pin_varobject usage

[Vladimir T. <vtz...@gm...>]

On 6/26/09, Sam Steingold <sd...@gn...> wrote:
> BTW, about pin_varobject -- does it have to be in the same block as
> unpin_varobject? (the code does not indicate that, but...)

yes, they should be in the same block.
In order to ensure that object is unpinned whatever happens (normal
success/failure, thread-interrupts with non-local exit) - pinning is
inside UNWIND_PROTECT frame - with two required cleanups - in case of
stack unwind and normal execution flow.

I wanted to write macro WITH_PINNED_OBJECT(obj) - but that would
require to push obj on the lisp stack. In stream.d there are many
places where this will cause quite a lot of changes (and at that time
I was afraid to do them). So I went with what we have now - both
pin_varobject() and unpin_varobject() should be inside the same block.

BTW: similar is WITH_[XXXX]_MUTEX_LOCK() used in package.d. In it's
case I copy lisp stack items to ensure "expected" stack layout after
UNWIND_PROTECT frame is established. It's possible to write
WITH_PINNED_OBJECT() in similar way but all gotos/return within it's
body (particularly in stream.d) should be carefully rewritten.

> e.g., in rawsock.c, I want to call pin_varobject inside parse_buffer_arg but
> unpin_varobject outside).

Compared to stream.d there are much fewer places where
pin_varobject()/unpin_varobject() should be used - so may be it is
better use them in the same block - or write local macro (with changed
stack layout within it).

Vladimir