title: Are there any drawbacks with ConcurrentHashMap?
body: <p>I need a HashMap that is accessible from multiple threads.</p>
  
  <p>There are two simple options, using a normal HashMap and synchronizing on it or using a ConcurrentHashMap.</p>
  
  <p>Since ConcurrentHashMap does not block on read operations it seems much better suited for my needs (almost exclusively reads, almost never updates). 
  On the other hand, I expect very low concurrency anyway, so there should be no blocking (just the cost of managing the lock).</p>
  
  <p>The Map will also be very small (under ten entries), if that makes a difference.</p>
  
  <p>Compared to a regular HashMap, how much more costly are the read and write operations (I am assuming that they are)? Or is ConcurrentHashMap just always better when there might be even a moderate level of concurrent access, regardless of read/update ratio and size?</p>