Add support for distributed cholla datasets.

yt/frontends/cholla/data_structures.py

@@ -5,19 +5,50 @@
 
 from yt.data_objects.index_subobjects.grid_patch import AMRGridPatch
 from yt.data_objects.static_output import Dataset
-from yt.funcs import setdefaultattr
+from yt.funcs import get_pbar, setdefaultattr
 from yt.geometry.api import Geometry
 from yt.geometry.grid_geometry_handler import GridIndex
 from yt.utilities.on_demand_imports import _h5py as h5py
 
 from .fields import ChollaFieldInfo
 
 
+def _split_fname_proc_suffix(filename: str):
+    """Splits ``filename`` at the '.' separating the beginning part of the
+    string from the process-id suffix, and returns both parts in a 2-tuple.
+
+    When cholla is compiled with MPI and it directly writes data-files, each
+    process appends a suffix to each filename that denotes the process-id. For
+    example, the MPI-compiled version might write '0.h5.0'. If that function is
+    passed such a string, then it returns ``('0.h5', '0')``.
+
+    In cases where there is no suffix, the output is ``(filename, '')``. This
+    might come up if the user concatenated the output files, which is common
+    practice.
+    """
+
+    # at this time, we expect the suffix to be the minimum number of characters
+    # that are necessary to represent the process id. For flexibility, we will
+    # allow extra zero-padding
+
+    sep_i = filename.rfind(".")
+    suf_len = len(filename) - (sep_i + 1)
+    if (sep_i == -1) or (suf_len == 0) or not filename[sep_i + 1 :].isdecimal():
+        return (filename, "")
+    elif (sep_i == 0) or ((sep_i - 1) == filename.rfind("/")):
+        raise ValueError(
+            f"can't split a process-suffix off of {filename!r} "
+            "since the remaining filename would be empty"
+        )
+    else:
+        return (filename[:sep_i], filename[sep_i + 1 :])
+
+
 class ChollaGrid(AMRGridPatch):
     _id_offset = 0
 
-    def __init__(self, id, index, level, dims):
-        super().__init__(id, filename=index.index_filename, index=index)
+    def __init__(self, id, index, level, dims, filename):
+        super().__init__(id, filename=filename, index=index)
         self.Parent = None
         self.Children = []
         self.Level = level
@@ -42,23 +73,92 @@ def _detect_output_fields(self):
             self.field_list = [("cholla", k) for k in h5f.keys()]
 
     def _count_grids(self):
-        self.num_grids = 1
+        # the number of grids is equal to the number of processes, unless the
+        # dataset has been concatenated. But, when the dataset is concatenated
+        # (a common post-processing step), the "nprocs" hdf5 attribute is
+        # usually dropped.
+
+        with h5py.File(self.index_filename, mode="r") as h5f:
+            nprocs = h5f.attrs.get("nprocs", np.array([1, 1, 1]))[:].astype("=i8")
+        self.num_grids = np.prod(nprocs)
+
+        if self.num_grids > 1:
+            # When there's more than 1 grid, we expect the user to
+            # - have not changed the names of the output files
+            # - have passed the file written by process 0 to ``yt.load``
+            # Let's perform a sanity-check that self.index_filename has the
+            # expected suffix for a file written by mpi-process 0
+            if int(_split_fname_proc_suffix(self.index_filename)[1]) != 0:
+                raise ValueError(
+                    "the primary file associated with a "
+                    "distributed cholla dataset must end in '.0'"
+                )
 
     def _parse_index(self):
-        self.grid_left_edge[0][:] = self.ds.domain_left_edge[:]
-        self.grid_right_edge[0][:] = self.ds.domain_right_edge[:]
-        self.grid_dimensions[0][:] = self.ds.domain_dimensions[:]
-        self.grid_particle_count[0][0] = 0
-        self.grid_levels[0][0] = 0
+        self.grids = np.empty(self.num_grids, dtype="object")
+
+        # construct an iterable over the pairs of grid-index and corresponding
+        # filename
+        if self.num_grids == 1:
+            ind_fname_pairs = [(0, self.index_filename)]
+        else:
+            # index_fname should has the form f'{self.directory}/<prefix>.0'
+            # strip off the '.0' and determine the contents of <prefix>
+            pref, suf = _split_fname_proc_suffix(self.index_filename)
+            assert int(suf) == 0  # sanity check!
+
+            ind_fname_pairs = ((i, f"{pref}.{i}") for i in range(self.num_grids))
+
+        dims_global = self.ds.domain_dimensions[:]
+        pbar = get_pbar("Parsing Hierarchy", self.num_grids)
+
+        # It would be nice if we could avoid reading in every hdf5 file during
+        # this step... (to do this, Cholla could probably encode how the blocks
+        # are sorted in an hdf5 attribute)
+
+        for i, fname in ind_fname_pairs:
+            if self.num_grids == 1:
+                # if the file was concatenated, we might be missing attributes
+                # that are accessed in the other branch. To avoid issues, we use
+                # hardcoded values
+                left_frac, right_frac, dims_local = 0.0, 1.0, dims_global
+            else:
+                with h5py.File(fname, "r") as f:
+                    offset = f.attrs["offset"][:].astype("=i8")
+                    dims_local = f.attrs["dims_local"][:].astype("=i8")
+                left_frac = offset / dims_global
+                right_frac = (offset + dims_local) / dims_global
+
+            level = 0
+
+            self.grids[i] = self.grid(
+                i,
+                index=self,
+                level=level,
+                dims=dims_local,
+                filename=self.index_filename,
+            )
+
+            self.grid_left_edge[i] = left_frac
+            self.grid_right_edge[i] = right_frac
+            self.grid_dimensions[i] = dims_local
+            self.grid_levels[i, 0] = level
+            self.grid_particle_count[i, 0] = 0
+
+            pbar.update(i + 1)
+        pbar.finish()
+
+        slope = self.ds.domain_width / self.ds.arr(np.ones(3), "code_length")
+        self.grid_left_edge = self.grid_left_edge * slope + self.ds.domain_left_edge
+        self.grid_right_edge = self.grid_right_edge * slope + self.ds.domain_left_edge
+
         self.max_level = 0
 
     def _populate_grid_objects(self):
-        self.grids = np.empty(self.num_grids, dtype="object")
         for i in range(self.num_grids):
-            g = self.grid(i, self, self.grid_levels.flat[i], self.grid_dimensions[i])
+            g = self.grids[i]
             g._prepare_grid()
             g._setup_dx()
-            self.grids[i] = g
 
 
 class ChollaDataset(Dataset):
@@ -103,9 +203,11 @@ def _parse_parameter_file(self):
             attrs = h5f.attrs
             self.parameters = dict(attrs.items())
             self.domain_left_edge = attrs["bounds"][:].astype("=f8")
-            self.domain_right_edge = attrs["domain"][:].astype("=f8")
+            self.domain_right_edge = self.domain_left_edge + attrs["domain"][:].astype(
+                "=f8"
+            )
             self.dimensionality = len(attrs["dims"][:])
-            self.domain_dimensions = attrs["dims"][:].astype("=f8")
+            self.domain_dimensions = attrs["dims"][:].astype("=i8")
             self.current_time = attrs["t"][:]
             self._periodicity = tuple(attrs.get("periodicity", (False, False, False)))
             self.gamma = attrs.get("gamma", 5.0 / 3.0)

yt/frontends/cholla/io.py

@@ -1,4 +1,3 @@
-import numpy as np
 
 from yt.utilities.io_handler import BaseIOHandler
 from yt.utilities.on_demand_imports import _h5py as h5py
@@ -14,22 +13,24 @@ def _read_particle_coords(self, chunks, ptf):
     def _read_particle_fields(self, chunks, ptf, selector):
         raise NotImplementedError
 
-    def _read_fluid_selection(self, chunks, selector, fields, size):
-        data = {}
-        for field in fields:
-            data[field] = np.empty(size, dtype="float64")
-
-        with h5py.File(self.ds.parameter_filename, "r") as fh:
-            ind = 0
-            for chunk in chunks:
-                for grid in chunk.objs:
-                    nd = 0
-                    for field in fields:
-                        ftype, fname = field
-                        values = fh[fname][:].astype("=f8")
-                        nd = grid.select(selector, values, data[field], ind)
-                    ind += nd
-        return data
+    def io_iter(self, chunks, fields):
+        # this is loosely inspired by the implementation used for Enzo/Enzo-E
+        # - those other options use the lower-level hdf5 interface. Unclear
+        #   whether that affords any advantages...
+        fh, filename = None, None
+        for chunk in chunks:
+            for obj in chunk.objs:
+                if obj.filename is None:  # unclear when this case arises...
+                    continue
+                elif obj.filename != filename:
+                    if fh is not None:
+                        fh.close()
+                    fh, filename = h5py.File(obj.filename, "r"), obj.filename
+                for field in fields:
+                    ftype, fname = field
+                    yield field, obj, fh[fname][:].astype("=f8")
+        if fh is not None:
+            fh.close()
 
     def _read_chunk_data(self, chunk, fields):
         raise NotImplementedError