From 63ad1453f7dcb861826fcb30206e687ba9eae2ef Mon Sep 17 00:00:00 2001
From: Axel Huebl <axel.huebl@plasma.ninja>
Date: Mon, 28 Jun 2021 14:52:41 -0700
Subject: [PATCH] FFTW: Initialize Threads

Co-authored-by: Severin Diederichs <severin.diederichs@desy.de>
---
 Source/FieldSolver/SpectralSolver/WrapFFTW.cpp | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/Source/FieldSolver/SpectralSolver/WrapFFTW.cpp b/Source/FieldSolver/SpectralSolver/WrapFFTW.cpp
index a4dfc8b293b..57a0fad046a 100644
--- a/Source/FieldSolver/SpectralSolver/WrapFFTW.cpp
+++ b/Source/FieldSolver/SpectralSolver/WrapFFTW.cpp
@@ -1,4 +1,4 @@
-/* Copyright 2019-2020
+/* Copyright 2019-2021
  *
  * This file is part of WarpX.
  *
@@ -32,6 +32,16 @@ namespace AnyFFT
     {
         FFTplan fft_plan;
 
+#if defined(AMREX_USE_OMP) && defined(WarpX_FFTW_OMP)
+#   ifdef AMREX_USE_FLOAT
+        fftwf_init_threads();
+        fftwf_plan_with_nthreads(omp_get_max_threads());
+#   else
+        fftw_init_threads();
+        fftw_plan_with_nthreads(omp_get_max_threads());
+#   endif
+#endif
+
         // Initialize fft_plan.m_plan with the vendor fft plan.
         // Swap dimensions: AMReX FAB are Fortran-order but FFTW is C-order
         if (dir == direction::R2C){