ffi: support programmable abort return value.

* ffi.c (stuct txr_ffi_closure): New member, abort_retval.
(ffi_closure_mark_op): Mark the new member.
(ffi_closure_dispatch_safe): Implement the abort_retval.
If it is not nil, use put to place the value into the
return buffer.  There is a risk that this could also throw
an exception, which is no longer protected: programer's
problem.
(ffi_make_closure): New abort_ret_in argument, which is
defaulted and stored.
(ffi_init): Update registration of ffi-make-closure to
reflect new argument.

* ffi.h (ffi_make_closure): Declaration updated.

* share/txr/stdlib/ffi.tl (sys:deffi-cb-expander):
Add abort-retval parameter; insert into ffi-make-closure
call.
(deffi-cb): Take optional abort-retval expression;
pass it down to the expander function.
(deffi-cb-unsafe): Pass nil as abort-retval down to expander.

* txr.1: Documented.

1 files changed, 5 insertions, 5 deletions

diff --git a/share/txr/stdlib/ffi.tl b/share/txr/stdlib/ffi.tl
index 739023fd..ec164b61 100644
--- a/share/txr/stdlib/ffi.tl
+++ b/share/txr/stdlib/ffi.tl
@@ -72,7 +72,7 @@
 (defmacro deffi-type (name type-expr)
   ^(ffi-typedef ',name (ffi-type-compile ',type-expr)))
 
-(defun sys:deffi-cb-expander (f name rettype argtypes safe-p)
+(defun sys:deffi-cb-expander (f name rettype argtypes safe-p abort-retval)
   (let ((ret-type-sym (gensym "ret-type-"))
         (arg-types-sym (gensym "arg-types-"))
         (call-desc-sym (gensym "call-desc-"))
@@ -85,13 +85,13 @@
                                                      ,ret-type-sym
                                                      ,arg-types-sym))
          (defun ,name (,fun-sym)
-           [ffi-make-closure ,fun-sym ,call-desc-sym ,safe-p])))))
+           [ffi-make-closure ,fun-sym ,call-desc-sym ,safe-p ,abort-retval])))))
 
-(defmacro deffi-cb (:form f name rettype argtypes)
-  (sys:deffi-cb-expander f name rettype argtypes t))
+(defmacro deffi-cb (:form f name rettype argtypes : abort-retval)
+  (sys:deffi-cb-expander f name rettype argtypes t abort-retval))
 
 (defmacro deffi-cb-unsafe (:form f name rettype argtypes)
-  (sys:deffi-cb-expander f name rettype argtypes nil))
+  (sys:deffi-cb-expander f name rettype argtypes nil nil))
 
 (defmacro sizeof (type)
   (ffi-size (ffi-type-compile type)))