Skip to content

Latest commit

 

History

History
118 lines (78 loc) · 6.06 KB

index.md

File metadata and controls

118 lines (78 loc) · 6.06 KB

% ROOT Version 6.40 Release Notes % 2026-5

Introduction

For more information, see:

http://root.cern

The following people have contributed to this new version:

Bertrand Bellenot, CERN/EP-SFT,
Jakob Blomer, CERN/EP-SFT,
Lukas Breitwieser, CERN/EP-SFT,
Philippe Canal, FNAL,
Olivier Couet, CERN/EP-SFT,
Marta Czurylo, CERN/EP-SFT,
Florine de Geus, CERN/EP-SFT and University of Twente,
Jonas Hahnfeld, CERN/EP-SFT and Goethe University Frankfurt,
Fernando Hueso Gonzalez, IFIC (CSIC-University of Valencia),
Stephan Hageboeck, CERN/EP-SFT,
Aaron Jomy, CERN/EP-SFT,
Sergey Linev, GSI Darmstadt,
Lorenzo Moneta, CERN/EP-SFT,
Vincenzo Eduardo Padulano, CERN/EP-SFT,
Giacomo Parolini, CERN/EP-SFT,
Danilo Piparo, CERN/EP-SFT,
Jonas Rembser, CERN/EP-SFT,
Silia Taider, CERN/EP-SFT,
Devajith Valaparambil Sreeramaswamy, CERN/EP-SFT,
Vassil Vassilev, Princeton,\

Deprecation and Removal

  • The TH1K class was removed. TMath::KNNDensity can be used in its stead.
  • The headers in RooStats/HistFactory for data classes related to the measurement definition were merged into the RooStats/HistFactory/Measurement.h header to simplify usage and development. For now, the whole set of header files is kept for backwards compatibility, but the empty headers will be removed in ROOT 7.
  • The TObject equality operator pythonization (TObject.__eq__) that was deprecated in ROOT 6.38 and scheduled for removal in ROOT 6.40 is removed.
  • Comparing C++ nullptr objects with None in Python now raises a TypeError, as announced in the ROOT 6.38 release notes. Use truth-value checks like if not x or x is None instead.
  • The TGLIncludes.h and TGLWSIncludes.h that were deprecated in ROOT 6.38 and scheduled for removal are gone now. Please include your required headers like <GL/gl.h> or <GL/glu.h> directly.
  • The GLEW headers (GL/eglew.h, GL/glew.h, GL/glxew.h, and GL/wglew.h) that were installed when building ROOT with builtin_glew=ON are no longer installed. This is done because ROOT is moving away from GLEW for loading OpenGL extensions.
  • The TMVA PyKeras method is deprecated. It was broken by the API changes in Keras 3, released in November 2023 and part of TensorFlow 2.16 or newer. The PyKeras method will be removed in ROOT 6.42 (unless an updated implementation for Keras 3 that matches usage, performance and stability requirements will be found unexpectedly).

Build System

Core Libraries

I/O

  • The behavior or TDirectoryFile::mkdir (which is also TFile::mkdir) was changed regarding the creation of directory hierarchies: calling mkdir("a/b/c", "myTitle") will now assign myTitle to the innermost directory "c" (before this change it would assign it to "a").
  • Fixed a bug in TDirectoryFile::mkdir where passing returnExistingDirectory = true would not work properly in case of directory hierarchies. The option is now correctly propagated to mkdir's inner invocations.

File Permissions Now Respect System umask

ROOT now respects the system umask when creating files, following standard Unix conventions.

Previous behavior: Files were created with hardcoded 0644 permissions (owner read/write, group/others read-only), ignoring the system umask.

New behavior: Files are created with 0666 permissions masked by the system umask (0666 & ~umask), consistent with standard Unix file creation functions like open() and fopen().

Impact:

  • Users with default umask 022 (most common): No change - files are still created as 0644
  • Users with stricter umask values (e.g., 0077): Files will now be created with more restrictive permissions (e.g., 0600 - user-only access)
  • Users with permissive umask values (e.g., 0002): Files may be created with slightly more open permissions (e.g., 0664 - group-writable)

Note: If you require specific file permissions regardless of umask, you can set umask explicitly before running ROOT (e.g., umask 022) or use chmod after file creation.

This change affects the following classes: TFile, TMapFile, TMemFile, TDCacheFile, TFTP, and TApplicationServer.

TTree

RNTuple

Math

Migration from VecCore/Vc to std::experimental::simd for Vectorization

We have migrated the vectorized backends of TMath and TFormula from VecCore/Vc to std::experimental::simd, where available.

On Linux, std::experimental::simd is assumed to be available when ROOT is compiled with C++20 or later, which in practice corresponds to sufficiently recent GCC and Clang compilers. To keep the build system simple and robust, ROOT does not explicitly check compiler versions: users opting into C++20 are expected to use modern toolchains.

Impact on Linux users

ROOT builds with C++17 on Linux no longer provide vectorized TMath and TFormula. This is an intentional and accepted trade-off of the migration. These vectorized features were rarely used, while maintaining them significantly complicated the codebase and build configuration.

Users who rely on vectorized TMath or the vectorized TFormula backend are encouraged to build ROOT with C++20. Doing so restores vectorization through std::experimental::simd, providing a more robust and future-proof implementation.

Windows and Apple silicon users are unaffected

VecCore/Vc did not work on Windows previously, and Vc never provided production-ready support for ARM/Neon, so Apple silicon did not benefit from vectorization before this change.

Build system changes

As part of this migration, the following build options are deprecated. From ROOT 6.42, setting them will result in configuration errors.

  • vc
  • veccore
  • builtin_vc
  • builtin_veccore

RooFit

RDataFrame

  • The message shown in ROOT 6.38 to inform users about change of default compression setting used by Snapshot (was 101 before 6.38, became 505 in 6.38) is now removed.

Python Interface

Command-line utilities

JavaScript ROOT

Experimental features

Versions of built-in packages

Items addressed for this release