[Discuss-gnuradio] Optimal way of performing multiple FFTs on a stream of data

Hi,
This is more of a programming question than a gnuradio question.

I am writing a C++ block that takes in a stream of complex data, an N element block {B} is chosen from the stream, this block is multiplied with a set {M1, M2, M3...Mn} where size of each set element is N (same as data block) too. I want to find FFT using FFTW library on each of the products {B.M1, B.M2, .... B.Mn} in the general_work() function. As this can be an intensive task can someone suggest me what could be the optimal strategy to do without compromising efficiency and risk losing samples that is entering the machine from the USRP. I was thinking about multithreading. Do you think this is the way to go?

Thanks,
John