René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"NURBS failure when ClassifyEdge fails (was: Difference fail depending on compilation options (was: Difference fail with OpenMP))","articleBody":"This was first [reported on the forum](https://solvespace.com/forum.pl?action=viewthread\u0026parent=6129\u0026tt=1755262509) using the attached file.\n\n[Issue_OpenMP.zip](https://github.com/user-attachments/files/21822164/Issue_OpenMP.zip)\n\nYou can make the problem go away by:\n1) Dragging the original extrusion the other direction\n2) Using a version of Solvespace built without OpenMP\n3) Open it using the web version (which does not use OpenMP)\n\nTreating it as a concurrency problem I have been able to make the issue go away by commenting out the following line in SShell::CopySurfacesTrimAgainst()\n```\n#pragma omp parallel for\n```\nThat function calls MakeCopyTrimAgainst() and inside of that we can \"fix\" things by adding #pragma omp critical  to either of the two big loops [1 here](https://github.com/solvespace/solvespace/blob/74a13ef61c490a400eaa49c5335622d91ada12fc/src/srf/boolean.cpp#L603) or the one under it [2 here](https://github.com/solvespace/solvespace/blob/74a13ef61c490a400eaa49c5335622d91ada12fc/src/srf/boolean.cpp#L637).\n\nI don't understand how it can be fixed by making a critical section for either of two loops. At this point I don't have any idea what's causing it.","author":{"url":"https://github.com/phkahler","@type":"Person","name":"phkahler"},"datePublished":"2025-08-17T12:37:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":17},"url":"https://github.com/1619/solvespace/issues/1619"}