From 3d70cee4034e4da37d125679345aa2a10c58cb34 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Tue, 14 Apr 2015 23:21:36 +0200 Subject: Update Kernel documentation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Language cleaned up by technical writers from Combitech. Proofreading and corrections by Björn Gustavsson and Hans Bolinder. --- lib/kernel/doc/src/application.xml | 457 +++++++++++++++++++------------------ 1 file changed, 238 insertions(+), 219 deletions(-) (limited to 'lib/kernel/doc/src/application.xml') diff --git a/lib/kernel/doc/src/application.xml b/lib/kernel/doc/src/application.xml index 4d8e6ce94b..16de17c901 100644 --- a/lib/kernel/doc/src/application.xml +++ b/lib/kernel/doc/src/application.xml @@ -33,23 +33,25 @@

In OTP, application denotes a component implementing some specific functionality, that can be started and stopped as a - unit, and which can be re-used in other systems as well. This - module interfaces the application controller, a process - started at every Erlang runtime system, and contains functions - for controlling applications (for example starting and stopping + unit, and that can be reused in other systems. This + module interacts with application controller, a process + started at every Erlang runtime system. This module contains functions + for controlling applications (for example, starting and stopping applications), and functions to access information about - applications (for example configuration parameters).

-

An application is defined by an application specification. The specification is normally located in an - application resource file called Application.app, - where Application is the name of the application. Refer to - app(4) for more information about - the application specification.

+ applications (for example, configuration parameters).

+

An application is defined by an application specification. + The specification is normally located in an + application resource file named Application.app, + where Application is the application name. For details + about the application specification, see + app(4).

This module can also be viewed as a behaviour for an application implemented according to the OTP design principles as a supervision tree. The definition of how to start and stop - the tree should be located in an application callback module exporting a pre-defined set of functions.

-

Refer to OTP Design Principles for more information about - applications and behaviours.

+ the tree is to be located in an application callback module, + exporting a predefined set of functions.

+

For details about applications and behaviours, see + OTP Design Principles.

 @@ -59,17 +61,44 @@ - tuple_of(T)

A tuple where the elements are of type T.

 + + + + Load and start an application and its dependencies, recursively. + +

Equivalent to calling + start/1,2 + repeatedly on all dependencies that are not yet started for an application.

+

Returns {ok, AppNames} for a successful start or for an already started + application (which is, however, omitted from the AppNames list).

+

The function reports {error, {AppName,Reason}} for errors, where + Reason is any possible reason returned by + start/1,2 + when starting a specific dependency.

+

If an error occurs, the applications started by the function are stopped + to bring the set of running applications back to its initial state.

+ + + + + + Load and start an application. + +

Equivalent to + start/1,2 + except it returns ok for already started applications.

+ + - Get the configuration parameters for an application + Get the configuration parameters for an application.

Returns the configuration parameters and their values for Application. If the argument is omitted, it defaults to @@ -82,7 +111,7 @@ - Get the application specification keys + Get the application specification keys.

Returns the application specification keys and their values for Application. If the argument is omitted, it @@ -96,7 +125,7 @@ - Get the name of an application containing a certain process or module + Get the name of an application containing a certain process or module.

Returns the name of the application to which the process Pid or the module Module belongs. Providing no @@ -110,222 +139,212 @@ - Get the value of a configuration parameter + Get the value of a configuration parameter. -

Returns the value of the configuration parameter Par +

Returns the value of configuration parameter Par for Application. If the application argument is omitted, it defaults to the application of the calling process.

-

If the specified application is not loaded, or - the configuration parameter does not exist, or if the process - executing the call does not belong to any application, - the function returns undefined.

+

Returns undefined if any of the following applies:

+ + The specified application is not loaded. + The configuration parameter does not exist. + The process executing the call does not belong to any application. + - Get the value of a configuration parameter using a default + Get the value of a configuration parameter using a default. -

Works like get_env/2 but returns - Def value when configuration parameter +

Works like get_env/2 but returns + value Def when configuration parameter Par does not exist.

 - Get the value of an application specification key + Get the value of an application specification key.

Returns the value of the application specification key Key for Application. If the application argument is omitted, it defaults to the application of the calling process.

-

If the specified application is not loaded, or - the specification key does not exist, or if the process - executing the call does not belong to any application, - the function returns undefined.

+

Returns undefined if any of the following applies:

+ + The specified application is not loaded. + The specification key does not exist. + The process executing the call does not belong to any application. + + - Load an application + Load an application.

Loads the application specification for an application into - the application controller. It will also load the application - specifications for any included applications. Note that - the function does not load the actual Erlang object code.

-

The application can be given by its name Application. - In this case the application controller will search the code + the application controller. It also loads the application + specifications for any included applications. Notice that + the function does not load the Erlang object code.

+

The application can be specified by its name Application. + In this case, the application controller searches the code path for the application resource file Application.app - and load the specification it contains.

-

The application specification can also be given directly as a - tuple AppSpec. This tuple should have the format and - contents as described in app(4).

+ and loads the specification it contains.

+

The application specification can also be specified directly as a + tuple AppSpec, having the format and + contents as described in + app(4).

If Distributed == {Application,[Time,]Nodes}, - the application will be distributed. The argument overrides - the value for the application in the Kernel configuration + the application becomes distributed. The argument overrides + the value for the application in the Kernel configuration parameter distributed. Application must be - the name of the application (same as in the first argument). - If a node crashes and Time has been specified, then - the application controller will wait for Time + the application name (same as in the first argument). + If a node crashes and Time is specified, + the application controller waits for Time milliseconds before attempting to restart the application on - another node. If Time is not specified, it will - default to 0 and the application will be restarted + another node. If Time is not specified, it + defaults to 0 and the application is restarted immediately.

Nodes is a list of node names where the application - may run, in priority from left to right. Node names can be + can run, in priority from left to right. Node names can be grouped using tuples to indicate that they have the same - priority. Example:

+ priority.

+

Example:

Nodes = [cp1@cave, {cp2@cave, cp3@cave}] -

This means that the application should preferably be started +

This means that the application is preferably to be started at cp1@cave. If cp1@cave is down, - the application should be started at either cp2@cave + the application is to be started at cp2@cave or cp3@cave.

If Distributed == default, the value for - the application in the Kernel configuration parameter - distributed will be used.

+ the application in the Kernel configuration parameter + distributed is used.

 - Get the currently loaded applications + Get the currently loaded applications. -

Returns a list with information about the applications which - have been loaded using load/1,2, also included - applications. Application is the application name. - Description and Vsn are the values of its - description and vsn application specification +

Returns a list with information about the applications, and included + applications, which are loaded using load/1,2. + Application is the application name. + Description and Vsn are the values + of their description and vsn application specification keys, respectively.

 - Change an application's permission to run on a node. + Change the permission for an application to run at a node.

Changes the permission for Application to run at - the current node. The application must have been loaded using + the current node. The application must be loaded using load/1,2 for the function to have effect.

If the permission of a loaded, but not started, application - is set to false, start will return ok but - the application will not be started until the permission is + is set to false, start returns ok but + the application is not started until the permission is set to true.

If the permission of a running application is set to - false, the application will be stopped. If - the permission later is set to true, it will be + false, the application is stopped. If + the permission later is set to true, it is restarted.

If the application is distributed, setting the permission to false means that the application will be started at, or moved to, another node according to how its distribution is - configured (see load/2 above).

+ configured + (see load/2).

The function does not return until the application is - started, stopped or successfully moved to another node. - However, in some cases where permission is set to true - the function may return ok even though the application - itself has not started. This is true when an application - cannot start because it has dependencies to other - applications which have not yet been started. When they have - been started, Application will be started as well.

+ started, stopped, or successfully moved to another node. + However, in some cases where permission is set to true, + the function returns ok even though the application + is not started. This is true when an application + cannot start because of dependencies to other + applications that are not yet started. When they are + started, Application is started as well.

By default, all applications are loaded with permission - true on all nodes. The permission is configurable by - using the Kernel configuration parameter permissions.

+ true on all nodes. The permission can be configured + using the Kernel configuration parameter permissions.

 - Set the value of a configuration parameter + Set the value of a configuration parameter. -

Sets the value of the configuration parameter Par for +

Sets the value of configuration parameter Par for Application.

-

set_env/4 uses the standard gen_server timeout - value (5000 ms). The timeout option can be provided - if another timeout value is useful, for example, in situations +

set_env/4 uses the standard gen_server time-out + value (5000 ms). Option timeout can be specified + if another time-out value is useful, for example, in situations where the application controller is heavily loaded.

If set_env/4 is called before the application is loaded, - the application environment values specified in the Application.app - file will override the ones previously set. This is also true for application + the application environment values specified in file Application.app + override the ones previously set. This is also true for application reloads.

-

The persistent option can be set to true - when there is a need to guarantee parameters set with set_env/4 - will not be overridden by the ones defined in the application resource - file on load. This means persistent values will stick after the application +

Option persistent can be set to true + to guarantee that parameters set with set_env/4 + are not overridden by those defined in the application resource + file on load. This means that persistent values will stick after the application is loaded and also on application reload.

-

Use this function only if you know what you are doing, - that is, on your own applications. It is very application - and configuration parameter dependent when and how often - the value is read by the application, and careless use - of this function may put the application in a - weird, inconsistent, and malfunctioning state.

+

Use this function only if you know what you are doing, + that is, on your own applications. It is very + application-dependent and + configuration parameter-dependent when and how often + the value is read by the application. Careless use + of this function can put the application in a + weird, inconsistent, and malfunctioning state.

 - - - - Load and start an application - -

Equivalent to application:start/1,2 except - it returns ok for already started applications.

- - - - - - Load and start an application and its dependencies, recursively - -

Equivalent to calling application:start/1,2 - repeatedly on all dependencies that have not yet been started for an application. - The function returns {ok, AppNames} for a successful start or for an already started - application (which are however omitted from the AppNames list), and reports - {error, {AppName,Reason}} for errors, where Reason is any possible reason - returned by application:start/1,2 when starting a - specific dependency. In case of an error, the applications that were started by the - function are stopped to bring the set of running applications back to its initial state.

- - - Load and start an application - + Load and start an application. +

Starts Application. If it is not loaded, - the application controller will first load it using - load/1. It will make sure any included applications - are loaded, but will not start them. That is assumed to be + the application controller first loads it using + load/1. It ensures that any included applications + are loaded, but does not start them. That is assumed to be taken care of in the code for Application.

The application controller checks the value of the application specification key applications, to - ensure that all applications that should be started before - this application are running. If not, + ensure that all applications needed to be started before + this application are running. Otherwise, {error,{not_started,App}} is returned, where App is the name of the missing application.

-

The application controller then creates an application master for the application. The application master is +

The application controller then creates an application master + for the application. The application master is the group leader of all the processes in the application. The application master starts the application by calling the application callback function Module:start/2 as defined by the application specification key mod.

-

The Type argument specifies the type of +

Argument Type specifies the type of the application. If omitted, it defaults to temporary.

If a permanent application terminates, all other applications and the entire Erlang node are also terminated. - If a transient application terminates with Reason == normal, this is reported but no other applications are - terminated. If a transient application terminates - abnormally, all other applications and the entire Erlang - node are also terminated. + + + If a transient application terminates with Reason == normal, + this is reported but no other applications are terminated. + If a transient application terminates abnormally, all other + applications and the entire Erlang node are also terminated. + + If a temporary application terminates, this is reported but no other applications are terminated. -

Note that it is always possible to stop an application +

Notice that an application can always be stopped explicitly by calling stop/1. Regardless of the type of - the application, no other applications will be affected.

-

Note also that the transient type is of little practical use, - since when a supervision tree terminates, the reason is set to + the application, no other applications are affected.

+

Notice also that the transient type is of little practical use, + because when a supervision tree terminates, the reason is set to shutdown, not normal.

 @@ -334,13 +353,13 @@ Nodes = [cp1@cave, {cp2@cave, cp3@cave}] Get the start type of an ongoing application startup.

This function is intended to be called by a process belonging - to an application, when the application is being started, to - determine the start type which is either StartType or + to an application, when the application is started, to + determine the start type, which is StartType or local.

-

See Module:start/2 for a description of - StartType.

-

local is returned if only parts of the application is - being restarted (by a supervisor), or if the function is +

For a description of StartType, see + Module:start/2.

+

local is returned if only parts of the application are + restarted (by a supervisor), or if the function is called outside a startup.

If the process executing the call does not belong to any application, the function returns undefined.

@@ -348,103 +367,106 @@ Nodes = [cp1@cave, {cp2@cave, cp3@cave}] - Stop an application + Stop an application.

Stops Application. The application master calls Module:prep_stop/1, if such a function is defined, and - then tells the top supervisor of the application to shutdown - (see supervisor(3)). This means that the entire + then tells the top supervisor of the application to shut down + (see supervisor(3)). + This means that the entire supervision tree, including included applications, is terminated in reversed start order. After the shutdown, the application master calls Module:stop/1. Module is the callback module as defined by the application specification key mod.

-

Last, the application master itself terminates. Note that all - processes with the application master as group leader, i.e. +

Last, the application master terminates. Notice that all + processes with the application master as group leader, that is, processes spawned from a process belonging to the application, - thus are terminated as well.

+ are also terminated.

When stopped, the application is still loaded.

-

In order to stop a distributed application, stop/1 - has to be called on all nodes where it can execute (that is, +

To stop a distributed application, stop/1 + must be called on all nodes where it can execute (that is, on all nodes where it has been started). The call to stop/1 on the node where the application currently - executes will stop its execution. The application will not be - moved between nodes due to stop/1 being called on + executes stops its execution. The application is not + moved between nodes, as stop/1 is called on the node where the application currently executes before stop/1 is called on the other nodes.

 - Take over a distributed application + Take over a distributed application. -

Performs a takeover of the distributed application +

Takes over the distributed application Application, which executes at another node Node. At the current node, the application is restarted by calling Module:start({takeover,Node},StartArgs). Module and StartArgs are retrieved from the loaded application specification. The application at the other node is not - stopped until the startup is completed, i.e. when + stopped until the startup is completed, that is, when Module:start/2 and any calls to Module:start_phase/3 have returned.

-

Thus two instances of the application will run simultaneously - during the takeover, which makes it possible to transfer data - from the old to the new instance. If this is not acceptable - behavior, parts of the old instance may be shut down when - the new instance is started. Note that the application may - not be stopped entirely however, at least the top supervisor +

Thus, two instances of the application run simultaneously + during the takeover, so that data can be transferred + from the old to the new instance. If this is not an acceptable + behavior, parts of the old instance can be shut down when + the new instance is started. However, the application cannot + be stopped entirely, at least the top supervisor must remain alive.

-

See start/1,2 for a description of Type.

+

For a description of Type, see + start/1,2.

 - Unload an application + Unload an application.

Unloads the application specification for Application - from the application controller. It will also unload + from the application controller. It also unloads the application specifications for any included applications. - Note that the function does not purge the actual Erlang + Notice that the function does not purge the Erlang object code.

 - Unset the value of a configuration parameter + Unset the value of a configuration parameter.

Removes the configuration parameter Par and its value for Application.

unset_env/2 uses the standard gen_server - timeout value (5000 ms). The timeout option can be - provided if another timeout value is useful, for example, in + time-out value (5000 ms). Option timeout can be + specified if another time-out value is useful, for example, in situations where the application controller is heavily loaded.

unset_env/3 also allows the persistent option to be passed - (see set_env/4 above).

- -

Use this function only if you know what you are doing, - that is, on your own applications. It is very application - and configuration parameter dependent when and how often - the value is read by the application, and careless use - of this function may put the application in a - weird, inconsistent, and malfunctioning state.

+ (see set_env/4).

+ +

Use this function only if you know what you are doing, + that is, on your own applications. It is very + application-dependent and configuration + parameter-dependent when and how often + the value is read by the application. Careless use + of this function can put the application in a + weird, inconsistent, and malfunctioning state.

 - Get the currently running applications + Get the currently running applications. -

Returns a list with information about the applications which +

Returns a list with information about the applications that are currently running. Application is the application - name. Description and Vsn are the values of its - description and vsn application specification + name. Description and Vsn are the + values of their description and vsn application specification keys, respectively.

which_applications/0 uses the standard - gen_server timeout value (5000 ms). A Timeout - argument can be provided if another timeout value is useful, + gen_server time-out value (5000 ms). A Timeout + argument can be specified if another time-out value is useful, for example, in situations where the application controller is heavily loaded.

 @@ -452,81 +474,81 @@ Nodes = [cp1@cave, {cp2@cave, cp3@cave}]
- CALLBACK MODULE -

The following functions should be exported from an + Callback Module +

The following functions are to be exported from an application callback module.

Module:start(StartType, StartArgs) -> {ok, Pid} | {ok, Pid, State} | {error, Reason} - Start an application + Start an application. - StartType = start_type() + StartType = start_type() StartArgs = term() Pid = pid() State = term()

This function is called whenever an application is started - using application:start/1,2, and should start + using start/1,2, and is to start the processes of the application. If the application is structured according to the OTP design principles as a supervision tree, this means starting the top supervisor of the tree.

StartType defines the type of start:

- normal if it's a normal startup. + normal if it is a normal startup. normal also if the application is distributed and - started at the current node due to a failover from another + started at the current node because of a failover from another node, and the application specification key start_phases == undefined. {takeover,Node} if the application is - distributed and started at the current node due to a + distributed and started at the current node because of a takeover from Node, either because - application:takeover/2 has been called or because + takeover/2 has been called or because the current node has higher priority than Node. {failover,Node} if the application is - distributed and started at the current node due to a + distributed and started at the current node because of a failover from Node, and the application specification key start_phases /= undefined.

StartArgs is the StartArgs argument defined by the application specification key mod.

-

The function should return {ok,Pid} or - {ok,Pid,State} where Pid is the pid of the top +

The function is to return {ok,Pid} or + {ok,Pid,State}, where Pid is the pid of the top supervisor and State is any term. If omitted, - State defaults to []. If later the application - is stopped, State is passed to + State defaults to []. If the application + is stopped later, State is passed to Module:prep_stop/1.

 Module:start_phase(Phase, StartType, PhaseArgs) -> ok | {error, Reason} - Extended start of an application + Extended start of an application. Phase = atom() - StartType = start_type() + StartType = start_type() PhaseArgs = term() Pid = pid() State = state() -

This function is used to start an application with included - applications, when there is a need for synchronization between +

Starts an application with included + applications, when synchronization is needed between processes in the different applications during startup.

-

The start phases is defined by the application specification +

The start phases are defined by the application specification key start_phases == [{Phase,PhaseArgs}]. For included applications, the set of phases must be a subset of the set of phases defined for the including application.

The function is called for each start phase (as defined for the primary application) for the primary application and all included applications, for which the start phase is defined.

-

See Module:start/2 for a description of - StartType.

+

For a description of StartType, see + Module:start/2.

 Module:prep_stop(State) -> NewState - Prepare an application for termination + Prepare an application for termination. State = NewState = term() @@ -536,28 +558,26 @@ Nodes = [cp1@cave, {cp2@cave, cp3@cave}] the application.

State is the state returned from Module:start/2, or [] if no state was returned. - NewState is any term and will be passed to + NewState is any term and is passed to Module:stop/1.

The function is optional. If it is not defined, the processes - will be terminated and then Module:stop(State) is - called.

+ are terminated and then Module:stop(State) is called.

 Module:stop(State) - Clean up after termination of an application + Clean up after termination of an application. State = term()

This function is called whenever an application has stopped. It is intended to be the opposite of Module:start/2 - and should do any necessary cleaning up. The return value is + and is to do any necessary cleaning up. The return value is ignored.

-

State is the return value of - Module:prep_stop/1, if such a function exists. - Otherwise State is taken from the return value of - Module:start/2.

+

State is the return value of Module:prep_stop/1, + if such a function exists. Otherwise State is taken from + the return value of Module:start/2.

 @@ -572,19 +592,18 @@ Nodes = [cp1@cave, {cp2@cave, cp3@cave}]

This function is called by an application after a code - replacement, if there are any changes to the configuration - parameters.

-

Changed is a list of parameter-value tuples with all - configuration parameters with changed values, New is - a list of parameter-value tuples with all configuration - parameters that have been added, and Removed is a list - of all parameters that have been removed.

+ replacement, if the configuration parameters have changed.

+

Changed is a list of parameter-value tuples including all + configuration parameters with changed values.

+

New is a list of parameter-value tuples including all + added configuration parameters.

+

Removed is a list of all removed parameters.
- SEE ALSO + See Also

OTP Design Principles, kernel(6), app(4)

-- cgit v1.2.3