setNbThreads() mandatory for OMP parallelization?

Summary

The documentation on multithreading(https://eigen.tuxfamily.org/dox/TopicMultiThreading.html) reads:

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You can control the number of threads that will be used using either the OpenMP API or Eigen's API using the following priority:

OMP_NUM_THREADS=n ./my_program
omp_set_num_threads(n);
Eigen::setNbThreads(n);

Unless setNbThreads has been called, Eigen uses the number of threads specified by OpenMP. You can restore this behavior by calling setNbThreads(0);. You can query the number of threads that will be used with:

n = Eigen::nbThreads( );

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However, I encountered that setNbThreads is now mandatory in Eigen 3.4.X for the OMP parallelizatzion to work, independent on what is set by OMP_NUM_THREADS (I tested it with different linear solvers like CG and BiCGSTAB). Is this a bug or a feature? Should the documentation be updated?

Environment

• Operating System : Linux
• Architecture : x64
• Eigen Version : 3.4.X
• Compiler Version : Gcc13.0
• Compile Flags : -O3 -march=native

Anything else that might help

• Have a plan to fix this issue.