Modifying hash map from a single thread and reading from multiple threads?

Question

I have a class in which I am populating a map liveSocketsByDatacenter from a single background thread every 30 seconds and then I have a method getNextSoc

Answer 1

As you can read in detail e.g. here, if multiple threads access a hash map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally to avoid an inconsistent view of the contents. So to be thread safe you should use either Java Collections synchronizedMap() method or a ConcurrentHashMap.

//synchronizedMap
private final Map> liveSocketsByDatacenter = Collections.synchronizedMap(new HashMap>());    

or

//ConcurrentHashMap
private final Map> liveSocketsByDatacenter = new ConcurrentHashMap>();

As you have very highly concurrent application modifying and reading key value in different threads, you should also have a look at the Producer-Consumer principle, e.g. here.