diff --git a/pocketfft_hdronly.h b/pocketfft_hdronly.h
index d75ada6..2f239d7 100644
--- a/pocketfft_hdronly.h
+++ b/pocketfft_hdronly.h
@@ -515,25 +515,12 @@ namespace threading {
 
 #ifdef POCKETFFT_NO_MULTITHREADING
 
-constexpr inline size_t thread_id() { return 0; }
-constexpr inline size_t num_threads() { return 1; }
-
 template <typename Func>
 void thread_map(size_t /* nthreads */, Func f)
-  { f(); }
+  { f(0, 1); }
 
 #else
 
-inline size_t &thread_id()
-  {
-  static thread_local size_t thread_id_=0;
-  return thread_id_;
-  }
-inline size_t &num_threads()
-  {
-  static thread_local size_t num_threads_=1;
-  return num_threads_;
-  }
 static const size_t max_threads = std::max(1u, std::thread::hardware_concurrency());
 
 class latch
@@ -786,7 +773,7 @@ void thread_map(size_t nthreads, Func f)
     nthreads = max_threads;
 
   if (nthreads == 1)
-    { f(); return; }
+    { f(0, 1); return; }
 
   auto & pool = get_pool();
   latch counter(nthreads);
@@ -796,9 +783,7 @@ void thread_map(size_t nthreads, Func f)
     {
     pool.submit(
       [&f, &counter, &ex, &ex_mut, i, nthreads] {
-      thread_id() = i;
-      num_threads() = nthreads;
-      try { f(); }
+      try { f(i, nthreads); }
       catch (...)
         {
         std::lock_guard<std::mutex> lock(ex_mut);
@@ -2881,15 +2866,14 @@ template<size_t N> class multi_iter
       }
 
   public:
-    multi_iter(const arr_info &iarr_, const arr_info &oarr_, size_t idim_)
+    multi_iter(const arr_info &iarr_, const arr_info &oarr_, size_t idim_,
+               size_t nshares, size_t myshare)
       : pos(iarr_.ndim(), 0), iarr(iarr_), oarr(oarr_), p_ii(0),
         str_i(iarr.stride(idim_)), p_oi(0), str_o(oarr.stride(idim_)),
         idim(idim_), rem(iarr.size()/iarr.shape(idim))
       {
-      auto nshares = threading::num_threads();
       if (nshares==1) return;
       if (nshares==0) throw std::runtime_error("can't run with zero threads");
-      auto myshare = threading::thread_id();
       if (myshare>=nshares) throw std::runtime_error("impossible share requested");
       size_t nbase = rem/nshares;
       size_t additional = rem%nshares;
@@ -3134,11 +3118,11 @@ POCKETFFT_NOINLINE void general_nd(const cndarr<T> &in, ndarr<T> &out,
 
     threading::thread_map(
       util::thread_count(nthreads, in.shape(), axes[iax], VLEN<T>::val),
-      [&] {
+      [&] (size_t tid, size_t nthreads) {
         constexpr auto vlen = VLEN<T0>::val;
         auto storage = alloc_tmp<T0>(in.shape(), len, sizeof(T));
         const auto &tin(iax==0? in : out);
-        multi_iter<vlen> it(tin, out, axes[iax]);
+        multi_iter<vlen> it(tin, out, axes[iax], nthreads, tid);
 #ifndef POCKETFFT_NO_VECTORS
         if (vlen>1)
           while (it.remaining()>=vlen)
@@ -3241,10 +3225,10 @@ template<typename T> POCKETFFT_NOINLINE void general_r2c(
   size_t len=in.shape(axis);
   threading::thread_map(
     util::thread_count(nthreads, in.shape(), axis, VLEN<T>::val),
-    [&] {
+    [&] (size_t tid, size_t nthreads) {
     constexpr auto vlen = VLEN<T>::val;
     auto storage = alloc_tmp<T>(in.shape(), len, sizeof(T));
-    multi_iter<vlen> it(in, out, axis);
+    multi_iter<vlen> it(in, out, axis, nthreads, tid);
 #ifndef POCKETFFT_NO_VECTORS
     if (vlen>1)
       while (it.remaining()>=vlen)
@@ -3296,10 +3280,10 @@ template<typename T> POCKETFFT_NOINLINE void general_c2r(
   size_t len=out.shape(axis);
   threading::thread_map(
     util::thread_count(nthreads, in.shape(), axis, VLEN<T>::val),
-    [&] {
+    [&] (size_t tid, size_t nthreads) {
       constexpr auto vlen = VLEN<T>::val;
       auto storage = alloc_tmp<T>(out.shape(), len, sizeof(T));
-      multi_iter<vlen> it(in, out, axis);
+      multi_iter<vlen> it(in, out, axis, nthreads, tid);
 #ifndef POCKETFFT_NO_VECTORS
       if (vlen>1)
         while (it.remaining()>=vlen)