NAME
app - Application resource file.
DESCRIPTION
The application resource file specifies the resources an application
uses, and how the application is started. There must always be one
application resource file called Application.app for each application
Application in the system.
The file is read by the application controller when an application is
loaded/started. It is also used by the functions in systools, for
example when generating start scripts.
FILE SYNTAX
The application resource file should be called Application.app where
Application is the name of the application. The file should be located
in the ebin directory for the application.
It must contain one single Erlang term, which is called an application
specification:
{application, Application,
[{description, Description},
{id, Id},
{vsn, Vsn},
{modules, Modules},
{maxP, MaxP},
{maxT, MaxT},
{registered, Names},
{included_applications, Apps},
{applications, Apps},
{env, Env},
{mod, Start},
{start_phases, Phases}]}.
Value Default
----- -------
Application atom() -
Description string() ""
Id string() ""
Vsn string() ""
Modules [Module] []
MaxP int() infinity
MaxT int() infinity
Names [Name] []
Apps [App] []
Env [{Par,Val}] []
Start {Module,StartArgs} undefined
Phases [{Phase,PhaseArgs}] undefined
Module = Name = App = Par = Phase = atom()
Val = StartArgs = PhaseArgs = term()
Application is the name of the application.
For the application controller, all keys are optional. The respective
default values are used for any omitted keys.
The functions in systools require more information. If they are used,
the following keys are mandatory: description, vsn, modules, registered
and applications. The other keys are ignored by systools.
description
A one-line description of the application.
id Product identification, or similar.
vsn
The version of the application.
modules
All modules introduced by this application. systools uses this
list when generating start scripts and tar files. A module can
only be defined in one application.
maxP
Deprecated - will be ignored .br The maximum number of processes
allowed in the application.
maxT
The maximum time in milliseconds that the application is allowed
to run. After the specified time the application will
automatically terminate.
registered
All names of registered processes started in this application.
systools uses this list to detect name clashes between different
applications.
included_applications
All applications which are included by this application. When
this application is started, all included application will
automatically be loaded, but not started, by the application
controller. It is assumed that the topmost supervisor of the
included application is started by a supervisor of this
application.
applications
All applications which must be started before this application is
allowed to be started. systools uses this list to generate
correct start scripts. Defaults to the empty list, but note that
all applications have dependencies to (at least) kernel and
stdlib.
env
Configuration parameters used by the application. The value of a
configuration parameter is retrieved by calling
application:get_env/1,2. The values in the application resource
file can be overridden by values in a configuration file (see
config(4)) or by command line flags (see erl(1)).
mod
Specifies the application callback module and a start argument,
see application(3erl).
The mod key is necessary for an application implemented as a
supervision tree, or the application controller will not know how
to start it. The mod key can be omitted for applications without
processes, typically code libraries such as the application
STDLIB.
start_phases
A list of start phases and corresponding start arguments for the
application. If this key is present, the application master will
- in addition to the usual call to Module:start/2 - also call
Module:start_phase(Phase,Type,PhaseArgs) for each start phase
defined by the start_phases key, and only after this extended
start procedure will application:start(Application) return.
Start phases may be used to synchronize startup of an application
and its included applications. In this case, the mod key must be
specified as:
{mod, {application_starter,[Module,StartArgs]}}
The application master will then call Module:start/2 for the
primary application, followed by calls to Module:start_phase/3
for each start phase (as defined for the primary application)
both for the primary application and for each of its included
application, for which the start phase is defined.
This implies that for an included application, the set of start
phases must be a subset of the set of phases defined for the
primary application. Refer to OTP Design Principles for more
information.
SEE ALSO
application(3erl), systools(3erl)