Add MemoryView.export and MemoryView#release (#80)

fix #79

Users can release memory views explicitly before process exit.

Reported by xtkoba. Thanks!!!

Author: kou

ext/fiddle/memory_view.c

@@ -36,12 +36,25 @@ fiddle_memview_mark(void *ptr)
 }
 
 static void
-fiddle_memview_free(void *ptr)
+fiddle_memview_release(struct memview_data *data)
 {
-    struct memview_data *data = ptr;
+    if (NIL_P(data->view.obj)) return;
+
     rb_memory_view_release(&data->view);
-    if (data->members)
+    data->view.obj = Qnil;
+    data->view.byte_size = 0;
+    if (data->members) {
         xfree(data->members);
+        data->members = NULL;
+        data->n_members = 0;
+    }
+}
+
+static void
+fiddle_memview_free(void *ptr)
+{
+    struct memview_data *data = ptr;
+    fiddle_memview_release(data);
     xfree(ptr);
 }
 
@@ -63,11 +76,32 @@ rb_fiddle_memview_s_allocate(VALUE klass)
     struct memview_data *data;
     VALUE obj = TypedData_Make_Struct(klass, struct memview_data, &fiddle_memview_data_type, data);
     data->view.obj = Qnil;
+    data->view.byte_size = 0;
     data->members = NULL;
     data->n_members = 0;
     return obj;
 }
 
+static VALUE
+rb_fiddle_memview_release(VALUE obj)
+{
+    struct memview_data *data;
+    TypedData_Get_Struct(obj, struct memview_data, &fiddle_memview_data_type, data);
+
+    if (NIL_P(data->view.obj)) return Qnil;
+    fiddle_memview_release(data);
+    return Qnil;
+}
+
+static VALUE
+rb_fiddle_memview_s_export(VALUE klass, VALUE target)
+{
+    ID id_new;
+    CONST_ID(id_new, "new");
+    VALUE memview = rb_funcall(klass, id_new, 1, target);
+    return rb_ensure(rb_yield, memview, rb_fiddle_memview_release, memview);
+}
+
 static VALUE
 rb_fiddle_memview_initialize(VALUE obj, VALUE target)
 {
@@ -269,7 +303,9 @@ Init_fiddle_memory_view(void)
 {
     rb_cMemoryView = rb_define_class_under(mFiddle, "MemoryView", rb_cObject);
     rb_define_alloc_func(rb_cMemoryView, rb_fiddle_memview_s_allocate);
+    rb_define_singleton_method(rb_cMemoryView, "export", rb_fiddle_memview_s_export, 1);
     rb_define_method(rb_cMemoryView, "initialize", rb_fiddle_memview_initialize, 1);
+    rb_define_method(rb_cMemoryView, "release", rb_fiddle_memview_release, 0);
     rb_define_method(rb_cMemoryView, "obj", rb_fiddle_memview_get_obj, 0);
     rb_define_method(rb_cMemoryView, "byte_size", rb_fiddle_memview_get_byte_size, 0);
     rb_define_method(rb_cMemoryView, "readonly?", rb_fiddle_memview_get_readonly, 0);

test/fiddle/test_memory_view.rb

@@ -112,6 +112,22 @@ def test_memory_view_multi_dimensional_with_multiple_members
       assert_equal([-7, -8], mview[1, 3])
     end
 
+    def test_export
+      str = "hello world"
+      mview_str = MemoryView.export(Pointer[str]) do |mview|
+        mview.to_s
+      end
+      assert_equal(str, mview_str)
+    end
+
+    def test_release
+      ptr = Pointer["hello world"]
+      mview = MemoryView.new(ptr)
+      assert_same(ptr, mview.obj)
+      mview.release
+      assert_nil(mview.obj)
+    end
+
     def test_to_s
       # U+3042 HIRAGANA LETTER A
       data = "\u{3042}"