From 7a731535a3c4eebac00bd56ae7862c2dac25284c Mon Sep 17 00:00:00 2001 From: Raimo Niskanen Date: Wed, 24 Feb 2016 16:52:01 +0100 Subject: Unify whitespace in XML doc --- lib/stdlib/doc/src/gen_statem.xml | 534 +++++++++++++++++++++++--------------- 1 file changed, 330 insertions(+), 204 deletions(-) (limited to 'lib/stdlib/doc') diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml index f21610d14c..da88bedf6b 100644 --- a/lib/stdlib/doc/src/gen_statem.xml +++ b/lib/stdlib/doc/src/gen_statem.xml @@ -31,7 +31,8 @@ gen_statem Generic State Machine Behaviour -

A behaviour module for implementing a state machine. +

+ A behaviour module for implementing a state machine. Two callback modes are supported. One for a finite state machine like gen_fsm that require the state to be an atom and use that state as @@ -45,9 +46,12 @@ and include functionality for tracing and error reporting. It will also fit into an OTP supervision tree. Refer to - OTP Design Principles for more information. + OTP Design Principles + + for more information.

-

A gen_statem assumes all specific parts to be located in a +

+ A gen_statem assumes all specific parts to be located in a callback module exporting a pre-defined set of functions. The relationship between the behaviour functions and the callback functions can be illustrated as follows:

@@ -68,29 +72,32 @@ erlang:'!' -----> Module:StateName/3 - -----> Module:terminate/3 - -----> Module:code_change/4 -

Events are of different +

+ Events are of different types so the callback functions can know the origin of an event and how to respond.

-

If a callback function fails or returns a bad value, +

+ If a callback function fails or returns a bad value, the gen_statem will terminate. An exception of class throw, however, is not regarded as an error but as a valid return.

-

The "state function" for a specific +

+ The "state function" for a specific state in a gen_statem is the callback function that is called for all events in this state, and is selected depending on callback_mode that the implementation specifies during gen_statem init.

-

When +

+ When callback_mode is state_functions the state has to be an atom and - is used as the state function name. - See + is used as the state function name. See Module:StateName/3 . @@ -101,8 +108,8 @@ erlang:'!' -----> Module:StateName/3 Module:terminate/3 makes the state name terminate unusable.

-

When - callback_mode +

+ When callback_mode is handle_event_function the state can be any term and the state function name is @@ -114,7 +121,8 @@ erlang:'!' -----> Module:StateName/3 states so you do not accidentally postpone one event forever creating an infinite busy loop.

-

The gen_statem enqueues incoming events in order of arrival +

+ The gen_statem enqueues incoming events in order of arrival and presents these to the state function in that order. The state function can postpone an event @@ -122,14 +130,15 @@ erlang:'!' -----> Module:StateName/3 After a state change all enqueued events (including postponed) are again presented to the state function.

-

The gen_statem event queue model is sufficient +

+ The gen_statem event queue model is sufficient to emulate the normal process message queue and selective receive with postponing an event corresponding to not matching it in a receive statement and changing states corresponding to entering a new receive statement.

-

The - state function +

+ The state function can insert events using the action() next_event @@ -143,7 +152,8 @@ erlang:'!' -----> Module:StateName/3 that can be used for such events making it impossible to mistake for an external event.

-

Inserting an event replaces the trick of calling your own +

+ Inserting an event replaces the trick of calling your own state handling functions that you often would have to resort to in e.g gen_fsm to force processing an inserted event before others. @@ -159,20 +169,24 @@ erlang:'!' -----> Module:StateName/3 for the details of a state transition.

-

A gen_statem handles system messages as documented in - sys. - The sys module - can be used for debugging a gen_statem. +

+ A gen_statem handles system messages as documented in + sys. + The sys module + can be used for debugging a gen_statem.

-

Note that a gen_statem does not trap exit signals +

+ Note that a gen_statem does not trap exit signals automatically, this must be explicitly initiated by the callback module.

-

Unless otherwise stated, all functions in this module fail if +

+ Unless otherwise stated, all functions in this module fail if the specified gen_statem does not exist or if bad arguments are given.

-

The gen_statem process can go into hibernation (see +

+ The gen_statem process can go into hibernation (see erlang:hibernate/3 ) if a @@ -192,11 +206,13 @@ erlang:'!' -----> Module:StateName/3 -

Name specification to use when starting - a gen_statem server. - See +

+ Name specification to use when starting + a gen_statem server. See + start_link/3 - and + + and server_ref() below. @@ -206,12 +222,14 @@ erlang:'!' -----> Module:StateName/3 -

Server specification to use when addressing +

+ Server specification to use when addressing a gen_statem server. See call/2 and server_name() - above. + + above.

It can be:

@@ -219,15 +237,18 @@ erlang:'!' -----> Module:StateName/3 LocalName The gen_statem is locally registered. Name, Node - The gen_statem is locally registered + + The gen_statem is locally registered on another node. GlobalName - The gen_statem is globally registered + + The gen_statem is globally registered in global. RegMod, ViaName - The gen_statem is registered through + + The gen_statem is registered through an alternative process registry. The registry callback module RegMod should export the functions @@ -244,11 +265,13 @@ erlang:'!' -----> Module:StateName/3 -

Debug option that can be used when starting +

+ Debug option that can be used when starting a gen_statem server through for example enter_loop/4.

-

For every entry in Dbgs +

+ For every entry in Dbgs the corresponding function in sys will be called.

@@ -257,7 +280,8 @@ erlang:'!' -----> Module:StateName/3 -

Options that can be used when starting +

+ Options that can be used when starting a gen_statem server through for example start_link/3.

@@ -266,7 +290,8 @@ erlang:'!' -----> Module:StateName/3 -

Return value from the start functions for_example +

+ Return value from the start functions for_example start_link/3.

@@ -275,7 +300,8 @@ erlang:'!' -----> Module:StateName/3 -

Destination to use when replying through for example the +

+ Destination to use when replying through for example the action() {reply,Caller,Reply} @@ -287,7 +313,8 @@ erlang:'!' -----> Module:StateName/3 -

After a state change (NewState =/= State) +

+ After a state change (NewState =/= State) all postponed events are retried.

@@ -295,10 +322,12 @@ erlang:'!' -----> Module:StateName/3 -

If +

+ If callback_mode - is state_functions, which is the default, + + is state_functions, which is the default, the state has to be of this type.

@@ -306,7 +335,8 @@ erlang:'!' -----> Module:StateName/3 -

A term in which the state machine implementation +

+ A term in which the state machine implementation should store any server data it needs. The difference between this and the state() itself is that a change in this data does not cause @@ -320,7 +350,8 @@ erlang:'!' -----> Module:StateName/3 -

External events are of 3 different type: +

+ External events are of 3 different type: {call,Caller}, cast or info. Calls (synchronous) and casts (asynchronous) originate from the corresponding API functions. @@ -337,7 +368,8 @@ erlang:'!' -----> Module:StateName/3 -

A fun() of arity 2 that takes an event +

+ A fun() of arity 2 that takes an event and returns a boolean. When used in the action() @@ -363,18 +395,22 @@ erlang:'!' -----> Module:StateName/3

state_functions - The state has to be of type + + The state has to be of type state_name() and one callback function per state that is Module:StateName/3 - is used. + + is used. handle_event_function - The state can be any term and the callback function + + The state can be any term and the callback function Module:handle_event/4 - is used for all states. + + is used for all states. @@ -388,9 +424,10 @@ erlang:'!' -----> Module:StateName/3 and they modify how the state transition is done:

- All - actions - are processed in order of appearance. + + All + actions + are processed in order of appearance. If the @@ -481,14 +518,16 @@ erlang:'!' -----> Module:StateName/3 -

These state transition actions may be invoked by +

+ These state transition actions may be invoked by returning them from the state function, from Module:init/1 or by giving them to enter_loop/6,7.

-

Actions are executed in the containing list order. +

+ Actions are executed in the containing list order. The order matters for some actions such as next_event and reply_action(). The order can in peculiar cases matter for remove_event with @@ -599,12 +638,14 @@ erlang:'!' -----> Module:StateName/3 -

Reply to a caller waiting for a reply in +

+ Reply to a caller waiting for a reply in call/2. Caller must be the term from the {call,Caller} - argument to the + + argument to the state function.

@@ -614,35 +655,42 @@ erlang:'!' -----> Module:StateName/3 stop - Terminate the gen_statem by calling + + Terminate the gen_statem by calling Module:terminate/3 - with Reason and + + with Reason and NewData, if given. stop_and_reply - Send all Replies + + Send all Replies then terminate the gen_statem by calling Module:terminate/3 - with Reason and + + with Reason and NewData, if given. next_state - The gen_statem will do a state transition to + + The gen_statem will do a state transition to NewState (which may be the same as the current state), set NewData and execute all Actions keep_state - The gen_statem will keep the current state, or + + The gen_statem will keep the current state, or do a state transition to the current state if you like, set NewData and execute all Actions keep_state_and_data - The gen_statem will keep the current state, or + + The gen_statem will keep the current state, or do a state transition to the current state if you like, keep the current server data, and execute all Actions @@ -659,7 +707,8 @@ erlang:'!' -----> Module:StateName/3 Create a linked gen_statem process -

Creates a gen_statem process according +

+ Creates a gen_statem process according to OTP design principles (using proc_lib @@ -668,82 +717,88 @@ erlang:'!' -----> Module:StateName/3 This is essential when the gen_statem shall be part of a supervision tree so it gets linked to its supervisor.

-

The gen_statem process calls +

+ The gen_statem process calls Module:init/1 to initialize the server. To ensure a synchronized start-up procedure, start_link/3,4 does not return until Module:init/1 has returned.

-

ServerName specifies the +

+ ServerName specifies the server_name() - to register for the gen_statem. + + to register for the gen_statem. If the gen_statem is started with start_link/3 no ServerName is provided and the gen_statem is not registered.

Module is the name of the callback module.

-

Args is an arbitrary term which is passed as +

+ Args is an arbitrary term which is passed as the argument to - Module:init/1 - . + Module:init/1.

-

If the option {timeout,Time} is present in +

+ If the option {timeout,Time} is present in Opts, the gen_statem is allowed to spend Time milliseconds initializing or it will be terminated and the start function will return - - {error,timeout} - . + {error,timeout}.

-

If the option +

+ If the option {debug,Dbgs} is present in Opts, debugging through sys is activated.

-

If the option {spawn_opt,SpawnOpts} is present in +

+ If the option {spawn_opt,SpawnOpts} is present in Opts, SpawnOpts will be passed as option list to spawn_opt/2 which is used to spawn the gen_statem process.

-

Using the spawn option monitor is currently not +

+ Using the spawn option monitor is currently not allowed, but will cause this function to fail with reason - badarg.

+ badarg. +

-

If the gen_statem is successfully created +

+ If the gen_statem is successfully created and initialized this function returns {ok,Pid}, - where Pid is the pid() + + where Pid is the pid() of the gen_statem. If there already exists a process with the specified ServerName this function returns - - {error,{already_started,Pid}} - , where Pid is the pid() of that process. + {error,{already_started,Pid}}, + where Pid is the pid() of that process.

-

If Module:init/1 fails with Reason, +

+ If Module:init/1 fails with Reason, this function returns - - {error,Reason} - . If Module:init/1 returns + {error,Reason}. + If Module:init/1 returns {stop,Reason} or - - ignore - , the process is terminated and this function + ignore, + the process is terminated and this function returns {error,Reason} - or - - ignore - , respectively. + + or + ignore, + respectively.

@@ -754,7 +809,8 @@ erlang:'!' -----> Module:StateName/3 Create a stand-alone gen_statem process -

Creates a stand-alone gen_statem process according to +

+ Creates a stand-alone gen_statem process according to OTP design principles (using proc_lib primitives). @@ -762,7 +818,8 @@ erlang:'!' -----> Module:StateName/3 this start function can not be used by a supervisor to start a child.

-

See start_link/3,4 +

+ See start_link/3,4 for a description of arguments and return values.

@@ -772,10 +829,9 @@ erlang:'!' -----> Module:StateName/3 Synchronously stop a generic server -

The same as - - stop(ServerRef, normal, infinity) - . +

+ The same as + stop(ServerRef, normal, infinity).

@@ -783,33 +839,37 @@ erlang:'!' -----> Module:StateName/3 Synchronously stop a generic server -

Orders the gen_statem +

+ Orders the gen_statem ServerRef - to exit with the given Reason + + to exit with the given Reason and waits for it to terminate. The gen_statem will call Module:terminate/3 - before exiting. + + before exiting.

-

This function returns ok if the server terminates +

+ This function returns ok if the server terminates with the expected reason. Any other reason than normal, shutdown, or {shutdown,Term} will cause an error report to be issued through - - error_logger:format/2 - . + error_logger:format/2. The default Reason is normal.

-

Timeout is an integer greater than zero +

+ Timeout is an integer greater than zero which specifies how many milliseconds to wait for the server to terminate, or the atom infinity to wait indefinitely. The default value is infinity. If the server has not terminated within the specified time, a timeout exception is raised.

-

If the process does not exist, a noproc exception +

+ If the process does not exist, a noproc exception is raised.

@@ -820,10 +880,12 @@ erlang:'!' -----> Module:StateName/3 Make a synchronous call to a gen_statem -

Makes a synchronous call to the gen_statem +

+ Makes a synchronous call to the gen_statem ServerRef - by sending a request + + by sending a request and waiting until its reply arrives. The gen_statem will call the state function with @@ -831,23 +893,24 @@ erlang:'!' -----> Module:StateName/3 {call,Caller} and event content Request.

-

A Reply is generated when a +

+ A Reply is generated when a state function returns with {reply,Caller,Reply} as one - - action() - , + action(), and that Reply becomes the return value of this function.

-

Timeout is an integer greater than zero +

+ Timeout is an integer greater than zero which specifies how many milliseconds to wait for a reply, or the atom infinity to wait indefinitely, which is the default. If no reply is received within the specified time, the function call fails. -

To avoid getting a late reply in the caller's +

+ To avoid getting a late reply in the caller's inbox this function spawns a proxy process that does the call. A late reply gets delivered to the dead proxy process hence gets discarded. This is @@ -856,7 +919,8 @@ erlang:'!' -----> Module:StateName/3

-

The call may fail for example if the gen_statem dies +

+ The call may fail for example if the gen_statem dies before or during this function call.

@@ -866,10 +930,12 @@ erlang:'!' -----> Module:StateName/3 Send an asynchronous event to a gen_statem -

Sends an asynchronous event to the gen_statem +

+ Sends an asynchronous event to the gen_statem ServerRef - and returns ok immediately, + + and returns ok immediately, ignoring if the destination node or gen_statem does not exist. The gen_statem will call the @@ -886,26 +952,31 @@ erlang:'!' -----> Module:StateName/3 Reply to a caller -

This function can be used by a gen_statem +

+ This function can be used by a gen_statem to explicitly send a reply to a process that waits in call/2 when the reply cannot be defined in the return value of a state function.

-

Caller must be the term from the +

+ Caller must be the term from the {call,Caller} - argument to the + + argument to the state function. Caller and Reply can also be specified using a reply_action() - and multiple replies with a list of them. + + and multiple replies with a list of them.

-

A reply sent with this function will not be visible +

+ A reply sent with this function will not be visible in sys debug output.

@@ -916,12 +987,14 @@ erlang:'!' -----> Module:StateName/3 Enter the gen_statem receive loop -

The same as +

+ The same as enter_loop/7 except that no server_name() - must have been registered. + + must have been registered.

@@ -929,16 +1002,19 @@ erlang:'!' -----> Module:StateName/3 Enter the gen_statem receive loop -

If Server_or_Actions is a list() +

+ If Server_or_Actions is a list() the same as enter_loop/7 except that no server_name() - must have been registered and + + must have been registered and Actions = Server_or_Actions.

-

Otherwise the same as +

+ Otherwise the same as enter_loop/7 with Server = Server_or_Actions and @@ -950,7 +1026,8 @@ erlang:'!' -----> Module:StateName/3 Enter the gen_statem receive loop -

Makes an the calling process become a gen_statem. +

+ Makes an the calling process become a gen_statem. Does not return, instead the calling process will enter the gen_statem receive loop and become a gen_statem server. @@ -960,35 +1037,36 @@ erlang:'!' -----> Module:StateName/3 The user is responsible for any initialization of the process, including registering a name for it.

-

This function is useful when a more complex initialization +

+ This function is useful when a more complex initialization procedure is needed than the gen_statem behaviour provides.

-

Module, Opts and +

+ Module, Opts and Server have the same meanings as when calling - - gen_statem:start[_link]/3,4 - . + gen_statem:start[_link]/3,4. However, the server_name() - name must have been registered accordingly + + name must have been registered accordingly before this function is called.

-

CallbackMode, State, +

+ CallbackMode, State, Data and Actions have the same meanings as in the return value of Module:init/1. Also, the callback module Module does not need to export an init/1 function.

-

Failure: If the calling process was not started by a +

+ Failure: If the calling process was not started by a proc_lib start function, or if it is not registered according to - - server_name() - . + server_name().

@@ -999,7 +1077,8 @@ erlang:'!' -----> Module:StateName/3
CALLBACK FUNCTIONS -

The following functions should be exported from a +

+ The following functions should be exported from a gen_statem callback module.

@@ -1013,13 +1092,16 @@ erlang:'!' -----> Module:StateName/3 Result = {CallbackMode,State,Data}  | {CallbackMode,State,Data,Actions}  | {stop,Reason} | ignore - CallbackMode = + + CallbackMode = callback_mode() State = state() - Data = data() + + Data = data() - Actions = + + Actions = [action()] | action() @@ -1027,16 +1109,20 @@ erlang:'!' -----> Module:StateName/3 -

Whenever a gen_statem is started using +

+ Whenever a gen_statem is started using start_link/3,4 or start/3,4, this function is called by the new process to initialize the implementation state and server data.

-

Args is the Args argument provided to the start - function.

-

If the initialization is successful, the function should +

+ Args is the Args argument provided to the start + function. +

+

+ If the initialization is successful, the function should return {CallbackMode,State,Data} or {CallbackMode,State,Data,Actions}. CallbackMode selects the @@ -1045,19 +1131,22 @@ erlang:'!' -----> Module:StateName/3 State is the initial state() and Data the initial server - data() + data().

-

The Actions +

+ The Actions are executed when entering the first state just as for a state function.

-

If something goes wrong during the initialization +

+ If something goes wrong during the initialization the function should return {stop,Reason} or ignore. See start_link/3,4.

-

This function may use +

+ This function may use throw to return Result.

@@ -1072,24 +1161,29 @@ erlang:'!' -----> Module:StateName/3 Handle an event - EventType = + + EventType = event_type() EventContent = term() - State = NewState = + + State = NewState = state() - Data = NewData = + + Data = NewData = data() - Result = + + Result = state_callback_result() -

Whenever a gen_statem receives an event from +

+ Whenever a gen_statem receives an event from call/2, cast/2 or as a normal process message one of these functions is called. @@ -1098,7 +1192,8 @@ erlang:'!' -----> Module:StateName/3 and if it is handle_event_function then Module:handle_event/4 is called.

-

If EventType is +

+ If EventType is {call,Caller} the caller is waiting for a reply. The reply can be sent from this or from any other @@ -1107,20 +1202,20 @@ erlang:'!' -----> Module:StateName/3 Actions, in Replies or by calling - - reply(Caller, Reply) - . + reply(Caller, Reply).

-

If this function returns with a new state that +

+ If this function returns with a new state that does not match equal (=/=) to the current state all postponed events will be retried in the new state.

-

See - action() +

+ See action() for options that can be set and actions that can be done by gen_statem after returning from this function.

-

These functions may use +

+ These functions may use throw, to return Result.

@@ -1133,22 +1228,24 @@ erlang:'!' -----> Module:StateName/3 Reason = normal | shutdown | {shutdown,term()} | term() State = state() - Data = data() - + Data = data() Ignored = term() -

This function is called by a gen_statem +

+ This function is called by a gen_statem when it is about to terminate. It should be the opposite of Module:init/1 and do any necessary cleaning up. When it returns, the gen_statem terminates with Reason. The return value is ignored.

-

Reason is a term denoting the stop reason and +

+ Reason is a term denoting the stop reason and State is the internal state of the gen_statem.

-

Reason depends on why the gen_statem +

+ Reason depends on why the gen_statem is terminating. If it is because another callback function has returned a stop tuple {stop,Reason} in @@ -1156,36 +1253,41 @@ erlang:'!' -----> Module:StateName/3 Reason will have the value specified in that tuple. If it is due to a failure, Reason is the error reason.

-

If the gen_statem is part of a supervision tree and is +

+ If the gen_statem is part of a supervision tree and is ordered by its supervisor to terminate, this function will be called with Reason = shutdown if the following conditions apply:

- the gen_statem has been set + + the gen_statem has been set to trap exit signals, and - the shutdown strategy as defined in the supervisor's + + the shutdown strategy as defined in the supervisor's child specification is an integer timeout value, not brutal_kill. -

Even if the gen_statem is not +

+ Even if the gen_statem is not part of a supervision tree, this function will be called if it receives an 'EXIT' message from its parent. Reason will be the same as in the 'EXIT' message.

-

Otherwise, the gen_statem will be immediately terminated. +

+ Otherwise, the gen_statem will be immediately terminated.

-

Note that for any other reason than normal, +

+ Note that for any other reason than normal, shutdown, or {shutdown,Term} the gen_statem is assumed to terminate due to an error and an error report is issued using - - error_logger:format/2 - . + error_logger:format/2.

-

This function may use +

+ This function may use throw to return Ignored, which is ignored anyway.

@@ -1203,16 +1305,19 @@ erlang:'!' -----> Module:StateName/3 OldState = NewState = term() Extra = term() Result = {ok,{NewState,NewData}} | Reason - OldState = NewState = + + OldState = NewState = state() - OldData = NewData = + + OldData = NewData = data() Reason = term() -

This function is called by a gen_statem when it should +

+ This function is called by a gen_statem when it should update its internal state during a release upgrade/downgrade, i.e. when the instruction {update,Module,Change,...} where Change={advanced,Extra} is given in @@ -1222,26 +1327,32 @@ erlang:'!' -----> Module:StateName/3 for more information.

-

In the case of an upgrade, OldVsn is Vsn, and +

+ In the case of an upgrade, OldVsn is Vsn, and in the case of a downgrade, OldVsn is {down,Vsn}. Vsn is defined by the vsn attribute(s) of the old version of the callback module Module. If no such attribute is defined, the version is the checksum of the BEAM file.

-

OldState and OldData is the internal state +

+ OldState and OldData is the internal state of the gen_statem.

-

Extra is passed as-is from the {advanced,Extra} +

+ Extra is passed as-is from the {advanced,Extra} part of the update instruction.

-

If successful, the function shall return the updated +

+ If successful, the function shall return the updated internal state in an {ok,{NewState,NewData}} tuple.

-

If the function returns Reason, the ongoing +

+ If the function returns Reason, the ongoing upgrade will fail and roll back to the old release.

-

This function may use +

+ This function may use throw to return Result or Reason.

@@ -1257,10 +1368,12 @@ erlang:'!' -----> Module:StateName/3 Opt = normal | terminate PDict = [{Key, Value}] - State = + + State = state() - Data = + + Data = data() Key = term() @@ -1269,7 +1382,8 @@ erlang:'!' -----> Module:StateName/3 -

This callback is optional, so a callback module need not +

+ This callback is optional, so a callback module need not export it. The gen_statem module provides a default implementation of this function that returns {State,Data}. If this callback fails the default @@ -1280,43 +1394,52 @@ erlang:'!' -----> Module:StateName/3

This function is called by a gen_statem process when:

- One of + + One of sys:get_status/1,2 is invoked to get the gen_statem status. Opt is set to the atom normal for this case. - The gen_statem terminates abnormally and logs an error. + + The gen_statem terminates abnormally and logs an error. Opt is set to the atom terminate for this case. -

This function is useful for customising the form and +

+ This function is useful for customising the form and appearance of the gen_statem status for these cases. A callback module wishing to customise the sys:get_status/1,2 - return value as well as how + + return value as well as how its status appears in termination error logs exports an instance of format_status/2 that returns a term describing the current status of the gen_statem.

-

PDict is the current value of the gen_statem's +

+ PDict is the current value of the gen_statem's process dictionary.

-

State +

+ State is the internal state of the gen_statem.

-

Data +

+ Data is the internal server data of the gen_statem.

-

The function should return Status, a term that +

+ The function should return Status, a term that customises the details of the current state and status of the gen_statem. There are no restrictions on the form Status can take, but for the sys:get_status/1,2 - case (when Opt + + case (when Opt is normal), the recommended form for the Status value is [{data, [{"State", Term}]}] where Term provides relevant details of @@ -1325,14 +1448,17 @@ erlang:'!' -----> Module:StateName/3 consistent with the rest of the sys:get_status/1,2 - return value. + + return value.

-

One use for this function is to return compact alternative +

+ One use for this function is to return compact alternative state representations to avoid having large state terms printed in logfiles. Another is to hide sensitive data from being written to the error log.

-

This function may use +

+ This function may use throw to return Status.

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