H5Part examples reviewed

examples/H5Part/read_canonicalview.c

@@ -9,21 +9,22 @@
 
 #include "H5hut.h"
 
-#define FNAME           "example_particles.h5"
-
+#define FNAME           "example_setview.h5"
+#define VERBOSITY       H5_VERBOSE_DEFAULT
 int
 main (
         int argc, char* argv[]
         ){
-        H5AbortOnError ();
-        H5SetVerbosityLevel (VERBOSITY);
-
-        int myproc;
+        // initialize MPI & H5hut
+        int mpi_rank = 0;
+        int mpi_size = 1;
         MPI_Init (&argc, &argv);
-        MPI_Comm_rank (MPI_COMM_WORLD, &myproc);
+        MPI_Comm comm = MPI_COMM_WORLD;
+        MPI_Comm_rank (comm, &mpi_rank);
+        MPI_Comm_size (comm, &mpi_size);
 
+        // open file and go to step#0
         h5_file_t file = H5OpenFile (FNAME, H5_O_RDONLY, H5_PROP_DEFAULT);
-
         H5SetStep (file, 0);
   
         H5PartSetCanonicalView (file);

examples/H5Part/read_setview.c

@@ -10,25 +10,54 @@
 #include "H5hut.h"
 #include "examples.h"
 
-#define FNAME           "example_particles.h5"
+#define FNAME           "example_setview.h5"
 
 int
 main (
         int argc, char* argv[]
         ){
-        H5AbortOnError ();
-        H5SetVerbosityLevel (VERBOSITY);
-
-        int myproc;
+        // initialize MPI & H5hut
+        int mpi_rank = 0;
+        int mpi_size = 1;
         MPI_Init (&argc, &argv);
-        MPI_Comm_rank (MPI_COMM_WORLD, &myproc);
+        MPI_Comm comm = MPI_COMM_WORLD;
+        MPI_Comm_rank (comm, &mpi_rank);
+        MPI_Comm_size (comm, &mpi_size);
 
+        // open file and go to step#0
         h5_file_t file = H5OpenFile (FNAME, H5_O_RDONLY, H5_PROP_DEFAULT);
-
         H5SetStep (file, 0);
 
-        // TODO
-  
+        // compute a "canonical" view: all cores get almost the same number of
+        // particles
+        h5_int64_t total_particles = H5PartGetNumParticles (file);
+        h5_int64_t nparticles = total_particles / mpi_size;
+        h5_int64_t remainder = total_particles % mpi_size;
+        h5_int64_t start = mpi_rank * nparticles;
+
+        // adjust number of local particles
+        if (mpi_rank < remainder)
+                nparticles++;
+
+        // adjust start
+        if (mpi_rank < remainder) 
+                start += mpi_rank;
+        else
+                start += remainder;
+        
+        // Note: if npartices is 0 end = start - 1
+        // this forces the selection of zero particles!
+        h5_int64_t end = start + nparticles - 1;
+        
+        printf ("[proc %d]: set view to [%lld..%lld]\n", mpi_rank, start, end);
+        H5PartSetView (file, start, end);
+        h5_int32_t* data = calloc (nparticles, sizeof (*data));
+
+        H5PartReadDataInt32 (file, "data", data);
+        for (int i = 0; i < nparticles; i++) {
+                printf ("[proc %d]: global index = %lld; local index = %d, value = %d\n",
+                        mpi_rank, start+i, i, data[i]);
+        }
         H5CloseFile (file);
         return MPI_Finalize ();
 }

examples/H5Part/write_setview.c

@@ -14,23 +14,24 @@
 #define DATASIZE        32
 #define ITERS           4
 
-int main (
+int
+main (
         int argc, char** argv
         ) {
-        h5_int64_t npoints = ITERS*DATASIZE
 
         // initialize MPI & H5hut
         MPI_Init (&argc, &argv);
         MPI_Comm comm = MPI_COMM_WORLD;
-        int rank = 0;
-        MPI_Comm_rank (comm, &rank);
+        int mpi_rank = 0;
+        MPI_Comm_rank (comm, &mpi_rank);
 
         H5AbortOnError ();
 
         // create fake data
+        h5_int64_t npoints = ITERS*DATASIZE;
         h5_int32_t data[ITERS*DATASIZE];
         for (int i = 0; i < npoints; i++) {
-                data[i] = i + rank*npoints;
+                data[i] = i + mpi_rank*npoints;
         }
 
         // open file and create step #0
@@ -42,7 +43,7 @@ int main (
         H5PartSetNumParticles(file, npoints);
 
         // write ITER consecutive blocks of size DATASIZE
-        h5_int64_t offset = rank * npoints;
+        h5_int64_t offset = mpi_rank * npoints;
         for (int i = 0; i < ITERS; i++) {
                 // set the "view" to select a subset of the dataset
                 H5PartSetView (