[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, 1 insertions, 1 deletions

diff --git a/ext/fiddle/fiddle.h b/ext/fiddle/fiddle.h
index 16f12cab74..46f5a1d737 100644
--- a/ext/fiddle/fiddle.h
+++ b/ext/fiddle/fiddle.h
@@ -164,7 +164,7 @@
 #define ALIGN_DOUBLE ALIGN_OF(double)
 
 extern VALUE mFiddle;
-extern VALUE rb_eFiddleError;
+extern VALUE rb_eFiddleDLError;
 
 VALUE rb_fiddle_new_function(VALUE address, VALUE arg_types, VALUE ret_type);