On Mon, 8 Aug 2011, Guillaume Yziquel wrote: > Le Monday 08 Aug 2011 ? 09:20:17 (+0400), malc a ?crit : > > On Mon, 8 Aug 2011, Erik de Castro Lopo wrote: > > > > > Hi all, > > > > > > I'm writing a C stub function to allow the calling of a C library > > > function from ocaml. The return from the stub is a tuple and I'm > > > doing this: > > > > > > /* 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) ; > > > > > > The above works now, but didn't work when I was using > > > caml_copy_nativeint() instead of Val_int() and I'd like to know > > > why. I found it especially confusing because caml_copy_string() > > > worked and was obvioulsy the right thing to do. > > > > 18.5.2 > > > > Rule 5 > > > > After a structured block (a block with tag less than No_scan_tag) > > is allocated with the low-level functions, all fields of this block must > > be filled with well-formed values before the next allocation operation. If > > the block has been allocated with caml_alloc_small, filling is performed > > by direct assignment to the fields of the block: > > Field(v, n) = vn; > > ... > > > > I'd say rule 5 has been violated here. > > No. caml_alloc_tuple is considered to be part of the simplified > interface, not part of the low-level interface. Rule 5 shouldn't apply > in this case. > > One of the reasons for rule 5 is that the contents of the allocated > block may not satisfy GC constraints. So you should not allocate with > the blocks item pointing to inconsistent garbage as the GC may the run > over them. > > 18.4.4 > > caml_alloc(n, t) returns a fresh block of size n with tag t. > If t is less than No_scan_tag, then the fields of the block > are initialized with a valid value in order to satisfy the > GC constraints. > > In caml_alloc function in alloc.c: > > if (tag < No_scan_tag){ > for (i = 0; i < wosize; i++) Field (result, i) = 0; > } > > and caml_alloc_tuple is roughly caml_alloc (in alloc.c) so definitely > part of the simplified interface: > > CAMLexport value caml_alloc_tuple(mlsize_t n) > { > return caml_alloc(n, 0); > } > >
I stand corrected. -- 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