[ruby/fiddle] Add a "pinning" reference (#44)

* Add a "pinning" reference

A `Fiddle::Pinned` objects will prevent the objects they point to from
moving.  This is useful in the case where you need to pass a reference
to a C extension that keeps the address in a global and needs the
address to be stable.

For example:

```ruby
class Foo
  A = "hi" # this is an embedded string

  some_c_function A # A might move!
end
```

If `A` moves, then the underlying string buffer may also move.
`Fiddle::Pinned` will prevent the object from moving:

```ruby
class Foo
  A = "hi" # this is an embedded string

  A_pinner = Fiddle::Pinned.new(A) # :nodoc:

  some_c_function A # A can't move because of `Fiddle::Pinned`
end
```

This is a similar strategy to what Graal uses:

  https://www.graalvm.org/sdk/javadoc/org/graalvm/nativeimage/PinnedObject.html#getObject--

* rename global to match exception name

* Introduce generic Fiddle::Error and rearrange error classes

Fiddle::Error is the generic exception base class for Fiddle exceptions.
This commit introduces the class and rearranges Fiddle exceptions to
inherit from it.

https://github.com/ruby/fiddle/commit/ac52d00223

1 files changed, 11 insertions, 1 deletions

diff --git a/ext/fiddle/fiddle.c b/ext/fiddle/fiddle.c
index e6435ba3f3..5f2bd5ae20 100644
--- a/ext/fiddle/fiddle.c
+++ b/ext/fiddle/fiddle.c
@@ -1,9 +1,11 @@
 #include <fiddle.h>
 
 VALUE mFiddle;
+VALUE rb_eFiddleDLError;
 VALUE rb_eFiddleError;
 
 void Init_fiddle_pointer(void);
+void Init_fiddle_pinned(void);
 
 /*
  * call-seq: Fiddle.malloc(size)
@@ -133,11 +135,18 @@ Init_fiddle(void)
     mFiddle = rb_define_module("Fiddle");
 
     /*
+     * Document-class: Fiddle::Error
+     *
+     * Generic error class for Fiddle
+     */
+    rb_eFiddleError = rb_define_class_under(mFiddle, "Error", rb_eStandardError);
+
+    /*
      * Document-class: Fiddle::DLError
      *
      * standard dynamic load exception
      */
-    rb_eFiddleError = rb_define_class_under(mFiddle, "DLError", rb_eStandardError);
+    rb_eFiddleDLError = rb_define_class_under(mFiddle, "DLError", rb_eFiddleError);
 
     /* Document-const: TYPE_VOID
      *
@@ -439,5 +448,6 @@ Init_fiddle(void)
     Init_fiddle_closure();
     Init_fiddle_handle();
     Init_fiddle_pointer();
+    Init_fiddle_pinned();
 }
 /* vim: set noet sws=4 sw=4: */