1app(5) Files app(5)
2
6 app - Application resource file.
7
9 The application resource file specifies the resources an application
10 uses, and how the application is started. There must always be one
11 application resource file called Application.app for each application
12 Application in the system.
13 The file is read by the application controller when an application is
15 loaded/started. It is also used by the functions in systools, for exam‐
16 ple when generating start scripts.
17
19 The application resource file is to be called Application.app, where
20 Application is the application name. The file is to be located in
21 directory ebin for the application.
22 The file must contain a single Erlang term, which is called an applica‐
24 tion specification:
25 {application, Application,
27 [{description, Description},
28 {id, Id},
29 {vsn, Vsn},
30 {modules, Modules},
31 {maxP, MaxP},
32 {maxT, MaxT},
33 {registered, Names},
34 {included_applications, Apps},
35 {applications, Apps},
36 {env, Env},
37 {mod, Start},
38 {start_phases, Phases},
39 {runtime_dependencies, RTDeps}]}.
40 Value Default
42 ----- -------
43 Application atom() -
44 Description string() ""
45 Id string() ""
46 Vsn string() ""
47 Modules [Module] []
48 MaxP int() infinity
49 MaxT int() infinity
50 Names [Name] []
51 Apps [App] []
52 Env [{Par,Val}] []
53 Start {Module,StartArgs} []
54 Phases [{Phase,PhaseArgs}] undefined
55 RTDeps [ApplicationVersion] []
56 Module = Name = App = Par = Phase = atom()
58 Val = StartArgs = PhaseArgs = term()
59 ApplicationVersion = string()
60 Application:
62 Application name.
63 For the application controller, all keys are optional. The respective
65 default values are used for any omitted keys.
66 The functions in systools require more information. If they are used,
68 the following keys are mandatory:
69 * description
71 * vsn
73 * modules
75 * registered
77 * applications
79 The other keys are ignored by systools.
81 description:
83 A one-line description of the application.
84 id:
86 Product identification, or similar.
87 vsn:
89 Version of the application.
90 modules:
92 All modules introduced by this application. systools uses this list
93 when generating start scripts and tar files. A module can only be
94 defined in one application.
95 maxP:
97 Deprecated - is ignored
98 Maximum number of processes allowed in the application.
100 maxT:
102 Maximum time, in milliseconds, that the application is allowed to
103 run. After the specified time, the application terminates automati‐
104 cally.
105 registered:
107 All names of registered processes started in this application. sys‐
108 tools uses this list to detect name clashes between different
109 applications.
110 included_applications:
112 All applications included by this application. When this applica‐
113 tion is started, all included applications are loaded automati‐
114 cally, but not started, by the application controller. It is
115 assumed that the top-most supervisor of the included application is
116 started by a supervisor of this application.
117 applications:
119 All applications that must be started before this application is
120 allowed to be started. systools uses this list to generate correct
121 start scripts. Defaults to the empty list, but notice that all
122 applications have dependencies to (at least) Kernel and STDLIB.
123 env:
125 Configuration parameters used by the application. The value of a
126 configuration parameter is retrieved by calling applica‐
127 tion:get_env/1,2. The values in the application resource file can
128 be overridden by values in a configuration file (see config(4)) or
129 by command-line flags (see erts:erl(1)).
130 mod:
132 Specifies the application callback module and a start argument, see
133 application(3).
134 Key mod is necessary for an application implemented as a supervi‐
136 sion tree, otherwise the application controller does not know how
137 to start it. mod can be omitted for applications without processes,
138 typically code libraries, for example, STDLIB.
139 start_phases:
141 A list of start phases and corresponding start arguments for the
142 application. If this key is present, the application master, in
143 addition to the usual call to Module:start/2, also calls Mod‐
144 ule:start_phase(Phase,Type,PhaseArgs) for each start phase defined
145 by key start_phases. Only after this extended start procedure,
146 application:start(Application) returns.
147 Start phases can be used to synchronize startup of an application
149 and its included applications. In this case, key mod must be speci‐
150 fied as follows:
151 {mod, {application_starter,[Module,StartArgs]}}
153 The application master then calls Module:start/2 for the primary
155 application, followed by calls to Module:start_phase/3 for each
156 start phase (as defined for the primary application), both for the
157 primary application and for each of its included applications, for
158 which the start phase is defined.
159 This implies that for an included application, the set of start
161 phases must be a subset of the set of phases defined for the pri‐
162 mary application. For more information, see OTP Design Principles.
163 runtime_dependencies:
165 A list of application versions that the application depends on. An
166 example of such an application version is "kernel-3.0". Application
167 versions specified as runtime dependencies are minimum require‐
168 ments. That is, a larger application version than the one specified
169 in the dependency satisfies the requirement. For information about
170 how to compare application versions, see section Versions in the
171 System Principles User's Guide.
172 Notice that the application version specifies a source code ver‐
174 sion. One more, indirect, requirement is that the installed binary
175 application of the specified version is built so that it is compat‐
176 ible with the rest of the system.
177 Some dependencies can only be required in specific runtime scenar‐
179 ios. When such optional dependencies exist, these are specified and
180 documented in the corresponding "App" documentation of the specific
181 application.
182 Warning:
184 The runtime_dependencies key was introduced in OTP 17.0. The type of
185 its value might be subject to changes during the OTP 17 release.
186 Warning:
189 All runtime dependencies specified in OTP applications during the OTP
190 17 release may not be completely correct. This is actively being
191 worked on. Declared runtime dependencies in OTP applications are
192 expected to be correct in OTP 18.
193
196 application(3), systools(3)
197Ericsson AB kernel 5.4.3.2 app(5)