nonblocking_write.py

#
# Copyright (C) 2024, Northwestern University and Argonne National Laboratory
# See COPYRIGHT notice in top-level directory.
#

"""
This example is similar to collective_write.py but using nonblocking APIs.
It creates a netcdf file in CDF-5 format and writes a number of
3D integer non-record variables. The measured write bandwidth is reported
at the end. Usage: (for example)

To run:
  mpiexec -n num_processes nonblocking_write.py [filename] [len]

  where len decides the size of each local array, which is len x len x len.
  So, each non-record variable is of size len*len*len * nprocs * sizeof(int)
  All variables are partitioned among all processes in a 3D
  block-block-block fashion.
"""

import sys, os, argparse
import numpy as np
from mpi4py import MPI
import pnetcdf

def pnetcdf_io(filename, length):
    NDIMS = 3
    NUM_VARS = 10

    if verbose and rank == 0:
        print("Number of variables = ", NUM_VARS)
        print("Number of dimensions = ", NDIMS)

    # set up subarray access pattern
    start = np.zeros(NDIMS, dtype=np.int32)
    count = np.zeros(NDIMS, dtype=np.int32)
    gsizes = np.zeros(NDIMS, dtype=np.int32)
    buf = []

    psizes = MPI.Compute_dims(nprocs, NDIMS)
    start[0] = rank % psizes[0]
    start[1] = (rank // psizes[1]) % psizes[1]
    start[2] = (rank // (psizes[0] * psizes[1])) % psizes[2]

    bufsize = 1
    for i in range(NDIMS):
        gsizes[i] = length * psizes[i]
        start[i] *= length
        count[i] = length
        bufsize *= length

    # Allocate buffer and initialize with non-zero numbers
    for i in range(NUM_VARS):
        buf.append(np.empty(bufsize, dtype=np.int32))
        for j in range(bufsize):
            buf[i][j] = rank * i + 123 + j

    # Create the file
    f = pnetcdf.File(filename = filename,
                     mode = 'w',
                     format = "NC_64BIT_DATA",
                     comm = comm,
                     info = None)

    # Define dimensions
    dims = []
    for i in range(NDIMS):
        dim = f.def_dim(chr(ord('x')+i), gsizes[i])
        dims.append(dim)

    # Define variables
    vars = []
    for i in range(NUM_VARS):
        var = f.def_var("var{}".format(i), pnetcdf.NC_INT, dims)
        vars.append(var)

    # Exit the define mode
    f.enddef()

    # Write one variable at a time, using iput APIs
    reqs = []
    for i in range(NUM_VARS):
        req_id = vars[i].iput_var(buf[i], start = start, count = count)
        reqs.append(req_id)

    # commit posted nonblocking requests
    req_errs = [None] * NUM_VARS
    f.wait_all(NUM_VARS, reqs, req_errs)

    # check errors
    for i in range(NUM_VARS):
        if pnetcdf.strerrno(req_errs[i]) != "NC_NOERR":
            print(f"Error on request {i}:",  pnetcdf.strerror(req_errs[i]))

    # call bput APIs, first calculate space needed
    bbufsize = bufsize * NUM_VARS * np.dtype(np.int32).itemsize
    f.attach_buff(bbufsize)

    # Write one variable at a time, using bput APIs
    reqs = []
    for i in range(NUM_VARS):
        req_id = vars[i].bput_var(buf[i], start = start, count = count)
        reqs.append(req_id)
        # can safely change contents or free up the buf[i] here

    # wait for the nonblocking I/O to complete
    req_errs = [None] * NUM_VARS
    f.wait_all(NUM_VARS, reqs, req_errs)

    # check errors
    for i in range(NUM_VARS):
        if pnetcdf.strerrno(req_errs[i]) != "NC_NOERR":
            print(f"Error on request {i}:",  pnetcdf.strerror(req_errs[i]))

    # detach the buffer
    f.detach_buff()

    # Close the file
    f.close()


def parse_help():
    help_flag = "-h" in sys.argv or "--help" in sys.argv
    if help_flag and rank == 0:
        help_text = (
            "Usage: {} [-h | -q | -l len] [file_name]\n"
            "       [-h] Print help\n"
            "       [-q] Quiet mode (reports when fail)\n"
            "       [-l len] size of each dimension of the local array\n"
            "       [filename] (Optional) output netCDF file name\n"
        ).format(sys.argv[0])
        print(help_text)
    return help_flag


if __name__ == "__main__":
    comm = MPI.COMM_WORLD
    rank = comm.Get_rank()
    nprocs = comm.Get_size()

    if parse_help():
        MPI.Finalize()
        sys.exit(1)

    # get command-line arguments
    args = None
    parser = argparse.ArgumentParser()
    parser.add_argument("dir", nargs="?", type=str, help="(Optional) output netCDF file name",\
                         default = "testfile.nc")
    parser.add_argument("-q", help="Quiet mode (reports when fail)", action="store_true")
    parser.add_argument("-l", help="Size of each dimension of the local array\n")
    args = parser.parse_args()

    verbose = False if args.q else True

    length = 10
    if args.l and int(args.l) > 0: length = int(args.l)

    filename = args.dir

    if verbose and rank == 0:
        print("{}: example of calling nonblocking write APIs".format(os.path.basename(__file__)))

    try:
        pnetcdf_io(filename, length)
    except BaseException as err:
        print("Error: type:", type(err), str(err))
        raise

    MPI.Finalize()