Application framework
=======

## Directory structure



This folder "app-native-shared" is for the source files shared by both WASM APP and native runtime

- The c files in this directory are compiled into both the WASM APP and runtime.
- The header files for distributing to SDK are placed in the "bi-inc" folder.



This folder "template" contains a pre-defined directory structure for a framework component. The developers can copy the template folder to create new components to the application framework.



Every other subfolder is framework component. Each component contains two library parts: **app and native**.

- The "base" component provide timer API and inter-app communication support. It must be enabled if other components are selected.
- Under the "app" folder of a component, the subfolder "wa_inc" holds all header files that should be included by the WASM applications



## Application framework basic model

The app framework is built on top of two fundamental operations:

- [Native calls into WASM function](../../doc/embed_wamr.md)

- [WASM app calls into native API](../../doc/export_native_api.md)

Asynchronized programming model is supported for WASM applications

- Every WASM app has its own sandbox and thread

- Queue and messaging

<img src="../../doc/pics/app_framework.PNG" style="zoom:67%;" />



## Customized building of app framework

A component can be compilation configurable to the runtime. The wamr SDK tool "build_sdk.sh" supports menu config to select app components for building a customized runtime.

A number of CMAKE variables are defined to control build of framework and components. You can create a cmake file for defining these variables and include it in the CMakeList.txt for your software, or pass it in "-x" argument when run the [build_sdk.sh](../../wamr-sdk/build_sdk.sh) for building the runtime SDK.

```cmake
set (WAMR_BUILD_APP_FRAMEWORK 1)
set (WAMR_BUILD_APP_LIST WAMR_APP_BUILD_BASE)
```

Variables:

- **WAMR_BUILD_APP_FRAMEWORK**: enable the application framework
- **WAMR_BUILD_APP_LIST**: the selected components to be built into the final runtime



The configuration file can be generated through the wamr-sdk menu config:

```bash
cd wamr-sdk
./build_sdk -n [profile] -i
```



## Create new components

Generally you should follow following steps to create a new component:

- Copy the “template” for creating a new folder

- Implement the app part

  - If your component exports native function to WASM, ensure your created a header file under app for declaring the function prototype.
  - If you component provides header files for the WASM applications to include, ensure it is placed under subfolder "wa_inc".

- Implement the native part

  - If your native function is exported to WASM, you need to create an inl file for the registration. It can be any file name, assuming the file name is "my_component.inl" here:

    ```c
    //use right signature for your functions
    EXPORT_WASM_API_WITH_SIG(wasm_my_component_api_1, "(i*~)i"),
    EXPORT_WASM_API_WITH_SIG(wasm_my_component_api_2, "(i)i"),
    ```

  - Ensure "wasm_lib.cmake" is provided as it will be included by the WAMR SDK building script

  - Add a definition in "wasm_lib.cmake" for your component, e.g.

    ```cmake
    add_definitions (-DAPP_FRAMEWORK_MY_COMPONENT)
    ```

- Modify the file [app_ext_lib_export.c](./app_ext_lib_export.c) to register native APIs exported for the new introduced component. Skip it if not exporting native functions.

  ```
  #include "lib_export.h"

  ...
  #ifdef APP_FRAMEWORK_MY_COMPONENT // this definition is created in wasm_lib.cmake
      #include "my_component_native_api.h"
  #endif

  static NativeSymbol extended_native_symbol_defs[] = {
  ...
  #ifdef APP_FRAMEWORK_MY_COMPONENT
      #include "my_component.inl"
  #endif
  };
  ```



## Sensor component working flow



![](../../doc/pics/sensor_callflow.PNG)