[joeykleingers]

Summary

Compute Triangle Face Ids fills the feature face labels and triangle counts in a parallel loop. Every worker read the shared face-count map with std::map::operator[]. Row 0 is the reserved (0,0) boundary. When no triangle uses that pair, the row 0 lookup inserted key 0 and could rebalance the tree while other workers searched it. That is a data race and undefined behavior on every platform. The workers now only read the map, and the filter output does not change. 2 files changed, +112 / −4 lines.

1. Read-only map lookup in the parallel loop

• src/Plugins/SimplnxCore/src/SimplnxCore/Filters/Algorithms/SharedFeatureFace.cpp — SharedFeatureFaceImpl

SharedFeatureFaceImpl takes the face-count map by const reference and looks each count up with find(). A missing entry gives a count of 0, the same value the old insert produced. The map is built serially before the parallel loop starts and is not changed after that.

2. Regression tests

• src/Plugins/SimplnxCore/test/SharedFeatureFaceTest.cpp — two new test cases and a shared helper, ExecuteAndCheckLabelPairs

SharedFeatureFace: Missing zero pair rotation race uses first-seen pairs (0,2) and (0,1), so the map holds keys 2 and 1 and an insert of key 0 would rotate the tree at its root. It runs the filter 300 times and checks every ID, label and count, plus the tuple shapes of the outputs. It takes about 0.04 s in a Release build.

SharedFeatureFace: Real zero pair counts uses a real (0,0) pair and checks that the reserved row and the real row both report its count of 2.

A plain test cannot fail on a data race reliably, so the race was checked with ThreadSanitizer on macOS arm64 (simplnx instrumented, TBB not instrumented). With the old lookup, the first test reported a write to the map from inside the parallel loop in every run (15 of 15 runs across two versions of the test). With the fix, no run reported one (15 runs). The other ThreadSanitizer warnings come from TBB's own scheduler, which is not instrumented, and appear with and without the fix. MSVC has no ThreadSanitizer, so on Windows the check is that the tests pass.

Test plan

• SimplnxCore::SharedFeatureFace* tests pass on macOS arm64 Release (3/3)
• ThreadSanitizer reports no write to the face-count map from the parallel loop with the fix, and reports one in every run without it
• CI passes on Windows, Linux and macOS

Related Issue

Closes #1772