Fortran API

Module: fortran/ReadConDb/src/readcon_db.f90 (bind(C) to rkrdb_*).

Link libreadcon_db from a checkout (cargo build --release) or from the prebuilt readcon-db-clib-$VERSION-$target.tar.gz Release asset (no local cargo). See install and fortran/README.md.

use readcon_db
integer(c_size_t) :: id
integer(c_int) :: status
integer(c_int32_t) :: n
call db_open("/tmp/corpus"//c_null_char, id, status)
call db_append(id, 1_c_int64_t, "run.con", n, status)
call db_append_units(id, 1_c_int64_t, "run.con", &
  '{"length":"A","energy":"ev"}', n, status)
call db_extend_units(id, 1_c_int64_t, "more.con", &
  '{"length":"angstrom","energy":"eV"}', n, status)
call db_select_basic(id, 1_c_int64_t, "Cu", 1, 100000, 0, status)

See helpers db_open, db_append, db_select_basic, db_result_count, db_result_key, db_frame_hash, db_xxh3_128 in the module source. Point your build system at include/ for the C header if needed and target/release/ (or the clib prefix lib/ + PKG_CONFIG_PATH). Campaign shard/drain/join is the CLI; a Fortran rank that owns one shard opens root/shard_XXXX with db_open (campaign ops).

MPI: pack on root, Bcast on the caller INTEGER communicator

Fortran MPI communicators are INTEGER. Pass the handle the host already has (LAMMPS world / sub-comm). MPI_Bcast on that integer; do not substitute MPI_COMM_WORLD unless that is the handle the host passed. Do not MPI_Init if the host already did (MPI_Initialized).

use mpi
use readcon_db
! comm is the INTEGER the host owns (LAMMPS world / a Dup)
if (rank == 0) then
  call db_open_readonly(corpus, id, status)
  call db_pack_frame(id, traj, frame, buf, buflen, nbytes, status)
  call db_close(id, status)
end if
call MPI_Bcast(nbytes, 1, MPI_INTEGER, 0, comm, ierr)
call MPI_Bcast(buf, nbytes, MPI_BYTE, 0, comm, ierr)
call db_unpack_positions(buf, int(nbytes, c_size_t), xyz, cap, natoms, status)

C helpers from Fortran INTEGER: rkrdb_bcast_packed_frame_f and rkrdb_bcast_packed_frames_f in include/readcon-db-mpi.h (MPI_Comm_f2c). Batched helper packs an RCSB envelope on root and MPI_Bcasts it on comm. Module db_pack_frame packs one RCSO blob (buflen=0 size-queries). db_pack_frames packs an RCSB envelope of many frames (buflen=0 size-queries). Unpack with db_unpack_batch_nframes and db_unpack_batch_item. Standalone: examples/mpi_bcast_frame.f90.

H5MD interchange and caller units: db_append_units, db_set_units, db_h5md_times, db_h5md_shape, db_h5md_positions (dest ps / Å). C symbols are rkrdb_append_trajectory_units, rkrdb_extend_trajectory_units, rkrdb_set_units, rkrdb_frame_units, rkrdb_h5md_times, rkrdb_h5md_shape, rkrdb_h5md_positions, rkrdb_h5md_edges, rkrdb_h5md_forces, rkrdb_h5md_velocities, rkrdb_h5md_species. Fortran also has db_extend, db_extend_units, db_frame_units, db_h5md_edges, db_h5md_forces, db_h5md_velocities, db_h5md_species, db_get_positions, db_get_forces, db_get_velocities, db_cook_frame, db_delete_cooked, db_has_valid_cooked, and db_recook_all. Status constants include rkrdb_ok, rkrdb_err, and rkrdb_not_found. CON line-2 units is the authority.

Cooked SoA (RCSO)

See docs/orgmode/cooked-soa.org. Tier is opt-in; CON text remains authority. Fortran exposes cook / delete / has-valid / db_get_positions / db_get_forces / db_get_velocities.