COMP: Update VXL to 2026-05-07 (64265ec3)

[hjmjohnson]

Routine VXL third-party sync from upstream vxl/vxl tip 64265ec3 (2026-05-07).

Commits

• 466960466d VXL 2026-05-07 (64265ec3) — subtree update from upstream-VXL tracking branch
• f425aebbeb Merge branch 'upstream-VXL' into vxl-update-vxl-7.0 — two-parent merge preserves upstream blame

Test plan

• CI: Linux / macOS / Windows green
• CI: Python wrapping green
• No new compiler warnings in Modules/ThirdParty/VNL/

[greptile-apps]

Greptile Summary

Routine sync of VXL third-party to upstream commit 64265ec3 (2026-05-07), bumping the bundled library to version 7.0.0.0 with a C++17 minimum and several modernisation passes across the vnl core.

• VXL 7.0 / C++17 minimum: cmake_minimum_required raised to 3.22.1, C++ standard floor moved from 11 to 17, version number bumped to 7.0.0.0, and the deprecated VXL_LEGACY_FUTURE_REMOVE CMake option removed; VXL_USE_HISTORICAL_IMPLICIT_CONVERSIONS and VXL_USE_HISTORICAL_PROTECTED_IVARS both flip their defaults to OFF (ITK's wrapper already forces them OFF, so no build impact for ITK itself).
• Thread-safety band-aid for iterative solvers: vnl_lbfgsb and vnl_sparse_symmetric_eigensystem each gain an internal std::mutex; the sparse eigensystem holds the lock for the full CalculateNPairs invocation, while lbfgsb holds it only around each individual setulb_() call (interleaving risk documented in the new README_threading.md).
• Modern C++ clean-up: raw C arrays replaced with std::array, typedef aliases converted to using, [[nodiscard]] applied to size/predicate accessors throughout vnl_matrix and vnl_vector, and a new vxl_platform_math INTERFACE CMake target centralises -lm linking logic.

Confidence Score: 4/5

The sync is largely safe for ITK builds; the one actionable gap is that the ITK wrapper CMakeLists.txt still sets the now-retired VNL_CONFIG_LEGACY_METHODS cache variable, which will emit a CMake warning on every clean configuration until the wrapper is updated.

All of ITK's forced-off historical-compatibility options are handled correctly in the wrapper, the C++17 bump aligns with ITK's own requirements, and the lbfgsb band-aid mutex limitation is documented as a known issue. The stale VNL_CONFIG_LEGACY_METHODS set in the unchanged wrapper will produce a noisy CMake deprecation warning on fresh builds but does not break compilation or runtime behaviour.

Modules/ThirdParty/VNL/CMakeLists.txt (wrapper still sets the retired VNL_CONFIG_LEGACY_METHODS variable) and Modules/ThirdParty/VNL/src/vxl/core/vnl/algo/vnl_lbfgsb.cxx (mutex scope known limitation).

Important Files Changed

Filename	Overview
Modules/ThirdParty/VNL/UpdateFromUpstream.sh	Points repo and tag to hjmjohnson's personal integration fork/branch instead of the canonical vxl/vxl master — already flagged in a prior review thread.
Modules/ThirdParty/VNL/src/vxl/CMakeLists.txt	Major VXL version bump to 7.0.0.0: raises C++ minimum to 17, removes policy boilerplate, flips VXL_USE_HISTORICAL_* defaults to OFF, and drops VXL_LEGACY_FUTURE_REMOVE option. ITK wrapper already forces both historical options OFF so the default flip is a no-op for ITK builds.
Modules/ThirdParty/VNL/src/vxl/core/vnl/CMakeLists.txt	Retires VNL_CONFIG_LEGACY_METHODS option with a deprecation warning+unset block, but the ITK wrapper CMakeLists.txt (unchanged in this PR) still force-sets this variable, triggering the warning on every ITK CMake configuration.
Modules/ThirdParty/VNL/src/vxl/core/vnl/algo/vnl_lbfgsb.cxx	Replaces raw C arrays with std::array and wraps each setulb_() call in a band-aid mutex. The mutex is released between reverse-communication iterations, leaving the SAVE'd state partially protected — documented in README_threading.md and tracked as issue #23.
Modules/ThirdParty/VNL/src/vxl/core/vnl/algo/vnl_sparse_symmetric_eigensystem.cxx	Adds a function-entry mutex guard (held for the full CalculateNPairs invocation) around the dnlaso/dsaupd/dseupd f2c paths and the static current_system shim; modernises casts and copy loops.
Modules/ThirdParty/VNL/src/vxl/config/cmake/Modules/ConfigurePlatformMathTarget.cmake	New file creating the vxl_platform_math INTERFACE target with implicit-math probe. Contains a CMAKE_VERSION VERSION_LESS 3.14.0 dead-code branch already flagged in a prior review thread.
Modules/ThirdParty/VNL/src/vxl/core/vnl/algo/README_threading.md	New documentation cataloguing thread-safety status of all vnl_algo solver paths; accurately describes the band-aid mutex strategy and the outstanding issue #23.
Modules/ThirdParty/VNL/src/vxl/core/vnl/vnl_matrix.h	Modernises typedef→using aliases, adds [[nodiscard]] to size/shape/predicate accessors, and adds a protected swap_memory_management helper for subclasses.
Modules/ThirdParty/VNL/src/vxl/core/vnl/vnl_vector.h	Mirrors vnl_matrix.h modernisation: typedef→using, [[nodiscard]] on size/predicate accessors, and adds swap_memory_management helper.

Sequence Diagram

sequenceDiagram
    participant ThreadA as Thread A (minimize)
    participant Mutex as lbfgsb_call_mutex
    participant setulb as setulb_() SAVE state
    participant CostFn as f_->compute()
    participant ThreadB as Thread B (minimize)

    ThreadA->>Mutex: lock_guard acquire
    ThreadA->>setulb: "call setulb_ task=FG"
    ThreadA->>Mutex: lock_guard release
    Note over ThreadA,Mutex: Cost function runs WITHOUT lock
    ThreadB->>Mutex: lock_guard acquire
    ThreadB->>setulb: call setulb_ corrupts A SAVE state
    ThreadB->>Mutex: lock_guard release
    ThreadA->>CostFn: compute x f gradient
    ThreadA->>Mutex: lock_guard acquire next iteration
    ThreadA->>setulb: call setulb_ reads corrupted state

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_{Reviews (2): Last reviewed commit: "COMP: Export vxl_platform_math interface..." | Re-trigger Greptile}

[greptile-apps]

Stale VNL_CONFIG_LEGACY_METHODS set in wrapper will trigger warning on every ITK build

The inner core/vnl/CMakeLists.txt now warns and unsets VNL_CONFIG_LEGACY_METHODS when the variable is defined in cache (DEFINED CACHE{VNL_CONFIG_LEGACY_METHODS}). The ITK wrapper at Modules/ThirdParty/VNL/CMakeLists.txt:29-35 still force-sets that cache variable (CACHE BOOL … FORCE), so every clean CMake configuration of ITK will produce this deprecation warning and an unnecessary cache mutation. The set(VNL_CONFIG_LEGACY_METHODS OFF CACHE BOOL … FORCE) block in the wrapper should be removed now that the variable is retired upstream.