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June 1, 2011 / stevebaer

Multithreaded Python

One of the nice bits that we have access to in Rhino python is the Task Parallel Library that is built into .NET 4

This set of classes and functions makes it relatively easy to write things like parallel for loops in which every iteration of the loop may be processed on different threads. This nice thing about parallel for loops is that they make coding with multiple threads much simpler since the “multi-threading” only occurs inside the for loop and once the loop is finished you know that the all of the threads have completed and you are back on the main execution thread.

Here’s a sample python script which runs many Plane-Brep intersections either on a single thread or using multiple threads.

import System.Threading.Tasks as tasks
import Rhino
import rhinoscriptsyntax as rs
import time, math
import scriptcontext
def radial_contour(brep, parallel, slice_count=360):
"""Generate series of curve slices through a brep by rotating a plane
multiple times and intersecting that plane with the brep. This function
demonstrates the use of .NET Parallel.For in order to run the function
in parallel
brep = the Brep to contour
parallel = If True, this function will compute intersections in multiple
threads using Parallel.For. If False, all intersections will be performed
on a single thread
slice_count = number of slices to generate. Slices are evenly distributed
over a full circle
if not brep: return
results = range(slice_count)
rotation_axis = Rhino.Geometry.Vector3d(0,1,0)
intersect_tol = scriptcontext.doc.ModelAbsoluteTolerance
# local function that does the intersection work. This function is called
# once for each angle in "slice_count" and needs to be thread-safe
def slice_brep_at_angle(i):
angle_rad = i/slice_count * 2.0 * math.pi
plane = Rhino.Geometry.Plane.WorldXY
plane.Rotate(angle_rad, rotation_axis, Rhino.Geometry.Point3d.Origin)
rc, crvs, pts = Rhino.Geometry.Intersect.Intersection.BrepPlane(brep, plane, intersect_tol)
if rc: results[i] = crvs
else: results[i] = None
if parallel:
tasks.Parallel.ForEach(xrange(slice_count), slice_brep_at_angle)
for i in xrange(slice_count): slice_brep_at_angle(i)
return results
if __name__=="__main__":
brep = rs.GetObject("Select Brep", rs.filter.polysurface)
brep = rs.coercebrep(brep)
if brep:
# Make sure the Brep is not under the control of the document. This is
# just done so we know we have a quick to access local copy of the brep
# and nothing else can interfere while performing calculations
#run the function on a sinlge thread
start = time.time()
slices1 = radial_contour(brep, False)
end = time.time()
print "serial = ", endstart
#run the function on mulitple threads
start = time.time()
slices2 = radial_contour(brep, True)
end = time.time()
print "parallel = ", endstart
if slices2:
for curveset in slices2:
if curveset:
for curve in curveset: scriptcontext.doc.Objects.AddCurve(curve)

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