switch between indep and collective modes

[Wei-keng Liao]

I don't remember why we created the functions
     ncmpi_begin_indep_data() and
     ncmpi_end_indep_data()
to switch between collective and independent data modes.

I can see pnetcdf creates a new file handler by opening the same file 
again with MPI_COMM_SELF, if the program ever switches to independent 
mode. I wonder why we cannot simply use the file handler created at 
collective mode to do independent I/O. Using MPI_COMM_SELF can eliminate 
any possibility to apply optimizations for MPI independent I/O.

According to the API document, "the separation of the two modes is 
necessary to provide consistent views of file data when moving between 
MPI-IO collective and independent operations". In what situation the 
inconsistency will occur if we don't enforce this mode switching?

Is pnetcdf's file consistency policy the same as MPI-IO?

Wei-keng