My program uses sockets, what Parallel computing APIs could I use that would help me without obligating me to go from sockets to anything else?
When we are on a cluster with a special, non-socket infrastructure system this API would emulate something like sockets but using that infrastructure (so programs perform much faster than on sockets, but still use the sockets API).
Are you familiar with the Message Passing Interface (MPI)? That's generally the way to go for scaling your code on parallel computers. As you noted it's not compatible with most socket APIs, but the benefits in scaling will almost certainly outweigh the costs in converting your code.
Sockets Direct Protocol is a protocol that supports high performance stream sockets without the overhead of TCP.
The purpose of the Sockets Direct Protocol is to provide an RDMA accelerated alternative to the TCP protocol on IP. The goal is to do this in a manner which is transparent to the application.