java single writer and multiple reader

Question

Sorry if this was asked before, but I could not find my exact scenario.

Currently I have a background thread that adds an element to a list and removes the old data every few minutes. Theoretically there can be at most 2 items in the list at a time and the items are immutable. I also have multiple threads that will grab the first element in the list whenever they need it. In this scenario, is it necessary to explicitly serialized operations on the list? My assumption that since I am just grabbing references to the elements, if the background thread deletes elements from the list, that should not matter since the thread already grabs a copy of the reference before the deletion. There is probably a better way to do this. Thanks in advanced.

Answer 1

Yes, synchronization is still needed here, because adding and removing are not atomic operations. If one thread calls add(0, new Object()) at the same time another calls remove(0) , the result is undefined; for example, the remove() might end up having no effect.

Depending on your usage, you might be able to use a non-blocking list class like ConcurrentLinkedQueue . However, given that you are pushing one change every few minutes, I doubt you are gaining much in performance by avoiding synchronization.