fix for windows tests

Author: nicolaloi

cpp/open3d/pipelines/integration/UniformTSDFVolume.cpp

@@ -265,8 +265,8 @@ std::shared_ptr<geometry::VoxelGrid> UniformTSDFVolume::ExtractVoxelGrid()
 #pragma omp parallel num_threads(utility::EstimateMaxThreads())
     {
 #pragma omp single
-        { per_thread_voxels.resize(omp_get_num_threads()); }
-        int thread_id = omp_get_thread_num();
+        { per_thread_voxels.resize(utility::GetNumThreads()); }
+        int thread_id = utility::GetThreadNum();
 
 #ifdef _WIN32
 #pragma omp for schedule(static)

cpp/open3d/utility/Parallel.cpp

@@ -45,6 +45,22 @@ int EstimateMaxThreads() {
 #endif
 }
 
+int GetNumThreads() {
+#ifdef _OPENMP
+    return omp_get_num_threads();
+#else
+    return 1;  // No parallelism available.
+#endif
+}
+
+int GetThreadNum() {
+#ifdef _OPENMP
+    return omp_get_thread_num();
+#else
+    return 0;  // No parallelism available, so thread ID is always 0.
+#endif
+}
+
 bool InParallel() {
     // TODO: when we add TBB/Parallel STL support to ParallelFor, update this.
 #ifdef _OPENMP

cpp/open3d/utility/Parallel.h

@@ -13,6 +13,12 @@ namespace utility {
 /// Estimate the maximum number of threads to be used in a parallel region.
 int EstimateMaxThreads();
 
+/// Returns the number of threads in the current parallel region.
+int GetNumThreads();
+
+/// Returns the thread ID in the current parallel region.
+int GetThreadNum();
+
 /// Returns true if in an parallel section.
 bool InParallel();