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import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
class Writer extends Producer implements Runnable {
  public void run() {
    synchronized (Shared.cache) {
      int[] referenceToValue = Shared.cache.get("key");
      
      for (int i = 0; i < referenceToValue.length; i++) {
        // Update value in-place; sum will add up to length
        referenceToValue[i] = produce();
      }
    }
  }
}
class Reader extends Consumer implements Runnable {
  public void run() {
    synchronized (Shared.cache) {
      consume(Shared.cache.get("key"));
    }
  }
}
// {...}
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