static final ConcurrentHashMap<String, Semaphore> map = new ConcurrentHashMap<>();
  13.  
  14.   private static void callLongRunningMethod() {
  15.     System.out.println("Start " + Thread.currentThread().getName());
  16.     try {
  17.       Thread.sleep(500);
  18.     } catch (InterruptedException e) {
  19.       Thread.currentThread().interrupt();
  20.       throw new RuntimeException(e);
  21.     }
  22.     System.out.println("End " + Thread.currentThread().getName());
  23.   }
  24.  
  25.   public static void test(String hash) {
  26.     Semaphore s = map.computeIfAbsent(hash, k -> new Semaphore(1));
  27.     try {
  28.     	s.acquire();
  29.     } catch (InterruptedException e) {
  30.     	throw new RuntimeException(e);
  31.     }
  32.     try {
  33.         callLongRunningMethod();
  34.     } finally {
  35.         s.release();
  36.         map.remove(hash, s);
  37.     }
  38. }
  39.  
  40.   public static void main(String[] args) throws java.lang.Exception {
  41.     new Thread(
  42.             () -> {
  43.               test("");
  44.               test("");
  45.             })
  46.         .start();
  47.     new Thread(
  48.             () -> {
  49.               test("");
  50.               test("");
  51.             })
  52.         .start();
  53.     // your code goes here
  54.   }
  55. }
  56.  
Success #stdin #stdout 0.19s 321344KB
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stdin
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Standard input is empty
stdout
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Start Thread-0
End Thread-0
Start Thread-0
Start Thread-1
End Thread-0
End Thread-1
Start Thread-1
End Thread-1
https://ideone.com/aCuopK
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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