Which methods are thread safe?

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
cpp
Domain
computer-graphics

Research direction

Start with the provided VectorHeatMethodSolver example, especially scalarDiffuse and its use inside tbb::parallel_for. Compare behavior with and without the initial scalarDiffuse call, then trace the solver routines involved. Done means establishing and documenting which routines are thread safe or identifying the changes needed for the example and the GCVT Lloyd loop.

Written by the indexing model from the issue text.

Description

question

As far as I can tell, some methods that seem like they'd be thread safe aren't.

I think this is because under the hood some quantities are being precomputed and saved. So for example, applying a VectorHeatMethodSolver object vSolver on dummy data before calling vSolver in a parallel routine seems to make it thread safe.

Is this true?

Here is a small example illustrating what I mean:

std::unique_ptr<ManifoldSurfaceMesh> mesh;
std::unique_ptr<VertexPositionGeometry> geometry;
std::tie(mesh, geometry) = readManifoldSurfaceMesh("filename.obj");

VertexData<double> rhs(mesh, 0.2);
VectorHeatMethodSolver vSolver(geom, 1);

vSolver.scalarDiffuse(rhs); // comment out this line to cause problems

tbb::parallel_for(
  tbb::blocked_range<size_t>(0, 100),
  [&](tbb::blocked_range<size_t> rng)
  {
    for (size_t i = rng.begin(); i < rng.end(); i++)
      vSolver.scalarDiffuse(rhs);
  }
);

In general is there a way to tell which routines are thread safe, or can be made thread safe?

(My main motivation here was to parallelize the outer loop inside each Lloyd iteration of a GCVT routine.)

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