Fix null optional dereference in temporal_partition_vertices

[esnvidia]

When vertex_labels is std::nullopt, the else branch incorrectly attempted to access vertex_labels_p1->begin() and vertex_labels_p2->begin(), causing cudaErrorIllegalAddress crash.

This fix removes the label iterators from thrust::make_zip_iterator calls in the else branch, since labels are not available when vertex_labels is nullopt.

Fixes temporal neighbor sampling when called without vertex labels, e.g., homogeneous_uniform_temporal_neighbor_sample with temporal_property_name=None.

All 210+ temporal sampling tests pass with this fix.

PR_TEMPORAL_SAMPLING_FIX.md

Pull Request: Fix null optional dereference in temporal_partition_vertices

Summary

Fixes a crash (cudaErrorIllegalAddress) when calling temporal neighbor sampling without vertex labels.

Description

The temporal_partition_vertices function in temporal_partition_vertices_impl.cuh has an else branch that handles the case when vertex_labels is std::nullopt. However, this branch incorrectly attempts to dereference the null optional when constructing thrust::make_zip_iterator, causing an illegal memory access.

Root Cause

The else branch was copy-pasted from the if branch but the label iterators were not removed:

// BUGGY: In else branch where vertex_labels is nullopt
thrust::make_zip_iterator(
    vertices_p1.begin(), 
    vertex_times_p1.begin(), 
    vertex_labels_p1->begin())  // <-- Dereferences nullopt!

The Fix

Remove label iterators from the else branch since labels are not available:

// FIXED: No labels in zip iterator when vertex_labels is nullopt
thrust::make_zip_iterator(
    vertices_p1.begin(), 
    vertex_times_p1.begin())  // Only vertices and times

Testing

C++ Tests (all pass)

100% tests passed, 0 tests failed out of 4

- TEMPORAL_GRAPH_TEST ..................... Passed    3.77 sec
- TEMPORAL_NEIGHBOR_SAMPLING_TEST ......... Passed  514.50 sec (210 tests)
- CAPI_UNIFORM_TEMPORAL_NEIGHBOR_SAMPLE_TEST Passed    0.85 sec

Python Verification

# This was crashing before the fix:
result = homogeneous_uniform_temporal_neighbor_sample(
    rh, G, 
    None,  # temporal_property_name=None triggers the bug
    start_vertices,
    start_times,
    None,  # no label offsets
    fanout,
    with_replacement=True, 
    do_expensive_check=False
)
# Now works: SUCCESS! Sampled 645 edges

Files Changed

• cpp/src/sampling/detail/temporal_partition_vertices_impl.cuh

Diff

diff --git a/cpp/src/sampling/detail/temporal_partition_vertices_impl.cuh b/cpp/src/sampling/detail/temporal_partition_vertices_impl.cuh
index ea1eb1e6e..97a42730f 100644
--- a/cpp/src/sampling/detail/temporal_partition_vertices_impl.cuh
+++ b/cpp/src/sampling/detail/temporal_partition_vertices_impl.cuh
@@ -141,28 +141,22 @@ temporal_partition_vertices(raft::handle_t const& handle,
       vertex_labels_p1->resize(vertices_p1.size(), handle.get_stream());
       vertex_times_p1.resize(vertices_p1.size(), handle.get_stream());
     } else {
+      // FIXED: When vertex_labels is std::nullopt, don't include labels in zip iterator
       copy_if_mask_unset(
         handle,
-        thrust::make_zip_iterator(
-          vertices_p1.begin(), vertex_times_p1.begin(), vertex_labels_p1->begin()),
-        thrust::make_zip_iterator(
-          vertices_p1.end(), vertex_times_p1.end(), vertex_labels_p1->end()),
+        thrust::make_zip_iterator(vertices_p1.begin(), vertex_times_p1.begin()),
+        thrust::make_zip_iterator(vertices_p1.end(), vertex_times_p1.end()),
         vertex_partition_mask.begin(),
-        thrust::make_zip_iterator(
-          vertices_p2.begin(), vertex_times_p2.begin(), vertex_labels_p2->begin()));
+        thrust::make_zip_iterator(vertices_p2.begin(), vertex_times_p2.begin()));
       vertices_p1.resize(
         thrust::distance(
-          thrust::make_zip_iterator(
-            vertices_p1.begin(), vertex_times_p1.begin(), vertex_labels_p1->begin()),
+          thrust::make_zip_iterator(vertices_p1.begin(), vertex_times_p1.begin()),
           copy_if_mask_set(
             handle,
-            thrust::make_zip_iterator(
-              vertices_p1.begin(), vertex_times_p1.begin(), vertex_labels_p1->begin()),
-            thrust::make_zip_iterator(
-              vertices_p1.end(), vertex_times_p1.end(), vertex_labels_p1->end()),
+            thrust::make_zip_iterator(vertices_p1.begin(), vertex_times_p1.begin()),
+            thrust::make_zip_iterator(vertices_p1.end(), vertex_times_p1.end()),
             vertex_partition_mask.begin(),
-            thrust::make_zip_iterator(
-              vertices_p1.begin(), vertex_times_p1.begin(), vertex_labels_p1->begin()))),
+            thrust::make_zip_iterator(vertices_p1.begin(), vertex_times_p1.begin()))),
         handle.get_stream());
 
       vertex_times_p1.resize(vertices_p1.size(), handle.get_stream());

Checklist

• Code compiles without errors
• All existing tests pass (210+ temporal sampling tests)
• No new warnings introduced
• Python API verified working with fix
• Fix is minimal and focused on the specific bug

Impact

• Before: Any call to temporal neighbor sampling without vertex labels crashes with cudaErrorIllegalAddress
• After: Temporal sampling works correctly with or without vertex labels

[copy-pr-bot]

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[ChuckHastings]

/ok to test 06a2380

[ChuckHastings]

You need to update the copyright date to be: 2025-2026. Then we can try and build it in our continuous integration system and get this merged.