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.TH app 4 "kernel 2.12.3" "Ericsson AB" "FILES"
.SH NAME
app \- Application resource file\&.
.SH DESCRIPTION
.LP
The \fIapplication resource file\fR specifies the resources an application uses, and how the application is started\&. There must always be one application resource file called \fIApplication\&.app\fR for each application \fIApplication\fR in the system\&.
.LP
The file is read by the application controller when an application is loaded/started\&. It is also used by the functions in \fIsystools\fR, for example when generating start scripts\&.
.SH FILE SYNTAX
.LP
The application resource file should be called \fIApplication\&.app\fR where \fIApplication\fR is the name of the application\&. The file should be located in the \fIebin\fR directory for the application\&.
.LP
It must contain one single Erlang term, which is called an \fIapplication specification\fR:
.nf
{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()
.fi
.LP
\fIApplication\fR is the name of the application\&.
.LP
For the application controller, all keys are optional\&. The respective default values are used for any omitted keys\&.
.LP
The functions in \fIsystools\fR require more information\&. If they are used, the following keys are mandatory: \fIdescription\fR, \fIvsn\fR, \fImodules\fR, \fIregistered\fR and \fIapplications\fR\&. The other keys are ignored by \fIsystools\fR\&.
.RS 2
.TP 4
.B
\fIdescription\fR:
A one-line description of the application\&.
.TP 4
.B
\fIid\fR:
Product identification, or similar\&.
.TP 4
.B
\fIvsn\fR:
The version of the application\&.
.TP 4
.B
\fImodules\fR:
All modules introduced by this application\&. \fIsystools\fR uses this list when generating start scripts and tar files\&. A module can only be defined in one application\&.
.TP 4
.B
\fImaxP\fR:
\fIDeprecated - will be ignored\fR
.br
The maximum number of processes allowed in the application\&.
.TP 4
.B
\fImaxT\fR:
The maximum time in milliseconds that the application is allowed to run\&. After the specified time the application will automatically terminate\&.
.TP 4
.B
\fIregistered\fR:
All names of registered processes started in this application\&. \fIsystools\fR uses this list to detect name clashes between different applications\&.
.TP 4
.B
\fIincluded_applications\fR:
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\&.
.TP 4
.B
\fIapplications\fR:
All applications which must be started before this application is allowed to be started\&. \fIsystools\fR uses this list to generate correct start scripts\&. Defaults to the empty list, but note that all applications have dependencies to (at least) \fIkernel\fR and \fIstdlib\fR\&.
.TP 4
.B
\fIenv\fR:
Configuration parameters used by the application\&. The value of a configuration parameter is retrieved by calling \fIapplication:get_env/1, 2\fR\&. The values in the application resource file can be overridden by values in a configuration file (see \fIconfig(4)\fR) or by command line flags (see \fIerl(1)\fR)\&.
.TP 4
.B
\fImod\fR:
Specifies the application callback module and a start argument, see \fIapplication(3)\fR\&.
.RS 4
.LP
.LP
The \fImod\fR key is necessary for an application implemented as a supervision tree, or the application controller will not know how to start it\&. The \fImod\fR key can be omitted for applications without processes, typically code libraries such as the application STDLIB\&.
.RE
.TP 4
.B
\fIstart_phases\fR:
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 \fIModule:start/2\fR - also call \fIModule:start_phase(Phase, Type, PhaseArgs)\fR for each start phase defined by the \fIstart_phases\fR key, and only after this extended start procedure will \fIapplication:start(Application)\fR return\&.
.RS 4
.LP
.LP
.LP
.LP
Start phases may be used to synchronize startup of an application and its included applications\&. In this case, the \fImod\fR key must be specified as:
.LP
.nf
{mod, {application_starter,[Module,StartArgs]}}
.fi
.LP
.LP
The application master will then call \fIModule:start/2\fR for the primary application, followed by calls to \fIModule:start_phase/3\fR 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\&.
.LP
.LP
.LP
.LP
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 \fIOTP Design Principles\fR for more information\&.
.RE
.RE
.SH SEE ALSO
.LP
application(3), systools(3)
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