There is currently a reference implementation of Portals 4.0 supporting InfiniBand and shared memory, utilizing a progress thread for each process. The implementation is developed through a collaboration between Sandia National Laboratories and System Fabric Works. The reference implementation is being extended to support more transports as well as to enable looking at alternative progress models.
More information on the reference implementation may be found at the Portals 4 @Github page.
The earliest reference implementation of Portals 4.0 was over shared memory only, and was optimized to examine overheads in the Portals semantics relative to other messaging interfaces. While the code can be found on the Portals 4 Google Code page, the implementation has been deprecated in preference to the reference implementation.