Javadoc
Indicates whether to allow a socket factory instance (which may be shared
across multiple connections) to be used create multiple sockets
concurrently. In general, socket factory implementations are threadsafe
and can be to create multiple connections simultaneously across separate
threads, but this is known to not be the case in some VM implementations
(e.g., SSL socket factories in IBM JVMs). This setting may be used to
indicate whether concurrent socket creation attempts should be allowed
(which may allow for better and more consistent performance, especially in
cases where a connection attempt fails due to a timeout) or prevented
(which may be necessary for non-threadsafe socket factory implementations).