I don't have a strong opinion here, but had a question and comment: Are there are implications from a project governance perspective of packaging Parquet and Arrow into a single shared library?
As a comment, but I'm a big +1 on trying to tease apart the circular dependencies between Parquet/Arrow (and any other modules). As noted above, I think this boils down to isolating IO and Buffer data structures into 1 library and having the Arrow Array data structures in their own separate libraries. Thanks, Micah On Mon, Sep 16, 2019 at 7:35 PM Sutou Kouhei <k...@clear-code.com> wrote: > Hi, > > If this is circular, it's a problem. But this isn't circular > for now. > > I think that we can use libarrow as the fundamental shared > library to provide common implementation like [1] if we need > to provide common implementation for template. (I think that > we don't provide common implementation for template.) > > [1] > https://github.com/apache/arrow/pull/5221/commits/e88b2579f04451d741eeddcb6697914bcc1019a6 > > Anyway, I'm not strongly oppose to this idea. If we choose > one shared library approach, Linux packages, GLib bindings > and Ruby bindings can follow the change. > > > Thanks, > -- > kou > > In <cajpuwmdwencjpbw+hrswaojfez7e_yci-fg2d3lwgvncf45...@mail.gmail.com> > "Re: [DISCUSS][C++] Rethinking our current C++ shared library (.so / > .dll) approach" on Thu, 12 Sep 2019 13:23:01 -0500, > Wes McKinney <wesmck...@gmail.com> wrote: > > > One thing I forgot to mention: > > > > One of the things driving the creation of new shared libraries is > > interdependencies. For example: > > > > libarrow -> libparquet > > libarrow -> libarrow_dataset > > libparquet -> libarrow_dataset > > > > With the modular LLVM-like approach this issue goes away. > > > > On Thu, Sep 12, 2019 at 1:16 PM Wes McKinney <wesmck...@gmail.com> > wrote: > >> > >> I forgot to add the link to the LLVM library listing > >> > >> https://gist.github.com/wesm/d13c2844db0c19477e8ee5c95e36a0dc > >> > >> On Thu, Sep 12, 2019 at 1:14 PM Wes McKinney <wesmck...@gmail.com> > wrote: > >> > > >> > hi folks, > >> > > >> > I wanted to share some concerns that I have about our current > >> > trajectory with regards to producing shared libraries from the Arrow > >> > build system. > >> > > >> > Currently, a comprehensive build produces many shared libraries: > >> > > >> > * libarrow > >> > * libarrow_dataset > >> > * libarrow_flight > >> > * libarrow_python > >> > * libgandiva > >> > * libparquet > >> > * libplasma > >> > > >> > There are some others. There are a number of problems with the > current approach: > >> > > >> > * Each DLL needs its own set of "visibility" macros to control the use > >> > of __declspec(dllimport/dllexport) on Windows, which is necessary to > >> > instruct the import or export of symbols between DLLs on Windows. See > >> > e.g. > https://github.com/apache/arrow/blob/master/cpp/src/arrow/flight/visibility.h > >> > > >> > * Templates instantiated in one DLL may cause a violation of the One > >> > Definition Rule during linking (we lost at least a day of work time > >> > collectively to issues around this in ARROW-6244). It is good to be > >> > able to share common template interfaces in general > >> > > >> > * Statically-linked dependencies in one shared lib may need to be > >> > statically linked into another library. For example, libgandiva > >> > statically links parts of LLVM, but we will likely have some other > >> > code that makes use of LLVM for other purposes (it has been discussed > >> > in the context of Avro parsing) > >> > > >> > Overall, my preferred solution to these issues is to move to a similar > >> > approach to what the LLVM project does. To help understand, let me > >> > have you first look at the libraries that come from the llvm-7-dev > >> > package on Ubuntu > >> > > >> > Here we have a collection of static "module" libraries that implement > >> > different parts of the LLVM platform. Finally, a _single_ shared > >> > library libLLVM-7.so is produced. > >> > > >> > I think we should do the same thing in Apache Arrow. So we only ever > >> > will produce a single shared library from the build. We can > >> > additionally make the "name" of this shared library configurable to > >> > suit different needs. For example, the default name could be simply > >> > "libarrow.so" or something. But if someone wants to produce a > >> > barebones Parquet shared library they can override the name to create > >> > a "libparquet.so" that contains only the "libarrow_core.a" and > >> > "libarrow_io.a" symbols needed for reading Parquet files. > >> > > >> > This would have additional benefits: > >> > > >> > * Use the same visibility macros for all exported C++ symbols, rather > >> > than having to define DLL-specific visibility > >> > > >> > * Improved modularization of builds and linking for third party users, > >> > similar to the way that LLVM's modular linking works, see the way that > >> > Gandiva requests specific components from LLVM to use for static > >> > linking > https://github.com/apache/arrow/blob/master/cpp/cmake_modules/FindLLVM.cmake#L53 > >> > > >> > * Net simpler linking and deployment. Only one shared library to deal > with > >> > > >> > There are some drawbacks, however: > >> > > >> > * Our C++ Linux packaging approach would need to be changed to be more > >> > LLVM-like (a single .deb/.yum package containing the C++ platform > >> > rather than many packages as now) > >> > > >> > Interested to hear from other C++ developers. > >> > > >> > Thanks > >> > Wes >
