A few months ago when we were trying to replace CMake with Bazel, @emailweixu suggested that we rewrite those handy Bazel functions using CMake. Now it seems that it's the right time to get this done, as we are facing problems from the porting of Majel and the development of new the parameter server using Go and C++.

Here are some initial thoughts. Your comments are welcome!

Required CMake Function

I think we need only the following few CMake functions to make a project description mean and clean:

C++ CUDA C++ Go
cc_library nv_library go_library
cc_binary nv_binary go_binary
cc_test nv_test go_test
  • The _library functions generate .a files from source code.
  • The _binary functions generate executable binary files.
  • The _test functions generate executable unit test files. They work like _binary but links -lgtest and -lgtest_main.

The difference between nv_ functions and cc_ functions is that the former use nvcc instead of the system-default C++ compiler.

Both nv_ and cc_ functions enables C++11 (-std=c++11).

Also,

  • to describe external dependencies, we need external_library.
  • to build shared libraries, we need shared_library.

An Example Project

Suppose that we have aforementioned functions defined in our /cmake directory. The following example CMakeLists.txt describes a project including the following source files:

  • tensor.h
  • tensor.cc
  • tensor_test.cc
  • ops.h
  • ops.cu
  • ops_test.cu
  • api.go
  • api_test.go

Suppose that ops.cu depends on CUDNN.

# cc_binary parses tensor.cc and figures out that target also depend
# on tensor.h.
cc_binary(tensor
  SRCS
  tensor.cc)

# The dependency to target tensor implies that if any of
# tensor{.h,.cc,_test.cc} is changed, tensor_test need to be re-built.
cc_test(tensor_test
  SRCS
  tensor_test.cc
  DEPS
  tensor)

# I don't have a clear idea what parameters external_library need to
# have.  @gangliao as a CMake expert would have better ideas.
external_library(cudnn
  ....)

# Suppose that ops.cu depends on external target CUDNN.  Also, ops.cu
# include global functions that take Tensor as their parameters, so
# ops depend on tensor.  This implies that if any of tensor.{h.cc},
# ops.{h,cu} is changed, ops need to be re-built.
nv_library(ops
  SRCS
  ops.cu
  DEPS
  tensor
  cudnn)  # cudnn is defined later.

nv_test(ops_test
  SRCS
  ops_test.cu
  DEPS
  ops)

# Because api.go defines a GO wrapper to ops and tensor, it depends on
# both.  This implies that if any of tensor.{h,cc}, ops.{h,cu}, or
# api.go is changed, api need to be re-built.
go_library(api
  SRCS
  api.go
  DEPS
  tensor # Because ops depend on tensor, this line is optional.
  ops)

go_test(api_test
  SRCS
  api_test.go
  DEPS
  api)


# This builds libapi.so.  shared_library might use CMake target
# api_shared so to distinguish it from above target api.
shared_library(api
  DEPS
  api)

Implementation

As above example CMakeLists.txt executes, each function invocation adds "nodes" to a dependency graph. It also use this graph to generate CMake commands including add_executable, add_dependencies, target_link_libraries, and add_test.

Using Package Manager For Go

Building Go binaries and libraries need to satisfy their dependencies, generally we can do go get ./... to download and compile all external dependencies. The problems are:

  1. go get will always get the latest code from the default branch of the remote repo, so changes of dependents might break the build. This is very different with what we already have in cmake/external which download a specific version or commit id of the dependency.
  2. Some locations can not access external dependencies through the internet, as mentioned in https://github.com/PaddlePaddle/Paddle/issues/2605. Using package management tools can package the dependencies as a "vendor" package, which can be mirrored at many cloud file hosting, so users what to compile paddle by themselves can download this "vendor" package from a mirror site.

Choose A Suitable Tool

As mentioned by @wangkuiyi, Here list dozens of Go package managers. We choose the tool using following principles:

  • Most "active" projects with more stars, more pull requests or commits
  • Widely used project

After comparing all these projects, we shall choose between the most popular tools: Godep and Glide.

Here's a brief comparison between Godep and Glide : https://github.com/Masterminds/glide/wiki/Go-Package-Manager-Comparison. There are also many complaints about using Godep. There's also a new "official" pakcage management tool has been started at: https://github.com/golang/dep to resolve such problems, but it's currently at Alpha stage. So the best choice now is glide obviously.

Manage Go Packages

  • Dependencies: go/glide.yaml will store the dependencies and their versions which is directly imported by paddle. go/glide.lock will store all dependencies recursively with their commit id. Builds will "lock" to these packages if we don't glide up them
  • Vendor package: go/vendor directory will generated when running cmake command. cmake will download the code corresponding to go/glide.lock. If we put a vendor folder under go/, cmake will just check the commit id to the packages under the folder, if commit id matches, there will be no download at all.