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Java has tons of different Collections designed for concurrency and thread safety, and I'm at a loss as to which one to choose for my situation.
Multiple threads may be calling .add() and .remove(), and I will be copying this list frequently with something like List<T> newList = new ArrayList<T>(concurrentList). I will never be looping over the concurrent list.
I thought about something like CopyOnWriteArrayList, but I've read that it can be very inefficient because it copies itself every time it's modified. I'm hoping to find a good compromise between safety and efficiency.
What is the best list (or set) for this situation?
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The collection classes that are thread-safe in Java are Stack, Vector, Properties, Hashtable, etc.
Most of the collections such as ArrayList, LinkedList, HashSet, HashMap, etc., are not thread-safe. If two parallel threads modify any of these collections parallelly, the user can get stale data or ConcurrentModificationException .
Any method that touches the Vector 's contents is thread safe. ArrayList , on the other hand, is unsynchronized, making them, therefore, not thread safe.
No it is not thread-safe. Thread A could call AddRange on your list. It could iterate partially over the collection and switch threads. Thread B could call Add/Remove, etc.
This method accepts an object of Set interface and, returns a synchronized (thread-safe) set backed by the specified set. This method accepts an object of the Map interface and, returns a synchronized (thread-safe) sorted map backed by the specified sorted map.
As @SpiderPig said, the best case scenario with a List would be an immutable, singly-linked list.
However, looking at what's being done here, a List is unnecessary (@bhspencer's comment). A ConcurrentSkipListSet will work most efficiently (@augray).
This Related Thread's accepted answer offers more insight on the pros and cons of different concurrent collections.
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