path: root/testpar/t_pread.c

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * Copyright by the Board of Trustees of the University of Illinois.         *
 * All rights reserved.                                                      *
 *                                                                           *
 * This file is part of HDF5.  The full HDF5 copyright notice, including     *
 * terms governing use, modification, and redistribution, is contained in    *
 * the COPYING file, which can be found at the root of the source code       *
 * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
 * If you do not have access to either file, you may request a copy from     *
 * help@hdfgroup.org.                                                        *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/*
 * Collective file open optimization tests
 *
 */

#include "h5test.h"
#include "testpar.h"

/* The collection of files is included below to aid
 * an external "cleanup" process if required.
 *
 * Note that the code below relies on the ordering of this array
 * since each set of three is used by the tests either to construct
 * or to read and validate.
 */
#define NFILENAME 9
const char *FILENAMES[NFILENAME + 1]={"t_pread_data_file",
                                      "reloc_t_pread_data_file",
                                      "prefix_file",
                                      "t_pread_group_0_file",
                                      "reloc_t_pread_group_0_file",
                                      "prefix_file_0",
                                      "t_pread_group_1_file",
                                      "reloc_t_pread_group_1_file",
                                      "prefix_file_1",
                                      NULL};
#define FILENAME_BUF_SIZE 1024

#define COUNT 1000

hbool_t pass = true;
static const char *random_hdf5_text = 
"Now is the time for all first-time-users of HDF5 to read their \
manual or go thru the tutorials!\n\
While you\'re at it, now is also the time to read up on MPI-IO.";

static const char *hitchhiker_quote =
"A common mistake that people make when trying to design something\n\
completely foolproof is to underestimate the ingenuity of complete\n\
fools.\n";

static int generate_test_file(MPI_Comm comm, int mpi_rank, int group);
static int test_parallel_read(MPI_Comm comm, int mpi_rank, int group);


/*-------------------------------------------------------------------------
 * Function:    generate_test_file
 *
 * Purpose:     This function is called to produce an HDF5 data file
 *              whose superblock is relocated to a non-zero offset by
 *              utilizing the 'h5jam' utility to write random text
 *              at the start of the file.  Unlike simple concatenation
 *              of files, h5jam is used to place the superblock on a
 *              power-of-2 boundary.
 *
 *              Since data will be read back and validated, we generate
 *              data in a predictable manner rather than randomly.
 *              For now, we simply use the global mpi_rank of the writing
 *              process as a starting component for the data generation.
 *              Subsequent writes are increments from the initial start
 *              value.
 *
 *              In the overall scheme of running the test, we'll call
 *              this function twice: first as a collection of all MPI
 *              processes and then a second time with the processes split
 *              more or less in half. Each sub group will operate 
 *              collectively on their assigned file.  This split into
 *              subgroups validates that parallel groups can successfully
 *              open and read data independantly from the other parallel
 *              operations taking place.
 *
 * Return:      Success: 0
 *
 *              Failure: 1
 *
 * Programmer:  Richard Warren
 *              10/1/17
 *
 * Modifications:
 * 
 *-------------------------------------------------------------------------
 */
static int
generate_test_file( MPI_Comm comm, int mpi_rank, int group_id )
{
    FILE *header = NULL;
    const char *fcn_name = "generate_test_file()";
    const char *failure_mssg = NULL;
    const char *group_filename = NULL;
    char data_filename[FILENAME_BUF_SIZE];
    char reloc_data_filename[FILENAME_BUF_SIZE];
    char prolog_filename[FILENAME_BUF_SIZE];
    int file_index;
    int group_size;
    int group_rank;
    int local_failure = 0;
    int global_failures = 0; 
    hsize_t count = COUNT;
    hsize_t i;
    hsize_t offset;
    hsize_t dims[1] = {0};
    hid_t file_id   = -1;
    hid_t memspace  = -1; 
    hid_t filespace = -1; 
    hid_t fapl_id   = -1;
    hid_t dxpl_id   = -1;
    hid_t dset_id   = -1;
    float nextValue;
    float *data_slice = NULL;

    pass = true;

    HDassert(comm != MPI_COMM_NULL);

    if ( (MPI_Comm_rank(comm, &group_rank)) != MPI_SUCCESS) {
        pass = FALSE;
        failure_mssg = "generate_test_file: MPI_Comm_rank failed.\n";
    }

    if ( (MPI_Comm_size(comm, &group_size)) != MPI_SUCCESS) {
        pass = FALSE;
        failure_mssg = "generate_test_file: MPI_Comm_size failed.\n";
    }

    if ( mpi_rank == 0 ) {

        HDfprintf(stdout, "Constructing test files...");
    }

    /* Setup the file names
     * The test specfic filenames are stored as consecutive
     * array entries in the global 'FILENAMES' array above.
     * Here, we simply decide on the starting index for
     * file construction.  The reading portion of the test
     * will have a similar setup process...
     */
    if ( pass ) {
        if ( comm == MPI_COMM_WORLD ) { /* Test 1 */
            file_index = 0;
        } 
        else if ( group_id == 0 ) {     /* Test 2 group 0 */
            file_index = 3;
        }
        else {                          /* Test 2 group 1 */
            file_index = 6;
        }

        /* The 'group_filename' is just a temp variable and 
         * is used to call into the h5_fixname function. No 
         * need to worry that we reassign it for each file!
         */
        HDassert((group_filename = FILENAMES[file_index]));

        /* Assign the 'data_filename' */
        if ( h5_fixname(group_filename, H5P_DEFAULT, data_filename,
                        sizeof(data_filename)) == NULL ) {
            pass = FALSE;
            failure_mssg = "h5_fixname(0) failed.\n";
        }
    }

    if ( pass ) {

        HDassert( (group_filename = FILENAMES[file_index+1]) );

        /* Assign the 'reloc_data_filename' */
        if ( h5_fixname(group_filename, H5P_DEFAULT, reloc_data_filename,
                        sizeof(reloc_data_filename)) == NULL ) {

            pass = FALSE;
            failure_mssg = "h5_fixname(1) failed.\n";
        }
    }

    if ( pass ) {

        HDassert( (group_filename = FILENAMES[file_index+2]) );

        /* Assign the 'prolog_filename' */
        if ( h5_fixname(group_filename, H5P_DEFAULT, prolog_filename,
                        sizeof(prolog_filename)) == NULL ) {
            pass = FALSE;
            failure_mssg = "h5_fixname(2) failed.\n";
        }
    }

    /* setup data to write */
    if ( pass ) {
        if ( (data_slice = (float *)HDmalloc(COUNT * sizeof(float))) == NULL ) {
            pass = FALSE;
            failure_mssg = "malloc of data_slice failed.\n";
        }
    }

    if ( pass ) {
        nextValue = (float)(mpi_rank * COUNT);

        for(i=0; i<COUNT; i++) {
            data_slice[i] = nextValue;
            nextValue += 1;
        }
    }

    /* setup FAPL */
    if ( pass ) {
        if ( (fapl_id = H5Pcreate(H5P_FILE_ACCESS)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Pcreate(H5P_FILE_ACCESS) failed.\n";
        }
    }

    if ( pass ) {
        if ( (H5Pset_fapl_mpio(fapl_id, comm, MPI_INFO_NULL)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Pset_fapl_mpio() failed\n";
        }
    }

    /* create the data file */ 
    if ( pass ) {
        if ( (file_id = H5Fcreate(data_filename, H5F_ACC_TRUNC, 
                                  H5P_DEFAULT, fapl_id)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Fcreate() failed.\n";
        }
    }

    /* create and write the dataset */
    if ( pass ) {
        if ( (dxpl_id = H5Pcreate(H5P_DATASET_XFER)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Pcreate(H5P_DATASET_XFER) failed.\n";
        }
    }

    if ( pass ) {
        if ( (H5Pset_dxpl_mpio(dxpl_id, H5FD_MPIO_COLLECTIVE)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Pset_dxpl_mpio() failed.\n";
        }
    }

    if ( pass ) {
        dims[0] = COUNT;
        if ( (memspace = H5Screate_simple(1, dims, NULL)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Screate_simple(1, dims, NULL) failed (1).\n";
        }
    }

    if ( pass ) {
        dims[0] *= (hsize_t)group_size;
        if ( (filespace = H5Screate_simple(1, dims, NULL)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Screate_simple(1, dims, NULL) failed (2).\n";
        }
    }

    if ( pass ) {
        offset = (hsize_t)group_rank * (hsize_t)COUNT;
        if ( (H5Sselect_hyperslab(filespace, H5S_SELECT_SET, &offset, 
                                  NULL, &count, NULL)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Sselect_hyperslab() failed.\n";
        }
    }

    if ( pass ) {
        if ( (dset_id = H5Dcreate2(file_id, "dataset0", H5T_NATIVE_FLOAT, 
                                   filespace, H5P_DEFAULT, H5P_DEFAULT, 
                                   H5P_DEFAULT)) < 0 ) {
            pass = false;
            failure_mssg = "H5Dcreate2() failed.\n";
        }
    }

    if ( pass ) {
        if ( (H5Dwrite(dset_id, H5T_NATIVE_FLOAT, memspace, 
                       filespace, dxpl_id, data_slice)) < 0 ) {
            pass = false;
            failure_mssg = "H5Dwrite() failed.\n";
        }
    }

    /* close file, etc. */
    if ( pass || (dset_id != -1)) {
        if ( H5Dclose(dset_id) < 0 ) {
            pass = false;
            failure_mssg = "H5Dclose(dset_id) failed.\n";
        }
    }

    if ( pass || (memspace != -1) ) {
        if ( H5Sclose(memspace) < 0 ) {
            pass = false;
            failure_mssg = "H5Sclose(memspace) failed.\n";
        }
    }

    if ( pass || (filespace != -1) ) {
        if ( H5Sclose(filespace) < 0 ) {
            pass = false;
            failure_mssg = "H5Sclose(filespace) failed.\n";
        }
    }

    if ( pass || (file_id != -1) ) {
        if ( H5Fclose(file_id) < 0 ) {
            pass = false;
            failure_mssg = "H5Fclose(file_id) failed.\n";
        }
    }

    if ( pass || (dxpl_id != -1) ) {
        if ( H5Pclose(dxpl_id) < 0 ) {
            pass = false;
            failure_mssg = "H5Pclose(dxpl_id) failed.\n";
        }
    }

    if ( pass || (fapl_id != -1) ) {
        if ( H5Pclose(fapl_id) < 0 ) {
            pass = false;
            failure_mssg = "H5Pclose(fapl_id) failed.\n";
        }
    }

    /* Add a userblock to the head of the datafile.
     * We will use this to for a functional test of the 
     * file open optimization.  This is superblock
     * relocation is done by the rank 0 process associated
     * with the communicator being used.  For test 1, we
     * utilize MPI_COMM_WORLD, so group_rank 0 is the
     * same as mpi_rank 0.  For test 2 which utilizes
     * two groups resulting from an MPI_Comm_split, we
     * will have parallel groups and hence two 
     * group_rank(0) processes. Each parallel group 
     * will create a unique file with different text
     * headers and different data.
     *
     * We also delete files that are no longer needed.
     */
    if ( group_rank == 0 ) {

        const char *text_to_write;
        size_t bytes_to_write; 

        if (group_id == 0)
            text_to_write = random_hdf5_text;
        else
            text_to_write = hitchhiker_quote;

        bytes_to_write = strlen(text_to_write);

        if ( pass ) {
            if ( (header = HDfopen(prolog_filename, "w+")) == NULL ) {
                pass = FALSE;
                failure_mssg = "HDfopen(prolog_filename, \"w+\") failed.\n";
            }
        }

        if ( pass ) {

            if ( HDfwrite(text_to_write, 1, bytes_to_write, header) !=
                 bytes_to_write ) {
                pass = FALSE;
                failure_mssg = "Unable to write header file.\n";
            }
        }

        if ( pass || (header != NULL) ) {
            if ( HDfclose(header) != 0 ) {
                pass = FALSE;
                failure_mssg = "HDfclose() failed.\n";
            }
        }

        if ( pass ) {
            char cmd[256];

            HDsprintf(cmd, "../tools/src/h5jam/h5jam -i %s -u %s -o %s", 
                      data_filename, prolog_filename, reloc_data_filename);

            if ( system(cmd) != 0 ) {
                pass = FALSE;
                failure_mssg = "invocation of h5jam failed.\n";
            }
        }

        HDremove(prolog_filename);
        HDremove(data_filename);
    }

    /* collect results from other processes.
     * Only overwrite the failure message if no preveious error 
     * has been detected
     */
    local_failure = ( pass ? 0 : 1 );

    /* This is a global all reduce (NOT group specific) */
    if ( MPI_Allreduce(&local_failure, &global_failures, 1, 
                       MPI_INT, MPI_SUM, MPI_COMM_WORLD) != MPI_SUCCESS ) {
        if ( pass ) {
            pass = FALSE;
            failure_mssg = "MPI_Allreduce() failed.\n";
        }
    } else if ( ( pass ) && ( global_failures > 0 ) ) {
        pass = FALSE;
        failure_mssg = "One or more processes report failure.\n";
    }

    /* report results */
    if ( mpi_rank == 0 ) {
        if ( pass ) {
            HDfprintf(stdout, "Done.\n");
        } else {
            HDfprintf(stdout, "FAILED.\n");
            HDfprintf(stdout, "%s: failure_mssg = \"%s\"\n",
                      fcn_name, failure_mssg);
        }
    }

    /* free data_slice if it has been allocated */
    if ( data_slice != NULL ) {
        HDfree(data_slice);
        data_slice = NULL;
    }

    return(! pass);

} /* generate_test_file() */


/*-------------------------------------------------------------------------
 * Function:    test_parallel_read
 *
 * Purpose:     This actually tests the superblock optimization
 *              and covers the two primary cases we're interested in.
 *              1). That HDF5 files can be opened in parallel by
 *                  the rank 0 process and that the superblock
 *                  offset is correctly broadcast to the other
 *                  parallel file readers.
 *              2). That a parallel application can correctly
 *                  handle reading multiple files by using
 *                  subgroups of MPI_COMM_WORLD and that each
 *                  subgroup operates as described in (1) to
 *                  collectively read the data.
 *
 *              The global MPI rank is used for reading and
 *              writing data for process specific data in the
 *              dataset.  We do this rather simplisticly, i.e.
 *               rank 0:  writes/reads 0-9999
 *               rank 1:  writes/reads 1000-1999
 *               rank 2:  writes/reads 2000-2999
 *               ...
 *
 * Return:      Success: 0
 *
 *              Failure: 1
 *
 * Programmer:  Richard Warren
 *              10/1/17
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static int
test_parallel_read(MPI_Comm comm, int mpi_rank, int group_id)
{
    const char *failure_mssg;
    const char *fcn_name = "test_parallel_read()";
    const char *group_filename = NULL;
    char reloc_data_filename[FILENAME_BUF_SIZE];
    int local_failure = 0;
    int global_failures = 0; 
    int group_size;
    int group_rank;
    hid_t fapl_id   = -1;
    hid_t file_id   = -1;
    hid_t dset_id   = -1;
    hid_t memspace  = -1;
    hid_t filespace = -1;
    hsize_t i;
    hsize_t offset;
    hsize_t count = COUNT;
    hsize_t dims[1] = {0};
    float nextValue;
    float *data_slice = NULL;

    pass = TRUE;

    HDassert(comm != MPI_COMM_NULL);

    if ( (MPI_Comm_rank(comm, &group_rank)) != MPI_SUCCESS) {
        pass = FALSE;
        failure_mssg = "test_parallel_read: MPI_Comm_rank failed.\n";
    }

    if ( (MPI_Comm_size(comm, &group_size)) != MPI_SUCCESS) {
        pass = FALSE;
        failure_mssg = "test_parallel_read: MPI_Comm_size failed.\n";
    }

    if ( mpi_rank == 0 ) {
        if ( comm == MPI_COMM_WORLD ) {
            TESTING("parallel file open test 1");
        }
        else {
            TESTING("parallel file open test 2");
        }
    }

    /* allocate space for the data_slice array */
    if ( pass ) {
        if ( (data_slice = (float *)HDmalloc(COUNT * sizeof(float))) == NULL ) {
            pass = FALSE;
            failure_mssg = "malloc of data_slice failed.\n";
        }
    }


    /* Select the file file name to read
     * Please see the comments in the 'generate_test_file' function
     * for more details...
     */
    if ( pass ) {

        if ( comm == MPI_COMM_WORLD )       /* test 1 */
            group_filename = FILENAMES[1];
        else if ( group_id == 0 )           /* test 2 group 0 */
            group_filename = FILENAMES[4];
        else                                /* test 2 group 1 */
            group_filename = FILENAMES[7];

        HDassert(group_filename);
        if ( h5_fixname(group_filename, H5P_DEFAULT, reloc_data_filename,
                        sizeof(reloc_data_filename)) == NULL ) {

            pass = FALSE;
            failure_mssg = "h5_fixname(1) failed.\n";
        }
    }

    /* setup FAPL */
    if ( pass ) {
        if ( (fapl_id = H5Pcreate(H5P_FILE_ACCESS)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Pcreate(H5P_FILE_ACCESS) failed.\n";
        }
    }

    if ( pass ) {
        if ( (H5Pset_fapl_mpio(fapl_id, comm, MPI_INFO_NULL)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Pset_fapl_mpio() failed\n";
        }
    }

    /* open the file -- should have user block, exercising the optimization */
    if ( pass ) {
        if ( (file_id = H5Fopen(reloc_data_filename, 
                                H5F_ACC_RDONLY, fapl_id)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Fopen() failed\n";
        }
    }

    /* open the data set */
    if ( pass ) {
        if ( (dset_id = H5Dopen2(file_id, "dataset0", H5P_DEFAULT)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Dopen2() failed\n";
        }
    }

    /* setup memspace */
    if ( pass ) {
        dims[0] = count;
        if ( (memspace = H5Screate_simple(1, dims, NULL)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Screate_simple(1, dims, NULL) failed\n";
        }
    }

    /* setup filespace */
    if ( pass ) {
        if ( (filespace = H5Dget_space(dset_id)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Dget_space(dataset) failed\n";
        }
    }

    if ( pass ) {
        offset = (hsize_t)group_rank * count;
        if ( (H5Sselect_hyperslab(filespace, H5S_SELECT_SET, 
                                  &offset, NULL, &count, NULL)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Sselect_hyperslab() failed\n";
        }
    }

    /* read this processes section of the data */
    if ( pass ) {
        if ( (H5Dread(dset_id, H5T_NATIVE_FLOAT, memspace, 
                      filespace, H5P_DEFAULT, data_slice)) < 0 ) {
            pass = FALSE;
            failure_mssg = "H5Dread() failed\n";
        }
    }
    
    /* verify the data */ 
    if ( pass ) {
        nextValue = (float)((hsize_t)mpi_rank * count);
        i = 0;
        while ( ( pass ) && ( i < count ) ) {
            /* what we really want is data_slice[i] != nextValue --
             * the following is a circumlocution to shut up the
             * the compiler.
             */
            if ( ( data_slice[i] > nextValue ) ||
                 ( data_slice[i] < nextValue ) ) {
                pass = FALSE;
                failure_mssg = "Unexpected dset contents.\n";
            }
            nextValue += 1;
            i++;
        }
    }

    /* close file, etc. */
    if ( pass || (dset_id != -1) ) {
        if ( H5Dclose(dset_id) < 0 ) {
            pass = false;
            failure_mssg = "H5Dclose(dset_id) failed.\n";
        }
    }

    if ( pass || (memspace != -1) ) {
        if ( H5Sclose(memspace) < 0 ) {
            pass = false;
            failure_mssg = "H5Sclose(memspace) failed.\n";
        }
    }

    if ( pass || (filespace != -1) ) {
        if ( H5Sclose(filespace) < 0 ) {
            pass = false;
            failure_mssg = "H5Sclose(filespace) failed.\n";
        }
    }

    if ( pass || (file_id != -1) ) {
        if ( H5Fclose(file_id) < 0 ) {
            pass = false;
            failure_mssg = "H5Fclose(file_id) failed.\n";
        }
    }

    if ( pass || (fapl_id != -1) ) {
        if ( H5Pclose(fapl_id) < 0 ) {
            pass = false;
            failure_mssg = "H5Pclose(fapl_id) failed.\n";
        }
    }

    /* collect results from other processes.
     * Only overwrite the failure message if no preveious error 
     * has been detected
     */
    local_failure = ( pass ? 0 : 1 );

    if ( MPI_Allreduce( &local_failure, &global_failures, 1, 
                        MPI_INT, MPI_SUM, MPI_COMM_WORLD) != MPI_SUCCESS ) {
        if ( pass ) {
            pass = FALSE;
            failure_mssg = "MPI_Allreduce() failed.\n";
        }
    } else if ( ( pass ) && ( global_failures > 0 ) ) {
        pass = FALSE;
        failure_mssg = "One or more processes report failure.\n";
    }

    /* report results and finish cleanup */
    if ( group_rank == 0 ) {
        if ( pass ) {
            PASSED();
        } else {
            H5_FAILED();
            HDfprintf(stdout, "%s: failure_mssg = \"%s\"\n",
                      fcn_name, failure_mssg);
        }

        HDremove(reloc_data_filename);
    }

    /* free data_slice if it has been allocated */
    if ( data_slice != NULL ) {
        HDfree(data_slice);
        data_slice = NULL;
    }


    return( ! pass );     

} /* test_parallel_read() */


/*-------------------------------------------------------------------------
 * Function:    main
 *
 * Purpose:     To implement a parallel test which validates whether the
 *              new superblock lookup functionality is working correctly.
 *
 *              The test consists of creating two seperate HDF datasets
 *              in which random text is inserted at the start of each
 *              file using the 'j5jam' application.  This forces the
 *              HDF5 file superblock to a non-zero offset.
 *              Having created the two independant files, we create two
 *              non-overlapping MPI groups, each of which is then tasked
 *              with the opening and validation of the data contained
 *              therein.
 *
 *              WARNING: This test uses fork() and execve(), and
 *                       therefore will not run on Windows.
 *
 * Return:      Success: 0
 *
 *              Failure: 1
 *
 * Programmer:  Richard Warren
 *              10/1/17
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */

int
main( int argc, char **argv)
{
    int nerrs = 0;
    int which_group = 0;
    int mpi_rank;
    int mpi_size;
    int split_size;
    MPI_Comm group_comm = MPI_COMM_WORLD;

    if ( (MPI_Init(&argc, &argv)) != MPI_SUCCESS) {
       HDfprintf(stderr, "FATAL: Unable to initialize MPI\n");
       HDexit(EXIT_FAILURE);
    }

    if ( (MPI_Comm_rank(MPI_COMM_WORLD, &mpi_rank)) != MPI_SUCCESS) {
        HDfprintf(stderr, "FATAL: MPI_Comm_rank returned an error\n");
        HDexit(EXIT_FAILURE);
    }

    if ( (MPI_Comm_size(MPI_COMM_WORLD, &mpi_size)) != MPI_SUCCESS) {
        HDfprintf(stderr, "FATAL: MPI_Comm_size returned an error\n");
        HDexit(EXIT_FAILURE);
    }

    H5open();

    if ( mpi_rank == 0 ) {
        HDfprintf(stdout, "========================================\n");
        HDfprintf(stdout, "Collective file open optimization tests\n");
        HDfprintf(stdout, "        mpi_size     = %d\n", mpi_size);
        HDfprintf(stdout, "========================================\n");
    }

    if ( mpi_size < 4 ) {

        if ( mpi_rank == 0 ) {

            HDprintf("    Need at least 4 processes.  Exiting.\n");
        }
        goto finish;
    }

    /* ------  Create two (2) MPI groups  ------
     *
     * We split MPI_COMM_WORLD into 2 more or less equal sized 
     * groups.  The resulting communicators will be used to generate
     * two HDF files which in turn will be opened in parallel and the
     * contents verified in the second read test below.
     */
    split_size = mpi_size / 2;
    which_group = (mpi_rank < split_size ? 0 : 1);

    if ( (MPI_Comm_split(MPI_COMM_WORLD,
                         which_group,
                         0,
                         &group_comm)) != MPI_SUCCESS) {

        HDfprintf(stderr, "FATAL: MPI_Comm_split returned an error\n");
        HDexit(EXIT_FAILURE);
    }

    /* ------  Generate all files ------ */

    /* We generate the file used for test 1 */
    nerrs += generate_test_file( MPI_COMM_WORLD, mpi_rank, which_group );

    if ( nerrs > 0 ) {
        if ( mpi_rank == 0 ) {
            HDprintf("    Test(1) file construction failed -- skipping tests.\n");
        }
        goto finish;
    }
    
    /* We generate the file used for test 2 */
    nerrs += generate_test_file( group_comm, mpi_rank, which_group );

    if ( nerrs > 0 ) {
        if ( mpi_rank == 0 ) {
            HDprintf("    Test(2) file construction failed -- skipping tests.\n");
        }
        goto finish;
    }

    /* Now read the generated test file (stil using MPI_COMM_WORLD) */
    nerrs += test_parallel_read( MPI_COMM_WORLD, mpi_rank, which_group);

    if ( nerrs > 0 ) {
        if ( mpi_rank == 0 ) {
            HDprintf("    Parallel read test(1) failed -- skipping tests.\n");
        }
        goto finish;
    }

    /* Update the user on our progress so far. */
    if ( mpi_rank == 0 ) {
        HDprintf("    Test 1 of 2 succeeded\n");
        HDprintf("    -- Starting multi-group parallel read test.\n");
    }

    /* run the 2nd set of tests */
    nerrs += test_parallel_read(group_comm, mpi_rank, which_group);

    if ( nerrs > 0 ) {
        if ( mpi_rank == 0 ) {
            HDprintf("    Multi-group read test(2) failed\n");
        }
        goto finish;
    }

    if ( mpi_rank == 0 ) {
        HDprintf("    Test 2 of 2 succeeded\n");
    }

finish:

    if ((group_comm != MPI_COMM_NULL) &&
        (MPI_Comm_free(&group_comm)) != MPI_SUCCESS) {
        HDfprintf(stderr, "MPI_Comm_free failed!\n");
    }


    /* make sure all processes are finished before final report, cleanup
     * and exit.
     */
    MPI_Barrier(MPI_COMM_WORLD);

    if ( mpi_rank == 0 ) {           /* only process 0 reports */
        const char *header = "Collective file open optimization tests";

        HDfprintf(stdout, "===================================\n");
        if ( nerrs > 0 ) {
            
            HDfprintf(stdout, "***%s detected %d failures***\n", header, nerrs);
        }
        else {
            HDfprintf(stdout, "%s finished with no failures\n", header);
        }
        HDfprintf(stdout, "===================================\n");
    }

    /* close HDF5 library */
    if (H5close() != SUCCEED) {
        HDfprintf(stdout, "H5close() failed. (Ignoring)\n");
    }

    /* MPI_Finalize must be called AFTER H5close which may use MPI calls */
    MPI_Finalize();

    /* cannot just return (nerrs) because exit code is limited to 1byte */
    return((nerrs > 0) ? EXIT_FAILURE : EXIT_SUCCESS );

} /* main() */