Node:Thread safety, Previous:Multi-threaded FFTW, Up:Parallel FFTW
Users writing multi-threaded programs must concern themselves with the thread safety of the libraries they use--that is, whether it is safe to call routines in parallel from multiple threads. FFTW can be used in such an environment, but some care must be taken because the planner routines share data (e.g. wisdom and trigonometric tables) between calls and plans.
The upshot is that the only thread-safe (re-entrant) routine in FFTW is
fftw_execute (and the guru variants thereof). All other routines
(e.g. the planner) should only be called from one thread at a time. So,
for example, you can wrap a semaphore lock around any calls to the
planner; even more simply, you can just create all of your plans from
one thread. We do not think this should be an important restriction
(FFTW is designed for the situation where the only performance-sensitive
code is the actual execution of the transform), and the benefits of
shared data between plans are great.
Note also that, since the plan is not modified by
it is safe to execute the same plan in parallel by multiple
(Users should note that these comments only apply to programs using shared-memory threads. Parallelism using MPI or forked processes involves a separate address-space and global variables for each process, and is not susceptible to problems of this sort.)