[Plplot-devel] The libltdl method of dynamically loading our drivers is now working (was Quick help needed with changing a struct and a typedef in PLplot)

[Alan W. I. <ir...@be...>]

OK.  I answered my own questions empirically. Turned out that lt_ptr_t was
obsolete (shows how quickly things have moved since autotools book), and
according to info pages for libtool version 1.4.2, lt_ptr should be used
instead.  After I fixed that problem, here are the answers I
discovered by seeing whether the build, install, and x08c test worked.

(1) is correct.

(2) should be changed to
typedef lt_ptr (*PLDispatchInit)( PLDispatchTable *pdt );

Any C expert on the list know why *PLDispatchInit rather than
PLDispatchInit? I naively thought you would drop the asterisk because the
type was going from void * to lt_ptr, but as you all know, my C programming
skills are not the best especially when dealing with pointers and
complicated typedefs. The example of typedef on p. 147 of the little white
K&R book is analogous to this one, but I don't understand the point of
(*PFI) rather than (PFI) in that case as well.

One other issue I ran into was how to initialize libltdl and release its
memory when done.  Same old problem (mentioned in the plcore.c comments) of
no clear PLplot library initialization . So I chose to do the initialize
whenever a stream was created and release whenever it was destroyed.  This
is overcomplicated, and it would be better to initialize just once before
any streams are created and release after they are all destroyed, but there
is no clear way to tell when plinit is first called so I had to do it stream
by stream.

A final issue was the top-level aclocal.m4 was one of those deleted files
that Rafael accidentally included during his merge from MAIN to AM-LT.  I
deleted that file from the AT branch since a new version of it (not a 7-yr
old version!) is automatically generated by one of the commands in
bootstrap.sh.

Anyhow, after those changes (just now committed) the AT cookbook just worked
again.  Also, a valgrind test of ./x08c -dev psc -o test.ps revealed no new
problems beyond what I have reported before.

Next step (tomorrow) is to try all this on a solaris platform to see if
there are any obvious cross-platform issues with dynamic drivers (or
anything else) there.  I will be following Rafael's old cookbook on making a
tarball to try out on solaris.  The neat thing about this approach is
nothing will be needed on the solaris machine other than a working compiler,
and the solaris version of scripting and make.

Once that is sorted out, the next steps are to try the tarball results of
the AT branch on as many platforms as the other developers here have access
to while I concentrate on expanding to more than the xwin and ps drivers
that are working now and more front ends than just the C front end that is
working now.

Once we have at least the current CVS HEAD functionality on the AT branch
(all dynamic drivers and all front ends working) with the addition of
cross-platform capability, I will want to merge the AT branch into CVS HEAD.

The AT effort is going much faster than I thought (because of the great
start by Rafael and because autotools is pretty easy to learn from scratch)
so the merge to HEAD *could* happen soon (i.e., maybe even sometime during
this week unless I run into unforseen problems.) So I suggest you should get
involved immediately if you want to evaluate the AT approach before the
merge!

Alan

email: ir...@be...
phone: 250-727-2902	FAX: 250-721-7715
snail-mail:
Dr. Alan W. Irwin
Department of Physics and Astronomy,
University of Victoria, P.O. Box 3055,
Victoria, British Columbia, Canada, V8W 3P6
__________________________

Linux-powered astrophysics
__________________________

---------- Forwarded message ----------
Date: Sun, 24 Nov 2002 13:36:25 -0800 (PST)
From: Alan W. Irwin <ir...@uv...>
To: PLplot development list <Plp...@li...>
Cc: Rafael Laboissiere <lab...@ps...>
Subject: [Plplot-devel] Quick help needed with changing a struct and a
    typedef in PLplot

I start with the background information that is required on the dlopen to
libltdl API change, then get to my two "simple" numbered questions at the
end which any C expert should be able to answer for me.

For the AT branch I am in the middle of changing from the dlopen API
to the libltdl API to increase cross-platform compatibility.

The old API:

void * dlopen (const char *filename, int flag)
void * dlsym (void *handle, char *name)
int dlclose (void *handle)
const char * dlerror (void)

The new API:

lt_dlhandle lt_dlopen (const char *filename)
lt_dlhandle lt_dlopenext (const char *filename)
lt_ptr_t lt_dlsym (lt_dlhandle handle, const char *name)
int lt_dlclose (lt_dlhandle handle)
const char * lt_dlerror (void)

Note: lt_dlopenext is the same as lt_dlopen except that it tries with
alternate suffixes if there is not an exact match to the name.

In the new plcore.c there is the following line:

driver->dlhand = lt_dlopenext( drvspec);

which replaces the old

driver->dlhand = dlopen( drvspec, flag);

Subsequently driver->dlhand is used as an argument to lt_dlsym


So in plplot.h I have changed from

typedef struct {
    char *drvnam;
    void *dlhand;

} PLLoadableDriver;

to

typedef struct {
    char *drvnam;
    lt_dlhandle dlhand;

} PLLoadableDriver;

With appropriate #include of the libltdl header and protection by
#ifdef ENABLE_DYNDRIVERS.

(1) Is that change to the struct the correct thing to do for the changed API?

(2) The new plcore.c code also has the following fragment:

PLDispatchInit dispatch_init = lt_dlsym( driver->dlhand, sym );

where the old disptab.h has

typedef void (*PLDispatchInit)( PLDispatchTable *pdt );

What should I change that typedef to?

My guess is something like

typedef lt_ptr_t (PLDispatchInit)( PLDispatchTable *pdt );

but I am not completely sure so any quick help would be much appreciated.
Of course I am going to try some variations on this theme this afternoon
and hopefully get something to work, but the definitive answer would be
most useful. C typedefs and pointers just plain drive me crazy!

Alan

email: ir...@be...
phone: 250-727-2902	FAX: 250-721-7715
snail-mail:
Dr. Alan W. Irwin
Department of Physics and Astronomy,
University of Victoria, P.O. Box 3055,
Victoria, British Columbia, Canada, V8W 3P6
__________________________

Linux-powered astrophysics
__________________________



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