I removed the mutex and placed the plan creation and plan destruction in `init_global()` and `cleanup_global()`, respectively, as suggested by @houz . It doesn't crash on my machine, and following FFTW's documentation, I don't expect it to. I will follow this u with a rebase, and cleanup, as suggested by @LebedevRI . As said, I always addressed all your review comments thus far, and if you find something else, just let me know.