[petsc-dev] --known-mpi-shared-library and --with-batch annoyance

[Barry Smith]

> On Apr 21, 2016, at 12:08 PM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Wed, Apr 20, 2016 at 2:09 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
>    When running with --batch one must provide the flag --known-mpi-shared-library this is annoying since no one will know this
> 
>    I am trying to understand the purpose of this flag. It is used in MPI.py in the code
> 
>   def checkSharedLibrary(self):
>     '''Sets flag indicating if MPI libraries are shared or not and
>     determines if MPI libraries CANNOT be used by shared libraries'''
>     self.executeTest(self.configureMPIEXEC)
>     try:
>       self.shared = self.libraries.checkShared('#include <mpi.h>\n','MPI_Init','MPI_Initialized','MPI_Finalize',checkLink = self.checkPackageLink,libraries = self.lib, defaultArg = 'known-mpi-shared-libraries', executor = self.mpiexec)
>     except RuntimeError, e:
>       if self.argDB['with-shared-libraries']:
>         raise RuntimeError('Shared libraries cannot be built using MPI provided.\nEither rebuild with --with-shared-libraries=0 or rebuild MPI with shared library support')
>       self.logPrint('MPI libraries cannot be used with shared libraries')
>       self.shared = 0
>     return
> 
>    It looks to me like the code says that if MPI is not a shared library then you cannot build PETSc with a shared library.
> 
> 1) Is this true? What if MPI was built with PIC but static, won't it still be possible to use it with a PETSc shared library? i.e. is this even the right test?
> 
> PETSc used to have multiple shared libraries, and its still possible. If you link MPI statically into multiple shared libraries,
> you duplicate symbols like isInitialized. This messes up tons of things in MPI.

   Matt,

     We generate (or should if we don't) our shared PETSc libraries by 

       sharedlink   petscsys.so  -lmpi

       sharedlink   petscvec.so -lpetscsys 

       etc.

    If it is done this way then will the problem with duplicate symbols be an issue?

     What if we make them with 

       sharedlink   petscsys.so  -lmpi

       sharedlink   petscvec.so -lpetscsys -lmpi

       etc.

   Maybe it is impossible to do the first case since we cannot remove from the link libraries "just" the MPI libraries whatever they happen to be?

   Barry


>  
> 2) Is there any way to get rid of this flag or will there be cases were configure goes through with success and accepts using shared libraries but then the build fails with unable to make the PETSc shared library?
> 
> If we allow --single-library=0, I do not see how we can avoid this.

   Could we not require --known-mpi-shared-libraries when --single-library=1 (which is the usual case most users will see?)

> 
>   Matt
>  
>    Thanks for any input
> 
>   Barry
> 
> 
> 
> 
> 
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener