Extending the MPI-2 Generalized Request Interface

The MPI-2 standard added a new feature to MPI called generalized requests. Generalized requests allow users to add new nonblocking operations to MPI while still using many pieces of MPI infrastructure such as request objects and the progress notification routines (MPI Test, MPI Wait). The generalized request design as it stands, however, has deficiencies regarding typical use cases. These deficiencies are particularly evident in environments that do not support threads or signals, such as the leading petascale systems (IBM Blue Gene/L, Cray XT3 and XT4). This paper examines these shortcomings, proposes extensions to the interface to overcome them, and presents implementation results.