[Jprogramming] j807 cd - pass array arguments

Mon Nov 19 02:37:57 UTC 2018

Dear Henry, Bill, Linda,
Thanks for your responses, I am getting the point/ers.
Perhaps in
https://code.jsoftware.com/wiki/Guides/DLLs/Calling_DLLs#J807_Incompatibilities
, the phrase: "The DLL can read or write this memory." is a bit confusing,
although it also says "The memory is unaliased." That means "copied if
required", and I thought it wouldn't be...
Anyway, all is well again,
Thanks,
Ben
On Mon, Nov 19, 2018 at 1:15 AM Henry Rich <henryhrich at gmail.com> wrote:
> What Bill is saying is that starting in 807, cd makes an copy of any
> argument to cd that might be shared by another noun. So, the value of
> 'res' is put into a temporary block and passed to the DLL. The
> temporary block is put into the boxed result of cd. You need to look in
> that boxed result, not in the name res, which has not been modified.
>> This change was made in 807 because that release has a much more
> aggressive policy of sharing nouns and parts of nouns without making
> separate copies; for example
>> ({. name)
>> actually gives you a pointer to the first item of name, without
> recopying it, and
>> (i. 3)
>> is liable to give you a pointer to unchangeable internal data. With all
> these pointers flying around we can no longer trust the user to know
> when it is safe to pass a pointer into a DLL that might modify the data.
>> Henry Rich
>> On 11/18/2018 7:55 AM, bill lam wrote:
> > j807 must get from result of cd, like this
> > 0 3{ (sqrdll, 'sqr i i *i *i') cd (#y);y;res
> >
> > On Sun, Nov 18, 2018, 2:22 PM Ben Gorte <bgorte at gmail.com wrote:
> >
> >> Dear All,
> >>
> >> Long ago I made quite a lot of c-functions that I am calling from J
> using
> >> the cd mechanism (load 'dll') in linux.
> >>
> >> They stopped working in j64-807. I see in the release notes that indeed
> >> something has changed, but I cannot quite relate that to my case (but
> maybe
> >> I should - I'm not sure I entirely understand the story).
> >>
> >> In the simplest form it looks like this:
> >> First the c-code, sqr.c :
> >> int sqr (int n, int a[], int b[])
> >> {
> >> int i, sumsqr=0;
> >> for (i=0; i<n; i++)
> >> sumsqr += b[i] = a[i] * a[i];
> >> return sumsqr;
> >> }
> >>
> >> which I compile with
> >> gcc -O3 -shared -fPIC -o sql.so -Wl,--no-as-needed sqr.c
> >> (omitting -O3 does not make a difference).
> >>
> >> In J I go like:
> >>
> >> load 'dll'
> >>
> >> sqrdll =: jpath '~user/ext/sqr.so '
> >>
> >>
> >> sqr =: 3 : 0
> >>
> >> res =. (#y)#4 NB. make sure it's integer
> >>
> >> ret =. (sqrdll, 'sqr > i i *i *i') cd (#y);y;res
> >>
> >> ret, res
> >>
> >> )
> >>
> >>
> >> Up until j806 I would get:
> >>
> >> sqr i.10
> >>
> >> 285 0 1 4 9 16 25 36 49 64 81
> >>
> >>
> >> But in j807:
> >>
> >> sqr i.10
> >>
> >> 285 4 4 4 4 4 4 4 4 4 4
> >>
> >>
> >>
> >> So my DLL 'reads' an array alright, but seems to be not 'writing' it.
> >>
> >>
> >> For completeness:
> >> JVERSION
> >> Engine: j807/j64/linux
> >> Release: commercial/2018-10-04T15:00:41
> >> Library: 8.07.20
> >> Qt IDE: 1.7.7/5.5.1
> >> Platform: Linux 64
> >> Installer: J807 install
> >> InstallPath: /home/ben/j64-807
> >> Contact: www.jsoftware.com
> >>
> >> Perhaps I'm overlooking something trivial; any help is highly
> appreciated!
> >>
> >> Ben
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