Thread safe reference assignment when working with ConcurrentHashSet

Question

A bit confused about the usage of ConcurrentHashSets in DTOs. This DTO is accessed by many threads at a time.

First Case

 public class LogDTO {
      private Set<String> person = ConcurrentHashMap.newKeySet();

      public void setPerson(Set<String> person) {
       this.person = person;
      }

      public Set<String> getPerson() {
       return this.person;
      }
    }

Does this give Thread Safety?

Second Case

 public class LogDTO {

     private volatile Set<String> person;
      public void setPerson(Set<String> person) {
       this.person = person;
      }

      public Set<String> getPerson() {
       return this.person;
      }
 }

or do I have to use AtomicReference?

Third Case

 public class LogDTO {

     private AtomicReference<Set<String>> ref = new AtAtomicReference<>();

      public void setPerson(Set<String> person) {
       this.ref.set(person);
      }

      public Set<String> getPerson() {
       return this.ref.get();
      }
 }

If to populate an entirely new HashSet then assigning it to the existing variable, then is it better to use volatile?

score 1 · Answer 1 · answered Oct 11 '19 at 08:45

First Case

it is not thread safe, ConcurrentHashMap only provides thread safety when working with the HashMap api meaning adding and removing things from the HashMap. it does not provide thread safety when changing the reference to the HashMap, if you think of it, changing the reference to the HashMap has no connection to how the HashMap is implemented.

Second and Third cases

Those cases are thread safe, in those cases you changed the way assigning and retrieving the HashMap reference is implemented to allow thread safety.

in regards to whether to use volatile or AtomicReference you can read this

to give you the tl;dr: AtomicReference has more functionality but uses additional memory to provide that functionality, my personal opinion is that if you are not that concerned with memory go ahead and use AtomicReference it is more readable and you dont't know when you will find your self needing additional functionality.

Thread safe reference assignment when working with ConcurrentHashSet

1 Answers1