new thoughts on dynamic libraries support

[Lisandro Dalcin]

No, Barry, I was not clear enough.

AFAIK, PFSTRING is broken at the time you want to actually create a PF
of type PFSTRING. This PF type is implemented by compiling on-the-fly
a new dynamic library called 'libpescdlib.so' (using a template file
src/vec/pf/impls/string/cstringbase.c and calling 'make' via popen
somewhere inside $TMP dir).

The current implementation approach has three problems:

1) It only works if PETSc compiled --with-dynamic. But this could work
even if PETSc is compiled with static libs, though that would require
some extra cares (users executables should be built with appropriate
flags for exporting symblols, like passing to the linker the flags
'-Xlinker -export-dynamic' when building executables).

2) If you look at src/vec/pf/impls/string/cstringbase.c, there is no
function 'PetscDLLibraryRegister_petscdlib' exported. Then the call to
PetscDLLibrarySym() in  FStringCreateFunction() will fail.

3) Even if the above issues are fixed, PETSc opens dynamic libraries
with RTLD_GLOBAL flags and then caches them in DLLibrariesLoaded list.
Then I'm not sure if this will let you create more than ONE PFSTRING.
If extra care is taken by using a mktemp-like routine, we still could
have issues with the RTLD_GLOBAL (though I'm not sure).

As you see, the PFSTRING implementation is somewhat broken, and this
was never noticed because there are no tests for PFSTRING.

BTW, You are completely right! Libraries (and specially dynamic) are
really overwhelming ;-)


On Mon, Oct 20, 2008 at 6:34 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
> On Oct 20, 2008, at 1:49 PM, Lisandro Dalcin wrote:
>>
>> PetscDLLibraryRegister_NAME. If the symbol is not exported, then
>> PetscDLLibraryOpen() fails!!  BTW, Because of this constraint,
>> PFSTRING implementation is currently broken.
>>
>
>   I don't understand why this would be. The PF stuff is in the Vec library.
>
> PetscErrorCode PETSCVEC_DLLEXPORT PetscDLLibraryRegister_petscvec(const char
> path[])
> {
>  PetscErrorCode ierr;
>
>  ierr = PetscInitializeNoArguments(); if (ierr) return 1;
>
>  PetscFunctionBegin;
>  /*
>      If we got here then PETSc was properly loaded
>  */
>  ierr = ISInitializePackage(path);CHKERRQ(ierr);
>  ierr = VecInitializePackage(path);CHKERRQ(ierr);
>  ierr = PFInitializePackage(path);CHKERRQ(ierr);
>  PetscFunctionReturn(0);
> }
>
> The PF is suppose to work in the same way as the IS, I'm guessing the IS
> works properly?
>
>  Thanks
>
>   Barry
>
>>
>
>



-- 
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
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