static char help[]= "Test event log of VecScatter with various block sizes\n\n";

#include <petscvec.h>

int main(int argc,char **argv)
{
  PetscInt           i,j,low,high,n=256,N,errors,tot_errors;
  PetscInt           bs=1,ix[2],iy[2];
  PetscMPIInt        nproc,rank;
  PetscScalar       *xval;
  const PetscScalar *yval;
  Vec                x,y;
  IS                 isx,isy;
  VecScatter         ctx;
  const PetscInt     niter = 10;
#if defined(PETSC_USE_LOG)
  PetscLogStage      stage1,stage2;
  PetscLogEvent      event1,event2;
  PetscLogDouble     numMessages,messageLength;
  PetscEventPerfInfo eventInfo;
  PetscInt           tot_msg,tot_len,avg_len;
#endif

  PetscFunctionBegin;
  PetscCall(PetscInitialize(&argc,&argv,(char*)0,help));
  PetscCall(PetscLogDefaultBegin());
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD,&nproc));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD,&rank));

  PetscCall(PetscLogStageRegister("Scatter(bs=1)", &stage1));
  PetscCall(PetscLogEventRegister("VecScatter(bs=1)", PETSC_OBJECT_CLASSID, &event1));
  PetscCall(PetscLogStageRegister("Scatter(bs=4)", &stage2));
  PetscCall(PetscLogEventRegister("VecScatter(bs=4)", PETSC_OBJECT_CLASSID, &event2));

  /* Create a parallel vector x and a sequential vector y */
  PetscCall(VecCreate(PETSC_COMM_WORLD,&x));
  PetscCall(VecSetSizes(x,n,PETSC_DECIDE));
  PetscCall(VecSetFromOptions(x));
  PetscCall(VecGetOwnershipRange(x,&low,&high));
  PetscCall(VecGetSize(x,&N));
  PetscCall(VecCreateSeq(PETSC_COMM_SELF,n,&y));

  /*=======================================
     test VecScatter with bs = 1
    ======================================*/

  /* the code works as if we are going to do 3-point stencil computations on a 1D domain x,
     which has periodic boundary conditions but the two ghosts are scatterred to beginning of y.
   */
  bs    = 1;
  ix[0] = rank? low-1 : N-1; /* ix[] contains global indices of the two ghost points */
  ix[1] = (rank != nproc-1)? high : 0;
  iy[0] = 0;
  iy[1] = 1;

  PetscCall(ISCreateGeneral(PETSC_COMM_SELF,2,ix,PETSC_COPY_VALUES,&isx));
  PetscCall(ISCreateGeneral(PETSC_COMM_SELF,2,iy,PETSC_COPY_VALUES,&isy));
  PetscCall(VecScatterCreate(x,isx,y,isy,&ctx));
  PetscCall(VecScatterSetUp(ctx));

  PetscCall(PetscLogStagePush(stage1));
  PetscCall(PetscLogEventBegin(event1,0,0,0,0));
  errors = 0;
  for (i=0; i<niter; i++) {
    /* set x = 0+i, 1+i, 2+i, ..., N-1+i */
    PetscCall(VecGetArray(x,&xval));
    for (j=0; j<n; j++) xval[j] = (PetscScalar)(low+j+i);
    PetscCall(VecRestoreArray(x,&xval));
    /* scatter the ghosts to y */
    PetscCall(VecScatterBegin(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD));
    PetscCall(VecScatterEnd(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD));
    /* check if y has correct values */
    PetscCall(VecGetArrayRead(y,&yval));
    if ((PetscInt)PetscRealPart(yval[0]) != ix[0]+i) errors++;
    if ((PetscInt)PetscRealPart(yval[1]) != ix[1]+i) errors++;
    PetscCall(VecRestoreArrayRead(y,&yval));
  }
  PetscCall(PetscLogEventEnd(event1,0,0,0,0));
  PetscCall(PetscLogStagePop());

  /* check if we found wrong values on any processors */
  PetscCallMPI(MPI_Allreduce(&errors,&tot_errors,1,MPIU_INT,MPI_SUM,PETSC_COMM_WORLD));
  if (tot_errors) PetscCall(PetscPrintf(PETSC_COMM_WORLD,"Error: wrong values were scatterred in vecscatter with bs = %" PetscInt_FMT "\n",bs));

  /* print out event log of VecScatter(bs=1) */
#if defined(PETSC_USE_LOG)
  PetscCall(PetscLogEventGetPerfInfo(stage1,event1,&eventInfo));
  PetscCallMPI(MPI_Allreduce(&eventInfo.numMessages,  &numMessages,  1,MPIU_PETSCLOGDOUBLE,MPI_SUM,PETSC_COMM_WORLD));
  PetscCallMPI(MPI_Allreduce(&eventInfo.messageLength,&messageLength,1,MPIU_PETSCLOGDOUBLE,MPI_SUM,PETSC_COMM_WORLD));
  tot_msg = (PetscInt)numMessages*0.5; /* two MPI calls (Send & Recv) per message */
  tot_len = (PetscInt)messageLength*0.5;
  avg_len = tot_msg? (PetscInt)(messageLength/numMessages) : 0;
  /* when nproc > 2, tot_msg = 2*nproc*niter, tot_len = tot_msg*sizeof(PetscScalar)*bs */
  PetscCall(PetscPrintf(PETSC_COMM_WORLD,"VecScatter(bs=%" PetscInt_FMT ") has sent out %" PetscInt_FMT " messages, total %" PetscInt_FMT " bytes, with average length %" PetscInt_FMT " bytes\n",bs,tot_msg,tot_len,avg_len));
#endif

  PetscCall(ISDestroy(&isx));
  PetscCall(ISDestroy(&isy));
  PetscCall(VecScatterDestroy(&ctx));

  /*=======================================
     test VecScatter with bs = 4
    ======================================*/

  /* similar to the 3-point stencil above, except that this time a ghost is a block */
  bs    = 4; /* n needs to be a multiple of bs to make the following code work */
  ix[0] = rank? low/bs-1 : N/bs-1; /* ix[] contains global indices of the two ghost blocks */
  ix[1] = (rank != nproc-1)? high/bs : 0;
  iy[0] = 0;
  iy[1] = 1;

  PetscCall(ISCreateBlock(PETSC_COMM_SELF,bs,2,ix,PETSC_COPY_VALUES,&isx));
  PetscCall(ISCreateBlock(PETSC_COMM_SELF,bs,2,iy,PETSC_COPY_VALUES,&isy));

  PetscCall(VecScatterCreate(x,isx,y,isy,&ctx));
   /* Call SetUp explicitly, otherwise messages in implicit SetUp will be counted in events below */
  PetscCall(VecScatterSetUp(ctx));

  PetscCall(PetscLogStagePush(stage2));
  PetscCall(PetscLogEventBegin(event2,0,0,0,0));
  errors = 0;
  for (i=0; i<niter; i++) {
    /* set x = 0+i, 1+i, 2+i, ..., N-1+i */
    PetscCall(VecGetArray(x,&xval));
    for (j=0; j<n; j++) xval[j] = (PetscScalar)(low+j+i);
    PetscCall(VecRestoreArray(x,&xval));
    /* scatter the ghost blocks to y */
    PetscCall(VecScatterBegin(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD));
    PetscCall(VecScatterEnd(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD));
    /* check if y has correct values */
    PetscCall(VecGetArrayRead(y,&yval));
    if ((PetscInt)PetscRealPart(yval[0])  != ix[0]*bs+i) errors++;
    if ((PetscInt)PetscRealPart(yval[bs]) != ix[1]*bs+i) errors++;
    PetscCall(VecRestoreArrayRead(y,&yval));
  }
  PetscCall(PetscLogEventEnd(event2,0,0,0,0));
  PetscCall(PetscLogStagePop());

  /* check if we found wrong values on any processors */
  PetscCallMPI(MPI_Allreduce(&errors,&tot_errors,1,MPIU_INT,MPI_SUM,PETSC_COMM_WORLD));
  if (tot_errors) PetscCall(PetscPrintf(PETSC_COMM_WORLD,"Error: wrong values were scatterred in vecscatter with bs = %" PetscInt_FMT "\n",bs));

  /* print out event log of VecScatter(bs=4) */
#if defined(PETSC_USE_LOG)
  PetscCall(PetscLogEventGetPerfInfo(stage2,event2,&eventInfo));
  PetscCallMPI(MPI_Allreduce(&eventInfo.numMessages,  &numMessages,  1,MPIU_PETSCLOGDOUBLE,MPI_SUM,PETSC_COMM_WORLD));
  PetscCallMPI(MPI_Allreduce(&eventInfo.messageLength,&messageLength,1,MPIU_PETSCLOGDOUBLE,MPI_SUM,PETSC_COMM_WORLD));
  tot_msg = (PetscInt)numMessages*0.5; /* two MPI calls (Send & Recv) per message */
  tot_len = (PetscInt)messageLength*0.5;
  avg_len = tot_msg? (PetscInt)(messageLength/numMessages) : 0;
  /* when nproc > 2, tot_msg = 2*nproc*niter, tot_len = tot_msg*sizeof(PetscScalar)*bs */
  PetscCall(PetscPrintf(PETSC_COMM_WORLD,"VecScatter(bs=%" PetscInt_FMT ") has sent out %" PetscInt_FMT " messages, total %" PetscInt_FMT " bytes, with average length %" PetscInt_FMT " bytes\n",bs,tot_msg,tot_len,avg_len));
#endif

  PetscCall(PetscPrintf(PETSC_COMM_WORLD,"Program finished\n"));
  PetscCall(ISDestroy(&isx));
  PetscCall(ISDestroy(&isy));
  PetscCall(VecScatterDestroy(&ctx));
  PetscCall(VecDestroy(&x));
  PetscCall(VecDestroy(&y));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      nsize: 4
      args:
      requires: double defined(PETSC_USE_LOG)

TEST*/