era, should be called by only a single thread at a time
(see <a href="Thread-safety.html#Thread-safety">Thread safety</a>).  <em>Unlike</em> FFTW 2, there is no special
<code>FFTW_THREADSAFE</code> flag for the planner to allow a given plan to be
usable by multiple threads in parallel; this is now the case by default.
</p>
<p>The multi-threaded version of FFTW 2 required you to pass the number of
threads each time you execute the transform.  The number of threads is
now stored in the plan, and is specified 