Use external linkage for global async variables

compiler/obc/c/async.ml

@@ -13,12 +13,21 @@ let filter_async_objs cd =
          | None -> false)
     cd.cd_objs
 
-let async_global_objs_defs cd =
+let async_global_objs_vars cd =
   List.map
     (fun od ->
        let name = async_global_var_name od in
        let ty = Cty_id (qn_append od.o_class "_async") in
-       Cvardef (name, ty))
+       name, ty)
     (filter_async_objs cd)
 
+let async_global_objs_defs cd =
+  List.map
+    (fun (name, ty) -> Cvardef (name, ty))
+    (async_global_objs_vars cd)
+
+let async_global_objs_decls cd =
+  List.map
+    (fun (name, ty) -> Cdecl_extern (name, ty))
+    (async_global_objs_vars cd)
 

compiler/obc/c/c.ml

@@ -143,6 +143,7 @@ type cdecl =
   (** C function declaration. *)
   | Cdecl_constant of string * cty * cexpr
   (** C constant declaration (alias, name)*)
+  | Cdecl_extern of string * cty
 
 (** C function definitions *)
 type cfundef = {
@@ -353,6 +354,9 @@ let pp_cdecl fmt cdecl = match cdecl with
   | Cdecl_constant (n, cty, ce) ->
       fprintf fmt "@[<v>static const %a = %a;@ @]@\n"
         pp_vardecl (n, cty)  pp_cconst_expr ce
+  | Cdecl_extern (n, cty) ->
+      fprintf fmt "@[<v>extern %a;@ @]@\n"
+        pp_vardecl (n, cty)
 
 let pp_cdef fmt cdef = match cdef with
   | Cfundef cfd ->

compiler/obc/c/cgen.ml

@@ -947,6 +947,7 @@ let cdefs_and_cdecls_of_class_def cd =
   let out_struct_decl = out_decl_of_class_def cd in
   let async_struct_decl = async_decl_of_class_def cd in
   let objs = async_global_objs_defs cd in
+  let objs_decls = async_global_objs_decls cd in
   let step = fun_def_of_step_fun cd.cd_name cd.cd_objs cd.cd_mems
     cd.cd_objs step_m in
   (* TODO(Arduino): let the user choose the backend they want *)
@@ -973,7 +974,7 @@ let cdefs_and_cdecls_of_class_def cd =
   let decls = List.map cdecl_of_cfundef defs in
 
   memory_struct_decl @ in_struct_decl @ out_struct_decl @ async_struct_decl
-    @ decls, objs @ defs
+    @ objs_decls @ decls, objs @ defs
 
 (** {2 Type translation} *)