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  1. import java.lang.invoke.MethodHandles;
  2. import java.lang.invoke.VarHandle;
  3.  
  4. class SimulateCAS {
  5.     private volatile int count;
  6.  
  7.     private static final VarHandle COUNT;
  8.     static {
  9.     	try {
  10. 			COUNT = MethodHandles.lookup().findVarHandle(SimulateCAS.class, "count", int.class);
  11. 		} catch (NoSuchFieldException | IllegalAccessException e) {
  12. 			throw new Error(e);
  13. 		}
  14.     }
  15.  
  16.     private int cas(int expectation, int newValue) {
  17.         return (int) COUNT.compareAndExchange(this, expectation, newValue);
  18.     }
  19.  
  20.     void add10k() {
  21.         int oldValue, newValue;
  22.         do {
  23.         	oldValue = count;
  24.             newValue = oldValue + 1;                       // ?
  25.         } while (oldValue != cas(oldValue, newValue));        // ?
  26.     }
  27.  
  28.     public static void main(String[] args) throws InterruptedException {
  29.         final SimulateCAS demo = new SimulateCAS();
  30.         Thread t1 = new Thread(() -> {
  31.             for (int i = 0; i < 10000; i++) {
  32.                 demo.add10k();
  33.             }
  34.         });
  35.         Thread t2 = new Thread(() -> {
  36.             for (int i = 0; i < 10000; i++) {
  37.                 demo.add10k();
  38.             }
  39.         });
  40.  
  41.         t1.start();
  42.         t2.start();
  43.         t1.join();
  44.         t2.join();
  45.         System.out.println(demo.count);
  46.     }
  47. }
Success #stdin #stdout 0.08s 33436KB
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https://ideone.com/sE9WhU
language:
Java (HotSpot 12)
created:
6 years ago
visibility:
public

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