Index: trunk/psLib/src/fft/psFFT.h
===================================================================
--- trunk/psLib/src/fft/psFFT.h	(revision 18956)
+++ trunk/psLib/src/fft/psFFT.h	(revision 19058)
@@ -2,7 +2,16 @@
 #define PS_FFT_H
 
-/// Set number of threads to use with all FFTs
+// Only fftw_execute is thread-safe: all other calls have to be wrapped in a mutex
+
+/// Lock FFT mutex
+void psFFTLock(void);
+
+/// Unlock FFT mutex
+void psFFTUnlock(void);
+
+/// Set number of threads for FFTW to use
 ///
-/// Pass zero to turn off threading
+/// Pass zero to turn off threading.  Note that the FFTW threads are *independent* of any other threads set up
+/// throuhg, e.g., psThread.
 bool psFFTThreads(int threads           // Number of threads
     );