Parallel Processing

Parallel Processing#

Both CadQuery and GMSH use parallel processing for operations like imprinting and meshing. By default, they use all available CPU cores.

When to Limit Threads#

  • Shared servers: Avoid monopolizing all cores

  • Memory constraints: Each thread requires memory; fewer threads = lower peak memory

  • Debugging: Single-threaded execution can make errors easier to diagnose

Limiting CadQuery Threads#

CadQuery provides a setThreads function:

from cadquery.occ_impl.shapes import setThreads

setThreads(4)  # Limit to 4 threads

# Now run your geometry operations
import cadquery as cq
from cad_to_dagmc import CadToDagmc

# ...

Alternative: Configure Before Import#

import OCP
OCP.OSD.OSD_ThreadPool.DefaultPool_s(4)  # Limit to 4 threads

import cadquery as cq
from cad_to_dagmc import CadToDagmc

# ...

Alternative: Environment Variable#

export OMP_NUM_THREADS=4
python my_script.py

Or in Python:

import os
os.environ["OMP_NUM_THREADS"] = "4"

import cadquery as cq
from cad_to_dagmc import CadToDagmc

# ...

Limiting GMSH Threads#

GMSH parallelism is controlled through its own options:

import gmsh
import cad_to_dagmc

gmsh_obj = cad_to_dagmc.init_gmsh()

# Limit parallel meshing to 4 threads
gmsh.option.setNumber("General.NumThreads", 4)
gmsh.option.setNumber("Mesh.MaxNumThreads1D", 4)
gmsh.option.setNumber("Mesh.MaxNumThreads2D", 4)
gmsh.option.setNumber("Mesh.MaxNumThreads3D", 4)

# ... continue with meshing ...

Thread Options Summary#

Component

Method

When Applied

CadQuery

setThreads()

Any time before operations

CadQuery

OSD_ThreadPool.DefaultPool_s()

Before importing CadQuery

CadQuery

OMP_NUM_THREADS env var

Before Python starts

GMSH

General.NumThreads

After GMSH initialization

GMSH

Mesh.MaxNumThreads*D

After GMSH initialization

Complete Example#

import os
os.environ["OMP_NUM_THREADS"] = "4"  # For CadQuery

import cadquery as cq
from cadquery.occ_impl.shapes import setThreads
import gmsh
import cad_to_dagmc

# Limit CadQuery threads
setThreads(4)

# Create geometry
assembly = cq.Assembly()
assembly.add(cq.Workplane("XY").sphere(10))

# Initialize model
model = cad_to_dagmc.CadToDagmc()
model.add_cadquery_object(assembly, material_tags=["mat1"])

# For advanced GMSH control
gmsh_obj = cad_to_dagmc.init_gmsh()
gmsh.option.setNumber("General.NumThreads", 4)
gmsh.option.setNumber("Mesh.MaxNumThreads2D", 4)

# ... continue with export ...

Performance Considerations#

  • More threads generally = faster for large models

  • Memory usage scales with thread count

  • On small models, threading overhead may negate benefits

  • I/O bound operations don’t benefit much from parallelism

See Also#

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