This file is intended to be notes about code structure in cxxnet.

• The project follows Google's C code style
  • All the module interface are heavily documented in doxygen format
• Contribution is to the code and this NOTE welcomed!
• If you have questions on code, fire an github issue
  • If you want to help improve this note, send a pullreq

• In each folder in the src, you can find a .h file with the same name as the folder
  • These are interface of that module, heavily documented with doxygen comment
  • Start with these the interface header to understand the interface
• All the rest of the -inl.hpp files are implementations of the interface
  • These are invisible to other modules
  • Templatized class with parameter xpu that can stands for cpu or gpu
• The project depends on mshadow for tensor operations
  • You can find the documentation on mshadow in its repo.

• Dependency order: nnet->updater->layer
  • All module depends on global.h and utils
  • io is an independent module
• layer is implementation of neural net layers and defines forward and backward propagation
• updater is the parameter updating module, it defines update rule of weights
  • AsyncUpdater is a special updater that handles asynchronize communication and update
  • It uses mshadow-ps to do async communication
• nnet is the neural net structure that combines layers together to form a neural net
  • Dependency in nnet: CXXNetThreadTrainer->NeuralNetThread->NeuralNet
• io is the input module to handle reading various data and preprocessing
  • io uses iterator pattern to handle data processing pipeline
  • The pipeline can be mult-threaded using threadbuffer trick

• Data is pulled from io module to feed into nnet
• nnet contains #gpu threads, that get part of data, call layer objects to do forwardbackprop
• For each weights, an updater is created
  • AsyncUpdater.AfterBackprop is called after backprop of the corresponding layer to push out gradient
  • AsyncUPdater.UpdateWait is called before forward to the layer
  • mshadow-ps does the async trick of parameter communication
• AsyncUpdater will call IUpdater, which does the updating trick
  • If update_on_server is on, IUpdater will be created on server-side instead

• .h files are data structures and interface
  • In each folder, there is one .h file that have same name as the folder, this file defines everything needed for other module to use this module
  • Interface headers: layer/layer.h, updater/updater.h
• -inl.hpp files are implementations of interface, like cpp file in most project.
  • You only need to understand the interface file to understand the usage of that layer
• In each folder, there can be a .cpp file, and .cu file that that compiles the module of that layer
  • the .cpp file and .cu file does not contain implementation, but reuse common implementation in file ends with _impl-inl.hpp