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
