Force installation of the threads module with findlib.dynload

Signed-off-by: François Bobot <francois.bobot@cea.fr>

doc/advanced-topics.rst

@@ -76,14 +76,16 @@ to add ``findlib.dynload`` to the set of library dependencies:
     (executable
       (name main)
       (public_name mytool)
-      (libraries mytool findlib.dynload)
+      (libraries mytool findlib.dynload threads)
       (modules ...)
     )
 
 
-Then you could use in your application ``Fl_dynload.load_packages l`` that
-will load the list ``l`` of packages. The packages are loaded only
-once. So trying to load a package statically linked does nothing.
+Then you could use in your application ``Fl_dynload.load_packages l``
+that will load the list ``l`` of packages. The packages are loaded
+only once. So trying to load a package statically linked does nothing.
+The builtin nature of the library ``threads`` forces to link it even
+if an application don't need it in case a plugin would use it.
 
 A plugin creator just need to link to your library:
 

src/link_time_code_gen.ml

@@ -24,20 +24,13 @@ let libraries_link ~name ~mode cctx libs =
         ~f:(fun lib -> match Lib.status lib with | Lib.Status.Private _ -> false | _ -> true)
         libs
     in
-    (* We can't use directly Findlib.Package.preds because there
-       are fixups in ocamlfind that adds the package "thread" as
-       dependency of all the packages when the predicate "mt" is
-       used. Also independently of ocamlfind it could be strange
-       if a library can be used without or with `thread` but
-       "thread" is forced during dynlink because we always add "mt". *)
-    let preds =
-      if List.exists libs ~f:(fun lib -> Lib.name lib = "threads")
-      then Findlib.Package.preds
-      else
-        Variant.Set.diff Findlib.Package.preds
-          (Variant.Set.of_list [Variant.mt;Variant.mt_posix])
-    in
-    let preds = Variant.Set.add preds (Mode.variant mode) in
+    (* If thread is not present we error out otherwise if a plugin need
+       it there is a linking error. *)
+    if not (List.exists libs ~f:(fun lib -> Lib.name lib = "threads"))
+    then
+      Arg_spec.Dyn (fun _ -> die "The threads package should always be present with package findlib.dynload")
+    else
+    let preds = Variant.Set.add Findlib.Package.preds (Mode.variant mode) in
     let s =
       Format.asprintf "%a@\nFindlib.record_package_predicates %a;;@."
         (Fmt.list ~pp_sep:Fmt.nl (fun fmt lib ->

test/blackbox-tests/test-cases/findlib-dynload/c_thread.ml

@@ -0,0 +1,7 @@
+let t =
+  Thread.create
+    (fun () -> print_endline "thread started"; Thread.delay 0.001; print_endline "thread stopping") ()
+
+let () = Thread.delay 0.001
+
+let () = Mytool.Register.register "c_thread" (fun () -> Thread.join t)

test/blackbox-tests/test-cases/findlib-dynload/dune

@@ -22,18 +22,19 @@
   (modules main)
   (public_name mytool)
   (package mytool)
-  (libraries mytool findlib.dynload)
+  (libraries mytool findlib.dynload threads)
  )
 
 
 (rule (copy main.ml main_with_a.ml))
+(rule (copy main.ml main_without_threads.ml))
 
 (executable
   (name main_with_a)
   (modules main_with_a)
   (public_name mytool_with_a)
   (package mytool)
-  (libraries mytool findlib.dynload a)
+  (libraries mytool findlib.dynload a threads)
  )
 
 
@@ -42,5 +43,22 @@
   (modules main_auto)
   (public_name mytool_auto)
   (package mytool)
+  (libraries mytool findlib.dynload findlib threads)
+ )
+
+
+(executable
+  (name main_without_threads)
+  (modules main_without_threads)
+  (public_name mytool_without_threads)
+  (package mytool)
   (libraries mytool findlib.dynload findlib)
  )
+
+
+(library
+  (name c_thread)
+  (public_name c_thread)
+  (modules c_thread)
+  (libraries threads mytool)
+)

test/blackbox-tests/test-cases/findlib-dynload/main.ml

@@ -4,6 +4,9 @@ let () =
   for i = 1 to (Array.length Sys.argv - 1); do
     try
       Fl_dynload.load_packages [Sys.argv.(i)]
-    with Fl_package_base.No_such_package(pkg, _) ->
+    with
+    | Fl_package_base.No_such_package(pkg, _) ->
       Printf.printf "The package %S can't be found.\n%!" pkg
+    | Dynlink.Error error ->
+      Printf.printf "Error during dynlink: %s\n%!" (Dynlink.error_message error)
   done

test/blackbox-tests/test-cases/findlib-dynload/run.t

@@ -1,4 +1,6 @@
   $ dune build
+  The threads package should always be present with package findlib.dynload
+  [1]
 
   $ dune exec mytool
   m: init
@@ -54,3 +56,9 @@
   b: registering
   b: called
   a: called
+
+  $ dune exe mytool c_thread
+  m: init
+  thread started
+  c_thread: registering
+  thread stopping