mxnet/include/mxnet/engine.h

在名字空间 mxnet engine 中定义了抽象类Engine，用以规范接口，其接口有

NotifyShutdown

NewVariable

DeleteVariable

NewOperator

DeleteOperator

Push

PushAsync

PushSync

WaitForVar

WaitForAll

DeduplicateVarHandle

等

mxnet/src/engine/engine_impl.h

定义了多态实现的

Engine *CreateNaiveEngine

Engine *CreateThreadedEnginePolled

Engine *CreateThreadedEnginePerDevice

 mxnet/src/engine/engine.cc

根据环境变量决定Engine *CreateEngine的选择情况。有三种形式

CreateNaiveEngine，CreateThreadedEnginePooled，CreateThreadEnginePerDevice。