Implementing MPI-IO Shared File Pointers Without File System Support

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The ROMIO implementation of the MPI-IO standard provides a portable infrastructure for use on top of any number of different underlying storage targets. These targets vary widely in their capabilities, and in some cases additional effort is needed within ROMIO to support all MPI-IO semantics. The MPI-2 standard defines a class of file access routines that use a shared file pointer. These routines require communication internal to the MPI-IO implementation in order to allow processes to atomically update this shared value. We discuss a technique that leverages MPI-2 one-sided operations and can be used to implement this concept without requiring any features from the underlying file system. We then demonstrate through a simulation that our algorithm adds reasonable overhead for independent accesses and very small overhead for collective accesses.