OTPApplication

An OTP Application

An OTP application is just a group of related code. They can be what we refer to as a library application: a collection of modules to be used by other applications. More often, an OTP applications are living things that are started, run for some time, and eventually shut down. These are active applications. An active application has an application behavior and a root supervisor whose job is to manage the processes of the application.

In the context of OTP, the word application has a specific meaning: an application is a software component consisting of a number of modules bundled together with a few additional metadata files, and organized on disk according to certain conventions. This allows the system to know which applications are currently installed, and, for example, lets you start or stop an application by its name.

OTP Application Directory Structure

Creating an OTP application consists mostly of setting up a standard directory struc- ture and writing some application metadata. This metadata tells the system what it Terminology: applications needs to know to start and stop the application. It also specifies the dependencies of the application, such as what other applications need to be present or started beforehand.

OTP applications use a simple directory layout.

<application-name>
    |- ebin
    |- src
    |- include
    |- doc

You should of course replace <application-name> with the name of your application. The names of the subdirectories are self-explanatory.

Subdirectories of the application directory

src : This is where your *.erl files and private *.hrl files go

doc : Documentation. If you generate documentation from EDoc, you put your overview.edoc file here.

ebin : It’s the location of the .app file, in a fully built system (as part of the release), sinan also puts the beam files here.

include : Public header files. Any .hrl file that is part of your public API should be kept in this directory. Private .hrl files that are only used within your code and aren’t intended for public consumption should be kept under src with the rest of your source code.