3.6 Extensions for Memory Efficiency

MPI functions usually require the user to preallocate the data buffers needed before the functions being called. For unblocking communication primitives, sometimes the user would like to do lazy memory allocation until the data actually arrives, which gives the oppotunities to write more memory efficient programs. We provide a set of AMPI functions as an extension to the standard MPI-2 one-sided calls, where we provide a split phase MPI_Get called MPI_IGet. MPI_IGet preserves the similar semantics as MPI_Get except that no user buffer is provided to hold incoming data. MPI_IGet_Wait will block until the requested data arrives and runtime system takes care to allocate space, do appropriate unpacking based on data type, and return. MPI_IGet_Free lets the runtime system free the resources being used for this get request including the data buffer. And MPI_IGet_Data is the utility program that returns the actual data.

int MPI_IGet(MPI_Aint orgdisp, int orgcnt, MPI_Datatype orgtype, int rank,
             MPI_Aint targdisp, int targcnt, MPI_Datatype targtype, MPI_Win win,
             MPI_Request *request);

int MPI_IGet_Wait(MPI_Request *request, MPI_Status *status, MPI_Win win);

int MPI_IGet_Free(MPI_Request *request, MPI_Status *status, MPI_Win win);

char* MPI_IGet_Data(MPI_Status status);