trusty (5) app.5.gz

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}   []
       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
           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(5)) 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)