[eigen] Parallel matrix multiplication causes heap allocation

[Rene Ahlsdorf <ahlsdorf@xxxxxxxxxxxxxxxxxx>]

Dear Eigen team,

first of all, thank you for all your effort to create such a great math library. I really love using it.

I’ve got a question about your parallelization routines. I want to calculate a parallel (omp based) matrix multiplication (result: 500 x 250 matrix) without allocating any new space in the meantime. So I have activated „Eigen::internal::set_is_malloc_allowed(false)“ to check that nothing goes wrong. However, my program crashes with the error message 

„Assertion failed: (is_malloc_allowed() && "heap allocation is forbidden (EIGEN_RUNTIME_NO_MALLOC is defined and g_is_malloc_allowed is false)"), function check_that_malloc_is_allowed, file /Users/xxx//libs/eigen/Eigen/src/Core/util/Memory.h, line 143.“. Is this behaviour desired? Should there be an allocation before doing parallel calculations? Or am I doing something wrong?

Thanks in advance.

Regards,
René Ahlsdorf

Eigen Version: 3.3.1 (commit f562a193118d)

My code: https://gist.github.com/anonymous/d57c835171b2068817b9f82493b43ea7

Attached: Screenshot showing the last function calls