ffi: malloc-free variants for str, dstr and buf.

The FFI types str-d, wstr-d and buf-d are like their
unsuffixed counterparts, but indicate that ownership of a
dynamically allocated object is being passed which the
receiver is responsible for freeing.

If we pass a str, wstr or buf into a foreign function, we are
generally only guaranteeing the lifetime of the buffer over
the function call. If we pass a str-d or buf-d, then the
callee keeps the pointer indefinitely, and must free it.

If we get str or buf return value from a function, it
is assumed that the pointer is static or something borrowed
with some limited lifetime. A copy of it is made.

If we get a str-d, wstr-d or buf-d, it is assumed that
the pointer has been malloc-ed for us. The object is
either duplicated, and the original one immediately
freed, or else the pointer is retained directly in the
Lisp object and freed if that object becomes garbage.

* ffi.c (str_d_s, wstr_d_s, buf_d_s): New symbol variables.
(ffi_str_get): Coalesce assignment with declaration.
(ffi_str_d_get, ffi_str_d_put): New static functions.
(ffi_buf_d_get, ffi_buf_d_put): New static functions.
(ffi_type_compile): Handle buf_d_s, str_d_s and wstr_d_s.
(ffi_init): Initialize str_d_s, wstr_d_s and buf_d_s.

* ffi.c (str_d_s, wstr_d_s, buf_d_s): Declared.

1 files changed, 3 insertions, 1 deletions

diff --git a/ffi.h b/ffi.h
index fafee40f..99c87a28 100644
--- a/ffi.h
+++ b/ffi.h
@@ -37,7 +37,9 @@ extern val long_s, ulong_s;
 
 extern val double_s;
 
-extern val wstr_s;
+extern val str_d_s, wstr_s, wstr_d_s;
+
+extern val buf_d_s;
 
 extern val ptr_in_s, ptr_out_s, ptr_in_out_s;