Re: [Plplot-devel] New way of getting device info from dyndrivers

[<jc...@fe...>]

On Wednesday 05 February 2003 16:55, Jo=E3o Cardoso wrote:
| On Wednesday 05 February 2003 13:55, Rafael Laboissiere wrote:
| | * Rafael Laboissiere <lab...@ps...> [2003-02-04 22:37]:
| | >    c) At build time (not configuration time), a small C program
| | > dlopen the <driver>.c files, get the symbols described above and
| | > write the associated device entries in <driver>.rc (or whichever
| | > name).
| |
| | Just to make things a bit more concrete, here is the design that I
| | have in mind.  I will take the ps.c driver as an example.  The
| | following global variables will be defined in the driver source:
| |
| |     char* DEVICES_ps      =3D "ps:psc";
| |
| |     char* DESCRIPTION_ps  =3D "PostScript File (monochrome)";
| |     int   TYPE_ps         =3D plDevType_FileOriented;
| |     int   SEQNUM_ps       =3D 29;
| |     char* SYMTAG_ps       =3D "psm";
| |
| |     char* DESCRIPTION_psc =3D "PostScript File (color)";
| |     int   TYPE_psc        =3D plDevType_FileOriented;
| |     int   SEQNUM_psc      =3D 30;
| |     char* SYMTAG_psc      =3D "psc";
| |
| | Of course, these variables should be used in the
| | plD_dispatch_init_* functions.  In the case of ps.c:
| |
| |     ps_dispatch_init_helper( pdt,
| |                              DESCRIPTION_ps, "ps",
| |                              TYPE_ps, SEQNUM_ps,
| |                              (plD_init_fp) plD_init_psm );
| |
| |     ps_dispatch_init_helper( pdt,
| |                              DESCRIPTION_psc, "psc",
| |                              TYPE_psc, SEQNUM_psc,
| |                              (plD_init_fp) plD_init_psc );
| |
| | This will insure that things are not defined twice in different
| | places (like with the current DEVICE_INFO_* variable).
| |
| | The small C program that will generate the <driver>.rc file from
| | the <driver>.la file, would do: (1) dlopen the module; (2) get the
| | DEVICES_* symbol and parse its device components (in the ps.c
| | exemple, that would be "ps" and "psc"); (3) for each one of the
| | devices found, get the symbols DESCRIPTION_<dev>, TYPE_<dev>,
| | SEQNUM_<dev>, and SYMTAG_<dev>; (4) create the temp file that is
| | parsed by Geoff's code. (This could be improved along Joao's
| | suggestion of creating a structure instead of writing the
| | information in a temp file.)
| |
| | We have to decide first whether it is not worth abandoning the
| | current approach and adopting this "cached info" approach above.

Now that HEAD is working again. lets continue.

I measure the time that your code in plInitDispatchTable() takes to load=20
all drivers, and it is only 20ms (wall clock) for all 33 drivers, on a=20
P3@700MHz (with a small but continuous load of 1). It looks like it is=20
pretty efficient.

Your concerns that dlopen() would load all libraries that a driver needs=20
does not apply, as this would only happens if some drivers code is=20
executed, which is not the case. As libtool's info says:

    "Unresolved symbols in the module are resolved using
     its dependency libraries"

As the symbols you are looking for are in the modules, no further=20
loading will occur.

Thus, given that the current implementation is efficient enough, avoids=20
the need of another program to build the drivers.rc file, is fully=20
dynamic because if more drivers are added to the directory they will be=20
recognized without further intervention,... lets keep it as is.

Joao

|
| I decided to give it a try but got a seg fault:
|
| [jcard@feup] gdb x01c
| (gdb) run -dev xwin
| Starting program: /usr/local/test/lib/plplot5.2.0/examples/c/x01c
| -dev xwin
|
| Program received signal SIGSEGV, Segmentation fault.
| 0x0806a46e in lt_dlsym (handle=3D0x807b0e0,
|     symbol=3D0xbfffef50 "DEVICE_INFO_pstex") at ltdl.c:3330
| 3330      lensym =3D LT_STRLEN (symbol) + LT_STRLEN
| (handle->loader->sym_prefix)
| (gdb) where
| #0  0x0806a46e in lt_dlsym (handle=3D0x807b0e0,
|     symbol=3D0xbfffef50 "DEVICE_INFO_pstex") at ltdl.c:3330
| #1  0x08053d38 in plInitDispatchTable () at plcore.c:1638
| #2  0x08049b9d in plMergeOpts (options=3D0x8073500,
|     name=3D0x11 <Address 0x11 out of bounds>, notes=3D0x11) at
| plargs.c:699 #3  0x08049362 in main ()
| #4  0x400674a2 in __libc_start_main () from /lib/libc.so.6
|
| | There is also Joao's suggestion for dynamically building the
| | drivers.db, but I am too lazy to implement that (and I am not sure
| | it is a superior approach).
| |
| | What do you think?  I accept suggestions for better variable names.
|
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