static char help[] = "Demonstrates BuildTwoSided functions.\n";

#include <petscsys.h>

typedef struct {
  PetscInt    rank;
  PetscScalar value;
  char        ok[3];
} Unit;

static PetscErrorCode MakeDatatype(MPI_Datatype *dtype)
{
  MPI_Datatype dtypes[3], tmptype;
  PetscMPIInt  lengths[3];
  MPI_Aint     displs[3];
  Unit         dummy;

  PetscFunctionBegin;
  dtypes[0]  = MPIU_INT;
  dtypes[1]  = MPIU_SCALAR;
  dtypes[2]  = MPI_CHAR;
  lengths[0] = 1;
  lengths[1] = 1;
  lengths[2] = 3;
  /* Curse the evil beings that made std::complex a non-POD type. */
  displs[0] = (char *)&dummy.rank - (char *)&dummy;  /* offsetof(Unit,rank); */
  displs[1] = (char *)&dummy.value - (char *)&dummy; /* offsetof(Unit,value); */
  displs[2] = (char *)&dummy.ok - (char *)&dummy;    /* offsetof(Unit,ok); */
  PetscCallMPI(MPI_Type_create_struct(3, lengths, displs, dtypes, &tmptype));
  PetscCallMPI(MPI_Type_commit(&tmptype));
  PetscCallMPI(MPI_Type_create_resized(tmptype, 0, sizeof(Unit), dtype));
  PetscCallMPI(MPI_Type_commit(dtype));
  PetscCallMPI(MPI_Type_free(&tmptype));
  {
    MPI_Aint lb, extent;
    PetscCallMPI(MPI_Type_get_extent(*dtype, &lb, &extent));
    PetscCheck(extent == sizeof(Unit), PETSC_COMM_WORLD, PETSC_ERR_LIB, "New type has extent %d != sizeof(Unit) %d", (int)extent, (int)sizeof(Unit));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

struct FCtx {
  PetscMPIInt    rank;
  PetscMPIInt    nto;
  PetscMPIInt   *toranks;
  Unit          *todata;
  PetscSegBuffer seg;
};

static PetscErrorCode FSend(MPI_Comm comm, const PetscMPIInt tag[], PetscMPIInt tonum, PetscMPIInt rank, void *todata, MPI_Request req[], PetscCtx ctx)
{
  struct FCtx *fctx = (struct FCtx *)ctx;

  PetscFunctionBegin;
  PetscCheck(rank == fctx->toranks[tonum], PETSC_COMM_SELF, PETSC_ERR_PLIB, "Rank %d does not match toranks[%d] %d", rank, tonum, fctx->toranks[tonum]);
  PetscCheck(fctx->rank == *(PetscMPIInt *)todata, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Todata %d does not match rank %d", *(PetscMPIInt *)todata, fctx->rank);
  PetscCallMPI(MPI_Isend(&fctx->todata[tonum].rank, 1, MPIU_INT, rank, tag[0], comm, &req[0]));
  PetscCallMPI(MPI_Isend(&fctx->todata[tonum].value, 1, MPIU_SCALAR, rank, tag[1], comm, &req[1]));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode FRecv(MPI_Comm comm, const PetscMPIInt tag[], PetscMPIInt rank, void *fromdata, MPI_Request req[], PetscCtx ctx)
{
  struct FCtx *fctx = (struct FCtx *)ctx;
  Unit        *buf;

  PetscFunctionBegin;
  PetscCheck(*(PetscMPIInt *)fromdata == rank, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Dummy data %d from rank %d corrupt", *(PetscMPIInt *)fromdata, rank);
  PetscCall(PetscSegBufferGet(fctx->seg, 1, &buf));
  PetscCallMPI(MPI_Irecv(&buf->rank, 1, MPIU_INT, rank, tag[0], comm, &req[0]));
  PetscCallMPI(MPI_Irecv(&buf->value, 1, MPIU_SCALAR, rank, tag[1], comm, &req[1]));
  buf->ok[0] = 'o';
  buf->ok[1] = 'k';
  buf->ok[2] = 0;
  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char **argv)
{
  PetscMPIInt  rank, size, *toranks, *fromranks, nto, nfrom;
  PetscInt     i, n;
  PetscBool    verbose, build_twosided_f;
  Unit        *todata, *fromdata;
  MPI_Datatype dtype;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, NULL, help));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

  verbose = PETSC_FALSE;
  PetscCall(PetscOptionsGetBool(NULL, NULL, "-verbose", &verbose, NULL));
  build_twosided_f = PETSC_FALSE;
  PetscCall(PetscOptionsGetBool(NULL, NULL, "-build_twosided_f", &build_twosided_f, NULL));

  for (i = 1, nto = 0; i < size; i *= 2) nto++;
  PetscCall(PetscMalloc2(nto, &todata, nto, &toranks));
  for (n = 0, i = 1; i < size; n++, i *= 2) {
    toranks[n]      = (rank + i) % size;
    todata[n].rank  = (rank + i) % size;
    todata[n].value = (PetscScalar)rank;
    todata[n].ok[0] = 'o';
    todata[n].ok[1] = 'k';
    todata[n].ok[2] = 0;
  }
  if (verbose) {
    for (i = 0; i < nto; i++) PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "[%d] TO %d: {%" PetscInt_FMT ", %g, \"%s\"}\n", rank, toranks[i], todata[i].rank, (double)PetscRealPart(todata[i].value), todata[i].ok));
    PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT));
  }

  PetscCall(MakeDatatype(&dtype));

  if (build_twosided_f) {
    struct FCtx  fctx;
    PetscMPIInt *todummy, *fromdummy;
    fctx.rank    = rank;
    fctx.nto     = nto;
    fctx.toranks = toranks;
    fctx.todata  = todata;
    PetscCall(PetscSegBufferCreate(sizeof(Unit), 1, &fctx.seg));
    PetscCall(PetscMalloc1(nto, &todummy));
    for (i = 0; i < nto; i++) todummy[i] = rank;
    PetscCall(PetscCommBuildTwoSidedF(PETSC_COMM_WORLD, 1, MPI_INT, nto, toranks, todummy, &nfrom, &fromranks, &fromdummy, 2, FSend, FRecv, &fctx));
    PetscCall(PetscFree(todummy));
    PetscCall(PetscFree(fromdummy));
    PetscCall(PetscSegBufferExtractAlloc(fctx.seg, &fromdata));
    PetscCall(PetscSegBufferDestroy(&fctx.seg));
  } else {
    PetscCall(PetscCommBuildTwoSided(PETSC_COMM_WORLD, 1, dtype, nto, toranks, todata, &nfrom, &fromranks, &fromdata));
  }
  PetscCallMPI(MPI_Type_free(&dtype));

  if (verbose) {
    PetscInt *iranks, *iperm;
    PetscCall(PetscMalloc2(nfrom, &iranks, nfrom, &iperm));
    for (i = 0; i < nfrom; i++) {
      iranks[i] = fromranks[i];
      iperm[i]  = i;
    }
    /* Receive ordering is non-deterministic in general, so sort to make verbose output deterministic. */
    PetscCall(PetscSortIntWithPermutation(nfrom, iranks, iperm));
    for (i = 0; i < nfrom; i++) {
      PetscInt ip = iperm[i];
      PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "[%d] FROM %d: {%" PetscInt_FMT ", %g, \"%s\"}\n", rank, fromranks[ip], fromdata[ip].rank, (double)PetscRealPart(fromdata[ip].value), fromdata[ip].ok));
    }
    PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT));
    PetscCall(PetscFree2(iranks, iperm));
  }

  PetscCheck(nto == nfrom, PETSC_COMM_SELF, PETSC_ERR_PLIB, "[%d] From ranks %d does not match To ranks %d", rank, nto, nfrom);
  for (i = 1; i < size; i *= 2) {
    PetscMPIInt expected_rank = (rank - i + size) % size;
    PetscBool   flg;
    for (n = 0; n < nfrom; n++) {
      if (expected_rank == fromranks[n]) goto found;
    }
    SETERRQ(PETSC_COMM_WORLD, PETSC_ERR_PLIB, "[%d] Could not find expected from rank %d", rank, expected_rank);
  found:
    PetscCheck(PetscRealPart(fromdata[n].value) == expected_rank, PETSC_COMM_SELF, PETSC_ERR_PLIB, "[%d] Got data %g from rank %d", rank, (double)PetscRealPart(fromdata[n].value), expected_rank);
    PetscCall(PetscStrcmp(fromdata[n].ok, "ok", &flg));
    PetscCheck(flg, PETSC_COMM_SELF, PETSC_ERR_PLIB, "[%d] Got string %s from rank %d", rank, fromdata[n].ok, expected_rank);
  }
  PetscCall(PetscFree2(todata, toranks));
  PetscCall(PetscFree(fromdata));
  PetscCall(PetscFree(fromranks));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      nsize: 4
      args: -verbose -build_twosided allreduce

   test:
      suffix: f
      nsize: 4
      args: -verbose -build_twosided_f -build_twosided allreduce
      output_file: output/ex8_1.out

   test:
      suffix: f_ibarrier
      nsize: 4
      args: -verbose -build_twosided_f -build_twosided ibarrier
      output_file: output/ex8_1.out
      requires: defined(PETSC_HAVE_MPI_NONBLOCKING_COLLECTIVES)

   test:
      suffix: ibarrier
      nsize: 4
      args: -verbose -build_twosided ibarrier
      output_file: output/ex8_1.out
      requires: defined(PETSC_HAVE_MPI_NONBLOCKING_COLLECTIVES)

   test:
      suffix: redscatter
      requires: mpi_reduce_scatter_block
      nsize: 4
      args: -verbose -build_twosided redscatter
      output_file: output/ex8_1.out

TEST*/