CODEWITHSUNDEEP
javaconcurrencythread-safety
user13806035
user13806035

Reputation:

Concurrency in Practice > Listing 4.13

Here is a snippet from page 72:

@ThreadSafe
public class BetterVector<E> extends Vector<E> {
  public synchronized boolean putIfAbsent(E x) {
    boolean absent = !contains(x);
    if (absent)
      add(x);
    return absent;
  }
}

According to Brian the above class is thread safe. But as you can see that E x is really a mutable class. What would happen if after evaluating absent to true the value of x changes? Isn't this a violation and might lead to pretty nasty bugs?

Upvotes: 0

Views: 61

Answers (1)

Jose Martinez
Jose Martinez

Reputation: 11992

Yes you are correct. But that is not an issue with threaded code or concurrency. That's a computer science type problem dealing with references and pointers in general. A reference points to an object. If you pass references around, as Java does, then those references can be used to access the underlying object.

Upvotes: 1

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