table of contents
other versions
- jessie 1:17.3-dfsg-4+deb8u2
- jessie-backports 1:19.2.1+dfsg-2+deb9u1~bpo8+1
- stretch 1:19.2.1+dfsg-2+deb9u2
- testing 1:21.2.5+dfsg-1
- unstable 1:21.2.6+dfsg-1
- experimental 1:22.0~rc1+dfsg-1
gen_fsm(3erl) | Erlang Module Definition | gen_fsm(3erl) |
NAME¶
gen_fsm - Generic finite state machine behavior.DESCRIPTION¶
Note:
There is a new behaviour gen_statem that is intended to replace
gen_fsm for new code. gen_fsm will not be removed for the
foreseeable future to keep old state machine implementations running.
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 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 -------------- --------------- gen_fsm:start gen_fsm:start_link -----> Module:init/1 gen_fsm:stop -----> Module:terminate/3 gen_fsm:send_event -----> Module:StateName/2 gen_fsm:send_all_state_event -----> Module:handle_event/3 gen_fsm:sync_send_event -----> Module:StateName/3 gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4 - -----> Module:handle_info/3 - -----> Module:terminate/3 - -----> Module:code_change/4If 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(3erl). 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 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.
EXPORTS¶
cancel_timer(Ref) -> RemainingTime | false
Types:
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)
Types:
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
Option = {debug,Dbgs}
Dbgs = [Dbg]
Dbg = trace | log | statistics
| {log_to_file,FileName} | {install,{Func,FuncState}}
| {via,Module,ViaName}
Name = atom()
GlobalName = ViaName = term()
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(3erl). 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
Types:
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
Types:
FsmRef = Name | {Name,Node} | {global,GlobalName}
| {via,Module,ViaName} | pid()
Name = Node = atom()
GlobalName = ViaName = term()
Event = term()
| {via,Module,ViaName} | pid()
Name = Node = atom()
GlobalName = ViaName = 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
Types:
FsmRef = Name | {Name,Node} | {global,GlobalName}
| {via,Module,ViaName} | pid()
Name = Node = atom()
GlobalName = ViaName = term()
Event = term()
| {via,Module,ViaName} | pid()
Name = Node = atom()
GlobalName = ViaName = 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:
Event is any term that is passed as one of the arguments to
Module:StateName/2.
send_event_after(Time, Event) -> Ref
- *
- 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
Types:
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
Types:
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()
| {via,Module,ViaName}
Name = atom()
GlobalName = ViaName = term()
Option = {debug,Dbgs} | {timeout,Time} | {spawn_opt,SOpts}
Dbgs = [Dbg]
Dbg = trace | log | statistics
| {log_to_file,FileName} | {install,{Func,FuncState}}
SOpts = [term()]
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
Types:
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 = [SOpt]
SOpt - see erlang:spawn_opt/2,3,4,5
Result = {ok,Pid} | ignore | {error,Error}
Pid = pid()
Error = {already_started,Pid} | term()
| {via,Module,ViaName}
Name = atom()
GlobalName = ViaName = term()
Option = {debug,Dbgs} | {timeout,Time} | {spawn_opt,SOpts}
Dbgs = [Dbg]
Dbg = trace | log | statistics
| {log_to_file,FileName} | {install,{Func,FuncState}}
SOpts = [SOpt]
SOpt - see erlang:spawn_opt/2,3,4,5
Pid = pid()
Error = {already_started,Pid} | term()
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 no name is provided, the gen_fsm process is not registered.
Module is the name of the callback module.
Args is any term that is passed as the argument to Module:init/1.
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 option {debug,Dbgs} is present, the corresponding sys function
is called for each item in Dbgs; see sys(3erl).
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.
start_timer(Time, Msg) -> Ref
- *
- 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.
Note:
Using spawn option monitor is not allowed, it causes the function to fail
with reason badarg.
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 Module:init/1 returns {stop,Reason} or
ignore, the process is terminated and the function returns
{error,Reason} or ignore, respectively.
Types:
Time = integer()
Msg = term()
Ref = reference()
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
Types:
FsmRef = Name | {Name,Node} | {global,GlobalName}
| {via,Module,ViaName} | pid()
Node = atom()
GlobalName = ViaName = term()
Reason = term()
Timeout = int()>0 | infinity
| {via,Module,ViaName} | pid()
Node = atom()
GlobalName = ViaName = term()
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 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 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.
sync_send_all_state_event(FsmRef, Event) -> Reply
Types:
FsmRef = Name | {Name,Node} | {global,GlobalName}
| {via,Module,ViaName} | pid()
Name = Node = atom()
GlobalName = ViaName = term()
Event = term()
Timeout = int()>0 | infinity
Reply = term()
| {via,Module,ViaName} | pid()
Name = Node = atom()
GlobalName = ViaName = term()
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
Types:
FsmRef = Name | {Name,Node} | {global,GlobalName}
| {via,Module,ViaName} | pid()
Name = Node = atom()
GlobalName = ViaName = term()
Event = term()
Timeout = int()>0 | infinity
Reply = term()
| {via,Module,ViaName} | pid()
Name = Node = atom()
GlobalName = ViaName = term()
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 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. Defaults to 5000. If no reply is received within the specified
time, the function call fails.
Return value Reply is defined in the return value of
Module:StateName/3.
Note:
The ancient behavior of sometimes consuming the server exit message if the
server died during the call while 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.EXPORTS¶
Module:code_change(OldVsn, StateName, StateData, Extra) -> {ok, NextStateName, NewStateData}
Types:
OldVsn = Vsn | {down, Vsn}
Vsn = term()
StateName = NextStateName = atom()
StateData = NewStateData = term()
Extra = term()
Vsn = term()
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.
Module:format_status(Opt, [PDict, StateData]) -> Status
Types:
Opt = normal | terminate
PDict = [{Key, Value}]
StateData = term()
Status = term()
Note:
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.
Types:
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()
| {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 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.
Module:handle_info(Info, StateName, StateData) -> Result
Types:
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()
| {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 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.
Module:handle_sync_event(Event, From, StateName, StateData) -> Result
Types:
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()
| {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 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.
Module:init(Args) -> Result
Types:
Args = term()
Result = {ok,StateName,StateData} | {ok,StateName,StateData,Timeout}
| {ok,StateName,StateData,hibernate}
| {stop,Reason} | ignore
StateName = atom()
StateData = term()
Timeout = int()>0 | infinity
Reason = term()
| {ok,StateName,StateData,hibernate}
| {stop,Reason} | ignore
StateName = atom()
StateData = term()
Timeout = int()>0 | infinity
Reason = term()
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 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 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 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 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
Types:
Event = timeout | term()
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()
| {next_state,NextStateName,NewStateData,Timeout}
| {next_state,NextStateName,NewStateData,hibernate}
| {stop,Reason,NewStateData}
NextStateName = atom()
NewStateData = term()
Timeout = int()>0 | infinity
Reason = term()
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 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 process.
If the function returns {next_state,NextStateName,NewStateData},
{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. For a description of Timeout and hibernate,
see Module:init/1.
If the function returns {stop,Reason,NewStateData}, the gen_fsm
process calls Module:terminate(Reason,StateName,NewStateData) and
terminates.
Module:StateName(Event, From, StateData) -> Result
Types:
Event = term()
From = {pid(),Tag}
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 = normal | term()
| {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 = normal | term()
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/2,3.
From is a tuple {Pid,Tag} where Pid is 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 process.
Module:terminate(Reason, StateName, StateData)
- *
- 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.
Types:
Reason = normal | shutdown | {shutdown,term()} | term()
StateName = atom()
StateData = term()
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 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 has the value specified in that tuple. If it is because of a
failure, Reason is the error reason.
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:
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.
- *
- 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.
SEE ALSO¶
gen_event(3erl), gen_server(3erl), gen_statem(3erl), proc_lib(3erl), supervisor(3erl), sys(3erl)stdlib 3.2 | Ericsson AB |