Remove USE_MMAP_MAP_STACK build option.

This build option is no longer has any effect in multicont, as we use
only the public API of the OCaml runtime to manage stacks.

README.md

@@ -62,7 +62,7 @@ $ make uninstall
 
 The primary reason to build from source is to toggle configurable
 options of this library, which are not readily available via OPAM
-install. Currently, the following options are supported:
+install. Currently, there is only one optional build:
 
 * `UNIQUE_FIBERS` (default: disabled): Since commit
 [ocaml/ocaml#e12b508](https://github.com/ocaml/ocaml/commit/e12b508876065723ed5fc35c0945030c9b7cd100)
@@ -71,17 +71,13 @@ this option to preserve unique identities amongst fibers as without
 this option a fiber clone is an exact copy of the original fiber,
 including its identity. By enabling this option, a cloned fiber will
 be assigned a new unique identity.
-* `USE_MMAP_MAP_STACK` (default: disabled): Enable to use [virtual
-memory mapped
-stacks](https://man7.org/linux/man-pages/man2/mmap.2.html) rather than
-stacks allocated by malloc.
 
 Configurable options are toggled directly on the command line as a
 prefix to the `make` command. For instance, the following enables
-unique fiber identities and mmap stacks:
+unique fiber identities:
 
 ```shell
-$ UNIQUE_FIBERS=1 USE_MMAP_MAP_STACK=1 make all
+$ UNIQUE_FIBERS=1 make all
 ```
 
 Setting an option to `1` enables it, whereas any other possible

config/configure.ml

@@ -11,8 +11,8 @@ let add_flag flag =
   add_native_flag flag
 
 let () =
-  let options = [ "USE_MMAP_MAP_STACK"
-                ; "UNIQUE_FIBERS"]
+  let options =
+    [ "UNIQUE_FIBERS" ]
   in
   let toggle option =
     match Sys.getenv_opt option with

lib/multicont_stubs.c

@@ -105,10 +105,10 @@ CAMLprim value multicont_clone_continuation(value k) {
 
       // Allocate a fresh stack segment the size of [current]
       clone = caml_alloc_stack_noexc(Stack_high(current) - Stack_base(current),
-                                          Stack_handle_value(current),
-                                          Stack_handle_exception(current),
-                                          Stack_handle_effect(current),
-                                          fiber_id);
+                                     Stack_handle_value(current),
+                                     Stack_handle_exception(current),
+                                     Stack_handle_effect(current),
+                                     fiber_id);
       // Check whether allocation failed
       if (!clone) caml_raise_out_of_memory();
 
@@ -160,3 +160,5 @@ CAMLprim value multicont_drop_continuation(value k) {
   }
   CAMLreturn(Val_unit);
 }
+
+#undef MULTICONT52