Solution for posix I/O where everyone writes

Author: mlouhivu

solutions/mpi/c/posix-io/separate-files.c

@@ -0,0 +1,91 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <mpi.h>
+
+#define DATASIZE   64
+#define WRITER_ID   0
+
+void single_writer(int, int *, int);
+void many_writers(int, int *, int);
+
+
+int main(int argc, char *argv[])
+{
+    int my_id, ntasks, i, localsize;
+    int *localvector;
+
+    MPI_Init(&argc, &argv);
+    MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
+    MPI_Comm_rank(MPI_COMM_WORLD, &my_id);
+
+    if (ntasks > 64) {
+        fprintf(stderr, "Datasize (64) should be divisible by number "
+                "of tasks.\n");
+        MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
+    }
+
+    if (DATASIZE % ntasks != 0) {
+        fprintf(stderr, "Datasize (64) should be divisible by number "
+                "of tasks.\n");
+        MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
+    }
+
+    localsize = DATASIZE / ntasks;
+    localvector = (int *) malloc(localsize * sizeof(int));
+
+    for (i = 0; i < localsize; i++) {
+        localvector[i] = i + 1 + localsize * my_id;
+    }
+
+    many_writers(my_id, localvector, localsize);
+
+    free(localvector);
+
+    MPI_Finalize();
+    return 0;
+}
+
+void single_writer(int my_id, int *localvector, int localsize)
+{
+    FILE *fp;
+    int *fullvector;
+
+    fullvector = (int *) malloc(DATASIZE * sizeof(int));
+
+    MPI_Gather(localvector, localsize, MPI_INT, fullvector, localsize,
+               MPI_INT, WRITER_ID, MPI_COMM_WORLD);
+
+    if (my_id == WRITER_ID) {
+        if ((fp = fopen("singlewriter.dat", "wb")) == NULL) {
+            fprintf(stderr, "Error: %d (%s)\n", errno, strerror(errno));
+            MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
+        } else {
+            fwrite(fullvector, sizeof(int), DATASIZE, fp);
+            fclose(fp);
+            printf("Wrote %d elements to file singlewriter.dat\n", DATASIZE);
+        }
+    }
+
+    free(fullvector);
+}
+
+void many_writers(int my_id, int *localvector, int localsize)
+{
+    FILE *fp;
+    char filename[64];
+
+    sprintf(filename, "manywriters-%d.dat", my_id);
+
+    if ((fp = fopen(filename, "wb")) == NULL) {
+        fprintf(stderr, "Error: %d (%s)\n", errno, strerror(errno));
+        MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
+    } else {
+        fwrite(localvector, sizeof(int), localsize, fp);
+        fclose(fp);
+        printf("Wrote %d elements to file manywriters-%d.dat\n", localsize,
+                my_id);
+    }
+}
+

solutions/mpi/fortran/posix-io/separate-files.f90

@@ -0,0 +1,66 @@
+program pario
+  use mpi
+  use, intrinsic :: iso_fortran_env, only : error_unit, output_unit
+  implicit none
+
+  integer, parameter :: datasize = 64, writer_id = 0
+  integer :: rc, my_id, ntasks, localsize, i
+  integer, dimension(:), allocatable :: localvector
+  integer, dimension(datasize) :: fullvector
+
+  call mpi_init(rc)
+  call mpi_comm_size(mpi_comm_world, ntasks, rc)
+  call mpi_comm_rank(mpi_comm_world, my_id, rc)
+
+  if (ntasks > 64) then
+    write(error_unit, *) 'Maximum number of tasks is 64!'
+    call mpi_abort(MPI_COMM_WORLD, -1, rc)
+  end if
+
+  if (mod(datasize, ntasks) /= 0) then
+    write(error_unit,*) 'Datasize (64) should be divisible by number of tasks'
+    call mpi_abort(MPI_COMM_WORLD, -1, rc)
+  end if
+
+  localsize = datasize / ntasks
+  allocate(localvector(localsize))
+
+  localvector = [(i + my_id * localsize, i=1,localsize)]
+
+  call many_writers()
+
+  deallocate(localvector)
+  call mpi_finalize(rc)
+
+contains
+
+  subroutine single_writer()
+    implicit none
+
+    call mpi_gather(localvector, localsize, mpi_integer, fullvector, &
+         & localsize, mpi_integer, writer_id, mpi_comm_world, rc)
+    if (my_id == writer_id) then
+      open(10, file='singlewriter.dat', status='replace', form='unformatted', &
+           & access='stream')
+      write(10, pos=1) fullvector
+      close (10)
+      write(output_unit,'(A,I0,A)') 'Wrote ', size(fullvector), &
+           & ' elements to file singlewriter.dat'
+    end if
+  end subroutine single_writer
+
+  subroutine many_writers()
+    implicit none
+    character(len=85) :: filename
+
+    write(filename, '(A,I0,A)') 'manywriters-', my_id, '.dat'
+
+    open(my_id+10, file=filename, status='replace', form='unformatted', &
+         & access='stream')
+    write(my_id+10, pos=1) localvector
+    close (my_id+10)
+    write(output_unit,'(A,I0,A,A)') 'Wrote ', size(localvector), &
+         & ' elements to file ', filename
+  end subroutine many_writers
+
+end program pario