1. A method of data processing in a hybrid computing environment, the hybrid computing environment comprising a host computer having a host computer architecture, an accelerator having an accelerator architecture, the accelerator architecture optimized, with respect to the host computer architecture, for speed of execution of a particular class of computing functions, the host computer and the accelerator adapted to one another for data communications by a system level message passing module, a host application process executing on the host computer, the method comprising: starting, by the system level message passing module at the behest of the host application process, a thread of execution on the accelerator; returning, by the system level message passing module to the host application process, a process identifier (‘PID’) for the thread of execution; and managing, by the host application process, the thread of execution on the accelerator as though the thread of execution were a thread of execution on the host computer.