Fix invalid device context error in ValidIfTest.ExplicitMemoryResourcesEmptyRange

[davidwendt]

Description

Fixes the BITMASK_TEST ValidIfTest.ExplicitMemoryResourcesEmptyRange failure when run with the cuda memory resource:

$ gtests/BITMASK_TEST --gtest_filter=ValidIfTest.ExplicitMemoryResourcesEmptyRange --rmm_mode=cuda
Note: Google Test filter = ValidIfTest.ExplicitMemoryResourcesEmptyRange
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from ValidIfTest
[ RUN      ] ValidIfTest.ExplicitMemoryResourcesEmptyRange
unknown file: Failure
C++ exception with description "/cudf/cpp/build/_deps/cccl-src/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/__driver/driver_api.h:664 invalid device context(201): Failed to synchronize a stream" thrown in the test body.

[  FAILED  ] ValidIfTest.ExplicitMemoryResourcesEmptyRange (3 ms)

The ExplicitMemoryResourcesEmptyRange test was calling harness.synchronize(stream) and harness.expect_no_live_allocations(stream) — both of which invoke cuda::stream_ref::sync() (which uses the CUDA driver API cuStreamSynchronize). Unlike the runtime API, the driver API requires an active CUDA context. For the empty-range case, valid_if makes no GPU calls at all (zero-size buffer, no kernel), so the context is never initialized, causing CUDA_ERROR_INVALID_CONTEXT (201).

The fix removes both sync calls — they're unnecessary because an empty range produces no GPU work and no allocations. The existing .total == 0 counter assertions are stricter than what expect_no_live_allocations checked .value == 0, so test coverage is preserved.

Error introduced by #23490

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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📥 Commits

Reviewing files that changed from the base of the PR and between a98ad61 and d7a387a.

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• cpp/tests/bitmask/valid_if_tests.cu

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Updated an empty-range memory-resource test to correctly handle cases where no GPU operations or allocations occur.
  • Removed unnecessary synchronization and allocation checks, improving test reliability.

Walkthrough

The empty-range memory-resource test now returns the scoped valid_if result directly. It removes synchronization and live-allocation checks because the empty range performs no GPU work or allocations.

Changes

valid_if test update

Layer / File(s)	Summary
Empty-range test behavior cpp/tests/bitmask/valid_if_tests.cu	The test removes explicit stream synchronization and the live-allocation assertion. It documents the absence of GPU work and allocations for an empty range.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to d7a38

This localized test-only change removes unnecessary synchronization for an empty-range case without changing product behavior. No actionable merge-blocking risk remains, so it is merge-ready after normal checks and review.

Suggested reviewers: abigalekim, pointkernel, bdice

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly explains the invalid device context failure and the removal of unnecessary synchronization calls.
Title check	✅ Passed	The title clearly identifies the invalid device context error and the affected ValidIfTest test.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[davidwendt]

/merge