On Tue, 9 Aug 2011, David Allsopp wrote: > Erik de Castro Lopo wrote: > > Xavier Leroy wrote: > > > > > On 08/08/2011 10:03 AM, Guillaume Yziquel wrote: > > > > > > > Then I do not see anything wrong if the code snippet you sent. > > > > However, when you change Val_int to caml_copy_nativeint, the layout > > > > of the tuple is different. [...] So if you keep the same OCaml code > > > > when reading the result value, it's no surprise that the pointer is > > > > shown in place of the integer you expected. > > > > > > This is good advice indeed: make sure your Caml type declaration > > > matches the data representation that your Caml/C stub implements... > > > > > > > /* Package up the result as a tuple. */ > > > > v_response = caml_alloc_tuple (3) ; > > > > Store_field (v_response, 0, Val_int (width)) ; > > > > Store_field (v_response, 1, Val_int (height)) ; > > > > Store_field (v_response, 2, caml_copy_string (code)) ; > > > > CAMLreturn (v_response) ; > > > > > > Additionally, do make sure that "v_response" is registered with the GC > > > (declared with one of the CAMLlocal macros). > > > > This is strange, it wasn't declared with a CAMLlocal macro and it was > > working, but if I do declare it with one the program segfaults during > > garbage collection (caml_oldify_local_roots). > > If you altered this but left the program exactly the same then you violated > rule 1 in 18.5.1 of the manual: CAMLparamn must come first. The result is > predictable - you attempt to allocate a local variable before the local root > is properly initialised... > > That said, in your specific example, my understanding is that it should > be OK not using CAMLlocal because you return v_response with CAMLreturn > before the GC could be triggered (no allocations or callbacks between > caml_alloc_tuple and CAMLreturn).
I'm puzzled by this, caml_copy_string does allocation.. > Whether that's a) correct and b) > sensible (i.e. whether the performance "boost" justifies the commenting > needed in the code to explain how brittle it is) is another matter! > > > David > > > -- mailto:av1...@comtv.ru -- Caml-list mailing list. Subscription management and archives: https://sympa-roc.inria.fr/wws/info/caml-list Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
