ed by <code>fftw_execute</code>,
it is safe to execute the <em>same plan</em> in parallel by multiple
threads.  However, since a given plan operates by default on a fixed
array, you need to use one of the new-array execute functions (see <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>) so that different threads compute the transform of different data.

   <p>(Users should note that these comments only apply to programs using
shared-memory thread