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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 exam‐
        ple when generating start scripts.
        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
               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 automati‐
              cally 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 auto‐
              matically be loaded, but not started,  by  the  application  con‐
              troller.  It  is  assumed  that  the  topmost  supervisor  of the
              included application is started by a supervisor of this  applica‐
              tion.
 
          applications:
              All applications which must be started before this application is
              allowed to be started. systools uses this list to  generate  cor‐
              rect 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  applica‐
              tion:get_env/1, 2. The values in the  application  resource  file
              can  be  overridden  by  values in a configuration file (see con‐
erl(1)).
 
          mod:
              Specifies the application callback module and a  start  argument,
application(3).
 
              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 pri‐
              mary  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 applica‐
              tion, 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 pri‐
              mary application. Refer to OTP Design Principles for more  infor‐
              mation.
systools(3)
 

AUTHORS

        Martin Björklund - support@erlang.ericsson.se
        Gunilla Arendt - support@erlang.ericsson.se
 

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