Partial GPU support

Author: willend

mcstas-comps/examples/Prototypes/ODIN_TOF_train4/ESS_butterfly.comp

@@ -549,19 +549,20 @@ TRACE
   vx = v*dx/r;
 
   int train_index;
+
+  long tmp;
 
   if (total_N_sent == 0) {
-    #pragma acc atomic
-    adaptive_N = N_trains;
+    tmp = N_trains;
   } else {
-    long tmp = ceil(target_tsplit*total_N_sent/total_arrived);
-    #pragma acc atomic
-    adaptive_N = tmp;
-    if (adaptive_N > N_trains) {
-      #pragma acc atomic
-      adaptive_N = N_trains;
+    tmp = ceil(target_tsplit*total_N_sent/total_arrived);
+    if (tmp > N_trains) {
+      tmp = N_trains;
     }
   } 
+
+  #pragma acc atomic write
+  adaptive_N = tmp;
 
   for (train_index=0; train_index<adaptive_N; train_index++) {
 

mcstas-comps/examples/Prototypes/ODIN_TOF_train4/ODIN_TOF_train4.instr

@@ -107,6 +107,7 @@ int adaptive_N;
 long total_arrived;
 long total_N_sent;
 long total_rays_sent;
+#pragma acc declare create(adaptive_N,total_arrived,total_N_sent,total_rays_sent)
 %}
 
 USERVARS
@@ -141,7 +142,8 @@ adaptive_N=NTOF;
 total_arrived=0;
 total_N_sent=0;
 total_rays_sent=0;
-
+#pragma acc update device(adaptive_N,total_arrived,total_N_sent,total_rays_sent)
+ 
 // Don't measure time on windows, CLOCK_REALTIME
 // macro is unknown...
 // It is indicated in this oagehttps://learn.microsoft.com/en-us/answers/questions/2147256/clock-realtime-is-undefined-in-visual-studio-but-c that it might work to add a high enough _POSIX_C_SOURCE define, i.e.