Generic filename extension for shared libraries

[sagetrac-gouezel]

Some places in the code and some doctests assume that the filename extension for shared libraries is .so, while it is .dll in cygwin. The attached patch defines once and for all the correct extension depending on the platform, and uses it where necessary.

CC: @jpflori

Component: porting: Cygwin

Author: Sebastien Gouezel

Branch/Commit: ad478d3

Reviewer: Jeroen Demeyer

Issue created by migration from https://trac.sagemath.org/ticket/17682

[sagetrac-gouezel]

Branch: u/gouezel/dll_extension

[sagetrac-gouezel]

Commit: 0233104

[sagetrac-gouezel]

comment:3

I put the definition of the generic filename extension in sage.misc.sageinspect, since its use is relevant for introspection. Tell me if there is a better place!

---

New commits:

0233104

More generic shared library file extension

[sagetrac-gouezel]

Author: Sebastien Gouezel

[tscrim]

comment:6

(and myself)

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

db7df5c

Ticket #17682: add generic extension in cython caching

[sagetrac-git]

Changed commit from 0233104 to db7df5c

[sagetrac-jakobkroeker]

comment:8

Ahem, I do not completely understand what the patch does (i'm new to sage/python);
Question: what are the consequences, e.g. for init_libsingular()
in src/sage/libs/singular/singular.pyx?

snip:

...
    for extension in ["so", "dylib", "dll"]:
        lib = os.environ['SAGE_LOCAL']+"/lib/libsingular."+extension
        if os.path.exists(lib):
            handle = dlopen(lib, RTLD_GLOBAL|RTLD_LAZY)
            break
...

[sagetrac-gouezel]

comment:9

Replying to @sagetrac-jakobkroeker:

Short answer: the code you show is fine, no need to change anything.

Long answer: shared libraries usually have the extension .so on unix-likes. So, some parts of sage's code assume that this is a universal extension, and use it for loading or doctesting purposes. This leads to problems on cygwin, where the extension is .dll. The patch fixes this code, replacing the universal .so with an extension depending on the platform (.dll on windows, .soanywhere else). Code that already considered the possibility of different extensions is fine.

There is yet another difference on MacOS, where the extension for shared libraries can be .so or .dylib -- this means that, in this case, there is no universal possible choice, so I picked .so since it is the most common in sage. In the case of libsingular, I don't know if it is built using .so or .dylib (and I don't have a Mac to test). If it is .so, one might consider using the patch to predict the correct extension, but in any case the current code works fine.

[jdemeyer]

comment:10

Replying to @sagetrac-gouezel:

There is yet another difference on MacOS, where the extension for shared libraries can be .so or .dylib -- this means that, in this case, there is no universal possible choice

It's more subtle than that. On OS X, both .so and .dylib exist but with a different purpose: .so is meant for "loadable modules" to be opened at runtime by some dlopen() mechanism, which .dylib is for dynamic linking of libraries (linking done when a program a started). For example, Cython extensions would use .so but the libraries in $SAGE_LOCAL/lib would use .dylib.

On Linux, this difference simply doesn't exist.

[sagetrac-gouezel]

Changed commit from db7df5c to 4286d97

[sagetrac-gouezel]

New commits:

e27535b	#17682: More generic shared library file extension
4286d97	Ticket #17682: add generic extension in cython caching

[sagetrac-gouezel]

Changed branch from u/gouezel/dll_extension to u/gouezel/dll_extension2

[jdemeyer]

comment:12

I dislike the complete lack of documentation. Given that constants are hard to document, it's probably better to make it a function def ..._extension() (fill in the ... to what this thing represents, generic_so doesn't mean much to me, see also [comment:10]).

[jdemeyer]

comment:13

Also: can you replace F[-len(generic_so_extension):] == generic_so_extension by F.endswith(extension).

[sagetrac-git]

Changed commit from 4286d97 to 8815433

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

8815433

#17682: use documented function instead of constant

[sagetrac-gouezel]

comment:15

Converted generic_so_extension to a documented function shared_lib_extension(). It is a little bit silly to recompute it every time, but given its triviality and the fact that it should never be time-critical, I don't think caching it is useful.

[jdemeyer]

comment:16

I think all this

sage: from site import getsitepackages
sage: site_packages = getsitepackages()[0]
sage: from sage_setup.find import installed_files_by_module
sage: files_by_module = installed_files_by_module(site_packages)
sage: from sage.misc.sageinspect import shared_lib_extension
sage: files_by_module['sage.structure.sage_object'].pop().endswith(shared_lib_extension())

can be replaced by

sage: sage.structure.sage_object.__file__.endswith(shared_lib_extension())

[jdemeyer]

Reviewer: Jeroen Demeyer

[jdemeyer]

comment:17

Can you replace the terminology shared_lib by loadable_module. As I said, these are different on OS X and Cython modules are "loadable modules" and not "shared libraries" (the latter would have a .dylib extension on OS X).

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

ad478d3

#17682: change to loadable_module_extension

[sagetrac-git]

Changed commit from 8815433 to ad478d3

[vbraun]

Changed branch from u/gouezel/dll_extension2 to ad478d3