Python coprocessing example

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This example is used to demonstrate how the co-processing library can be used with a python based simulation code. Note that this example requires MPI to be available on your system as well as pyMPI to initialize and finalize MPI from the python script. The executable takes in a python co-processing script and a number of time steps to be run for. Note to remember to set your system environment properly. See [[1]] for details.

Serial python driver code

import sys
if len(sys.argv) != 3:
    print "command is 'python <python driver code> <script name> <number of time steps>'"
    sys.exit(1)
import paraview
import paraview.vtk as vtk
 
def coProcess(grid, time, step, scriptname):
    import vtkCoProcessorPython # import libvtkCoProcessorPython for older PV versions
    if scriptname.endswith(".py"):
        scriptname = scriptname[0:len(scriptname)-3]#scriptname.rstrip(".py")
    try:
        cpscript = __import__(scriptname)
    except:
        print 'Cannot find ', scriptname, ' -- no coprocessing will be performed.'
        return
 
    datadescription = vtkCoProcessorPython.vtkCPDataDescription()
    datadescription.SetTimeData(time, step)
    datadescription.AddInput("input")
    cpscript.RequestDataDescription(datadescription)
    inputdescription = datadescription.GetInputDescriptionByName("input")
    if inputdescription.GetIfGridIsNecessary() == False:
        return
 
    inputdescription.SetGrid(grid)
    inputdescription.SetWholeExtent(grid.GetWholeExtent())
    cpscript.DoCoProcessing(datadescription)
 
try:
    numsteps = int(sys.argv[2])
except ValueError:
    print 'the last argument should be a number, setting the number of time steps to 10'
    numsteps = 10
 
for step in range(numsteps):
    # assume simulation time starts at 0
    time = step/float(numsteps)
 
    # create the input to the coprocessing library.  normally
    # this will come from the adaptor
    imageData = vtk.vtkImageData()
    imageData.SetOrigin(0, 0, 0)
    imageData.SetSpacing(.1, .1, .1)
    imageData.SetExtent(0, 10, 0, 12, 0, 12)
    imageData.SetWholeExtent(imageData.GetExtent())
    pointArray = vtk.vtkDoubleArray()
    pointArray.SetNumberOfTuples(imageData.GetNumberOfPoints())
    for i in range(imageData.GetNumberOfPoints()):
        pointArray.SetValue(i, i)
    pointArray.SetName("pointData")
    imageData.GetPointData().AddArray(pointArray)
 
    # "perform" coprocessing.  results are outputted only if
    # the passed in script says we should at time/step
    coProcess(imageData, time, step, sys.argv[1])

Parallel python driver code

import sys
if len(sys.argv) != 3:
  print "command is 'mpirun -np <#> pyMPI parallelexample.py <script name> <number of time steps>'"
  sys.exit(1)
 
import paraview
import paraview.vtk as vtk
 
import mpi
mpi.initialized()
 
import paraview
import libvtkParallelPython
import paraview.simple
import vtk
 
# set up ParaView to properly use MPI
pm = paraview.servermanager.vtkProcessModule.GetProcessModule()
globalController = pm.GetGlobalController()
if globalController == None or globalController.IsA("vtkDummyController") == True:
  globalController = vtk.vtkMPIController()
  globalController.Initialize()
  globalController.SetGlobalController(globalController)
 
def coProcess(grid, simtime, simstep, scriptname):
  # the name of the library was changed so for previous version of ParaView
  # you have to import libvtkCoProcessorPython instead of vtkCoProcessorPython
  #import libvtkCoProcessorPython as vtkCoProcessorPython
  import vtkCoProcessorPython
  if scriptname.endswith(".py"):
    scriptname = scriptname[0:len(scriptname)-3]#scriptname.rstrip(".py")
  try:
    cpscript = __import__(scriptname)
  except:
    print 'Cannot find ', scriptname, ' -- no coprocessing will be performed.'
    return
 
  datadescription = vtkCoProcessorPython.vtkCPDataDescription()
  datadescription.SetTimeData(simtime, simstep)
  datadescription.AddInput("input")
  cpscript.RequestDataDescription(datadescription)
  inputdescription = datadescription.GetInputDescriptionByName("input")
  if inputdescription.GetIfGridIsNecessary() == False:
    return
  import paraview.simple
  extents = grid.GetWholeExtent()
  inputdescription.SetWholeExtent(extents)
  inputdescription.SetGrid(grid)
  cpscript.DoCoProcessing(datadescription)
 
def createGrid(time):
  """
  Create a vtkImageData and a point data field called 'pointData'.
  time is used to make the field time varying. The grid is
  partitioned in slices in the x-direction here but that is
  not required.
  """
  imageData = vtk.vtkImageData()
  imageData.Initialize()
  imageData.SetOrigin(0, 0, 0)
  imageData.SetSpacing(.1, .1, .1)
  imageData.SetWholeExtent(0, 2*mpi.size, 0, 5, 0, 5)
  imageData.SetExtent(mpi.rank*2, (mpi.rank+1)*2, 0, 5, 0, 5)
  pointArray = vtk.vtkDoubleArray()
  pointArray.SetNumberOfTuples(imageData.GetNumberOfPoints())
  for i in range(imageData.GetNumberOfPoints()):
    pointArray.SetValue(i, i+time)
  pointArray.SetName("pointData")
  imageData.GetPointData().AddArray(pointArray)
 
  return imageData
 
try:
  numsteps = int(sys.argv[2])
except ValueError:
  print 'the last argument should be a number, setting the number of time steps to 10'
  numsteps = 10
 
for step in range(numsteps):
  # assume simulation time starts at 0
  time = step/float(numsteps)
 
  # create the input to the coprocessing library.  normally
  # this will come from the adaptor
  grid = createGrid(time)
 
  # "perform" coprocessing.  results are outputted only if
  # the passed in script says we should at time/step
  coProcess(grid, time, step, sys.argv[1])
 
 
globalController.SetGlobalController(None)
globalController = None
mpi.finalized()

Sample coprocessing script

try: paraview.simple
except: from paraview.simple import *
 
def RequestDataDescription(datadescription):
    "Callback to populate the request for current timestep"
    timestep = datadescription.GetTimeStep()
    input_name = 'input'
    if (timestep % 1 == 0) :
        datadescription.GetInputDescriptionByName(input_name).AllFieldsOn()
        datadescription.GetInputDescriptionByName(input_name).GenerateMeshOn()
    else:
        datadescription.GetInputDescriptionByName(input_name).AllFieldsOff()
        datadescription.GetInputDescriptionByName(input_name).GenerateMeshOff()
 
def DoCoProcessing(datadescription):
    "Callback to do co-processing for current timestep"
    cp_writers = []
    timestep = datadescription.GetTimeStep()
 
    grid = CreateProducer( datadescription, "input" )
    ImageWriter1 = CreateWriter( XMLPImageDataWriter, "input_grid_%t.pvti", 1, cp_writers )
 
    for writer in cp_writers:
        if timestep % writer.cpFrequency == 0:
            writer.FileName = writer.cpFileName.replace("%t", str(timestep))
            writer.UpdatePipeline()
 
    # explicitly delete the proxies -- we do it this way to avoid problems with prototypes
    tobedeleted = GetNextProxyToDelete()
    while tobedeleted != None:
        Delete(tobedeleted)
        tobedeleted = GetNextProxyToDelete()
 
def GetNextProxyToDelete():
    proxyiterator = servermanager.ProxyIterator()
    for proxy in proxyiterator:
        group = proxyiterator.GetGroup()
        if group.find("prototypes") != -1:
            continue
        if group != 'timekeeper' and group.find("pq_helper_proxies") == -1 :
            return proxy
    return None
 
def CreateProducer(datadescription, gridname):
    "Creates a producer proxy for the grid"
    if not datadescription.GetInputDescriptionByName(gridname):
        raise RuntimeError, "Simulation input name '%s' does not exist" % gridname
    grid = datadescription.GetInputDescriptionByName(gridname).GetGrid()
    producer = PVTrivialProducer()
    producer.GetClientSideObject().SetOutput(grid)
    if grid.IsA("vtkImageData") == True or grid.IsA("vtkStructuredGrid") == True or grid.IsA("vtkRectilinearGrid") == True:
        extent = datadescription.GetInputDescriptionByName(gridname).GetWholeExtent()
        producer.WholeExtent= [ extent[0], extent[1], extent[2], extent[3], extent[4], extent[5] ]
    producer.UpdatePipeline()
    return producer
 
def CreateWriter(proxy_ctor, filename, freq, cp_writers):
    writer = proxy_ctor()
    writer.FileName = filename
    writer.add_attribute("cpFrequency", freq)
    writer.add_attribute("cpFileName", filename)
    cp_writers.append(writer)
    return writer