aboutsummaryrefslogtreecommitdiffstats
path: root/lib/stdlib/doc/src/gen_fsm.xml
diff options
context:
space:
mode:
authorBjörn Gustavsson <bjorn@erlang.org>2016-06-13 12:33:50 +0200
committerBjörn Gustavsson <bjorn@erlang.org>2016-06-13 12:33:50 +0200
commit1280c70da91b90592ae4be88f1f045956e716de7 (patch)
tree42a0b48e54a9b5c982ce606b8c7e7ff9c564ade6 /lib/stdlib/doc/src/gen_fsm.xml
parent3873cb650711342aced0036e3c2d640df8a73c4b (diff)
parent68d53c01b0b8e9a007a6a30158c19e34b2d2a34e (diff)
downloadotp-1280c70da91b90592ae4be88f1f045956e716de7.tar.gz
otp-1280c70da91b90592ae4be88f1f045956e716de7.tar.bz2
otp-1280c70da91b90592ae4be88f1f045956e716de7.zip
Merge branch 'bjorn/stdlib/doc'
* bjorn/stdlib/doc: Update STDLIB documentation
Diffstat (limited to 'lib/stdlib/doc/src/gen_fsm.xml')
-rw-r--r--lib/stdlib/doc/src/gen_fsm.xml1262
1 files changed, 677 insertions, 585 deletions
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 @@
<rev></rev>
</header>
<module>gen_fsm</module>
- <modulesummary>Generic Finite State Machine Behaviour</modulesummary>
+ <modulesummary>Generic finite state machine behavior.</modulesummary>
<description>
<note>
<p>
There is a new behaviour
<seealso marker="gen_statem"><c>gen_statem</c></seealso>
that is intended to replace <c>gen_fsm</c> for new code.
- It has the same features and add some really useful.
- This module will not be removed for the foreseeable future
+ <c>gen_fsm</c> will not be removed for the foreseeable future
to keep old state machine implementations running.
</p>
</note>
- <p>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
- <seealso marker="doc/design_principles:fsm">OTP Design Principles</seealso> for more information.
+ <p>This behavior module provides a finite state machine.
+ A generic finite state machine process (<c>gen_fsm</c>) 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
+ <seealso marker="doc/design_principles:fsm">OTP Design Principles</seealso>.
</p>
- <p>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:</p>
+
+ <p>A <c>gen_fsm</c> 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:</p>
+
<pre>
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</pre>
- <p>If a callback function fails or returns a bad value, the gen_fsm
- will terminate.</p>
- <p>A gen_fsm handles system messages as documented in
- <seealso marker="sys">sys(3)</seealso>. The <c>sys</c> module
- can be used for debugging a gen_fsm.</p>
- <p>Note that a gen_fsm does not trap exit signals automatically,
- this must be explicitly initiated in the callback module.</p>
+
+ <p>If a callback function fails or returns a bad value, the <c>gen_fsm</c>
+ process terminates.</p>
+
+ <p>A <c>gen_fsm</c> process handles system messages as described in
+ <seealso marker="sys"><c>sys(3)</c></seealso>. The <c>sys</c> module
+ can be used for debugging a <c>gen_fsm</c> process.</p>
+
+ <p>Notice that a <c>gen_fsm</c> process does not trap exit signals
+ automatically, this must be explicitly initiated in the callback
+ module.</p>
+
<p>Unless otherwise stated, all functions in this module fail if
- the specified gen_fsm does not exist or if bad arguments are
- given.</p>
- <p>The gen_fsm process can go into hibernation
- (see <seealso marker="erts:erlang#erlang:hibernate/3">erlang(3)</seealso>) if a callback
- function specifies <c>'hibernate'</c> 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.</p>
+ the specified <c>gen_fsm</c> process does not exist or if bad arguments
+ are specified.</p>
+ <p>The <c>gen_fsm</c> process can go into hibernation
+ (see <seealso marker="erts:erlang#hibernate/3">
+ <c>erlang:hibernate/3</c></seealso>) if a callback function
+ specifies <c>'hibernate'</c> 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.</p>
</description>
+
<funcs>
<func>
+ <name>cancel_timer(Ref) -> RemainingTime | false</name>
+ <fsummary>Cancel an internal timer in a generic FSM.</fsummary>
+ <type>
+ <v>Ref = reference()</v>
+ <v>RemainingTime = integer()</v>
+ </type>
+ <desc>
+ <p>Cancels an internal timer referred by <c>Ref</c> in the
+ <c>gen_fsm</c> process that calls this function.</p>
+ <p><c>Ref</c> is a reference returned from
+ <seealso marker="#send_event_after/2">
+ <c>send_event_after/2</c></seealso> or
+ <seealso marker="#start_timer/2"><c>start_timer/2</c></seealso>.</p>
+ <p>If the timer has already timed out, but the event not yet
+ been delivered, it is cancelled as if it had <em>not</em>
+ timed out, so there is no false timer event after
+ returning from this function.</p>
+ <p>Returns the remaining time in milliseconds until the timer would
+ have expired if <c>Ref</c> referred to an active timer, otherwise
+ <c>false</c>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name>enter_loop(Module, Options, StateName, StateData)</name>
+ <name>enter_loop(Module, Options, StateName, StateData, FsmName)</name>
+ <name>enter_loop(Module, Options, StateName, StateData, Timeout)</name>
+ <name>enter_loop(Module, Options, StateName, StateData, FsmName, Timeout)</name>
+ <fsummary>Enter the <c>gen_fsm</c> receive loop.</fsummary>
+ <type>
+ <v>Module = atom()</v>
+ <v>Options = [Option]</v>
+ <v>&nbsp;Option = {debug,Dbgs}</v>
+ <v>&nbsp;&nbsp;Dbgs = [Dbg]</v>
+ <v>&nbsp;&nbsp;&nbsp;Dbg = trace | log | statistics</v>
+ <v>&nbsp;&nbsp;&nbsp;&nbsp;| {log_to_file,FileName} | {install,{Func,FuncState}}</v>
+ <v>StateName = atom()</v>
+ <v>StateData = term()</v>
+ <v>FsmName = {local,Name} | {global,GlobalName}</v>
+ <v>&nbsp;&nbsp;| {via,Module,ViaName}</v>
+ <v>&nbsp;Name = atom()</v>
+ <v>&nbsp;GlobalName = ViaName = term()</v>
+ <v>Timeout = int() | infinity</v>
+ </type>
+ <desc>
+ <p>Makes an existing process into a <c>gen_fsm</c> process.
+ Does not return,
+ instead the calling process enters the <c>gen_fsm</c> receive
+ loop and becomes a <c>gen_fsm</c> process. The process <em>must</em>
+ have been started using one of the start functions in
+ <seealso marker="proc_lib"><c>proc_lib(3)</c></seealso>. The user is
+ responsible for any initialization of the process, including
+ registering a name for it.</p>
+ <p>This function is useful when a more complex initialization
+ procedure is needed than the <c>gen_fsm</c> behavior provides.</p>
+ <p><c>Module</c>, <c>Options</c>, and <c>FsmName</c> have
+ the same meanings as when calling
+ <seealso marker="#start_link/3"><c>start[_link]/3,4</c></seealso>.
+ However, if <c>FsmName</c> is specified, the process must have
+ been registered accordingly <em>before</em> this function is
+ called.</p>
+ <p><c>StateName</c>, <c>StateData</c>, and <c>Timeout</c> have
+ the same meanings as in the return value of
+ <seealso marker="#Moduleinit"><c>Module:init/1</c></seealso>.
+ The callback module <c>Module</c> does not need to
+ export an <c>init/1</c> function.</p>
+ <p>The function fails if the calling process was not started by a
+ <c>proc_lib</c> start function, or if it is not registered
+ according to <c>FsmName</c>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name>reply(Caller, Reply) -> Result</name>
+ <fsummary>Send a reply to a caller.</fsummary>
+ <type>
+ <v>Caller - see below</v>
+ <v>Reply = term()</v>
+ <v>Result = term()</v>
+ </type>
+ <desc>
+ <p>This function can be used by a <c>gen_fsm</c> process to
+ explicitly send a reply to a client process that called
+ <seealso marker="#sync_send_event/2">
+ <c>sync_send_event/2,3</c></seealso> or
+ <seealso marker="#sync_send_all_state_event/2">
+ <c>sync_send_all_state_event/2,3</c></seealso>
+ when the reply cannot be defined in the return value of
+ <seealso marker="#Module:StateName/3">
+ <c>Module:StateName/3</c></seealso> or
+ <seealso marker="#Module:handle_sync_event/4">
+ <c>Module:handle_sync_event/4</c></seealso>.</p>
+ <p><c>Caller</c> must be the <c>From</c> argument provided to
+ the callback function. <c>Reply</c> is any term
+ given back to the client as the return value of
+ <c>sync_send_event/2,3</c> or
+ <c>sync_send_all_state_event/2,3</c>.</p>
+ <p>Return value <c>Result</c> is not further defined, and
+ is always to be ignored.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name>send_all_state_event(FsmRef, Event) -> ok</name>
+ <fsummary>Send an event asynchronously to a generic FSM.</fsummary>
+ <type>
+ <v>FsmRef = Name | {Name,Node} | {global,GlobalName}</v>
+ <v>&nbsp;&nbsp;| {via,Module,ViaName} | pid()</v>
+ <v>&nbsp;Name = Node = atom()</v>
+ <v>&nbsp;GlobalName = ViaName = term()</v>
+ <v>Event = term()</v>
+ </type>
+ <desc>
+ <p>Sends an event asynchronously to the <c>FsmRef</c> of the
+ <c>gen_fsm</c> process and returns <c>ok</c> immediately.
+ The <c>gen_fsm</c> process calls
+ <seealso marker="#Module:handle_event/3">
+ <c>Module:handle_event/3</c></seealso> to handle the event.</p>
+ <p>For a description of the arguments, see
+ <seealso marker="#send_event/2"><c>send_event/2</c></seealso>.</p>
+ <p>The difference between <c>send_event/2</c> and
+ <c>send_all_state_event/2</c> 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 <c>handle_event</c> clause is needed to handle
+ the event instead of one clause in each state name function.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name>send_event(FsmRef, Event) -> ok</name>
+ <fsummary>Send an event asynchronously to a generic FSM.</fsummary>
+ <type>
+ <v>FsmRef = Name | {Name,Node} | {global,GlobalName}</v>
+ <v>&nbsp;&nbsp;| {via,Module,ViaName} | pid()</v>
+ <v>&nbsp;Name = Node = atom()</v>
+ <v>&nbsp;GlobalName = ViaName = term()</v>
+ <v>Event = term()</v>
+ </type>
+ <desc>
+ <p>Sends an event asynchronously to the <c>FsmRef</c> of the
+ <c>gen_fsm</c> process
+ and returns <c>ok</c> immediately. The <c>gen_fsm</c> process calls
+ <seealso marker="#Module:StateName/2">
+ <c>Module:StateName/2</c></seealso> to handle the event, where
+ <c>StateName</c> is the name of the current state of
+ the <c>gen_fsm</c> process.</p>
+ <p><c>FsmRef</c> can be any of the following:</p>
+ <list type="bulleted">
+ <item>The pid</item>
+ <item><c>Name</c>, if the <c>gen_fsm</c> process is locally
+ registered</item>
+ <item><c>{Name,Node}</c>, if the <c>gen_fsm</c> process is locally
+ registered at another node</item>
+ <item><c>{global,GlobalName}</c>, if the <c>gen_fsm</c> process is
+ globally registered</item>
+ <item><c>{via,Module,ViaName}</c>, if the <c>gen_fsm</c> process is
+ registered through an alternative process registry</item>
+ </list>
+ <p><c>Event</c> is any term that is passed as one of
+ the arguments to <c>Module:StateName/2</c>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name>send_event_after(Time, Event) -> Ref</name>
+ <fsummary>Send a delayed event internally in a generic FSM.</fsummary>
+ <type>
+ <v>Time = integer()</v>
+ <v>Event = term()</v>
+ <v>Ref = reference()</v>
+ </type>
+ <desc>
+ <p>Sends a delayed event internally in the <c>gen_fsm</c> process
+ that calls this function after <c>Time</c> milliseconds.
+ Returns immediately a
+ reference that can be used to cancel the delayed send using
+ <seealso marker="#cancel_timer/1"><c>cancel_timer/1</c></seealso>.</p>
+ <p>The <c>gen_fsm</c> process calls
+ <seealso marker="#Module:StateName/2">
+ <c>Module:StateName/2</c></seealso> to handle
+ the event, where <c>StateName</c> is the name of the current
+ state of the <c>gen_fsm</c> process at the time the delayed event is
+ delivered.</p>
+ <p><c>Event</c> is any term that is passed as one of
+ the arguments to <c>Module:StateName/2</c>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name>start(Module, Args, Options) -> Result</name>
+ <name>start(FsmName, Module, Args, Options) -> Result</name>
+ <fsummary>Create a standalone <c>gen_fsm</c> process.</fsummary>
+ <type>
+ <v>FsmName = {local,Name} | {global,GlobalName}</v>
+ <v>&nbsp;&nbsp;| {via,Module,ViaName}</v>
+ <v>&nbsp;Name = atom()</v>
+ <v>&nbsp;GlobalName = ViaName = term()</v>
+ <v>Module = atom()</v>
+ <v>Args = term()</v>
+ <v>Options = [Option]</v>
+ <v>&nbsp;Option = {debug,Dbgs} | {timeout,Time} | {spawn_opt,SOpts}</v>
+ <v>&nbsp;&nbsp;Dbgs = [Dbg]</v>
+ <v>&nbsp;&nbsp;&nbsp;Dbg = trace | log | statistics</v>
+ <v>&nbsp;&nbsp;&nbsp;&nbsp;| {log_to_file,FileName} | {install,{Func,FuncState}}</v>
+ <v>&nbsp;&nbsp;SOpts = [term()]</v>
+ <v>Result = {ok,Pid} | ignore | {error,Error}</v>
+ <v>&nbsp;Pid = pid()</v>
+ <v>&nbsp;Error = {already_started,Pid} | term()</v>
+ </type>
+ <desc>
+ <p>Creates a standalone <c>gen_fsm</c> process, that is, a process that
+ is not part of a supervision tree and thus has no supervisor.</p>
+ <p>For a description of arguments and return values, see
+ <seealso marker="#start_link/3"><c>start_link/3,4</c></seealso>.</p>
+ </desc>
+ </func>
+
+ <func>
<name>start_link(Module, Args, Options) -> Result</name>
<name>start_link(FsmName, Module, Args, Options) -> Result</name>
- <fsummary>Create a gen_fsm process in a supervision tree.</fsummary>
+ <fsummary>Create a <c>gen_fsm</c> process in a supervision tree.
+ </fsummary>
<type>
- <v>FsmName = {local,Name} | {global,GlobalName}
- | {via,Module,ViaName}</v>
+ <v>FsmName = {local,Name} | {global,GlobalName}</v>
+ <v>&nbsp;&nbsp;| {via,Module,ViaName}</v>
<v>&nbsp;Name = atom()</v>
<v>&nbsp;GlobalName = ViaName = term()</v>
<v>Module = atom()</v>
@@ -117,54 +345,64 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
<v>&nbsp;Error = {already_started,Pid} | term()</v>
</type>
<desc>
- <p>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.</p>
- <p>The gen_fsm process calls <c>Module:init/1</c> to
- initialize. To ensure a synchronized start-up procedure,
+ <p>Creates a <c>gen_fsm</c> 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 <c>gen_fsm</c> process is linked to the supervisor.</p>
+ <p>The <c>gen_fsm</c> process calls
+ <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> to
+ initialize. To ensure a synchronized startup procedure,
<c>start_link/3,4</c> does not return until
<c>Module:init/1</c> has returned.</p>
- <p>If <c>FsmName={local,Name}</c>, the gen_fsm is registered
- locally as <c>Name</c> using <c>register/2</c>.
- If <c>FsmName={global,GlobalName}</c>, the gen_fsm is
- registered globally as <c>GlobalName</c> using
- <c>global:register_name/2</c>.
- If <c>FsmName={via,Module,ViaName}</c>, the gen_fsm will
- register with the registry represented by <c>Module</c>.
- The <c>Module</c> callback should export the functions
- <c>register_name/2</c>, <c>unregister_name/1</c>,
- <c>whereis_name/1</c> and <c>send/2</c>, which should behave like the
- corresponding functions in <c>global</c>. Thus,
- <c>{via,global,GlobalName}</c> is a valid reference.</p>
- <p>If no name is provided,
- the gen_fsm is not registered.</p>
+ <list type="bulleted">
+ <item>
+ <p>If <c>FsmName={local,Name}</c>, the <c>gen_fsm</c> process is
+ registered locally as <c>Name</c> using <c>register/2</c>.</p>
+ </item>
+ <item>
+ <p>If <c>FsmName={global,GlobalName}</c>, the <c>gen_fsm</c> process
+ is registered globally as <c>GlobalName</c> using
+ <seealso marker="kernel:global#register_name/2">
+ <c>global:register_name/2</c></seealso>.</p>
+ </item>
+ <item>
+ <p>If <c>FsmName={via,Module,ViaName}</c>, the <c>gen_fsm</c>
+ process registers with the registry represented by <c>Module</c>.
+ The <c>Module</c> callback is to export the functions
+ <c>register_name/2</c>, <c>unregister_name/1</c>,
+ <c>whereis_name/1</c>, and <c>send/2</c>, which are to behave
+ like the corresponding functions in
+ <seealso marker="kernel:global"><c>global</c></seealso>.
+ Thus, <c>{via,global,GlobalName}</c> is a valid reference.</p>
+ </item>
+ </list>
+ <p>If no name is provided, the <c>gen_fsm</c> process is not
+ registered.</p>
<p><c>Module</c> is the name of the callback module.</p>
- <p><c>Args</c> is an arbitrary term which is passed as
+ <p><c>Args</c> is any term that is passed as
the argument to <c>Module:init/1</c>.</p>
- <p>If the option <c>{timeout,Time}</c> is present, the gen_fsm
- is allowed to spend <c>Time</c> milliseconds initializing
- or it will be terminated and the start function will return
+ <p>If option <c>{timeout,Time}</c> is present, the <c>gen_fsm</c>
+ process is allowed to spend <c>Time</c> milliseconds initializing
+ or it terminates and the start function returns
<c>{error,timeout}</c>.</p>
- <p>If the option <c>{debug,Dbgs}</c> is present,
- the corresponding <c>sys</c> function will be called for each
- item in <c>Dbgs</c>. See
- <seealso marker="sys">sys(3)</seealso>.</p>
- <p>If the option <c>{spawn_opt,SOpts}</c> is present,
- <c>SOpts</c> will be passed as option list to
- the <c>spawn_opt</c> BIF which is used to spawn the gen_fsm
- process. See
- <seealso marker="erts:erlang#spawn_opt/2">erlang(3)</seealso>.</p>
+ <p>If option <c>{debug,Dbgs}</c> is present, the corresponding
+ <c>sys</c> function is called for each item in <c>Dbgs</c>; see
+ <seealso marker="sys"><c>sys(3)</c></seealso>.</p>
+ <p>If option <c>{spawn_opt,SOpts}</c> is present, <c>SOpts</c> is
+ passed as option list to the <c>spawn_opt</c> BIF that is used to
+ spawn the <c>gen_fsm</c> process; see
+ <seealso marker="erts:erlang#spawn_opt/2">
+ <c>spawn_opt/2</c></seealso>.</p>
<note>
- <p>Using the spawn option <c>monitor</c> is currently not
- allowed, but will cause the function to fail with reason
+ <p>Using spawn option <c>monitor</c> is not
+ allowed, it causes the function to fail with reason
<c>badarg</c>.</p>
</note>
- <p>If the gen_fsm is successfully created and initialized
- the function returns <c>{ok,Pid}</c>, where <c>Pid</c> is
- the pid of the gen_fsm. If there already exists a process with
- the specified <c>FsmName</c>, the function returns
- <c>{error,{already_started,Pid}}</c> where <c>Pid</c> is
+ <p>If the <c>gen_fsm</c> process is successfully created and
+ initialized, the function returns <c>{ok,Pid}</c>, where <c>Pid</c>
+ is the pid of the <c>gen_fsm</c> process. If a process with the
+ specified <c>FsmName</c> exists already, the function returns
+ <c>{error,{already_started,Pid}}</c>, where <c>Pid</c> is
the pid of that process.</p>
<p>If <c>Module:init/1</c> fails with <c>Reason</c>,
the function returns <c>{error,Reason}</c>. If
@@ -173,129 +411,106 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
returns <c>{error,Reason}</c> or <c>ignore</c>, respectively.</p>
</desc>
</func>
+
<func>
- <name>start(Module, Args, Options) -> Result</name>
- <name>start(FsmName, Module, Args, Options) -> Result</name>
- <fsummary>Create a stand-alone gen_fsm process.</fsummary>
+ <name>start_timer(Time, Msg) -> Ref</name>
+ <fsummary>Send a time-out event internally in a generic FSM.</fsummary>
<type>
- <v>FsmName = {local,Name} | {global,GlobalName}
- | {via,Module,ViaName}</v>
- <v>&nbsp;Name = atom()</v>
- <v>&nbsp;GlobalName = ViaName = term()</v>
- <v>Module = atom()</v>
- <v>Args = term()</v>
- <v>Options = [Option]</v>
- <v>&nbsp;Option = {debug,Dbgs} | {timeout,Time} | {spawn_opt,SOpts}</v>
- <v>&nbsp;&nbsp;Dbgs = [Dbg]</v>
- <v>&nbsp;&nbsp;&nbsp;Dbg = trace | log | statistics</v>
- <v>&nbsp;&nbsp;&nbsp;&nbsp;| {log_to_file,FileName} | {install,{Func,FuncState}}</v>
- <v>&nbsp;&nbsp;SOpts = [term()]</v>
- <v>Result = {ok,Pid} | ignore | {error,Error}</v>
- <v>&nbsp;Pid = pid()</v>
- <v>&nbsp;Error = {already_started,Pid} | term()</v>
+ <v>Time = integer()</v>
+ <v>Msg = term()</v>
+ <v>Ref = reference()</v>
</type>
<desc>
- <p>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.</p>
- <p>See <seealso marker="#start_link/3">start_link/3,4</seealso>
- for a description of arguments and return values.</p>
+ <p>Sends a time-out event internally in the <c>gen_fsm</c>
+ process that calls this function after <c>Time</c> milliseconds.
+ Returns immediately a
+ reference that can be used to cancel the timer using
+ <seealso marker="#cancel_timer/1"><c>cancel_timer/1</c></seealso>.</p>
+ <p>The <c>gen_fsm</c> process calls
+ <seealso marker="#Module:StateName/2">
+ <c>Module:StateName/2</c></seealso> to handle
+ the event, where <c>StateName</c> is the name of the current
+ state of the <c>gen_fsm</c> process at the time the time-out
+ message is delivered.</p>
+ <p><c>Msg</c> is any term that is passed in the
+ time-out message, <c>{timeout, Ref, Msg}</c>, as one of
+ the arguments to <c>Module:StateName/2</c>.</p>
</desc>
</func>
+
<func>
<name>stop(FsmRef) -> ok</name>
<name>stop(FsmRef, Reason, Timeout) -> ok</name>
<fsummary>Synchronously stop a generic FSM.</fsummary>
<type>
- <v>FsmRef = Name | {Name,Node} | {global,GlobalName}
- | {via,Module,ViaName} | pid()</v>
+ <v>FsmRef = Name | {Name,Node} | {global,GlobalName}</v>
+ <v>&nbsp;&nbsp;| {via,Module,ViaName} | pid()</v>
<v>&nbsp;Node = atom()</v>
<v>&nbsp;GlobalName = ViaName = term()</v>
<v>Reason = term()</v>
<v>Timeout = int()>0 | infinity</v>
</type>
<desc>
- <p>Orders a generic FSM to exit with the given <c>Reason</c>
- and waits for it to terminate. The gen_fsm will call
- <seealso marker="#Module:terminate/3">Module:terminate/3</seealso>
- before exiting.</p>
- <p>The function returns <c>ok</c> if the generic FSM terminates
- with the expected reason. Any other reason than <c>normal</c>,
- <c>shutdown</c>, or <c>{shutdown,Term}</c> will cause an
+ <p>Orders a generic finite state machine to exit with the specified
+ <c>Reason</c> and waits for it to terminate. The <c>gen_fsm</c>
+ process calls <seealso marker="#Module:terminate/3">
+ <c>Module:terminate/3</c></seealso> before exiting.</p>
+ <p>The function returns <c>ok</c> if the generic finite state machine
+ terminates with the expected reason. Any other reason than
+ <c>normal</c>, <c>shutdown</c>, or <c>{shutdown,Term}</c> causes an
error report to be issued using
- <seealso marker="kernel:error_logger#format/2">error_logger:format/2</seealso>.
- The default <c>Reason</c> is <c>normal</c>.</p>
- <p><c>Timeout</c> is an integer greater than zero which
+ <seealso marker="kernel:error_logger#format/2">
+ <c>error_logger:format/2</c></seealso>.
+ The default <c>Reason</c> is <c>normal</c>.</p>
+ <p><c>Timeout</c> is an integer greater than zero that
specifies how many milliseconds to wait for the generic FSM
to terminate, or the atom <c>infinity</c> to wait
indefinitely. The default value is <c>infinity</c>. If the
- generic FSM has not terminated within the specified time, a
- <c>timeout</c> exception is raised.</p>
- <p>If the process does not exist, a <c>noproc</c> exception
- is raised.</p>
- </desc>
- </func>
- <func>
- <name>send_event(FsmRef, Event) -> ok</name>
- <fsummary>Send an event asynchronously to a generic FSM.</fsummary>
- <type>
- <v>FsmRef = Name | {Name,Node} | {global,GlobalName}
- | {via,Module,ViaName} | pid()</v>
- <v>&nbsp;Name = Node = atom()</v>
- <v>&nbsp;GlobalName = ViaName = term()</v>
- <v>Event = term()</v>
- </type>
- <desc>
- <p>Sends an event asynchronously to the gen_fsm <c>FsmRef</c>
- and returns <c>ok</c> immediately. The gen_fsm will call
- <c>Module:StateName/2</c> to handle the event, where
- <c>StateName</c> is the name of the current state of
- the gen_fsm.</p>
- <p><c>FsmRef</c> can be:</p>
- <list type="bulleted">
- <item>the pid,</item>
- <item><c>Name</c>, if the gen_fsm is locally registered,</item>
- <item><c>{Name,Node}</c>, if the gen_fsm is locally
- registered at another node, or</item>
- <item><c>{global,GlobalName}</c>, if the gen_fsm is globally
- registered.</item>
- <item><c>{via,Module,ViaName}</c>, if the gen_fsm is registered
- through an alternative process registry.</item>
- </list>
- <p><c>Event</c> is an arbitrary term which is passed as one of
- the arguments to <c>Module:StateName/2</c>.</p>
+ generic finite state machine has not terminated within the specified
+ time, a <c>timeout</c> exception is raised.</p>
+ <p>If the process does not exist, a <c>noproc</c> exception
+ is raised.</p>
</desc>
</func>
+
<func>
- <name>send_all_state_event(FsmRef, Event) -> ok</name>
- <fsummary>Send an event asynchronously to a generic FSM.</fsummary>
+ <name>sync_send_all_state_event(FsmRef, Event) -> Reply</name>
+ <name>sync_send_all_state_event(FsmRef, Event, Timeout) -> Reply</name>
+ <fsummary>Send an event synchronously to a generic FSM.</fsummary>
<type>
- <v>FsmRef = Name | {Name,Node} | {global,GlobalName}
- | {via,Module,ViaName} | pid()</v>
+ <v>FsmRef = Name | {Name,Node} | {global,GlobalName}</v>
+ <v>&nbsp;&nbsp;| {via,Module,ViaName} | pid()</v>
<v>&nbsp;Name = Node = atom()</v>
<v>&nbsp;GlobalName = ViaName = term()</v>
<v>Event = term()</v>
+ <v>Timeout = int()>0 | infinity</v>
+ <v>Reply = term()</v>
</type>
<desc>
- <p>Sends an event asynchronously to the gen_fsm <c>FsmRef</c>
- and returns <c>ok</c> immediately. The gen_fsm will call
- <c>Module:handle_event/3</c> to handle the event.</p>
- <p>See <seealso marker="#send_event/2">send_event/2</seealso>
- for a description of the arguments.</p>
- <p>The difference between <c>send_event</c> and
- <c>send_all_state_event</c> 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 <c>handle_event</c> clause is needed to handle
- the event instead of one clause in each state name function.</p>
+ <p>Sends an event to the <c>FsmRef</c> of the <c>gen_fsm</c>
+ process and waits until a reply arrives or a time-out occurs.
+ The <c>gen_fsm</c> process calls
+ <seealso marker="#Module:handle_sync_event/4">
+ <c>Module:handle_sync_event/4</c></seealso> to handle the event.</p>
+ <p>For a description of <c>FsmRef</c> and <c>Event</c>, see
+ <seealso marker="#send_event/2">send_event/2</seealso>.
+ For a description of <c>Timeout</c> and <c>Reply</c>, see
+ <seealso marker="#sync_send_event/3">
+ <c>sync_send_event/3</c></seealso>.</p>
+ <p>For a discussion about the difference between
+ <c>sync_send_event</c> and <c>sync_send_all_state_event</c>, see
+ <seealso marker="#send_all_state_event/2">
+ <c>send_all_state_event/2</c></seealso>.</p>
</desc>
</func>
+
<func>
<name>sync_send_event(FsmRef, Event) -> Reply</name>
<name>sync_send_event(FsmRef, Event, Timeout) -> Reply</name>
<fsummary>Send an event synchronously to a generic FSM.</fsummary>
<type>
- <v>FsmRef = Name | {Name,Node} | {global,GlobalName}
- | {via,Module,ViaName} | pid()</v>
+ <v>FsmRef = Name | {Name,Node} | {global,GlobalName}</v>
+ <v>&nbsp;&nbsp;| {via,Module,ViaName} | pid()</v>
<v>&nbsp;Name = Node = atom()</v>
<v>&nbsp;GlobalName = ViaName = term()</v>
<v>Event = term()</v>
@@ -303,210 +518,231 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
<v>Reply = term()</v>
</type>
<desc>
- <p>Sends an event to the gen_fsm <c>FsmRef</c> and waits until a
- reply arrives or a timeout occurs. The gen_fsm will call
- <c>Module:StateName/3</c> to handle the event, where
+ <p>Sends an event to the <c>FsmRef</c> of the <c>gen_fsm</c>
+ process and waits until a reply arrives or a time-out occurs.
+ <c>The gen_fsm</c> process calls
+ <seealso marker="#Module:StateName/3">
+ <c>Module:StateName/3</c></seealso> to handle the event, where
<c>StateName</c> is the name of the current state of
- the gen_fsm.</p>
- <p>See <seealso marker="#send_event/2">send_event/2</seealso>
- for a description of <c>FsmRef</c> and <c>Event</c>.</p>
- <p><c>Timeout</c> is an integer greater than zero which
+ the <c>gen_fsm</c> process.</p>
+ <p>For a description of <c>FsmRef</c> and <c>Event</c>, see
+ <seealso marker="#send_event/2"><c>send_event/2</c></seealso>.</p>
+ <p><c>Timeout</c> is an integer greater than zero that
specifies how many milliseconds to wait for a reply, or
- the atom <c>infinity</c> to wait indefinitely. Default value
- is 5000. If no reply is received within the specified time,
+ the atom <c>infinity</c> to wait indefinitely. Defaults
+ to 5000. If no reply is received within the specified time,
the function call fails.</p>
- <p>The return value <c>Reply</c> is defined in the return value
+ <p>Return value <c>Reply</c> is defined in the return value
of <c>Module:StateName/3</c>.</p>
- <p>The ancient behaviour of sometimes consuming the server
+ <note>
+ <p>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.</p>
+ linked to the client was removed in Erlang 5.6/OTP R12B.</p>
+ </note>
</desc>
</func>
+ </funcs>
+
+ <section>
+ <title>Callback Functions</title>
+ <p>The following functions are to be exported from a <c>gen_fsm</c>
+ callback module.</p>
+
+ <p><em>state name</em> denotes a state of the state machine.</p>
+
+ <p><em>state data</em> denotes the internal state of the Erlang process
+ that implements the state machine.</p>
+ </section>
+
+ <funcs>
<func>
- <name>sync_send_all_state_event(FsmRef, Event) -> Reply</name>
- <name>sync_send_all_state_event(FsmRef, Event, Timeout) -> Reply</name>
- <fsummary>Send an event synchronously to a generic FSM.</fsummary>
+ <name>Module:code_change(OldVsn, StateName, StateData, Extra) -> {ok, NextStateName, NewStateData}</name>
+ <fsummary>Update the internal state data during upgrade/downgrade.
+ </fsummary>
<type>
- <v>FsmRef = Name | {Name,Node} | {global,GlobalName}
- | {via,Module,ViaName} | pid()</v>
- <v>&nbsp;Name = Node = atom()</v>
- <v>&nbsp;GlobalName = ViaName = term()</v>
- <v>Event = term()</v>
- <v>Timeout = int()>0 | infinity</v>
- <v>Reply = term()</v>
+ <v>OldVsn = Vsn | {down, Vsn}</v>
+ <v>&nbsp;&nbsp;Vsn = term()</v>
+ <v>StateName = NextStateName = atom()</v>
+ <v>StateData = NewStateData = term()</v>
+ <v>Extra = term()</v>
</type>
<desc>
- <p>Sends an event to the gen_fsm <c>FsmRef</c> and waits until a
- reply arrives or a timeout occurs. The gen_fsm will call
- <c>Module:handle_sync_event/4</c> to handle the event.</p>
- <p>See <seealso marker="#send_event/2">send_event/2</seealso>
- for a description of <c>FsmRef</c> and <c>Event</c>. See
- <seealso marker="#sync_send_event/3">sync_send_event/3</seealso>
- for a description of <c>Timeout</c> and <c>Reply</c>.</p>
- <p>See
- <seealso marker="#send_all_state_event/2">send_all_state_event/2</seealso>
- for a discussion about the difference between
- <c>sync_send_event</c> and <c>sync_send_all_state_event</c>.</p>
+ <p>This function is called by a <c>gen_fsm</c> process when it is to
+ update its internal state data during a release upgrade/downgrade,
+ that is, when instruction <c>{update,Module,Change,...}</c>,
+ where <c>Change={advanced,Extra}</c>, is given in
+ the <c>appup</c> file; see section
+ <seealso marker="doc/design_principles:release_handling#instr">
+ Release Handling Instructions</seealso> in OTP Design Principles.</p>
+ <p>For an upgrade, <c>OldVsn</c> is <c>Vsn</c>, and for a downgrade,
+ <c>OldVsn</c> is <c>{down,Vsn}</c>. <c>Vsn</c> is defined by the
+ <c>vsn</c> attribute(s) of the old version of the callback module
+ <c>Module</c>. If no such attribute is defined, the version is
+ the checksum of the Beam file.</p>
+ <p><c>StateName</c> is the current state name and <c>StateData</c> the
+ internal state data of the <c>gen_fsm</c> process.</p>
+ <p><c>Extra</c> is passed "as is" from the <c>{advanced,Extra}</c>
+ part of the update instruction.</p>
+ <p>The function is to return the new current state name and
+ updated internal data.</p>
</desc>
</func>
+
<func>
- <name>reply(Caller, Reply) -> Result</name>
- <fsummary>Send a reply to a caller.</fsummary>
+ <name>Module:format_status(Opt, [PDict, StateData]) -> Status</name>
+ <fsummary>Optional function for providing a term describing the
+ current <c>gen_fsm</c> process status.</fsummary>
<type>
- <v>Caller - see below</v>
- <v>Reply = term()</v>
- <v>Result = term()</v>
+ <v>Opt = normal | terminate</v>
+ <v>PDict = [{Key, Value}]</v>
+ <v>StateData = term()</v>
+ <v>Status = term()</v>
</type>
<desc>
- <p>This function can be used by a gen_fsm to explicitly send a
- reply to a client process that called
- <seealso marker="#sync_send_event/2">sync_send_event/2,3</seealso>
- or
- <seealso marker="#sync_send_all_state_event/2">sync_send_all_state_event/2,3</seealso>,
- when the reply cannot be defined in the return value of
- <c>Module:State/3</c> or <c>Module:handle_sync_event/4</c>.</p>
- <p><c>Caller</c> must be the <c>From</c> argument provided to
- the callback function. <c>Reply</c> is an arbitrary term,
- which will be given back to the client as the return value of
- <c>sync_send_event/2,3</c> or
- <c>sync_send_all_state_event/2,3</c>.</p>
- <p>The return value <c>Result</c> is not further defined, and
- should always be ignored.</p>
+ <note>
+ <p>This callback is optional, so callback modules need not
+ export it. The <c>gen_fsm</c> module provides a default
+ implementation of this function that returns the callback
+ module state data.</p>
+ </note>
+ <p>This function is called by a <c>gen_fsm</c> process in the
+ following situations:</p>
+ <list type="bulleted">
+ <item>One of <seealso marker="sys#get_status/1">
+ <c>sys:get_status/1,2</c></seealso>
+ is invoked to get the <c>gen_fsm</c> status. <c>Opt</c> is set to
+ the atom <c>normal</c> for this case.</item>
+ <item>The <c>gen_fsm</c> process terminates abnormally and logs an
+ error. <c>Opt</c> is set to the atom <c>terminate</c> for
+ this case.</item>
+ </list>
+ <p>This function is useful for changing the form and
+ appearance of the <c>gen_fsm</c> status for these cases. A callback
+ module wishing to change the <c>sys:get_status/1,2</c>
+ return value as well as how its status appears in
+ termination error logs, exports an instance
+ of <c>format_status/2</c> that returns a term describing the
+ current status of the <c>gen_fsm</c> process.</p>
+ <p><c>PDict</c> is the current value of the process dictionary of the
+ <c>gen_fsm</c> process.</p>
+ <p><c>StateData</c> is the internal state data of the
+ <c>gen_fsm</c> process.</p>
+ <p>The function is to return <c>Status</c>, a term that
+ change the details of the current state and status of
+ the <c>gen_fsm</c> process. There are no restrictions on the
+ form <c>Status</c> can take, but for
+ the <c>sys:get_status/1,2</c> case (when <c>Opt</c>
+ is <c>normal</c>), the recommended form for
+ the <c>Status</c> value is <c>[{data, [{"StateData",
+ Term}]}]</c>, where <c>Term</c> provides relevant details of
+ the <c>gen_fsm</c> state data. Following this recommendation is not
+ required, but it makes the callback module status
+ consistent with the rest of the <c>sys:get_status/1,2</c>
+ return value.</p>
+ <p>One use for this function is to return compact alternative
+ state data representations to avoid that large state terms
+ are printed in log files.</p>
</desc>
</func>
+
<func>
- <name>send_event_after(Time, Event) -> Ref</name>
- <fsummary>Send a delayed event internally in a generic FSM.</fsummary>
+ <name>Module:handle_event(Event, StateName, StateData) -> Result</name>
+ <fsummary>Handle an asynchronous event.</fsummary>
<type>
- <v>Time = integer()</v>
<v>Event = term()</v>
- <v>Ref = reference()</v>
- </type>
- <desc>
- <p>Sends a delayed event internally in the gen_fsm that calls
- this function after <c>Time</c> ms. Returns immediately a
- reference that can be used to cancel the delayed send using
- <seealso marker="#cancel_timer/1">cancel_timer/1</seealso>.</p>
- <p>The gen_fsm will call <c>Module:StateName/2</c> to handle
- the event, where <c>StateName</c> is the name of the current
- state of the gen_fsm at the time the delayed event is
- delivered.</p>
- <p><c>Event</c> is an arbitrary term which is passed as one of
- the arguments to <c>Module:StateName/2</c>.</p>
- </desc>
- </func>
- <func>
- <name>start_timer(Time, Msg) -> Ref</name>
- <fsummary>Send a timeout event internally in a generic FSM.</fsummary>
- <type>
- <v>Time = integer()</v>
- <v>Msg = term()</v>
- <v>Ref = reference()</v>
+ <v>StateName = atom()</v>
+ <v>StateData = term()</v>
+ <v>Result = {next_state,NextStateName,NewStateData}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
+ <v>&nbsp;&nbsp;| {stop,Reason,NewStateData}</v>
+ <v>&nbsp;NextStateName = atom()</v>
+ <v>&nbsp;NewStateData = term()</v>
+ <v>&nbsp;Timeout = int()>0 | infinity</v>
+ <v>&nbsp;Reason = term()</v>
</type>
<desc>
- <p>Sends a timeout event internally in the gen_fsm that calls
- this function after <c>Time</c> ms. Returns immediately a
- reference that can be used to cancel the timer using
- <seealso marker="#cancel_timer/1">cancel_timer/1</seealso>.</p>
- <p>The gen_fsm will call <c>Module:StateName/2</c> to handle
- the event, where <c>StateName</c> is the name of the current
- state of the gen_fsm at the time the timeout message is
- delivered.</p>
- <p><c>Msg</c> is an arbitrary term which is passed in the
- timeout message, <c>{timeout, Ref, Msg}</c>, as one of
- the arguments to <c>Module:StateName/2</c>.</p>
+ <p>Whenever a <c>gen_fsm</c> process receives an event sent using
+ <seealso marker="#send_all_state_event/2">
+ <c>send_all_state_event/2</c></seealso>,
+ this function is called to handle the event.</p>
+ <p><c>StateName</c> is the current state name of the <c>gen_fsm</c>
+ process.</p>
+ <p>For a description of the other arguments and possible return values,
+ see <seealso marker="#Module:StateName/2">
+ <c>Module:StateName/2</c></seealso>.</p>
</desc>
</func>
+
<func>
- <name>cancel_timer(Ref) -> RemainingTime | false</name>
- <fsummary>Cancel an internal timer in a generic FSM.</fsummary>
+ <name>Module:handle_info(Info, StateName, StateData) -> Result</name>
+ <fsummary>Handle an incoming message.</fsummary>
<type>
- <v>Ref = reference()</v>
- <v>RemainingTime = integer()</v>
+ <v>Info = term()</v>
+ <v>StateName = atom()</v>
+ <v>StateData = term()</v>
+ <v>Result = {next_state,NextStateName,NewStateData}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
+ <v>&nbsp;&nbsp;| {stop,Reason,NewStateData}</v>
+ <v>&nbsp;NextStateName = atom()</v>
+ <v>&nbsp;NewStateData = term()</v>
+ <v>&nbsp;Timeout = int()>0 | infinity</v>
+ <v>&nbsp;Reason = normal | term()</v>
</type>
<desc>
- <p>Cancels an internal timer referred by <c>Ref</c> in the
- gen_fsm that calls this function.</p>
- <p><c>Ref</c> is a reference returned from
- <seealso marker="#send_event_after/2">send_event_after/2</seealso>
- or
- <seealso marker="#start_timer/2">start_timer/2</seealso>.</p>
- <p>If the timer has already timed out, but the event not yet
- been delivered, it is cancelled as if it had <em>not</em>
- timed out, so there will be no false timer event after
- returning from this function.</p>
- <p>Returns the remaining time in ms until the timer would
- have expired if <c>Ref</c> referred to an active timer,
- <c>false</c> otherwise.</p>
+ <p>This function is called by a <c>gen_fsm</c> process when it receives
+ any other message than a synchronous or asynchronous event (or a
+ system message).</p>
+ <p><c>Info</c> is the received message.</p>
+ <p>For a description of the other arguments and possible return values,
+ see <seealso marker="#Module:StateName/2">
+ <c>Module:StateName/2</c></seealso>.</p>
</desc>
</func>
+
<func>
- <name>enter_loop(Module, Options, StateName, StateData)</name>
- <name>enter_loop(Module, Options, StateName, StateData, FsmName)</name>
- <name>enter_loop(Module, Options, StateName, StateData, Timeout)</name>
- <name>enter_loop(Module, Options, StateName, StateData, FsmName, Timeout)</name>
- <fsummary>Enter the gen_fsm receive loop</fsummary>
+ <name>Module:handle_sync_event(Event, From, StateName, StateData) -> Result</name>
+ <fsummary>Handle a synchronous event.</fsummary>
<type>
- <v>Module = atom()</v>
- <v>Options = [Option]</v>
- <v>&nbsp;Option = {debug,Dbgs}</v>
- <v>&nbsp;&nbsp;Dbgs = [Dbg]</v>
- <v>&nbsp;&nbsp;&nbsp;Dbg = trace | log | statistics</v>
- <v>&nbsp;&nbsp;&nbsp;&nbsp;| {log_to_file,FileName} | {install,{Func,FuncState}}</v>
+ <v>Event = term()</v>
+ <v>From = {pid(),Tag}</v>
<v>StateName = atom()</v>
<v>StateData = term()</v>
- <v>FsmName = {local,Name} | {global,GlobalName}
- | {via,Module,ViaName}</v>
- <v>&nbsp;Name = atom()</v>
- <v>&nbsp;GlobalName = ViaName = term()</v>
- <v>Timeout = int() | infinity</v>
+ <v>Result = {reply,Reply,NextStateName,NewStateData}</v>
+ <v>&nbsp;&nbsp;| {reply,Reply,NextStateName,NewStateData,Timeout}</v>
+ <v>&nbsp;&nbsp;| {reply,Reply,NextStateName,NewStateData,hibernate}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
+ <v>&nbsp;&nbsp;| {stop,Reason,Reply,NewStateData} | {stop,Reason,NewStateData}</v>
+ <v>&nbsp;Reply = term()</v>
+ <v>&nbsp;NextStateName = atom()</v>
+ <v>&nbsp;NewStateData = term()</v>
+ <v>&nbsp;Timeout = int()>0 | infinity</v>
+ <v>&nbsp;Reason = term()</v>
</type>
<desc>
- <p>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 <em>must</em>
- have been started using one of the start functions in
- <c>proc_lib</c>, see
- <seealso marker="proc_lib">proc_lib(3)</seealso>. The user is
- responsible for any initialization of the process, including
- registering a name for it.</p>
- <p>This function is useful when a more complex initialization
- procedure is needed than the gen_fsm behaviour provides.</p>
- <p><c>Module</c>, <c>Options</c> and <c>FsmName</c> have
- the same meanings as when calling
- <seealso marker="#start_link/3">start[_link]/3,4</seealso>.
- However, if <c>FsmName</c> is specified, the process must have
- been registered accordingly <em>before</em> this function is
- called.</p>
- <p><c>StateName</c>, <c>StateData</c> and <c>Timeout</c> have
- the same meanings as in the return value of
- <seealso marker="#Moduleinit">Module:init/1</seealso>.
- Also, the callback module <c>Module</c> does not need to
- export an <c>init/1</c> function.</p>
- <p>Failure: If the calling process was not started by a
- <c>proc_lib</c> start function, or if it is not registered
- according to <c>FsmName</c>.</p>
+ <p>Whenever a <c>gen_fsm</c> process receives an event sent using
+ <seealso marker="#sync_send_all_state_event/2">
+ <c>sync_send_all_state_event/2,3</c></seealso>,
+ this function is called to handle the event.</p>
+ <p><c>StateName</c> is the current state name of the <c>gen_fsm</c>
+ process.</p>
+ <p>For a description of the other arguments and possible return values,
+ see <seealso marker="#Module:StateName/3">
+ <c>Module:StateName/3</c></seealso>.</p>
</desc>
</func>
- </funcs>
- <section>
- <title>CALLBACK FUNCTIONS</title>
- <p>The following functions should be exported from a <c>gen_fsm</c>
- callback module.</p>
- <p>In the description, the expression <em>state name</em> is used to
- denote a state of the state machine. <em>state data</em> is used
- to denote the internal state of the Erlang process which
- implements the state machine.</p>
- </section>
- <funcs>
<func>
<name>Module:init(Args) -> Result</name>
- <fsummary>Initialize process and internal state name and state data.</fsummary>
+ <fsummary>Initialize process and internal state name and state data.
+ </fsummary>
<type>
<v>Args = term()</v>
<v>Result = {ok,StateName,StateData} | {ok,StateName,StateData,Timeout}</v>
- <v>&nbsp;&nbsp;| {ok,StateName,StateData,hibernate}</v>
+ <v>&nbsp;&nbsp;| {ok,StateName,StateData,hibernate}</v>
<v>&nbsp;&nbsp;| {stop,Reason} | ignore</v>
<v>&nbsp;StateName = atom()</v>
<v>&nbsp;StateData = term()</v>
@@ -515,33 +751,36 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
</type>
<desc>
<marker id="Moduleinit"></marker>
- <p>Whenever a gen_fsm is started using
- <seealso marker="#start/3">gen_fsm:start/3,4</seealso> or
- <seealso marker="#start_link/3">gen_fsm:start_link/3,4</seealso>,
+ <p>Whenever a <c>gen_fsm</c> process is started using
+ <seealso marker="#start/3"><c>start/3,4</c></seealso> or
+ <seealso marker="#start_link/3"><c>start_link/3,4</c></seealso>,
this function is called by the new process to initialize.</p>
<p><c>Args</c> is the <c>Args</c> argument provided to the start
function.</p>
- <p>If initialization is successful, the function should return
- <c>{ok,StateName,StateData}</c>,
- <c>{ok,StateName,StateData,Timeout}</c> or <c>{ok,StateName,StateData,hibernate}</c>,
- where <c>StateName</c>
+ <p>If initialization is successful, the function is to return
+ <c>{ok,StateName,StateData}</c>,
+ <c>{ok,StateName,StateData,Timeout}</c>, or
+ <c>{ok,StateName,StateData,hibernate}</c>, where <c>StateName</c>
is the initial state name and <c>StateData</c> the initial
- state data of the gen_fsm.</p>
- <p>If an integer timeout value is provided, a timeout will occur
+ state data of the <c>gen_fsm</c> process.</p>
+ <p>If an integer time-out value is provided, a time-out occurs
unless an event or a message is received within <c>Timeout</c>
- milliseconds. A timeout is represented by the atom
- <c>timeout</c> and should be handled by
- the <c>Module:StateName/2</c> callback functions. The atom
+ milliseconds. A time-out is represented by the atom
+ <c>timeout</c> and is to be handled by the
+ <seealso marker="#Module:StateName/2">
+ <c>Module:StateName/2</c></seealso> callback functions. The atom
<c>infinity</c> can be used to wait indefinitely, this is
the default value.</p>
- <p>If <c>hibernate</c> is specified instead of a timeout value, the process will go
- into hibernation when waiting for the next message to arrive (by calling
- <seealso marker="proc_lib#hibernate/3">proc_lib:hibernate/3</seealso>).</p>
- <p>If something goes wrong during the initialization
- the function should return <c>{stop,Reason}</c>, where
- <c>Reason</c> is any term, or <c>ignore</c>.</p>
+ <p>If <c>hibernate</c> is specified instead of a time-out value, the
+ process goes into hibernation when waiting for the next message
+ to arrive (by calling <seealso marker="proc_lib#hibernate/3">
+ <c>proc_lib:hibernate/3</c></seealso>).</p>
+ <p>If the initialization fails, the function returns
+ <c>{stop,Reason}</c>, where <c>Reason</c> is any term,
+ or <c>ignore</c>.</p>
</desc>
</func>
+
<func>
<name>Module:StateName(Event, StateData) -> Result</name>
<fsummary>Handle an asynchronous event.</fsummary>
@@ -549,8 +788,8 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
<v>Event = timeout | term()</v>
<v>StateData = term()</v>
<v>Result = {next_state,NextStateName,NewStateData} </v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
<v>&nbsp;&nbsp;| {stop,Reason,NewStateData}</v>
<v>&nbsp;NextStateName = atom()</v>
<v>&nbsp;NewStateData = term()</v>
@@ -558,56 +797,33 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
<v>&nbsp;Reason = term()</v>
</type>
<desc>
- <p>There should be one instance of this function for each
- possible state name. Whenever a gen_fsm receives an event
- sent using
- <seealso marker="#send_event/2">gen_fsm:send_event/2</seealso>,
+ <p>There is to be one instance of this function for each
+ possible state name. Whenever a <c>gen_fsm</c> process receives
+ an event sent using
+ <seealso marker="#send_event/2"><c>send_event/2</c></seealso>,
the instance of this function with the same name as
the current state name <c>StateName</c> is called to handle
- the event. It is also called if a timeout occurs.</p>
- <p><c>Event</c> is either the atom <c>timeout</c>, if a timeout
+ the event. It is also called if a time-out occurs.</p>
+ <p><c>Event</c> is either the atom <c>timeout</c>, if a time-out
has occurred, or the <c>Event</c> argument provided to
<c>send_event/2</c>.</p>
- <p><c>StateData</c> is the state data of the gen_fsm.</p>
+ <p><c>StateData</c> is the state data of the <c>gen_fsm</c> process.</p>
<p>If the function returns
<c>{next_state,NextStateName,NewStateData}</c>,
- <c>{next_state,NextStateName,NewStateData,Timeout}</c> or
- <c>{next_state,NextStateName,NewStateData,hibernate}</c>,
- the gen_fsm will continue executing with the current state
+ <c>{next_state,NextStateName,NewStateData,Timeout}</c>, or
+ <c>{next_state,NextStateName,NewStateData,hibernate}</c>, the
+ <c>gen_fsm</c> process continues executing with the current state
name set to <c>NextStateName</c> and with the possibly
- updated state data <c>NewStateData</c>. See
- <c>Module:init/1</c> for a description of <c>Timeout</c> and <c>hibernate</c>.</p>
+ updated state data <c>NewStateData</c>. For a description of
+ <c>Timeout</c> and <c>hibernate</c>, see
+ <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>.</p>
<p>If the function returns <c>{stop,Reason,NewStateData}</c>,
- the gen_fsm will call
+ the <c>gen_fsm</c> process calls
<c>Module:terminate(Reason,StateName,NewStateData)</c> and
- terminate.</p>
- </desc>
- </func>
- <func>
- <name>Module:handle_event(Event, StateName, StateData) -> Result</name>
- <fsummary>Handle an asynchronous event.</fsummary>
- <type>
- <v>Event = term()</v>
- <v>StateName = atom()</v>
- <v>StateData = term()</v>
- <v>Result = {next_state,NextStateName,NewStateData} </v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
- <v>&nbsp;&nbsp;| {stop,Reason,NewStateData}</v>
- <v>&nbsp;NextStateName = atom()</v>
- <v>&nbsp;NewStateData = term()</v>
- <v>&nbsp;Timeout = int()>0 | infinity</v>
- <v>&nbsp;Reason = term()</v>
- </type>
- <desc>
- <p>Whenever a gen_fsm receives an event sent using
- <seealso marker="#send_all_state_event/2">gen_fsm:send_all_state_event/2</seealso>,
- this function is called to handle the event.</p>
- <p><c>StateName</c> is the current state name of the gen_fsm.</p>
- <p>See <c>Module:StateName/2</c> for a description of the other
- arguments and possible return values.</p>
+ terminates.</p>
</desc>
</func>
+
<func>
<name>Module:StateName(Event, From, StateData) -> Result</name>
<fsummary>Handle a synchronous event.</fsummary>
@@ -616,11 +832,11 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
<v>From = {pid(),Tag}</v>
<v>StateData = term()</v>
<v>Result = {reply,Reply,NextStateName,NewStateData}</v>
- <v>&nbsp;&nbsp;| {reply,Reply,NextStateName,NewStateData,Timeout}</v>
- <v>&nbsp;&nbsp;| {reply,Reply,NextStateName,NewStateData,hibernate}</v>
+ <v>&nbsp;&nbsp;| {reply,Reply,NextStateName,NewStateData,Timeout}</v>
+ <v>&nbsp;&nbsp;| {reply,Reply,NextStateName,NewStateData,hibernate}</v>
<v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
+ <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
<v>&nbsp;&nbsp;| {stop,Reason,Reply,NewStateData} | {stop,Reason,NewStateData}</v>
<v>&nbsp;Reply = term()</v>
<v>&nbsp;NextStateName = atom()</v>
@@ -629,102 +845,56 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
<v>&nbsp;Reason = normal | term()</v>
</type>
<desc>
- <p>There should be one instance of this function for each
- possible state name. Whenever a gen_fsm receives an event
- sent using
- <seealso marker="#sync_send_event/2">gen_fsm:sync_send_event/2,3</seealso>,
+ <p>There is to be one instance of this function for each
+ possible state name. Whenever a <c>gen_fsm</c> process receives an
+ event sent using <seealso marker="#sync_send_event/2">
+ <c>sync_send_event/2,3</c></seealso>,
the instance of this function with the same name as
the current state name <c>StateName</c> is called to handle
the event.</p>
<p><c>Event</c> is the <c>Event</c> argument provided to
- <c>sync_send_event</c>.</p>
+ <c>sync_send_event/2,3</c>.</p>
<p><c>From</c> is a tuple <c>{Pid,Tag}</c> where <c>Pid</c> is
- the pid of the process which called <c>sync_send_event/2,3</c>
+ the pid of the process that called <c>sync_send_event/2,3</c>
and <c>Tag</c> is a unique tag.</p>
- <p><c>StateData</c> is the state data of the gen_fsm.</p>
- <p>If the function returns
- <c>{reply,Reply,NextStateName,NewStateData}</c>,
- <c>{reply,Reply,NextStateName,NewStateData,Timeout}</c> or
- <c>{reply,Reply,NextStateName,NewStateData,hibernate}</c>,
- <c>Reply</c> will be given back to <c>From</c> as the return
- value of <c>sync_send_event/2,3</c>. The gen_fsm then
- continues executing with the current state name set to
- <c>NextStateName</c> and with the possibly updated state data
- <c>NewStateData</c>. See <c>Module:init/1</c> for a
- description of <c>Timeout</c> and <c>hibernate</c>.</p>
- <p>If the function returns
- <c>{next_state,NextStateName,NewStateData}</c>,
- <c>{next_state,NextStateName,NewStateData,Timeout}</c> or
- <c>{next_state,NextStateName,NewStateData,hibernate}</c>,
- the gen_fsm will continue executing in <c>NextStateName</c>
- with <c>NewStateData</c>. Any reply to <c>From</c> must be
- given explicitly using
- <seealso marker="#reply/2">gen_fsm:reply/2</seealso>.</p>
- <p>If the function returns
- <c>{stop,Reason,Reply,NewStateData}</c>, <c>Reply</c> will be
- given back to <c>From</c>. If the function returns
- <c>{stop,Reason,NewStateData}</c>, any reply to <c>From</c>
- must be given explicitly using <c>gen_fsm:reply/2</c>.
- The gen_fsm will then call
- <c>Module:terminate(Reason,StateName,NewStateData)</c> and
- terminate.</p>
- </desc>
- </func>
- <func>
- <name>Module:handle_sync_event(Event, From, StateName, StateData) -> Result</name>
- <fsummary>Handle a synchronous event.</fsummary>
- <type>
- <v>Event = term()</v>
- <v>From = {pid(),Tag}</v>
- <v>StateName = atom()</v>
- <v>StateData = term()</v>
- <v>Result = {reply,Reply,NextStateName,NewStateData}</v>
- <v>&nbsp;&nbsp;| {reply,Reply,NextStateName,NewStateData,Timeout}</v>
- <v>&nbsp;&nbsp;| {reply,Reply,NextStateName,NewStateData,hibernate}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
- <v>&nbsp;&nbsp;| {stop,Reason,Reply,NewStateData} | {stop,Reason,NewStateData}</v>
- <v>&nbsp;Reply = term()</v>
- <v>&nbsp;NextStateName = atom()</v>
- <v>&nbsp;NewStateData = term()</v>
- <v>&nbsp;Timeout = int()>0 | infinity</v>
- <v>&nbsp;Reason = term()</v>
- </type>
- <desc>
- <p>Whenever a gen_fsm receives an event sent using
- <seealso marker="#sync_send_all_state_event/2">gen_fsm:sync_send_all_state_event/2,3</seealso>,
- this function is called to handle the event.</p>
- <p><c>StateName</c> is the current state name of the gen_fsm.</p>
- <p>See <c>Module:StateName/3</c> for a description of the other
- arguments and possible return values.</p>
- </desc>
- </func>
- <func>
- <name>Module:handle_info(Info, StateName, StateData) -> Result</name>
- <fsummary>Handle an incoming message.</fsummary>
- <type>
- <v>Info = term()</v>
- <v>StateName = atom()</v>
- <v>StateData = term()</v>
- <v>Result = {next_state,NextStateName,NewStateData}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,Timeout}</v>
- <v>&nbsp;&nbsp;| {next_state,NextStateName,NewStateData,hibernate}</v>
- <v>&nbsp;&nbsp;| {stop,Reason,NewStateData}</v>
- <v>&nbsp;NextStateName = atom()</v>
- <v>&nbsp;NewStateData = term()</v>
- <v>&nbsp;Timeout = int()>0 | infinity</v>
- <v>&nbsp;Reason = normal | term()</v>
- </type>
- <desc>
- <p>This function is called by a gen_fsm when it receives any
- other message than a synchronous or asynchronous event (or a
- system message).</p>
- <p><c>Info</c> is the received message.</p>
- <p>See <c>Module:StateName/2</c> for a description of the other
- arguments and possible return values.</p>
+ <p><c>StateData</c> is the state data of the <c>gen_fsm</c> process.</p>
+ <list type="bulleted">
+ <item>
+ <p>If <c>{reply,Reply,NextStateName,NewStateData}</c>,
+ <c>{reply,Reply,NextStateName,NewStateData,Timeout}</c>, or
+ <c>{reply,Reply,NextStateName,NewStateData,hibernate}</c> is
+ returned, <c>Reply</c> is given back to <c>From</c> as the return
+ value of <c>sync_send_event/2,3</c>. The <c>gen_fsm</c> process
+ then continues executing with the current state name set to
+ <c>NextStateName</c> and with the possibly updated state data
+ <c>NewStateData</c>. For a description of <c>Timeout</c> and
+ <c>hibernate</c>, see
+ <seealso marker="#Module:init/1">
+ <c>Module:init/1</c></seealso>.</p>
+ </item>
+ <item>
+ <p>If <c>{next_state,NextStateName,NewStateData}</c>,
+ <c>{next_state,NextStateName,NewStateData,Timeout}</c>, or
+ <c>{next_state,NextStateName,NewStateData,hibernate}</c> is
+ returned, the <c>gen_fsm</c> process continues executing in
+ <c>NextStateName</c> with <c>NewStateData</c>.
+ Any reply to <c>From</c> must be specified explicitly using
+ <seealso marker="#reply/2"><c>reply/2</c></seealso>.</p>
+ </item>
+ <item>
+ <p>If the function returns
+ <c>{stop,Reason,Reply,NewStateData}</c>, <c>Reply</c> is
+ given back to <c>From</c>. If the function returns
+ <c>{stop,Reason,NewStateData}</c>, any reply to <c>From</c>
+ must be specified explicitly using <c>reply/2</c>.
+ The <c>gen_fsm</c> process then calls
+ <c>Module:terminate(Reason,StateName,NewStateData)</c> and
+ terminates.</p>
+ </item>
+ </list>
</desc>
</func>
+
<func>
<name>Module:terminate(Reason, StateName, StateData)</name>
<fsummary>Clean up before termination.</fsummary>
@@ -734,134 +904,56 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
<v>StateData = term()</v>
</type>
<desc>
- <p>This function is called by a gen_fsm when it is about to
- terminate. It should be the opposite of <c>Module:init/1</c>
- and do any necessary cleaning up. When it returns, the gen_fsm
- terminates with <c>Reason</c>. The return value is ignored.</p>
+ <p>This function is called by a <c>gen_fsm</c> process when it is about
+ to terminate. It is to be the opposite of
+ <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
+ and do any necessary cleaning up. When it returns, the <c>gen_fsm</c>
+ process terminates with <c>Reason</c>. The return value is ignored.
+ </p>
<p><c>Reason</c> is a term denoting the stop reason,
<c>StateName</c> is the current state name, and
- <c>StateData</c> is the state data of the gen_fsm.</p>
- <p><c>Reason</c> depends on why the gen_fsm is terminating. If
+ <c>StateData</c> is the state data of the <c>gen_fsm</c> process.</p>
+ <p><c>Reason</c> depends on why the <c>gen_fsm</c> process is
+ terminating. If
it is because another callback function has returned a stop
- tuple <c>{stop,..}</c>, <c>Reason</c> will have the value
- specified in that tuple. If it is due to a failure,
+ tuple <c>{stop,..}</c>, <c>Reason</c> has the value
+ specified in that tuple. If it is because of a failure,
<c>Reason</c> is the error reason.</p>
- <p>If the gen_fsm is part of a supervision tree and is ordered
- by its supervisor to terminate, this function will be called
+ <p>If the <c>gen_fsm</c> process is part of a supervision tree and is
+ ordered by its supervisor to terminate, this function is called
with <c>Reason=shutdown</c> if the following conditions apply:</p>
<list type="bulleted">
- <item>the gen_fsm has been set to trap exit signals, and</item>
- <item>the shutdown strategy as defined in the supervisor's
- child specification is an integer timeout value, not
- <c>brutal_kill</c>.</item>
+ <item>
+ <p>The <c>gen_fsm</c> process has been set to trap exit signals.</p>
+ </item>
+ <item>
+ <p>The shutdown strategy as defined in the child specification of
+ the supervisor is an integer time-out value, not
+ <c>brutal_kill</c>.</p>
+ </item>
</list>
- <p>Even if the gen_fsm is <em>not</em> part of a supervision tree,
- this function will be called if it receives an <c>'EXIT'</c>
- message from its parent. <c>Reason</c> will be the same as in
- the <c>'EXIT'</c> message.</p>
- <p>Otherwise, the gen_fsm will be immediately terminated.</p>
- <p>Note that for any other reason than <c>normal</c>,
- <c>shutdown</c>, or <c>{shutdown,Term}</c> the gen_fsm is
- assumed to terminate due to an error and
- an error report is issued using
- <seealso marker="kernel:error_logger#format/2">error_logger:format/2</seealso>.</p>
- </desc>
- </func>
- <func>
- <name>Module:code_change(OldVsn, StateName, StateData, Extra) -> {ok, NextStateName, NewStateData}</name>
- <fsummary>Update the internal state data during upgrade/downgrade.</fsummary>
- <type>
- <v>OldVsn = Vsn | {down, Vsn}</v>
- <v>&nbsp;&nbsp;Vsn = term()</v>
- <v>StateName = NextStateName = atom()</v>
- <v>StateData = NewStateData = term()</v>
- <v>Extra = term()</v>
- </type>
- <desc>
- <p>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 <c>{update,Module,Change,...}</c>
- where <c>Change={advanced,Extra}</c> is given in
- the <c>appup</c> file. See
- <seealso marker="doc/design_principles:release_handling#instr">OTP Design Principles</seealso>.</p>
- <p>In the case of an upgrade, <c>OldVsn</c> is <c>Vsn</c>, and
- in the case of a downgrade, <c>OldVsn</c> is
- <c>{down,Vsn}</c>. <c>Vsn</c> is defined by the <c>vsn</c>
- attribute(s) of the old version of the callback module
- <c>Module</c>. If no such attribute is defined, the version is
- the checksum of the BEAM file.</p>
- <p><c>StateName</c> is the current state name and
- <c>StateData</c> the internal state data of the gen_fsm.</p>
- <p><c>Extra</c> is passed as-is from the <c>{advanced,Extra}</c>
- part of the update instruction.</p>
- <p>The function should return the new current state name and
- updated internal data.</p>
- </desc>
- </func>
- <func>
- <name>Module:format_status(Opt, [PDict, StateData]) -> Status</name>
- <fsummary>Optional function for providing a term describing the
- current gen_fsm status.</fsummary>
- <type>
- <v>Opt = normal | terminate</v>
- <v>PDict = [{Key, Value}]</v>
- <v>StateData = term()</v>
- <v>Status = term()</v>
- </type>
- <desc>
- <note>
- <p>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.</p>
- </note>
- <p>This function is called by a gen_fsm process when:</p>
- <list type="bulleted">
- <item>One
- of <seealso marker="sys#get_status/1">sys:get_status/1,2</seealso>
- is invoked to get the gen_fsm status. <c>Opt</c> is set to
- the atom <c>normal</c> for this case.</item>
- <item>The gen_fsm terminates abnormally and logs an
- error. <c>Opt</c> is set to the atom <c>terminate</c> for
- this case.</item>
- </list>
- <p>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 <c>sys:get_status/1,2</c>
- return value as well as how its status appears in
- termination error logs exports an instance
- of <c>format_status/2</c> that returns a term describing the
- current status of the gen_fsm.</p>
- <p><c>PDict</c> is the current value of the gen_fsm's
- process dictionary.</p>
- <p><c>StateData</c> is the internal state data of the
- gen_fsm.</p>
- <p>The function should return <c>Status</c>, a term that
- customises the details of the current state and status of
- the gen_fsm. There are no restrictions on the
- form <c>Status</c> can take, but for
- the <c>sys:get_status/1,2</c> case (when <c>Opt</c>
- is <c>normal</c>), the recommended form for
- the <c>Status</c> value is <c>[{data, [{"StateData",
- Term}]}]</c> where <c>Term</c> 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 <c>sys:get_status/1,2</c>
- return value.</p>
- <p>One use for this function is to return compact alternative
- state data representations to avoid having large state terms
- printed in logfiles.</p>
+ <p>Even if the <c>gen_fsm</c> process is <em>not</em> part of a
+ supervision tree,
+ this function is called if it receives an <c>'EXIT'</c>
+ message from its parent. <c>Reason</c> is the same as in
+ the <c>'EXIT'</c> message.</p>
+ <p>Otherwise, the <c>gen_fsm</c> process terminates immediately.</p>
+ <p>Notice that for any other reason than <c>normal</c>,
+ <c>shutdown</c>, or <c>{shutdown,Term}</c> the <c>gen_fsm</c> process
+ is assumed to terminate because of an error and an error report is
+ issued using <seealso marker="kernel:error_logger#format/2">
+ <c>error_logger:format/2</c></seealso>.</p>
</desc>
</func>
</funcs>
<section>
- <title>SEE ALSO</title>
- <p><seealso marker="gen_event">gen_event(3)</seealso>,
- <seealso marker="gen_server">gen_server(3)</seealso>,
- <seealso marker="gen_statem">gen_statem(3)</seealso>,
- <seealso marker="supervisor">supervisor(3)</seealso>,
- <seealso marker="proc_lib">proc_lib(3)</seealso>,
- <seealso marker="sys">sys(3)</seealso></p>
+ <title>See Also</title>
+ <p><seealso marker="gen_event"><c>gen_event(3)</c></seealso>,
+ <seealso marker="gen_server"><c>gen_server(3)</c></seealso>,
+ <seealso marker="gen_statem"><c>gen_statem(3)</c></seealso>,
+ <seealso marker="proc_lib"><c>proc_lib(3)</c></seealso>,
+ <seealso marker="supervisor"><c>supervisor(3)</c></seealso>,
+ <seealso marker="sys"><c>sys(3)</c></seealso></p>
</section>
</erlref>