From 68d53c01b0b8e9a007a6a30158c19e34b2d2a34e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Wed, 18 May 2016 15:53:35 +0200 Subject: Update STDLIB documentation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Language cleaned up by the technical writers xsipewe and tmanevik from Combitech. Proofreading and corrections by Björn Gustavsson and Hans Bolinder. --- lib/stdlib/doc/src/gen_fsm.xml | 1262 +++++++++++++++++++++------------------- 1 file changed, 677 insertions(+), 585 deletions(-) (limited to 'lib/stdlib/doc/src/gen_fsm.xml') diff --git a/lib/stdlib/doc/src/gen_fsm.xml b/lib/stdlib/doc/src/gen_fsm.xml index 835e252704..de06987d38 100644 --- a/lib/stdlib/doc/src/gen_fsm.xml +++ b/lib/stdlib/doc/src/gen_fsm.xml @@ -29,29 +29,30 @@ gen_fsm - Generic Finite State Machine Behaviour + Generic finite state machine behavior.

There is a new behaviour gen_statem that is intended to replace gen_fsm for new code. - It has the same features and add some really useful. - This module will not be removed for the foreseeable future + gen_fsm will not be removed for the foreseeable future to keep old state machine implementations running.

-

A behaviour module for implementing a finite state machine. - A generic finite state machine process (gen_fsm) implemented - using this module will have a standard set of interface functions - 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. +

This behavior module provides a finite state machine. + A generic finite state machine process (gen_fsm) implemented + using this module has a standard set of interface functions + and includes functionality for tracing and error reporting. It + also fits into an OTP supervision tree. For more information, see + OTP Design Principles.

-

A gen_fsm 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:

+ +

A gen_fsm process assumes all specific parts to be located in a + callback module exporting a predefined set of functions. The relationship + between the behavior functions and the callback functions is as + follows:

+ 
 gen_fsm module                    Callback module
 --------------                    ---------------
@@ -73,34 +74,261 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
 -                                 -----> Module:terminate/3
 
 -                                 -----> Module:code_change/4
-

If a callback function fails or returns a bad value, the gen_fsm - will terminate.

-

A gen_fsm handles system messages as documented in - sys(3). The sys module - can be used for debugging a gen_fsm.

-

Note that a gen_fsm does not trap exit signals automatically, - this must be explicitly initiated in the callback module.

+ +

If a callback function fails or returns a bad value, the gen_fsm + process terminates.

+ +

A gen_fsm process handles system messages as described in + sys(3). The sys module + can be used for debugging a gen_fsm process.

+ +

Notice that a gen_fsm process does not trap exit signals + automatically, this must be explicitly initiated in the callback + module.

+

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

-

The gen_fsm process can go into hibernation - (see erlang(3)) if a callback - function specifies 'hibernate' instead of a timeout value. This - might be useful if the server is expected to be idle for a long - time. However this feature should be used with care as hibernation - implies at least two garbage collections (when hibernating and - shortly after waking up) and is not something you'd want to do - between each call to a busy state machine.

+ the specified gen_fsm process does not exist or if bad arguments + are specified.

+

The gen_fsm process can go into hibernation + (see + erlang:hibernate/3) if a callback function + specifies 'hibernate' instead of a time-out value. This + can be useful if the server is expected to be idle for a long + time. However, use this feature with care, as hibernation + implies at least two garbage collections (when hibernating and + shortly after waking up) and is not something you want to do + between each call to a busy state machine.

 + + + cancel_timer(Ref) -> RemainingTime | false + Cancel an internal timer in a generic FSM. + + Ref = reference() + RemainingTime = integer() + + +

Cancels an internal timer referred by Ref in the + gen_fsm process that calls this function.

+

Ref is a reference returned from + + send_event_after/2 or + start_timer/2.

+

If the timer has already timed out, but the event not yet + been delivered, it is cancelled as if it had not + timed out, so there is no false timer event after + returning from this function.

+

Returns the remaining time in milliseconds until the timer would + have expired if Ref referred to an active timer, otherwise + false.

+ + + + + enter_loop(Module, Options, StateName, StateData) + enter_loop(Module, Options, StateName, StateData, FsmName) + enter_loop(Module, Options, StateName, StateData, Timeout) + enter_loop(Module, Options, StateName, StateData, FsmName, Timeout) + Enter the gen_fsm receive loop. + + Module = atom() + Options = [Option] +  Option = {debug,Dbgs} +   Dbgs = [Dbg] +    Dbg = trace | log | statistics +     | {log_to_file,FileName} | {install,{Func,FuncState}} + StateName = atom() + StateData = term() + FsmName = {local,Name} | {global,GlobalName} +   | {via,Module,ViaName} +  Name = atom() +  GlobalName = ViaName = term() + Timeout = int() | infinity + + +

Makes an existing process into a gen_fsm process. + Does not return, + instead the calling process enters the gen_fsm receive + loop and becomes a gen_fsm process. The process must + have been started using one of the start functions in + proc_lib(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 + procedure is needed than the gen_fsm behavior provides.

+

Module, Options, and FsmName have + the same meanings as when calling + start[_link]/3,4. + However, if FsmName is specified, the process must have + been registered accordingly before this function is + called.

+

StateName, StateData, and Timeout have + the same meanings as in the return value of + Module:init/1. + The callback module Module does not need to + export an init/1 function.

+

The function fails if the calling process was not started by a + proc_lib start function, or if it is not registered + according to FsmName.

+ + + + + reply(Caller, Reply) -> Result + Send a reply to a caller. + + Caller - see below + Reply = term() + Result = term() + + +

This function can be used by a gen_fsm process to + explicitly send a reply to a client process that called + + sync_send_event/2,3 or + + sync_send_all_state_event/2,3 + when the reply cannot be defined in the return value of + + Module:StateName/3 or + + Module:handle_sync_event/4.

+

Caller must be the From argument provided to + the callback function. Reply is any term + given back to the client as the return value of + sync_send_event/2,3 or + sync_send_all_state_event/2,3.

+

Return value Result is not further defined, and + is always to be ignored.

+ + + + + send_all_state_event(FsmRef, Event) -> ok + Send an event asynchronously to a generic FSM. + + FsmRef = Name | {Name,Node} | {global,GlobalName} +   | {via,Module,ViaName} | pid() +  Name = Node = atom() +  GlobalName = ViaName = term() + Event = term() + + +

Sends an event asynchronously to the FsmRef of the + gen_fsm process and returns ok immediately. + The gen_fsm process calls + + Module:handle_event/3 to handle the event.

+

For a description of the arguments, see + send_event/2.

+

The difference between send_event/2 and + send_all_state_event/2 is which callback function is + used to handle the event. This function is useful when + sending events that are handled the same way in every state, + as only one handle_event clause is needed to handle + the event instead of one clause in each state name function.

+ + + + + send_event(FsmRef, Event) -> ok + Send an event asynchronously to a generic FSM. + + FsmRef = Name | {Name,Node} | {global,GlobalName} +   | {via,Module,ViaName} | pid() +  Name = Node = atom() +  GlobalName = ViaName = term() + Event = term() + + +

Sends an event asynchronously to the FsmRef of the + gen_fsm process + and returns ok immediately. The gen_fsm process calls + + Module:StateName/2 to handle the event, where + StateName is the name of the current state of + the gen_fsm process.

+

FsmRef can be any of the following:

+ + The pid + Name, if the gen_fsm process is locally + registered + {Name,Node}, if the gen_fsm process is locally + registered at another node + {global,GlobalName}, if the gen_fsm process is + globally registered + {via,Module,ViaName}, if the gen_fsm process is + registered through an alternative process registry + +

Event is any term that is passed as one of + the arguments to Module:StateName/2.

+ + + + + send_event_after(Time, Event) -> Ref + Send a delayed event internally in a generic FSM. + + Time = integer() + Event = term() + Ref = reference() + + +

Sends a delayed event internally in the gen_fsm process + that calls this function after Time milliseconds. + Returns immediately a + reference that can be used to cancel the delayed send using + cancel_timer/1.

+

The gen_fsm process calls + + Module:StateName/2 to handle + the event, where StateName is the name of the current + state of the gen_fsm process at the time the delayed event is + delivered.

+

Event is any term that is passed as one of + the arguments to Module:StateName/2.

+ + + + + start(Module, Args, Options) -> Result + start(FsmName, Module, Args, Options) -> Result + Create a standalone gen_fsm process. + + FsmName = {local,Name} | {global,GlobalName} +   | {via,Module,ViaName} +  Name = atom() +  GlobalName = ViaName = term() + Module = atom() + Args = term() + Options = [Option] +  Option = {debug,Dbgs} | {timeout,Time} | {spawn_opt,SOpts} +   Dbgs = [Dbg] +    Dbg = trace | log | statistics +     | {log_to_file,FileName} | {install,{Func,FuncState}} +   SOpts = [term()] + Result = {ok,Pid} | ignore | {error,Error} +  Pid = pid() +  Error = {already_started,Pid} | term() + + +

Creates a standalone gen_fsm process, that is, a process that + is not part of a supervision tree and thus has no supervisor.

+

For a description of arguments and return values, see + start_link/3,4.

+ + + start_link(Module, Args, Options) -> Result start_link(FsmName, Module, Args, Options) -> Result - Create a gen_fsm process in a supervision tree. + Create a gen_fsm process in a supervision tree. + - FsmName = {local,Name} | {global,GlobalName} - | {via,Module,ViaName} + FsmName = {local,Name} | {global,GlobalName} +   | {via,Module,ViaName}  Name = atom()  GlobalName = ViaName = term() Module = atom() @@ -117,54 +345,64 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4  Error = {already_started,Pid} | term() -

Creates a gen_fsm process as part of a supervision tree. - The function should be called, directly or indirectly, by - the supervisor. It will, among other things, ensure that - the gen_fsm is linked to the supervisor.

-

The gen_fsm process calls Module:init/1 to - initialize. To ensure a synchronized start-up procedure, +

Creates a gen_fsm process as part of a supervision tree. + The function is to be called, directly or indirectly, by + the supervisor. For example, it ensures that + the gen_fsm process is linked to the supervisor.

+

The gen_fsm process calls + Module:init/1 to + initialize. To ensure a synchronized startup procedure, start_link/3,4 does not return until Module:init/1 has returned.

-

If FsmName={local,Name}, the gen_fsm is registered - locally as Name using register/2. - If FsmName={global,GlobalName}, the gen_fsm is - registered globally as GlobalName using - global:register_name/2. - If FsmName={via,Module,ViaName}, the gen_fsm will - register with the registry represented by Module. - The Module callback should export the functions - register_name/2, unregister_name/1, - whereis_name/1 and send/2, which should behave like the - corresponding functions in global. Thus, - {via,global,GlobalName} is a valid reference.

-

If no name is provided, - the gen_fsm is not registered.

+ + +

If FsmName={local,Name}, the gen_fsm process is + registered locally as Name using register/2.

+ + +

If FsmName={global,GlobalName}, the gen_fsm process + is registered globally as GlobalName using + + global:register_name/2.

+ + +

If FsmName={via,Module,ViaName}, the gen_fsm + process registers with the registry represented by Module. + The Module callback is to export the functions + register_name/2, unregister_name/1, + whereis_name/1, and send/2, which are to behave + like the corresponding functions in + global. + Thus, {via,global,GlobalName} is a valid reference.

+ + +

If no name is provided, the gen_fsm process is not + registered.

Module is the name of the callback module.

-

Args is an arbitrary term which is passed as +

Args is any term that is passed as the argument to Module:init/1.

-

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

If option {timeout,Time} is present, the gen_fsm + process is allowed to spend Time milliseconds initializing + or it terminates and the start function returns {error,timeout}.

-

If the option {debug,Dbgs} is present, - the corresponding sys function will be called for each - item in Dbgs. See - sys(3).

-

If the option {spawn_opt,SOpts} is present, - SOpts will be passed as option list to - the spawn_opt BIF which is used to spawn the gen_fsm - process. See - erlang(3).

+

If option {debug,Dbgs} is present, the corresponding + sys function is called for each item in Dbgs; see + sys(3).

+

If option {spawn_opt,SOpts} is present, SOpts is + passed as option list to the spawn_opt BIF that is used to + spawn the gen_fsm process; see + + spawn_opt/2.

-

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

Using spawn option monitor is not + allowed, it causes the function to fail with reason badarg.

 -

If the gen_fsm is successfully created and initialized - the function returns {ok,Pid}, where Pid is - the pid of the gen_fsm. If there already exists a process with - the specified FsmName, the function returns - {error,{already_started,Pid}} where Pid is +

If the gen_fsm process is successfully created and + initialized, the function returns {ok,Pid}, where Pid + is the pid of the gen_fsm process. If a process with the + specified FsmName exists already, the function returns + {error,{already_started,Pid}}, where Pid is the pid of that process.

If Module:init/1 fails with Reason, the function returns {error,Reason}. If @@ -173,129 +411,106 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4 returns {error,Reason} or ignore, respectively.

 + - start(Module, Args, Options) -> Result - start(FsmName, Module, Args, Options) -> Result - Create a stand-alone gen_fsm process. + start_timer(Time, Msg) -> Ref + Send a time-out event internally in a generic FSM. - FsmName = {local,Name} | {global,GlobalName} - | {via,Module,ViaName} -  Name = atom() -  GlobalName = ViaName = term() - Module = atom() - Args = term() - Options = [Option] -  Option = {debug,Dbgs} | {timeout,Time} | {spawn_opt,SOpts} -   Dbgs = [Dbg] -    Dbg = trace | log | statistics -     | {log_to_file,FileName} | {install,{Func,FuncState}} -   SOpts = [term()] - Result = {ok,Pid} | ignore | {error,Error} -  Pid = pid() -  Error = {already_started,Pid} | term() + Time = integer() + Msg = term() + Ref = reference() -

Creates a stand-alone gen_fsm process, i.e. a gen_fsm which - is not part of a supervision tree and thus has no supervisor.

-

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

+

Sends a time-out event internally in the gen_fsm + process that calls this function after Time milliseconds. + Returns immediately a + reference that can be used to cancel the timer using + cancel_timer/1.

+

The gen_fsm process calls + + Module:StateName/2 to handle + the event, where StateName is the name of the current + state of the gen_fsm process at the time the time-out + message is delivered.

+

Msg is any term that is passed in the + time-out message, {timeout, Ref, Msg}, as one of + the arguments to Module:StateName/2.

 + stop(FsmRef) -> ok stop(FsmRef, Reason, Timeout) -> ok Synchronously stop a generic FSM. - FsmRef = Name | {Name,Node} | {global,GlobalName} - | {via,Module,ViaName} | pid() + FsmRef = Name | {Name,Node} | {global,GlobalName} +   | {via,Module,ViaName} | pid()  Node = atom()  GlobalName = ViaName = term() Reason = term() Timeout = int()>0 | infinity -

Orders a generic FSM to exit with the given Reason - and waits for it to terminate. The gen_fsm will call - Module:terminate/3 - before exiting.

-

The function returns ok if the generic FSM terminates - with the expected reason. Any other reason than normal, - shutdown, or {shutdown,Term} will cause an +

Orders a generic finite state machine to exit with the specified + Reason and waits for it to terminate. The gen_fsm + process calls + Module:terminate/3 before exiting.

+

The function returns ok if the generic finite state machine + terminates with the expected reason. Any other reason than + normal, shutdown, or {shutdown,Term} causes an error report to be issued using - error_logger:format/2. - The default Reason is normal.

-

Timeout is an integer greater than zero which + + error_logger:format/2. + The default Reason is normal.

+

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

-

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

- - - - send_event(FsmRef, Event) -> ok - Send an event asynchronously to a generic FSM. - - FsmRef = Name | {Name,Node} | {global,GlobalName} - | {via,Module,ViaName} | pid() -  Name = Node = atom() -  GlobalName = ViaName = term() - Event = term() - - -

Sends an event asynchronously to the gen_fsm FsmRef - and returns ok immediately. The gen_fsm will call - Module:StateName/2 to handle the event, where - StateName is the name of the current state of - the gen_fsm.

-

FsmRef can be:

- - the pid, - Name, if the gen_fsm is locally registered, - {Name,Node}, if the gen_fsm is locally - registered at another node, or - {global,GlobalName}, if the gen_fsm is globally - registered. - {via,Module,ViaName}, if the gen_fsm is registered - through an alternative process registry. - -

Event is an arbitrary term which is passed as one of - the arguments to Module:StateName/2.

+ generic finite state machine has not terminated within the specified + time, a timeout exception is raised.

+

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

 + - send_all_state_event(FsmRef, Event) -> ok - Send an event asynchronously to a generic FSM. + sync_send_all_state_event(FsmRef, Event) -> Reply + sync_send_all_state_event(FsmRef, Event, Timeout) -> Reply + Send an event synchronously to a generic FSM. - FsmRef = Name | {Name,Node} | {global,GlobalName} - | {via,Module,ViaName} | pid() + FsmRef = Name | {Name,Node} | {global,GlobalName} +   | {via,Module,ViaName} | pid()  Name = Node = atom()  GlobalName = ViaName = term() Event = term() + Timeout = int()>0 | infinity + Reply = term() -

Sends an event asynchronously to the gen_fsm FsmRef - and returns ok immediately. The gen_fsm will call - Module:handle_event/3 to handle the event.

-

See send_event/2 - for a description of the arguments.

-

The difference between send_event and - send_all_state_event is which callback function is - used to handle the event. This function is useful when - sending events that are handled the same way in every state, - as only one handle_event clause is needed to handle - the event instead of one clause in each state name function.

+

Sends an event to the FsmRef of the gen_fsm + process and waits until a reply arrives or a time-out occurs. + The gen_fsm process calls + + Module:handle_sync_event/4 to handle the event.

+

For a description of FsmRef and Event, see + send_event/2. + For a description of Timeout and Reply, see + + sync_send_event/3.

+

For a discussion about the difference between + sync_send_event and sync_send_all_state_event, see + + send_all_state_event/2.

 + sync_send_event(FsmRef, Event) -> Reply sync_send_event(FsmRef, Event, Timeout) -> Reply Send an event synchronously to a generic FSM. - FsmRef = Name | {Name,Node} | {global,GlobalName} - | {via,Module,ViaName} | pid() + FsmRef = Name | {Name,Node} | {global,GlobalName} +   | {via,Module,ViaName} | pid()  Name = Node = atom()  GlobalName = ViaName = term() Event = term() @@ -303,210 +518,231 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4 Reply = term() -

Sends an event to the gen_fsm FsmRef and waits until a - reply arrives or a timeout occurs. The gen_fsm will call - Module:StateName/3 to handle the event, where +

Sends an event to the FsmRef of the gen_fsm + process and waits until a reply arrives or a time-out occurs. + The gen_fsm process calls + + Module:StateName/3 to handle the event, where StateName is the name of the current state of - the gen_fsm.

-

See send_event/2 - for a description of FsmRef and Event.

-

Timeout is an integer greater than zero which + the gen_fsm process.

+

For a description of FsmRef and Event, see + send_event/2.

+

Timeout is an integer greater than zero that specifies how many milliseconds to wait for a reply, or - the atom infinity to wait indefinitely. Default value - is 5000. If no reply is received within the specified time, + the atom infinity to wait indefinitely. Defaults + to 5000. If no reply is received within the specified time, the function call fails.

-

The return value Reply is defined in the return value +

Return value Reply is defined in the return value of Module:StateName/3.

-

The ancient behaviour of sometimes consuming the server + +

The ancient behavior of sometimes consuming the server exit message if the server died during the call while - linked to the client has been removed in OTP R12B/Erlang 5.6.

+ linked to the client was removed in Erlang 5.6/OTP R12B.

+ + + +
+ Callback Functions +

The following functions are to be exported from a gen_fsm + callback module.

+ +

state name denotes a state of the state machine.

+ +

state data denotes the internal state of the Erlang process + that implements the state machine.

+
+ + - sync_send_all_state_event(FsmRef, Event) -> Reply - sync_send_all_state_event(FsmRef, Event, Timeout) -> Reply - Send an event synchronously to a generic FSM. + Module:code_change(OldVsn, StateName, StateData, Extra) -> {ok, NextStateName, NewStateData} + Update the internal state data during upgrade/downgrade. + - FsmRef = Name | {Name,Node} | {global,GlobalName} - | {via,Module,ViaName} | pid() -  Name = Node = atom() -  GlobalName = ViaName = term() - Event = term() - Timeout = int()>0 | infinity - Reply = term() + OldVsn = Vsn | {down, Vsn} +   Vsn = term() + StateName = NextStateName = atom() + StateData = NewStateData = term() + Extra = term() -

Sends an event to the gen_fsm FsmRef and waits until a - reply arrives or a timeout occurs. The gen_fsm will call - Module:handle_sync_event/4 to handle the event.

-

See send_event/2 - for a description of FsmRef and Event. See - sync_send_event/3 - for a description of Timeout and Reply.

-

See - send_all_state_event/2 - for a discussion about the difference between - sync_send_event and sync_send_all_state_event.

+

This function is called by a gen_fsm process when it is to + update its internal state data during a release upgrade/downgrade, + that is, when instruction {update,Module,Change,...}, + where Change={advanced,Extra}, is given in + the appup file; see section + + Release Handling Instructions in OTP Design Principles.

+

For an upgrade, OldVsn is Vsn, and for 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.

+

StateName is the current state name and StateData the + internal state data of the gen_fsm process.

+

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

+

The function is to return the new current state name and + updated internal data.

 + - reply(Caller, Reply) -> Result - Send a reply to a caller. + Module:format_status(Opt, [PDict, StateData]) -> Status + Optional function for providing a term describing the + current gen_fsm process status. - Caller - see below - Reply = term() - Result = term() + Opt = normal | terminate + PDict = [{Key, Value}] + StateData = term() + Status = term() -

This function can be used by a gen_fsm to explicitly send a - reply to a client process that called - sync_send_event/2,3 - or - sync_send_all_state_event/2,3, - when the reply cannot be defined in the return value of - Module:State/3 or Module:handle_sync_event/4.

-

Caller must be the From argument provided to - the callback function. Reply is an arbitrary term, - which will be given back to the client as the return value of - sync_send_event/2,3 or - sync_send_all_state_event/2,3.

-

The return value Result is not further defined, and - should always be ignored.

+ +

This callback is optional, so callback modules need not + export it. The gen_fsm module provides a default + implementation of this function that returns the callback + module state data.

+ +

This function is called by a gen_fsm process in the + following situations:

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

This function is useful for changing the form and + appearance of the gen_fsm status for these cases. A callback + module wishing to change the sys:get_status/1,2 + 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_fsm process.

+

PDict is the current value of the process dictionary of the + gen_fsm process.

+

StateData is the internal state data of the + gen_fsm process.

+

The function is to return Status, a term that + change the details of the current state and status of + the gen_fsm process. There are no restrictions on the + form Status can take, but for + the sys:get_status/1,2 case (when Opt + is normal), the recommended form for + the Status value is [{data, [{"StateData", + Term}]}], where Term provides relevant details of + the gen_fsm state data. Following this recommendation is not + required, but it makes the callback module status + consistent with the rest of the sys:get_status/1,2 + return value.

+

One use for this function is to return compact alternative + state data representations to avoid that large state terms + are printed in log files.

 + - send_event_after(Time, Event) -> Ref - Send a delayed event internally in a generic FSM. + Module:handle_event(Event, StateName, StateData) -> Result + Handle an asynchronous event. - Time = integer() Event = term() - Ref = reference() - - -

Sends a delayed event internally in the gen_fsm that calls - this function after Time ms. Returns immediately a - reference that can be used to cancel the delayed send using - cancel_timer/1.

-

The gen_fsm will call Module:StateName/2 to handle - the event, where StateName is the name of the current - state of the gen_fsm at the time the delayed event is - delivered.

-

Event is an arbitrary term which is passed as one of - the arguments to Module:StateName/2.

- - - - start_timer(Time, Msg) -> Ref - Send a timeout event internally in a generic FSM. - - Time = integer() - Msg = term() - Ref = reference() + StateName = atom() + StateData = term() + Result = {next_state,NextStateName,NewStateData} +   | {next_state,NextStateName,NewStateData,Timeout} +   | {next_state,NextStateName,NewStateData,hibernate} +   | {stop,Reason,NewStateData} +  NextStateName = atom() +  NewStateData = term() +  Timeout = int()>0 | infinity +  Reason = term() -

Sends a timeout event internally in the gen_fsm that calls - this function after Time ms. Returns immediately a - reference that can be used to cancel the timer using - cancel_timer/1.

-

The gen_fsm will call Module:StateName/2 to handle - the event, where StateName is the name of the current - state of the gen_fsm at the time the timeout message is - delivered.

-

Msg is an arbitrary term which is passed in the - timeout message, {timeout, Ref, Msg}, as one of - the arguments to Module:StateName/2.

+

Whenever a gen_fsm process receives an event sent using + + send_all_state_event/2, + this function is called to handle the event.

+

StateName is the current state name of the gen_fsm + process.

+

For a description of the other arguments and possible return values, + see + Module:StateName/2.

 + - cancel_timer(Ref) -> RemainingTime | false - Cancel an internal timer in a generic FSM. + Module:handle_info(Info, StateName, StateData) -> Result + Handle an incoming message. - Ref = reference() - RemainingTime = integer() + Info = term() + StateName = atom() + StateData = term() + Result = {next_state,NextStateName,NewStateData} +   | {next_state,NextStateName,NewStateData,Timeout} +   | {next_state,NextStateName,NewStateData,hibernate} +   | {stop,Reason,NewStateData} +  NextStateName = atom() +  NewStateData = term() +  Timeout = int()>0 | infinity +  Reason = normal | term() -

Cancels an internal timer referred by Ref in the - gen_fsm that calls this function.

-

Ref is a reference returned from - send_event_after/2 - or - start_timer/2.

-

If the timer has already timed out, but the event not yet - been delivered, it is cancelled as if it had not - timed out, so there will be no false timer event after - returning from this function.

-

Returns the remaining time in ms until the timer would - have expired if Ref referred to an active timer, - false otherwise.

+

This function is called by a gen_fsm process when it receives + any other message than a synchronous or asynchronous event (or a + system message).

+

Info is the received message.

+

For a description of the other arguments and possible return values, + see + Module:StateName/2.

 + - enter_loop(Module, Options, StateName, StateData) - enter_loop(Module, Options, StateName, StateData, FsmName) - enter_loop(Module, Options, StateName, StateData, Timeout) - enter_loop(Module, Options, StateName, StateData, FsmName, Timeout) - Enter the gen_fsm receive loop + Module:handle_sync_event(Event, From, StateName, StateData) -> Result + Handle a synchronous event. - Module = atom() - Options = [Option] -  Option = {debug,Dbgs} -   Dbgs = [Dbg] -    Dbg = trace | log | statistics -     | {log_to_file,FileName} | {install,{Func,FuncState}} + Event = term() + From = {pid(),Tag} StateName = atom() StateData = term() - FsmName = {local,Name} | {global,GlobalName} - | {via,Module,ViaName} -  Name = atom() -  GlobalName = ViaName = term() - Timeout = int() | infinity + Result = {reply,Reply,NextStateName,NewStateData} +   | {reply,Reply,NextStateName,NewStateData,Timeout} +   | {reply,Reply,NextStateName,NewStateData,hibernate} +   | {next_state,NextStateName,NewStateData} +   | {next_state,NextStateName,NewStateData,Timeout} +   | {next_state,NextStateName,NewStateData,hibernate} +   | {stop,Reason,Reply,NewStateData} | {stop,Reason,NewStateData} +  Reply = term() +  NextStateName = atom() +  NewStateData = term() +  Timeout = int()>0 | infinity +  Reason = term() -

Makes an existing process into a gen_fsm. Does not return, - instead the calling process will enter the gen_fsm receive - loop and become a gen_fsm process. The process must - have been started using one of the start functions in - proc_lib, see - proc_lib(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 - procedure is needed than the gen_fsm behaviour provides.

-

Module, Options and FsmName have - the same meanings as when calling - start[_link]/3,4. - However, if FsmName is specified, the process must have - been registered accordingly before this function is - called.

-

StateName, StateData and Timeout 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 - proc_lib start function, or if it is not registered - according to FsmName.

+

Whenever a gen_fsm process receives an event sent using + + sync_send_all_state_event/2,3, + this function is called to handle the event.

+

StateName is the current state name of the gen_fsm + process.

+

For a description of the other arguments and possible return values, + see + Module:StateName/3.

 - -
- CALLBACK FUNCTIONS -

The following functions should be exported from a gen_fsm - callback module.

-

In the description, the expression state name is used to - denote a state of the state machine. state data is used - to denote the internal state of the Erlang process which - implements the state machine.

-
- Module:init(Args) -> Result - Initialize process and internal state name and state data. + Initialize process and internal state name and state data. + Args = term() Result = {ok,StateName,StateData} | {ok,StateName,StateData,Timeout} -   | {ok,StateName,StateData,hibernate} +   | {ok,StateName,StateData,hibernate}   | {stop,Reason} | ignore  StateName = atom()  StateData = term() @@ -515,33 +751,36 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4 -

Whenever a gen_fsm is started using - gen_fsm:start/3,4 or - gen_fsm:start_link/3,4, +

Whenever a gen_fsm process is started using + start/3,4 or + start_link/3,4, this function is called by the new process to initialize.

Args is the Args argument provided to the start function.

-

If initialization is successful, the function should return - {ok,StateName,StateData}, - {ok,StateName,StateData,Timeout} or {ok,StateName,StateData,hibernate}, - where StateName +

If initialization is successful, the function is to return + {ok,StateName,StateData}, + {ok,StateName,StateData,Timeout}, or + {ok,StateName,StateData,hibernate}, where StateName is the initial state name and StateData the initial - state data of the gen_fsm.

-

If an integer timeout value is provided, a timeout will occur + state data of the gen_fsm process.

+

If an integer time-out value is provided, a time-out occurs unless an event or a message is received within Timeout - milliseconds. A timeout is represented by the atom - timeout and should be handled by - the Module:StateName/2 callback functions. The atom + milliseconds. A time-out is represented by the atom + timeout and is to be handled by the + + Module:StateName/2 callback functions. The atom infinity can be used to wait indefinitely, this is the default value.

-

If hibernate is specified instead of a timeout value, the process will go - into hibernation when waiting for the next message to arrive (by calling - proc_lib:hibernate/3).

-

If something goes wrong during the initialization - the function should return {stop,Reason}, where - Reason is any term, or ignore.

+

If hibernate is specified instead of a time-out value, the + process goes into hibernation when waiting for the next message + to arrive (by calling + proc_lib:hibernate/3).

+

If the initialization fails, the function returns + {stop,Reason}, where Reason is any term, + or ignore.

 + Module:StateName(Event, StateData) -> Result Handle an asynchronous event. @@ -549,8 +788,8 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4 Event = timeout | term() StateData = term() Result = {next_state,NextStateName,NewStateData} -   | {next_state,NextStateName,NewStateData,Timeout} -   | {next_state,NextStateName,NewStateData,hibernate} +   | {next_state,NextStateName,NewStateData,Timeout} +   | {next_state,NextStateName,NewStateData,hibernate}   | {stop,Reason,NewStateData}  NextStateName = atom()  NewStateData = term() @@ -558,56 +797,33 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4  Reason = term() -

There should be one instance of this function for each - possible state name. Whenever a gen_fsm receives an event - sent using - gen_fsm:send_event/2, +

There is to be one instance of this function for each + possible state name. Whenever a gen_fsm process receives + an event sent using + send_event/2, the instance of this function with the same name as the current state name StateName is called to handle - the event. It is also called if a timeout occurs.

-

Event is either the atom timeout, if a timeout + the event. It is also called if a time-out occurs.

+

Event is either the atom timeout, if a time-out has occurred, or the Event argument provided to send_event/2.

-

StateData is the state data of the gen_fsm.

+

StateData is the state data of the gen_fsm process.

If the function returns {next_state,NextStateName,NewStateData}, - {next_state,NextStateName,NewStateData,Timeout} or - {next_state,NextStateName,NewStateData,hibernate}, - the gen_fsm will continue executing with the current state + {next_state,NextStateName,NewStateData,Timeout}, or + {next_state,NextStateName,NewStateData,hibernate}, the + gen_fsm process continues executing with the current state name set to NextStateName and with the possibly - updated state data NewStateData. See - Module:init/1 for a description of Timeout and hibernate.

+ updated state data NewStateData. For a description of + Timeout and hibernate, see + Module:init/1.

If the function returns {stop,Reason,NewStateData}, - the gen_fsm will call + the gen_fsm process calls Module:terminate(Reason,StateName,NewStateData) and - terminate.

- - - - Module:handle_event(Event, StateName, StateData) -> Result - Handle an asynchronous event. - - Event = term() - StateName = atom() - StateData = term() - Result = {next_state,NextStateName,NewStateData} -   | {next_state,NextStateName,NewStateData,Timeout} -   | {next_state,NextStateName,NewStateData,hibernate} -   | {stop,Reason,NewStateData} -  NextStateName = atom() -  NewStateData = term() -  Timeout = int()>0 | infinity -  Reason = term() - - -

Whenever a gen_fsm receives an event sent using - gen_fsm:send_all_state_event/2, - this function is called to handle the event.

-

StateName is the current state name of the gen_fsm.

-

See Module:StateName/2 for a description of the other - arguments and possible return values.

+ terminates.

 + Module:StateName(Event, From, StateData) -> Result Handle a synchronous event. @@ -616,11 +832,11 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4 From = {pid(),Tag} StateData = term() Result = {reply,Reply,NextStateName,NewStateData} -   | {reply,Reply,NextStateName,NewStateData,Timeout} -   | {reply,Reply,NextStateName,NewStateData,hibernate} +   | {reply,Reply,NextStateName,NewStateData,Timeout} +   | {reply,Reply,NextStateName,NewStateData,hibernate}   | {next_state,NextStateName,NewStateData} -   | {next_state,NextStateName,NewStateData,Timeout} -   | {next_state,NextStateName,NewStateData,hibernate} +   | {next_state,NextStateName,NewStateData,Timeout} +   | {next_state,NextStateName,NewStateData,hibernate}   | {stop,Reason,Reply,NewStateData} | {stop,Reason,NewStateData}  Reply = term()  NextStateName = atom() @@ -629,102 +845,56 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4  Reason = normal | term() -

There should be one instance of this function for each - possible state name. Whenever a gen_fsm receives an event - sent using - gen_fsm:sync_send_event/2,3, +

There is to be one instance of this function for each + possible state name. Whenever a gen_fsm process receives an + event sent using + sync_send_event/2,3, the instance of this function with the same name as the current state name StateName is called to handle the event.

Event is the Event argument provided to - sync_send_event.

+ sync_send_event/2,3.

From is a tuple {Pid,Tag} where Pid is - the pid of the process which called sync_send_event/2,3 + the pid of the process that called sync_send_event/2,3 and Tag is a unique tag.

-

StateData is the state data of the gen_fsm.

-

If the function returns - {reply,Reply,NextStateName,NewStateData}, - {reply,Reply,NextStateName,NewStateData,Timeout} or - {reply,Reply,NextStateName,NewStateData,hibernate}, - Reply will be given back to From as the return - value of sync_send_event/2,3. The gen_fsm then - continues executing with the current state name set to - NextStateName and with the possibly updated state data - NewStateData. See Module:init/1 for a - description of Timeout and hibernate.

-

If the function returns - {next_state,NextStateName,NewStateData}, - {next_state,NextStateName,NewStateData,Timeout} or - {next_state,NextStateName,NewStateData,hibernate}, - the gen_fsm will continue executing in NextStateName - with NewStateData. Any reply to From must be - given explicitly using - gen_fsm:reply/2.

-

If the function returns - {stop,Reason,Reply,NewStateData}, Reply will be - given back to From. If the function returns - {stop,Reason,NewStateData}, any reply to From - must be given explicitly using gen_fsm:reply/2. - The gen_fsm will then call - Module:terminate(Reason,StateName,NewStateData) and - terminate.

- - - - Module:handle_sync_event(Event, From, StateName, StateData) -> Result - Handle a synchronous event. - - Event = term() - From = {pid(),Tag} - StateName = atom() - StateData = term() - Result = {reply,Reply,NextStateName,NewStateData} -   | {reply,Reply,NextStateName,NewStateData,Timeout} -   | {reply,Reply,NextStateName,NewStateData,hibernate} -   | {next_state,NextStateName,NewStateData} -   | {next_state,NextStateName,NewStateData,Timeout} -   | {next_state,NextStateName,NewStateData,hibernate} -   | {stop,Reason,Reply,NewStateData} | {stop,Reason,NewStateData} -  Reply = term() -  NextStateName = atom() -  NewStateData = term() -  Timeout = int()>0 | infinity -  Reason = term() - - -

Whenever a gen_fsm receives an event sent using - gen_fsm:sync_send_all_state_event/2,3, - this function is called to handle the event.

-

StateName is the current state name of the gen_fsm.

-

See Module:StateName/3 for a description of the other - arguments and possible return values.

- - - - Module:handle_info(Info, StateName, StateData) -> Result - Handle an incoming message. - - Info = term() - StateName = atom() - StateData = term() - Result = {next_state,NextStateName,NewStateData} -   | {next_state,NextStateName,NewStateData,Timeout} -   | {next_state,NextStateName,NewStateData,hibernate} -   | {stop,Reason,NewStateData} -  NextStateName = atom() -  NewStateData = term() -  Timeout = int()>0 | infinity -  Reason = normal | term() - - -

This function is called by a gen_fsm when it receives any - other message than a synchronous or asynchronous event (or a - system message).

-

Info is the received message.

-

See Module:StateName/2 for a description of the other - arguments and possible return values.

+

StateData is the state data of the gen_fsm process.

+ + +

If {reply,Reply,NextStateName,NewStateData}, + {reply,Reply,NextStateName,NewStateData,Timeout}, or + {reply,Reply,NextStateName,NewStateData,hibernate} is + returned, Reply is given back to From as the return + value of sync_send_event/2,3. The gen_fsm process + then continues executing with the current state name set to + NextStateName and with the possibly updated state data + NewStateData. For a description of Timeout and + hibernate, see + + Module:init/1.

+ + +

If {next_state,NextStateName,NewStateData}, + {next_state,NextStateName,NewStateData,Timeout}, or + {next_state,NextStateName,NewStateData,hibernate} is + returned, the gen_fsm process continues executing in + NextStateName with NewStateData. + Any reply to From must be specified explicitly using + reply/2.

+ + +

If the function returns + {stop,Reason,Reply,NewStateData}, Reply is + given back to From. If the function returns + {stop,Reason,NewStateData}, any reply to From + must be specified explicitly using reply/2. + The gen_fsm process then calls + Module:terminate(Reason,StateName,NewStateData) and + terminates.

+ + + Module:terminate(Reason, StateName, StateData) Clean up before termination. @@ -734,134 +904,56 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4 StateData = term() -

This function is called by a gen_fsm 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_fsm - terminates with Reason. The return value is ignored.

+

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

Reason is a term denoting the stop reason, StateName is the current state name, and - StateData is the state data of the gen_fsm.

-

Reason depends on why the gen_fsm is terminating. If + StateData is the state data of the gen_fsm process.

+

Reason depends on why the gen_fsm process is + terminating. If it is because another callback function has returned a stop - tuple {stop,..}, Reason will have the value - specified in that tuple. If it is due to a failure, + tuple {stop,..}, Reason has the value + specified in that tuple. If it is because of a failure, Reason is the error reason.

-

If the gen_fsm is part of a supervision tree and is ordered - by its supervisor to terminate, this function will be called +

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

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

The gen_fsm process has been set to trap exit signals.

+ + +

The shutdown strategy as defined in the child specification of + the supervisor is an integer time-out value, not + brutal_kill.

+ -

Even if the gen_fsm 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_fsm will be immediately terminated.

-

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

- - - - Module:code_change(OldVsn, StateName, StateData, Extra) -> {ok, NextStateName, NewStateData} - Update the internal state data during upgrade/downgrade. - - OldVsn = Vsn | {down, Vsn} -   Vsn = term() - StateName = NextStateName = atom() - StateData = NewStateData = term() - Extra = term() - - -

This function is called by a gen_fsm when it should update - its internal state data during a release upgrade/downgrade, - i.e. when the instruction {update,Module,Change,...} - where Change={advanced,Extra} is given in - the appup file. See - OTP Design Principles.

-

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.

-

StateName is the current state name and - StateData the internal state data of the gen_fsm.

-

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

-

The function should return the new current state name and - updated internal data.

- - - - Module:format_status(Opt, [PDict, StateData]) -> Status - Optional function for providing a term describing the - current gen_fsm status. - - Opt = normal | terminate - PDict = [{Key, Value}] - StateData = term() - Status = term() - - - -

This callback is optional, so callback modules need not - export it. The gen_fsm module provides a default - implementation of this function that returns the callback - module state data.

- -

This function is called by a gen_fsm process when:

- - One - of sys:get_status/1,2 - is invoked to get the gen_fsm status. Opt is set to - the atom normal for this case. - The gen_fsm 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 - appearance of the gen_fsm status for these cases. A callback - module wishing to customise the sys:get_status/1,2 - 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_fsm.

-

PDict is the current value of the gen_fsm's - process dictionary.

-

StateData is the internal state data of the - gen_fsm.

-

The function should return Status, a term that - customises the details of the current state and status of - the gen_fsm. There are no restrictions on the - form Status can take, but for - the sys:get_status/1,2 case (when Opt - is normal), the recommended form for - the Status value is [{data, [{"StateData", - Term}]}] where Term provides relevant details of - the gen_fsm state data. Following this recommendation isn't - required, but doing so will make the callback module status - consistent with the rest of the sys:get_status/1,2 - return value.

-

One use for this function is to return compact alternative - state data representations to avoid having large state terms - printed in logfiles.

+

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

+

Otherwise, the gen_fsm process terminates immediately.

+

Notice that for any other reason than normal, + shutdown, or {shutdown,Term} the gen_fsm process + is assumed to terminate because of an error and an error report is + issued using + error_logger:format/2.
- SEE ALSO -

gen_event(3), - gen_server(3), - gen_statem(3), - supervisor(3), - proc_lib(3), - sys(3)

+ See Also +

gen_event(3), + gen_server(3), + gen_statem(3), + proc_lib(3), + supervisor(3), + sys(3)

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