ad_nfs_write.c

MPICH是MPI的重要研究,提供了一系列的接口函数,为并行计算的实现提供了编程环境.

    else {  /* noncontiguous in file */

/* filetype already flattened in ADIO_Open */
	flat_file = ADIOI_Flatlist;
	while (flat_file->type != fd->filetype) flat_file = flat_file->next;
	disp = fd->disp;

	if (file_ptr_type == ADIO_INDIVIDUAL) {
	    offset = fd->fp_ind; /* in bytes */
	    n_filetypes = -1;
	    flag = 0;
	    while (!flag) {
                n_filetypes++;
		for (i=0; i<flat_file->count; i++) {
		    if (disp + flat_file->indices[i] + 
                        (ADIO_Offset) n_filetypes*filetype_extent + flat_file->blocklens[i] 
                            >= offset) {
			st_index = i;
			fwr_size = (int) (disp + flat_file->indices[i] + 
			        (ADIO_Offset) n_filetypes*filetype_extent
			         + flat_file->blocklens[i] - offset);
			flag = 1;
			break;
		    }
		}
	    }
	}
	else {
	    n_etypes_in_filetype = filetype_size/etype_size;
	    n_filetypes = (int) (offset / n_etypes_in_filetype);
	    etype_in_filetype = (int) (offset % n_etypes_in_filetype);
	    size_in_filetype = etype_in_filetype * etype_size;
 
	    sum = 0;
	    for (i=0; i<flat_file->count; i++) {
		sum += flat_file->blocklens[i];
		if (sum > size_in_filetype) {
		    st_index = i;
		    fwr_size = sum - size_in_filetype;
		    abs_off_in_filetype = flat_file->indices[i] +
			size_in_filetype - (sum - flat_file->blocklens[i]);
		    break;
		}
	    }

	    /* abs. offset in bytes in the file */
	    offset = disp + (ADIO_Offset) n_filetypes*filetype_extent + abs_off_in_filetype;
	}

        start_off = offset;

       /* Calculate end_offset, the last byte-offset that will be accessed.
         e.g., if start_offset=0 and 100 bytes to be write, end_offset=99*/

	st_fwr_size = fwr_size;
	st_n_filetypes = n_filetypes;
	i = 0;
	j = st_index;
	off = offset;
	fwr_size = ADIOI_MIN(st_fwr_size, bufsize);
	while (i < bufsize) {
	    i += fwr_size;
	    end_offset = off + fwr_size - 1;

	    if (j < (flat_file->count - 1)) j++;
	    else {
		j = 0;
		n_filetypes++;
	    }

	    off = disp + flat_file->indices[j] + (ADIO_Offset) n_filetypes*filetype_extent;
	    fwr_size = ADIOI_MIN(flat_file->blocklens[j], bufsize-i);
	}

/* if atomicity is true, lock the region to be accessed */
        if (fd->atomicity) 
            ADIOI_WRITE_LOCK(fd, start_off, SEEK_SET, end_offset-start_off+1);

        /* initial read for the read-modify-write */
        writebuf_off = offset;
        writebuf = (char *) ADIOI_Malloc(max_bufsize);
        writebuf_len = (int)(ADIOI_MIN(max_bufsize,end_offset-writebuf_off+1));
	if (!(fd->atomicity)) ADIOI_WRITE_LOCK(fd, writebuf_off, SEEK_SET, writebuf_len);
	lseek(fd->fd_sys, writebuf_off, SEEK_SET); 
	err = read(fd->fd_sys, writebuf, writebuf_len); 
        if (err == -1) {
            FPRINTF(stderr, "ADIOI_NFS_WriteStrided: ROMIO tries to optimize this access by doing a read-modify-write, but is unable to read the file. Please give the file read permission and open it with MPI_MODE_RDWR.\n"); 
            MPI_Abort(MPI_COMM_WORLD, 1); 
        } 

	if (buftype_is_contig && !filetype_is_contig) {

/* contiguous in memory, noncontiguous in file. should be the most
   common case. */

	    i = 0;
	    j = st_index;
	    off = offset;
	    n_filetypes = st_n_filetypes;
	    fwr_size = ADIOI_MIN(st_fwr_size, bufsize);
	    while (i < bufsize) {
                if (fwr_size) { 
                    /* TYPE_UB and TYPE_LB can result in 
                       fwr_size = 0. save system call in such cases */ 
		    /* lseek(fd->fd_sys, off, SEEK_SET);
		    err = write(fd->fd_sys, ((char *) buf) + i, fwr_size);*/

		    req_off = off;
		    req_len = fwr_size;
		    userbuf_off = i;
		    ADIOI_BUFFERED_WRITE
		}
		i += fwr_size;

                if (off + fwr_size < disp + flat_file->indices[j] +
                   flat_file->blocklens[j] + (ADIO_Offset) n_filetypes*filetype_extent)
                       off += fwr_size;
                /* did not reach end of contiguous block in filetype.
                   no more I/O needed. off is incremented by fwr_size. */
                else {
		    if (j < (flat_file->count - 1)) j++;
		    else {
			j = 0;
			n_filetypes++;
		    }
		    off = disp + flat_file->indices[j] + 
                                        (ADIO_Offset) n_filetypes*filetype_extent;
		    fwr_size = ADIOI_MIN(flat_file->blocklens[j], bufsize-i);
		}
	    }
	}
	else {
/* noncontiguous in memory as well as in file */

	    ADIOI_Flatten_datatype(datatype);
	    flat_buf = ADIOI_Flatlist;
	    while (flat_buf->type != datatype) flat_buf = flat_buf->next;

	    k = num = buf_count = 0;
	    i = (int) (flat_buf->indices[0]);
	    j = st_index;
	    off = offset;
	    n_filetypes = st_n_filetypes;
	    fwr_size = st_fwr_size;
	    bwr_size = flat_buf->blocklens[0];

	    while (num < bufsize) {
		size = ADIOI_MIN(fwr_size, bwr_size);
		if (size) {
		    /* lseek(fd->fd_sys, off, SEEK_SET);
		    err = write(fd->fd_sys, ((char *) buf) + i, size); */

		    req_off = off;
		    req_len = size;
		    userbuf_off = i;
		    ADIOI_BUFFERED_WRITE
		}

		new_fwr_size = fwr_size;
		new_bwr_size = bwr_size;

		if (size == fwr_size) {
/* reached end of contiguous block in file */
		    if (j < (flat_file->count - 1)) j++;
		    else {
			j = 0;
			n_filetypes++;
		    }

		    off = disp + flat_file->indices[j] + 
                                  (ADIO_Offset) n_filetypes*filetype_extent;

		    new_fwr_size = flat_file->blocklens[j];
		    if (size != bwr_size) {
			i += size;
			new_bwr_size -= size;
		    }
		}

		if (size == bwr_size) {
/* reached end of contiguous block in memory */

		    k = (k + 1)%flat_buf->count;
		    buf_count++;
		    i = (int) (buftype_extent*(buf_count/flat_buf->count) +
			flat_buf->indices[k]); 
		    new_bwr_size = flat_buf->blocklens[k];
		    if (size != fwr_size) {
			off += size;
			new_fwr_size -= size;
		    }
		}
		num += size;
		fwr_size = new_fwr_size;
                bwr_size = new_bwr_size;
	    }
	}

        /* write the buffer out finally */	
	lseek(fd->fd_sys, writebuf_off, SEEK_SET); 
	if (!(fd->atomicity)) ADIOI_WRITE_LOCK(fd, writebuf_off, SEEK_SET, writebuf_len);
	err = write(fd->fd_sys, writebuf, writebuf_len); 

        if (!(fd->atomicity))
	    ADIOI_UNLOCK(fd, writebuf_off, SEEK_SET, writebuf_len);
	else ADIOI_UNLOCK(fd, start_off, SEEK_SET, end_offset-start_off+1);

        if (err == -1) err_flag = 1; 

	ADIOI_Free(writebuf); /* malloced in the buffered_write macro */

	if (file_ptr_type == ADIO_INDIVIDUAL) fd->fp_ind = off;
#ifdef PRINT_ERR_MSG
	*error_code = (err_flag) ? MPI_ERR_UNKNOWN : MPI_SUCCESS;
#else
	if (err_flag) {
	    *error_code = MPIR_Err_setmsg(MPI_ERR_IO, MPIR_ADIO_ERROR,
			      myname, "I/O Error", "%s", strerror(errno));
	    ADIOI_Error(fd, *error_code, myname);
	}
	else *error_code = MPI_SUCCESS;
#endif
    }

    fd->fp_sys_posn = -1;   /* set it to null. */

#ifdef HAVE_STATUS_SET_BYTES
    MPIR_Status_set_bytes(status, datatype, bufsize);
/* This is a temporary way of filling in status. The right way is to 
   keep track of how much data was actually written by ADIOI_BUFFERED_WRITE. */
#endif

    if (!buftype_is_contig) ADIOI_Delete_flattened(datatype);
}