diff options
Diffstat (limited to 'lib/stdlib/doc/src/gen_statem.xml')
| -rw-r--r-- | lib/stdlib/doc/src/gen_statem.xml | 1056 |
1 files changed, 782 insertions, 274 deletions
diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml index c57a31fa21..a7caa71dcb 100644 --- a/lib/stdlib/doc/src/gen_statem.xml +++ b/lib/stdlib/doc/src/gen_statem.xml @@ -4,7 +4,7 @@ <erlref> <header> <copyright> - <year>2016</year> + <year>2016</year><year>2017</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -54,30 +54,37 @@ <p> This is a new behavior in Erlang/OTP 19.0. It has been thoroughly reviewed, is stable enough - to be used by at least two heavy OTP applications, and is here to stay. + to be used by at least two heavy OTP applications, + and is here to stay. Depending on user feedback, we do not expect but can find it necessary to make minor not backward compatible changes into Erlang/OTP 20.0. </p> </note> <p> - The <c>gen_statem</c> behavior is intended to replace - <seealso marker="gen_fsm"><c>gen_fsm</c></seealso> for new code. + The <c>gen_statem</c> behavior replaces + <seealso marker="gen_fsm"><c>gen_fsm</c> </seealso> in Erlang/OTP 20.0. It has the same features and adds some really useful: </p> <list type="bulleted"> - <item>State code is gathered.</item> - <item>The state can be any term.</item> - <item>Events can be postponed.</item> - <item>Events can be self-generated.</item> - <item>A reply can be sent from a later state.</item> - <item>There can be multiple <c>sys</c> traceable replies.</item> + <item>Gathered state code.</item> + <item>Arbitrary term state.</item> + <item>Event postponing.</item> + <item>Self-generated events.</item> + <item>State time-out.</item> + <item>Multiple generic named time-outs.</item> + <item>Absolute time-out time.</item> + <item>Automatic state enter calls.</item> + <item>Reply from other state than the request.</item> + <item>Multiple <c>sys</c> traceable replies.</item> </list> <p> The callback model(s) for <c>gen_statem</c> differs from the one for <seealso marker="gen_fsm"><c>gen_fsm</c></seealso>, - but it is still fairly easy to rewrite - from <c>gen_fsm</c> to <c>gen_statem</c>. + but it is still fairly easy to + <seealso marker="gen_fsm#Migration to gen_statem"> + rewrite from + </seealso> <c>gen_fsm</c> to <c>gen_statem</c>. </p> <p> A generic state machine process (<c>gen_statem</c>) implemented @@ -97,6 +104,9 @@ gen_statem module Callback module gen_statem:start gen_statem:start_link -----> Module:init/1 +Server start or code change + -----> Module:callback_mode/0 + gen_statem:stop -----> Module:terminate/3 gen_statem:call @@ -116,37 +126,40 @@ erlang:'!' -----> Module:StateName/3 </p> <p> If a callback function fails or returns a bad value, - the <c>gen_statem</c> terminates. However, an exception of class + the <c>gen_statem</c> terminates, unless otherwise stated. + However, an exception of class <seealso marker="erts:erlang#throw/1"><c>throw</c></seealso> - is not regarded as an error but as a valid return. + is not regarded as an error but as a valid return + from all callback functions. </p> - <marker id="state_function"/> + <marker id="state callback"/> <p> - The "<em>state function</em>" for a specific + The "<em>state callback</em>" for a specific <seealso marker="#type-state">state</seealso> in a <c>gen_statem</c> is the callback function that is called for all events in this state. It is selected depending on which <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> - that the implementation specifies when the server starts. + that the callback module defines with the callback function + <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>. </p> <p> When the <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> is <c>state_functions</c>, the state must be an atom and - is used as the state function name; see + is used as the state callback name; see <seealso marker="#Module:StateName/3"><c>Module:StateName/3</c></seealso>. This gathers all code for a specific state in one function as the <c>gen_statem</c> engine branches depending on state name. - Notice that in this mode the mandatory callback function + Note the fact that the callback function <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso> - makes the state name <c>terminate</c> unusable. + makes the state name <c>terminate</c> unusable in this mode. </p> <p> When the <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> is <c>handle_event_function</c>, the state can be any term - and the state function name is + and the state callback name is <seealso marker="#Module:handle_event/4"><c>Module:handle_event/4</c></seealso>. This makes it easy to branch depending on state or event as you desire. Be careful about which events you handle in which @@ -156,8 +169,8 @@ erlang:'!' -----> Module:StateName/3 <p> The <c>gen_statem</c> enqueues incoming events in order of arrival and presents these to the - <seealso marker="#state_function">state function</seealso> - in that order. The state function can postpone an event + <seealso marker="#state callback">state callback</seealso> + in that order. The state callback can postpone an event so it is not retried in the current state. After a state change the queue restarts with the postponed events. </p> @@ -169,12 +182,12 @@ erlang:'!' -----> Module:StateName/3 to entering a new receive statement. </p> <p> - The <seealso marker="#state_function">state function</seealso> + The <seealso marker="#state callback">state callback</seealso> can insert events using the <seealso marker="#type-action"><c>action()</c></seealso> <c>next_event</c> and such an event is inserted as the next to present - to the state function. That is, as if it is + to the state callback. That is, as if it is the oldest incoming event. A dedicated <seealso marker="#type-event_type"><c>event_type()</c></seealso> <c>internal</c> can be used for such events making them impossible @@ -187,9 +200,19 @@ erlang:'!' -----> Module:StateName/3 <seealso marker="gen_fsm"><c>gen_fsm</c></seealso> to force processing an inserted event before others. </p> + <p> + The <c>gen_statem</c> engine can automatically + make a specialized call to the + <seealso marker="#state callback">state callback</seealso> + whenever a new state is entered; see + <seealso marker="#type-state_enter"><c>state_enter()</c></seealso>. + This is for writing code common to all state entries. + Another way to do it is to insert events at state transitions, + but you have to do so everywhere it is needed. + </p> <note> <p>If you in <c>gen_statem</c>, for example, postpone - an event in one state and then call another state function + an event in one state and then call another state callback of yours, you have not changed states and hence the postponed event is not retried, which is logical but can be confusing. </p> @@ -218,7 +241,7 @@ erlang:'!' -----> Module:StateName/3 The <c>gen_statem</c> process can go into hibernation; see <seealso marker="proc_lib#hibernate/3"><c>proc_lib:hibernate/3</c></seealso>. It is done when a - <seealso marker="#state_function">state function</seealso> or + <seealso marker="#state callback">state callback</seealso> or <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> specifies <c>hibernate</c> in the returned <seealso marker="#type-action"><c>Actions</c></seealso> @@ -249,11 +272,10 @@ erlang:'!' -----> Module:StateName/3 -behaviour(gen_statem). -export([start/0,push/0,get_count/0,stop/0]). --export([terminate/3,code_change/4,init/1]). +-export([terminate/3,code_change/4,init/1,callback_mode/0]). -export([on/3,off/3]). name() -> pushbutton_statem. % The registered server name -callback_mode() -> state_functions. %% API. This example uses a registered name name() %% and does not link to the caller. @@ -270,15 +292,14 @@ stop() -> terminate(_Reason, _State, _Data) -> void. code_change(_Vsn, State, Data, _Extra) -> - {callback_mode(),State,Data}. + {ok,State,Data}. init([]) -> - %% Set the callback mode and initial state + data. - %% Data is used only as a counter. + %% Set the initial state + data. Data is used only as a counter. State = off, Data = 0, - {callback_mode(),State,Data}. - + {ok,State,Data}. +callback_mode() -> state_functions. -%%% State functions +%%% state callback(s) off({call,From}, push, Data) -> %% Go to 'on', increment count and reply @@ -325,19 +346,14 @@ ok <p> To compare styles, here follows the same example using <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> - <c>state_functions</c>, or rather the code to replace - from function <c>init/1</c> of the <c>pushbutton.erl</c> + <c>handle_event_function</c>, or rather the code to replace + after function <c>init/1</c> of the <c>pushbutton.erl</c> example file above: </p> <code type="erl"> -init([]) -> - %% Set the callback mode and initial state + data. - %% Data is used only as a counter. - State = off, Data = 0, - {handle_event_function,State,Data}. - +callback_mode() -> handle_event_function. -%%% Event handling +%%% state callback(s) handle_event({call,From}, push, off, Data) -> %% Go to 'on', increment count and reply @@ -426,8 +442,8 @@ handle_event(_, _, State, Data) -> <desc> <p> Debug option that can be used when starting - a <c>gen_statem</c> server through, for example, - <seealso marker="#enter_loop/5"><c>enter_loop/5</c></seealso>. + a <c>gen_statem</c> server through, + <seealso marker="#enter_loop/4"><c>enter_loop/4-6</c></seealso>. </p> <p> For every entry in <c><anno>Dbgs</anno></c>, @@ -437,6 +453,21 @@ handle_event(_, _, State, Data) -> </desc> </datatype> <datatype> + <name name="hibernate_after_opt"/> + <desc> + <p> + hibernate_after option that can be used when starting + a <c>gen_statem</c> server through, + <seealso marker="#enter_loop/4"><c>enter_loop/4-6</c></seealso>. + </p> + <p>If option<seealso marker="#type-hibernate_after_opt"><c>{hibernate_after,HibernateAfterTimeout}</c></seealso> is present, the <c>gen_statem</c> + process awaits any message for <c>HibernateAfterTimeout</c> milliseconds and + if no message is received, the process goes into hibernation automatically + (by calling <seealso marker="proc_lib#hibernate/3"><c>proc_lib:hibernate/3</c></seealso>). + </p> + </desc> + </datatype> + <datatype> <name name="start_opt"/> <desc> <p> @@ -471,6 +502,10 @@ handle_event(_, _, State, Data) -> <name name="state"/> <desc> <p> + If the + <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> + is <c>handle_event_function</c>, + the state can be any term. After a state change (<c>NextState =/= State</c>), all postponed events are retried. </p> @@ -484,6 +519,8 @@ handle_event(_, _, State, Data) -> <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> is <c>state_functions</c>, the state must be of this type. + After a state change (<c>NextState =/= State</c>), + all postponed events are retried. </p> </desc> </datatype> @@ -514,9 +551,26 @@ handle_event(_, _, State, Data) -> originate from the corresponding API functions. For calls, the event contains whom to reply to. Type <c>info</c> originates from regular process messages sent - to the <c>gen_statem</c>. Also, the state machine - implementation can generate events of types - <c>timeout</c> and <c>internal</c> to itself. + to the <c>gen_statem</c>. The state machine + implementation can, in addition to the above, + generate + <seealso marker="#type-event_type"><c>events of types</c></seealso> + <c>timeout</c>, <c>{timeout,<anno>Name</anno>}</c>, + <c>state_timeout</c>, and <c>internal</c> to itself. + </p> + </desc> + </datatype> + <datatype> + <name name="callback_mode_result"/> + <desc> + <p> + This is the return type from + <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso> + and selects + <seealso marker="#type-callback_mode">callback mode</seealso> + and whether to do + <seealso marker="#type-state_enter">state enter calls</seealso>, + or not. </p> </desc> </datatype> @@ -525,12 +579,9 @@ handle_event(_, _, State, Data) -> <desc> <p> The <em>callback mode</em> is selected when starting the - <c>gen_statem</c> using the return value from - <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> - or when calling - <seealso marker="#enter_loop/5"><c>enter_loop/5,6,7</c></seealso>, - and with the return value from - <seealso marker="#Module:code_change/4"><c>Module:code_change/4</c></seealso>. + <c>gen_statem</c> and after code change + using the return value from + <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>. </p> <taglist> <tag><c>state_functions</c></tag> @@ -555,16 +606,93 @@ handle_event(_, _, State, Data) -> </desc> </datatype> <datatype> + <name name="state_enter"/> + <desc> + <p> + Whether the state machine should use <em>state enter calls</em> + or not is selected when starting the <c>gen_statem</c> + and after code change using the return value from + <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>. + </p> + <p> + If + <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso> + returns a list containing <c>state_enter</c>, + the <c>gen_statem</c> engine will, at every state change, + call the + <seealso marker="#state callback">state callback</seealso> + with arguments <c>(enter, OldState, Data)</c>. + This may look like an event but is really a call + performed after the previous state callback returned + and before any event is delivered to the new state callback. + See + <seealso marker="#Module:StateName/3"><c>Module:StateName/3</c></seealso> + and + <seealso marker="#Module:handle_event/4"><c>Module:handle_event/4</c></seealso>. + Such a call can be repeated by returning a + <seealso marker="#type-state_callback_result"> + <c>repeat_state</c> + </seealso> + or + <seealso marker="#type-state_callback_result"> + <c>repeat_state_and_data</c> + </seealso> + tuple from the state callback. + </p> + <p> + If + <seealso marker="#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso> + does not return such a list, no state enter calls are done. + </p> + <p> + If + <seealso marker="#Module:code_change/4"><c>Module:code_change/4</c></seealso> + should transform the state to a state with a different + name it is still regarded as the same state so this + does not cause a state enter call. + </p> + <p> + Note that a state enter call <em>will</em> be done + right before entering the initial state even though this + formally is not a state change. + In this case <c>OldState</c> will be the same as <c>State</c>, + which can not happen for a subsequent state change, + but will happen when repeating the state enter call. + </p> + </desc> + </datatype> + <datatype> <name name="transition_option"/> <desc> <p> Transition options can be set by <seealso marker="#type-action">actions</seealso> - and they modify the following in how - the state transition is done: + and they modify how the state transition is done: </p> <list type="ordered"> <item> + <p> + If the state changes, is the initial state, + <seealso marker="#type-state_callback_result"> + <c>repeat_state</c> + </seealso> + or + <seealso marker="#type-state_callback_result"> + <c>repeat_state_and_data</c> + </seealso> + is used, and also + <seealso marker="#type-state_enter"><em>state enter calls</em></seealso> + are used, the <c>gen_statem</c> calls + the new state callback with arguments + <seealso marker="#type-state_enter">(enter, OldState, Data)</seealso>. + Any + <seealso marker="#type-enter_action"><c>actions</c></seealso> + returned from this call are handled as if they were + appended to the actions + returned by the state callback that changed states. + </p> + </item> + <item> <p> All <seealso marker="#type-action">actions</seealso> @@ -590,27 +718,47 @@ handle_event(_, _, State, Data) -> All events stored with <seealso marker="#type-action"><c>action()</c></seealso> <c>next_event</c> - are inserted in the queue to be processed before - all other events. + are inserted to be processed before the other queued events. </p> </item> <item> <p> - If an + Time-out timers + <seealso marker="#type-event_timeout"><c>event_timeout()</c></seealso>, + <seealso marker="#type-generic_timeout"><c>generic_timeout()</c></seealso> + and + <seealso marker="#type-state_timeout"><c>state_timeout()</c></seealso> + are handled. Time-outs with zero time are guaranteed to be + delivered to the state machine before any external + not yet received event so if there is such a time-out requested, + the corresponding time-out zero event is enqueued as + the newest event. + </p> + <p> + Any event cancels an <seealso marker="#type-event_timeout"><c>event_timeout()</c></seealso> - is set through - <seealso marker="#type-action"><c>action()</c></seealso> - <c>timeout</c>, - an event timer can be started or a time-out zero event - can be enqueued. + so a zero time event time-out is only generated + if the event queue is empty. + </p> + <p> + A state change cancels a + <seealso marker="#type-state_timeout"><c>state_timeout()</c></seealso> + and any new transition option of this type + belongs to the new state. + </p> + </item> + <item> + <p> + If there are enqueued events the + <seealso marker="#state callback">state callback</seealso> + for the possibly new state + is called with the oldest enqueued event, + and we start again from the top of this list. </p> </item> <item> <p> - The (possibly new) - <seealso marker="#state_function">state function</seealso> - is called with the oldest enqueued event if there is any, - otherwise the <c>gen_statem</c> goes into <c>receive</c> + Otherwise the <c>gen_statem</c> goes into <c>receive</c> or hibernation (if <seealso marker="#type-hibernate"><c>hibernate()</c></seealso> @@ -618,8 +766,11 @@ handle_event(_, _, State, Data) -> to wait for the next message. In hibernation the next non-system event awakens the <c>gen_statem</c>, or rather the next incoming message awakens the <c>gen_statem</c>, - but if it is a system event - it goes right back into hibernation. + but if it is a system event it goes right back into hibernation. + When a new message arrives the + <seealso marker="#state callback">state callback</seealso> + is called with the corresponding event, + and we start again from the top of this list. </p> </item> </list> @@ -657,41 +808,140 @@ handle_event(_, _, State, Data) -> <name name="event_timeout"/> <desc> <p> - Generates an event of + Starts a timer set by + <seealso marker="#type-enter_action"><c>enter_action()</c></seealso> + <c>timeout</c>. + When the timer expires an event of <seealso marker="#type-event_type"><c>event_type()</c></seealso> - <c>timeout</c> - after this time (in milliseconds) unless another - event arrives in which case this time-out is cancelled. - Notice that a retried or inserted event - counts like a new in this respect. + <c>timeout</c> will be generated. + See + <seealso marker="erts:erlang#start_timer/4"><c>erlang:start_timer/4</c></seealso> + for how <c>Time</c> and + <seealso marker="#type-timeout_option"><c>Options</c></seealso> + are interpreted. Future <c>erlang:start_timer/4</c> <c>Options</c> + will not necessarily be supported. </p> <p> - If the value is <c>infinity</c>, no timer is started, as - it never triggers anyway. + Any event that arrives cancels this time-out. + Note that a retried or inserted event counts as arrived. + So does a state time-out zero event, if it was generated + before this time-out is requested. </p> <p> - If the value is <c>0</c>, the time-out event is immediately enqueued - unless there already are enqueued events, as the - time-out is then immediately cancelled. - This is a feature ensuring that a time-out <c>0</c> event - is processed before any not yet received external event. + If <c>Time</c> is <c>infinity</c>, + no timer is started, as it never would expire anyway. </p> <p> - Notice that it is not possible or needed to cancel this time-out, + If <c>Time</c> is relative and <c>0</c> + no timer is actually started, + instead the the time-out event is enqueued to ensure + that it gets processed before any not yet + received external event. + </p> + <p> + Note that it is not possible nor needed to cancel this time-out, as it is cancelled automatically by any other event. </p> </desc> </datatype> <datatype> + <name name="generic_timeout"/> + <desc> + <p> + Starts a timer set by + <seealso marker="#type-enter_action"><c>enter_action()</c></seealso> + <c>{timeout,Name}</c>. + When the timer expires an event of + <seealso marker="#type-event_type"><c>event_type()</c></seealso> + <c>{timeout,Name}</c> will be generated. + See + <seealso marker="erts:erlang#start_timer/4"><c>erlang:start_timer/4</c></seealso> + for how <c>Time</c> and + <seealso marker="#type-timeout_option"><c>Options</c></seealso> + are interpreted. Future <c>erlang:start_timer/4</c> <c>Options</c> + will not necessarily be supported. + </p> + <p> + If <c>Time</c> is <c>infinity</c>, + no timer is started, as it never would expire anyway. + </p> + <p> + If <c>Time</c> is relative and <c>0</c> + no timer is actually started, + instead the the time-out event is enqueued to ensure + that it gets processed before any not yet + received external event. + </p> + <p> + Setting a timer with the same <c>Name</c> while it is running + will restart it with the new time-out value. + Therefore it is possible to cancel + a specific time-out by setting it to <c>infinity</c>. + </p> + </desc> + </datatype> + <datatype> + <name name="state_timeout"/> + <desc> + <p> + Starts a timer set by + <seealso marker="#type-enter_action"><c>enter_action()</c></seealso> + <c>state_timeout</c>. + When the timer expires an event of + <seealso marker="#type-event_type"><c>event_type()</c></seealso> + <c>state_timeout</c> will be generated. + See + <seealso marker="erts:erlang#start_timer/4"><c>erlang:start_timer/4</c></seealso> + for how <c>Time</c> and + <seealso marker="#type-timeout_option"><c>Options</c></seealso> + are interpreted. Future <c>erlang:start_timer/4</c> <c>Options</c> + will not necessarily be supported. + </p> + <p> + If <c>Time</c> is <c>infinity</c>, + no timer is started, as it never would expire anyway. + </p> + <p> + If <c>Time</c> is relative and <c>0</c> + no timer is actually started, + instead the the time-out event is enqueued to ensure + that it gets processed before any not yet + received external event. + </p> + <p> + Setting this timer while it is running will restart it with + the new time-out value. Therefore it is possible to cancel + this time-out by setting it to <c>infinity</c>. + </p> + </desc> + </datatype> + <datatype> + <name name="timeout_option"/> + <desc> + <p> + If <c>Abs</c> is <c>true</c> an absolute timer is started, + and if it is <c>false</c> a relative, which is the default. + See + <seealso marker="erts:erlang#start_timer/4"><c>erlang:start_timer/4</c></seealso> + for details. + </p> + <p> + </p> + </desc> + </datatype> + <datatype> <name name="action"/> <desc> <p> These state transition actions can be invoked by returning them from the - <seealso marker="#state_function">state function</seealso>, from + <seealso marker="#state callback">state callback</seealso> + when it is called with an + <seealso marker="#type-event_type">event</seealso>, + from <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> or by giving them to - <seealso marker="#enter_loop/6"><c>enter_loop/6,7</c></seealso>. + <seealso marker="#enter_loop/5"><c>enter_loop/5,6</c></seealso>. </p> <p> Actions are executed in the containing list order. @@ -702,8 +952,8 @@ handle_event(_, _, State, Data) -> override any previous of the same type, so the last in the containing list wins. For example, the last - <seealso marker="#type-event_timeout"><c>event_timeout()</c></seealso> - overrides any other <c>event_timeout()</c> in the list. + <seealso marker="#type-postpone"><c>postpone()</c></seealso> + overrides any previous <c>postpone()</c> in the list. </p> <taglist> <tag><c>postpone</c></tag> @@ -720,6 +970,53 @@ handle_event(_, _, State, Data) -> as there is no event to postpone in those cases. </p> </item> + <tag><c>next_event</c></tag> + <item> + <p> + Stores the specified <c><anno>EventType</anno></c> + and <c><anno>EventContent</anno></c> for insertion after all + actions have been executed. + </p> + <p> + The stored events are inserted in the queue as the next to process + before any already queued events. The order of these stored events + is preserved, so the first <c>next_event</c> in the containing + list becomes the first to process. + </p> + <p> + An event of type + <seealso marker="#type-event_type"><c>internal</c></seealso> + is to be used when you want to reliably distinguish + an event inserted this way from any external event. + </p> + </item> + </taglist> + </desc> + </datatype> + <datatype> + <name name="enter_action"/> + <desc> + <p> + These state transition actions can be invoked by + returning them from the + <seealso marker="#state callback">state callback</seealso>, from + <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> + or by giving them to + <seealso marker="#enter_loop/5"><c>enter_loop/5,6</c></seealso>. + </p> + <p> + Actions are executed in the containing list order. + </p> + <p> + Actions that set + <seealso marker="#type-transition_option">transition options</seealso> + override any previous of the same type, + so the last in the containing list wins. + For example, the last + <seealso marker="#type-event_timeout"><c>event_timeout()</c></seealso> + overrides any previous <c>event_timeout()</c> in the list. + </p> + <taglist> <tag><c>hibernate</c></tag> <item> <p> @@ -735,10 +1032,9 @@ handle_event(_, _, State, Data) -> Short for <c>{timeout,Timeout,Timeout}</c>, that is, the time-out message is the time-out time. This form exists to make the - <seealso marker="#state_function">state function</seealso> + <seealso marker="#state callback">state callback</seealso> return value <c>{next_state,NextState,NewData,Timeout}</c> allowed like for <c>gen_fsm</c>'s - <seealso marker="gen_fsm#Module:StateName/2"><c>Module:StateName/2</c></seealso>. </p> </item> <tag><c>timeout</c></tag> @@ -747,33 +1043,32 @@ handle_event(_, _, State, Data) -> Sets the <seealso marker="#type-transition_option"><c>transition_option()</c></seealso> <seealso marker="#type-event_timeout"><c>event_timeout()</c></seealso> - to <c><anno>Time</anno></c> with <c><anno>EventContent</anno></c>. + to <c><anno>Time</anno></c> with <c><anno>EventContent</anno></c> + and time-out options + <seealso marker="#type-timeout_option"><c><anno>Options</anno></c></seealso>. </p> </item> - <tag><c>reply_action()</c></tag> + <tag><c>{timeout,<anno>Name</anno>}</c></tag> <item> <p> - Replies to a caller. + Sets the + <seealso marker="#type-transition_option"><c>transition_option()</c></seealso> + <seealso marker="#type-generic_timeout"><c>generic_timeout()</c></seealso> + to <c><anno>Time</anno></c> for <c><anno>Name</anno></c> + with <c><anno>EventContent</anno></c> + and time-out options + <seealso marker="#type-timeout_option"><c><anno>Options</anno></c></seealso>. </p> - </item> - <tag><c>next_event</c></tag> + </item> + <tag><c>state_timeout</c></tag> <item> <p> - Stores the specified <c><anno>EventType</anno></c> - and <c><anno>EventContent</anno></c> for insertion after all - actions have been executed. - </p> - <p> - The stored events are inserted in the queue as the next to process - before any already queued events. The order of these stored events - is preserved, so the first <c>next_event</c> in the containing - list becomes the first to process. - </p> - <p> - An event of type - <seealso marker="#type-event_type"><c>internal</c></seealso> - is to be used when you want to reliably distinguish - an event inserted this way from any external event. + Sets the + <seealso marker="#type-transition_option"><c>transition_option()</c></seealso> + <seealso marker="#type-state_timeout"><c>state_timeout()</c></seealso> + to <c><anno>Time</anno></c> with <c><anno>EventContent</anno></c> + and time-out options + <seealso marker="#type-timeout_option"><c><anno>Options</anno></c></seealso>. </p> </item> </taglist> @@ -783,39 +1078,97 @@ handle_event(_, _, State, Data) -> <name name="reply_action"/> <desc> <p> - Replies to a caller waiting for a reply in + This state transition action can be invoked by + returning it from the + <seealso marker="#state callback">state callback</seealso>, from + <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> + or by giving it to + <seealso marker="#enter_loop/5"><c>enter_loop/5,6</c></seealso>. + </p> + <p> + It replies to a caller waiting for a reply in <seealso marker="#call/2"><c>call/2</c></seealso>. <c><anno>From</anno></c> must be the term from argument <seealso marker="#type-event_type"><c>{call,<anno>From</anno>}</c></seealso> - to the - <seealso marker="#state_function">state function</seealso>. + in a call to a + <seealso marker="#state callback">state callback</seealso>. + </p> + <p> + Note that using this action from + <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> + or + <seealso marker="#enter_loop/5"><c>enter_loop/5,6</c></seealso> + would be weird on the border of witchcraft + since there has been no earlier call to a + <seealso marker="#state callback">state callback</seealso> + in this server. + </p> + </desc> + </datatype> + <datatype> + <name name="init_result"/> + <desc> + <p> + For a succesful initialization, + <c><anno>State</anno></c> is the initial + <seealso marker="#type-state"><c>state()</c></seealso> + and <c><anno>Data</anno></c> the initial server + <seealso marker="#type-data"><c>data()</c></seealso> + of the <c>gen_statem</c>. + </p> + <p> + The <seealso marker="#type-action"><c>Actions</c></seealso> + are executed when entering the first + <seealso marker="#type-state">state</seealso> just as for a + <seealso marker="#state callback">state callback</seealso>, + except that the action <c>postpone</c> is forced to + <c>false</c> since there is no event to postpone. + </p> + <p> + For an unsuccesful initialization, + <c>{stop,<anno>Reason</anno>}</c> + or <c>ignore</c> should be used; see + <seealso marker="#start_link/3"><c>start_link/3,4</c></seealso>. </p> </desc> </datatype> <datatype> - <name name="state_function_result"/> + <name name="state_enter_result"/> <desc> + <p> + <c><anno>State</anno></c> is the current state + and it can not be changed since the state callback + was called with a + <seealso marker="#type-state_enter"><em>state enter call</em></seealso>. + </p> <taglist> <tag><c>next_state</c></tag> <item> <p> The <c>gen_statem</c> does a state transition to - <c><anno>NextStateName</anno></c> - (which can be the same as the current state), + <c><anno>State</anno></c>, which has to be + the current state, sets <c><anno>NewData</anno></c>, and executes all <c><anno>Actions</anno></c>. </p> </item> </taglist> - <p> - All these terms are tuples or atoms and this property - will hold in any future version of <c>gen_statem</c>. - </p> </desc> </datatype> <datatype> - <name name="handle_event_result"/> + <name name="event_handler_result"/> <desc> + <p> + <c><anno>StateType</anno></c> is + <seealso marker="#type-state_name"><c>state_name()</c></seealso> + if + <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> + is <c>state_functions</c>, or + <seealso marker="#type-state"><c>state()</c></seealso> + if + <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> + is <c>handle_event_function</c>. + </p> <taglist> <tag><c>next_state</c></tag> <item> @@ -828,55 +1181,91 @@ handle_event(_, _, State, Data) -> </p> </item> </taglist> - <p> - All these terms are tuples or atoms and this property - will hold in any future version of <c>gen_statem</c>. - </p> </desc> </datatype> <datatype> - <name name="common_state_callback_result"/> + <name name="state_callback_result"/> <desc> + <p> + <c><anno>ActionType</anno></c> is + <seealso marker="#type-enter_action"><c>enter_action()</c></seealso> + if the state callback was called with a + <seealso marker="#type-state_enter"><em>state enter call</em></seealso> + and + <seealso marker="#type-action"><c>action()</c></seealso> + if the state callback was called with an event. + </p> <taglist> - <tag><c>stop</c></tag> + <tag><c>keep_state</c></tag> <item> <p> - Terminates the <c>gen_statem</c> by calling - <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso> - with <c>Reason</c> and - <c><anno>NewData</anno></c>, if specified. + The <c>gen_statem</c> keeps the current state, or + does a state transition to the current state if you like, + sets <c><anno>NewData</anno></c>, + and executes all <c><anno>Actions</anno></c>. + This is the same as + <c>{next_state,CurrentState,<anno>NewData</anno>,<anno>Actions</anno>}</c>. </p> </item> - <tag><c>stop_and_reply</c></tag> + <tag><c>keep_state_and_data</c></tag> <item> <p> - Sends all <c><anno>Replies</anno></c>, - then terminates the <c>gen_statem</c> by calling - <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso> - with <c>Reason</c> and - <c><anno>NewData</anno></c>, if specified. + The <c>gen_statem</c> keeps the current state or + does a state transition to the current state if you like, + keeps the current server data, + and executes all <c><anno>Actions</anno></c>. + This is the same as + <c>{next_state,CurrentState,CurrentData,<anno>Actions</anno>}</c>. </p> </item> - <tag><c>keep_state</c></tag> + <tag><c>repeat_state</c></tag> <item> <p> The <c>gen_statem</c> keeps the current state, or does a state transition to the current state if you like, sets <c><anno>NewData</anno></c>, and executes all <c><anno>Actions</anno></c>. - This is the same as - <c>{next_state,CurrentState,<anno>NewData</anno>,<anno>Actions</anno>}</c>. + If the <c>gen_statem</c> runs with + <seealso marker="#type-state_enter"><em>state enter calls</em></seealso>, + the state enter call is repeated, see type + <seealso marker="#type-transition_option"><c>transition_option()</c></seealso>, + otherwise <c>repeat_state</c> is the same as + <c>keep_state</c>. </p> </item> - <tag><c>keep_state_and_data</c></tag> + <tag><c>repeat_state_and_data</c></tag> <item> <p> - The <c>gen_statem</c> keeps the current state or + The <c>gen_statem</c> keeps the current state and data, or does a state transition to the current state if you like, - keeps the current server data, and executes all <c><anno>Actions</anno></c>. This is the same as - <c>{next_state,CurrentState,CurrentData,<anno>Actions</anno>}</c>. + <c>{repeat_state,CurrentData,<anno>Actions</anno>}</c>. + If the <c>gen_statem</c> runs with + <seealso marker="#type-state_enter"><em>state enter calls</em></seealso>, + the state enter call is repeated, see type + <seealso marker="#type-transition_option"><c>transition_option()</c></seealso>, + otherwise <c>repeat_state_and_data</c> is the same as + <c>keep_state_and_data</c>. + </p> + </item> + <tag><c>stop</c></tag> + <item> + <p> + Terminates the <c>gen_statem</c> by calling + <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso> + with <c>Reason</c> and + <c><anno>NewData</anno></c>, if specified. + </p> + </item> + <tag><c>stop_and_reply</c></tag> + <item> + <p> + Sends all <c><anno>Replies</anno></c>, + then terminates the <c>gen_statem</c> by calling + <seealso marker="#Module:terminate/3"><c>Module:terminate/3</c></seealso> + with <c>Reason</c> and + <c><anno>NewData</anno></c>, if specified. </p> </item> </taglist> @@ -900,14 +1289,14 @@ handle_event(_, _, State, Data) -> by sending a request and waiting until its reply arrives. The <c>gen_statem</c> calls the - <seealso marker="#state_function">state function</seealso> with + <seealso marker="#state callback">state callback</seealso> with <seealso marker="#type-event_type"><c>event_type()</c></seealso> <c>{call,From}</c> and event content <c><anno>Request</anno></c>. </p> <p> A <c><anno>Reply</anno></c> is generated when a - <seealso marker="#state_function">state function</seealso> + <seealso marker="#state callback">state callback</seealso> returns with <c>{reply,From,<anno>Reply</anno>}</c> as one <seealso marker="#type-action"><c>action()</c></seealso>, @@ -923,17 +1312,40 @@ handle_event(_, _, State, Data) -> </p> <note> <p> - To avoid getting a late reply in the caller's - inbox, this function spawns a proxy process that + For <c><anno>Timeout</anno> < infinity</c>, + to avoid getting a late reply in the caller's + inbox if the caller should catch exceptions, + this function spawns a proxy process that does the call. A late reply gets delivered to the dead proxy process, hence gets discarded. This is less efficient than using - <c><anno>Timeout</anno> =:= infinity</c>. + <c><anno>Timeout</anno> == infinity</c>. + </p> + </note> + <p> + <c><anno>Timeout</anno></c> can also be a tuple + <c>{clean_timeout,<anno>T</anno>}</c> or + <c>{dirty_timeout,<anno>T</anno>}</c>, where + <c><anno>T</anno></c> is the time-out time. + <c>{clean_timeout,<anno>T</anno>}</c> works like + just <c>T</c> described in the note above + and uses a proxy process for <c>T < infinity</c>, + while <c>{dirty_timeout,<anno>T</anno>}</c> + bypasses the proxy process which is more lightweight. + </p> + <note> + <p> + If you combine catching exceptions from this function + with <c>{dirty_timeout,<anno>T</anno>}</c> + to avoid that the calling process dies when the call + times out, you will have to be prepared to handle + a late reply. + So why not just let the calling process die? </p> </note> <p> - The call can fail, for example, if the <c>gen_statem</c> dies - before or during this function call. + The call can also fail, for example, if the <c>gen_statem</c> + dies before or during this function call. </p> </desc> </func> @@ -949,7 +1361,7 @@ handle_event(_, _, State, Data) -> ignoring if the destination node or <c>gen_statem</c> does not exist. The <c>gen_statem</c> calls the - <seealso marker="#state_function">state function</seealso> with + <seealso marker="#state callback">state callback</seealso> with <seealso marker="#type-event_type"><c>event_type()</c></seealso> <c>cast</c> and event content <c><anno>Msg</anno></c>. @@ -958,35 +1370,36 @@ handle_event(_, _, State, Data) -> </func> <func> - <name name="enter_loop" arity="5"/> + <name name="enter_loop" arity="4"/> <fsummary>Enter the <c>gen_statem</c> receive loop.</fsummary> <desc> <p> The same as - <seealso marker="#enter_loop/7"><c>enter_loop/7</c></seealso> - except that no + <seealso marker="#enter_loop/6"><c>enter_loop/6</c></seealso> + with <c>Actions = []</c> except that no <seealso marker="#type-server_name"><c>server_name()</c></seealso> - must have been registered. + must have been registered. This creates an anonymous server. </p> </desc> </func> <func> - <name name="enter_loop" arity="6"/> + <name name="enter_loop" arity="5"/> <fsummary>Enter the <c>gen_statem</c> receive loop.</fsummary> <desc> <p> If <c><anno>Server_or_Actions</anno></c> is a <c>list()</c>, the same as - <seealso marker="#enter_loop/7"><c>enter_loop/7</c></seealso> + <seealso marker="#enter_loop/6"><c>enter_loop/6</c></seealso> except that no <seealso marker="#type-server_name"><c>server_name()</c></seealso> must have been registered and <c>Actions = <anno>Server_or_Actions</anno></c>. + This creates an anonymous server. </p> <p> Otherwise the same as - <seealso marker="#enter_loop/7"><c>enter_loop/7</c></seealso> + <seealso marker="#enter_loop/6"><c>enter_loop/6</c></seealso> with <c>Server = <anno>Server_or_Actions</anno></c> and <c>Actions = []</c>. @@ -995,7 +1408,7 @@ handle_event(_, _, State, Data) -> </func> <func> - <name name="enter_loop" arity="7"/> + <name name="enter_loop" arity="6"/> <fsummary>Enter the <c>gen_statem</c> receive loop.</fsummary> <desc> <p> @@ -1015,21 +1428,31 @@ handle_event(_, _, State, Data) -> the <c>gen_statem</c> behavior provides. </p> <p> - <c><anno>Module</anno></c>, <c><anno>Opts</anno></c>, and - <c><anno>Server</anno></c> have the same meanings - as when calling + <c><anno>Module</anno></c>, <c><anno>Opts</anno></c> + have the same meaning as when calling <seealso marker="#start_link/3"><c>start[_link]/3,4</c></seealso>. + </p> + <p> + If <c><anno>Server</anno></c> is <c>self()</c> an anonymous + server is created just as when using + <seealso marker="#start_link/3"><c>start[_link]/3</c></seealso>. + If <c><anno>Server</anno></c> is a + <seealso marker="#type-server_name"><c>server_name()</c></seealso> + a named server is created just as when using + <seealso marker="#start_link/4"><c>start[_link]/4</c></seealso>. However, the <seealso marker="#type-server_name"><c>server_name()</c></seealso> name must have been registered accordingly - <em>before</em> this function is called.</p> + <em>before</em> this function is called. + </p> <p> - <c><anno>CallbackMode</anno></c>, <c><anno>State</anno></c>, - <c><anno>Data</anno></c>, and <c><anno>Actions</anno></c> + <c><anno>State</anno></c>, <c><anno>Data</anno></c>, + and <c><anno>Actions</anno></c> have the same meanings as in the return value of <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>. - Also, the callback module <c><anno>Module</anno></c> - does not need to export an <c>init/1</c> function. + Also, the callback module does not need to export a + <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> + function. </p> <p> The function fails if the calling process was not started by a @@ -1052,17 +1475,18 @@ handle_event(_, _, State, Data) -> <seealso marker="#call/2"><c>call/2</c></seealso> when the reply cannot be defined in the return value of a - <seealso marker="#state_function">state function</seealso>. + <seealso marker="#state callback">state callback</seealso>. </p> <p> <c><anno>From</anno></c> must be the term from argument <seealso marker="#type-event_type"><c>{call,<anno>From</anno>}</c></seealso> to the - <seealso marker="#state_function">state function</seealso>. - <c><anno>From</anno></c> and <c><anno>Reply</anno></c> - can also be specified using a - <seealso marker="#type-reply_action"><c>reply_action()</c></seealso> - and multiple replies with a list of them. + <seealso marker="#state callback">state callback</seealso>. + A reply or multiple replies canalso be sent + using one or several + <seealso marker="#type-reply_action"><c>reply_action()</c></seealso>s + from a + <seealso marker="#state callback">state callback</seealso>. </p> <note> <p> @@ -1142,6 +1566,13 @@ handle_event(_, _, State, Data) -> </p> </item> <item> + <p>If option<seealso marker="#type-hibernate_after_opt"><c>{hibernate_after,HibernateAfterTimeout}</c></seealso> is present, the <c>gen_statem</c> + process awaits any message for <c>HibernateAfterTimeout</c> milliseconds and + if no message is received, the process goes into hibernation automatically + (by calling <seealso marker="proc_lib#hibernate/3"><c>proc_lib:hibernate/3</c></seealso>). + </p> + </item> + <item> <p> If option <seealso marker="#type-debug_opt"><c>{debug,Dbgs}</c></seealso> @@ -1253,6 +1684,57 @@ handle_event(_, _, State, Data) -> <funcs> <func> + <name>Module:callback_mode() -> CallbackMode</name> + <fsummary>Update the internal state during upgrade/downgrade.</fsummary> + <type> + <v> + CallbackMode = + <seealso marker="#type-callback_mode">callback_mode()</seealso> | + [ <seealso marker="#type-callback_mode">callback_mode()</seealso> + | <seealso marker="#type-state_enter">state_enter()</seealso> ] + </v> + </type> + <desc> + <p> + This function is called by a <c>gen_statem</c> + when it needs to find out the + <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> + of the callback module. The value is cached by <c>gen_statem</c> + for efficiency reasons, so this function is only called + once after server start and after code change, + but before the first + <seealso marker="#state callback">state callback</seealso> + in the current code version is called. + More occasions may be added in future versions + of <c>gen_statem</c>. + </p> + <p> + Server start happens either when + <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso> + returns or when + <seealso marker="#enter_loop/4"><c>enter_loop/4-6</c></seealso> + is called. Code change happens when + <seealso marker="#Module:code_change/4"><c>Module:code_change/4</c></seealso> + returns. + </p> + <p> + The <c>CallbackMode</c> is either just + <seealso marker="#type-callback_mode"><c>callback_mode()</c></seealso> + or a list containing + <seealso marker="#type-callback_mode"><c>callback_mode()</c></seealso> + and possibly the atom + <seealso marker="#type-state_enter"><c>state_enter</c></seealso>. + </p> + <note> + <p> + If this function's body does not return an inline constant + value the callback module is doing something strange. + </p> + </note> + </desc> + </func> + + <func> <name>Module:code_change(OldVsn, OldState, OldData, Extra) -> Result </name> @@ -1262,11 +1744,7 @@ handle_event(_, _, State, Data) -> <v> Vsn = term()</v> <v>OldState = NewState = term()</v> <v>Extra = term()</v> - <v>Result = {NewCallbackMode,NewState,NewData} | Reason</v> - <v> - NewCallbackMode = - <seealso marker="#type-callback_mode">callback_mode()</seealso> - </v> + <v>Result = {ok,NewState,NewData} | Reason</v> <v> OldState = NewState = <seealso marker="#type-state">state()</seealso> @@ -1278,6 +1756,16 @@ handle_event(_, _, State, Data) -> <v>Reason = term()</v> </type> <desc> + <note> + <p> + This callback is optional, so callback modules need not export it. + If a release upgrade/downgrade with + <c>Change={advanced,Extra}</c> + specified in the <c>.appup</c> file is made + when <c>code_change/4</c> is not implemented + the process will crash with exit reason <c>undef</c>. + </p> + </note> <p> This function is called by a <c>gen_statem</c> when it is to update its internal state during a release upgrade/downgrade, @@ -1295,21 +1783,6 @@ handle_event(_, _, State, Data) -> <c>Module</c>. If no such attribute is defined, the version is the checksum of the Beam file. </p> - <note> - <p> - If you would dare to change - <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> - during release upgrade/downgrade, the upgrade is no problem, - as the new code surely knows what <em>callback mode</em> - it needs. However, for a downgrade this function must - know from argument <c>Extra</c> that comes from the - <seealso marker="sasl:appup"><c>sasl:appup</c></seealso> - file what <em>callback mode</em> the old code did use. - It can also be possible to figure this out - from argument <c>{down,Vsn}</c>, as <c>Vsn</c> - in effect defines the old callback module version. - </p> - </note> <p> <c>OldState</c> and <c>OldData</c> is the internal state of the <c>gen_statem</c>. @@ -1321,41 +1794,46 @@ handle_event(_, _, State, Data) -> <p> If successful, the function must return the updated internal state in an - <c>{NewCallbackMode,NewState,NewData}</c> tuple. - </p> - <p> - If the function returns <c>Reason</c>, the ongoing - upgrade fails and rolls back to the old release.</p> - <p> - This function can use - <seealso marker="erts:erlang#throw/1"><c>erlang:throw/1</c></seealso> - to return <c>Result</c> or <c>Reason</c>. + <c>{ok,NewState,NewData}</c> tuple. + </p> + <p> + If the function returns a failure <c>Reason</c>, the ongoing + upgrade fails and rolls back to the old release. + Note that <c>Reason</c> can not be an <c>{ok,_,_}</c> tuple + since that will be regarded as a + <c>{ok,NewState,NewData}</c> tuple, + and that a tuple matching <c>{ok,_}</c> + is an also invalid failure <c>Reason</c>. + It is recommended to use an atom as <c>Reason</c> since + it will be wrapped in an <c>{error,Reason}</c> tuple. + </p> + <p> + Also note when upgrading a <c>gen_statem</c>, + this function and hence + the <c>Change={advanced,Extra}</c> parameter in the + <seealso marker="sasl:appup"><c>appup</c></seealso> file + is not only needed to update the internal state + or to act on the <c>Extra</c> argument. + It is also needed if an upgrade or downgrade should change + <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>, + or else the callback mode after the code change + will not be honoured, + most probably causing a server crash. </p> </desc> </func> <func> - <name>Module:init(Args) -> Result</name> - <fsummary>Initialize process and internal state.</fsummary> + <name>Module:init(Args) -> Result(StateType)</name> + <fsummary> + Initializing process and internal state. + </fsummary> <type> <v>Args = term()</v> - <v>Result = {CallbackMode,State,Data}</v> - <v> | {CallbackMode,State,Data,Actions}</v> - <v> | {stop,Reason} | ignore</v> <v> - CallbackMode = - <seealso marker="#type-callback_mode">callback_mode()</seealso> + Result(StateType) = + <seealso marker="#type-init_result">init_result(StateType)</seealso> </v> - <v>State = <seealso marker="#type-state">state()</seealso></v> - <v> - Data = <seealso marker="#type-data">data()</seealso> - </v> - <v> - Actions = - [<seealso marker="#type-action">action()</seealso>] | - <seealso marker="#type-action">action()</seealso> - </v> - <v>Reason = term()</v> </type> <desc> <marker id="Module:init-1"/> @@ -1368,38 +1846,22 @@ handle_event(_, _, State, Data) -> the implementation state and server data. </p> <p> - <c>Args</c> is the <c>Args</c> argument provided to the start + <c>Args</c> is the <c>Args</c> argument provided to that start function. </p> - <p> - If the initialization is successful, the function is to - return <c>{CallbackMode,State,Data}</c> or - <c>{CallbackMode,State,Data,Actions}</c>. - <c>CallbackMode</c> selects the - <seealso marker="#type-callback_mode"><em>callback mode</em></seealso> - of the <c>gen_statem</c>. - <c>State</c> is the initial - <seealso marker="#type-state"><c>state()</c></seealso> - and <c>Data</c> the initial server - <seealso marker="#type-data"><c>data()</c></seealso>. - </p> - <p> - The <seealso marker="#type-action"><c>Actions</c></seealso> - are executed when entering the first - <seealso marker="#type-state">state</seealso> just as for a - <seealso marker="#state_function">state function</seealso>. - </p> - <p> - If the initialization fails, - the function is to return <c>{stop,Reason}</c> - or <c>ignore</c>; see - <seealso marker="#start_link/3"><c>start_link/3,4</c></seealso>. - </p> - <p> - This function can use - <seealso marker="erts:erlang#throw/1"><c>erlang:throw/1</c></seealso> - to return <c>Result</c>. - </p> + <note> + <p> + Note that if the <c>gen_statem</c> is started trough + <seealso marker="proc_lib"><c>proc_lib</c></seealso> + and + <seealso marker="#enter_loop/4"><c>enter_loop/4-6</c></seealso>, + this callback will never be called. + Since this callback is not optional it can + in that case be implemented as: + </p> + <pre> +init(Args) -> erlang:error(not_implemented, [Args]).</pre> + </note> </desc> </func> @@ -1430,10 +1892,14 @@ handle_event(_, _, State, Data) -> This callback is optional, so a callback module does not need to export it. The <c>gen_statem</c> module provides a default implementation of this function that returns - <c>{State,Data}</c>. If this callback fails, the default - function returns <c>{State,Info}</c>, - where <c>Info</c> informs of the crash but no details, - to hide possibly sensitive data. + <c>{State,Data}</c>. + </p> + <p> + If this callback is exported but fails, + to hide possibly sensitive data, + the default function will instead return <c>{State,Info}</c>, + where <c>Info</c> says nothing but the fact that + <c>format_status/2</c> has crashed. </p> </note> <p>This function is called by a <c>gen_statem</c> process when @@ -1474,7 +1940,8 @@ handle_event(_, _, State, Data) -> </p> <p> The function is to return <c>Status</c>, a term that - changes the details of the current state and status of + contains the appropriate details + of the current state and status of the <c>gen_statem</c>. There are no restrictions on the form <c>Status</c> can take, but for the <seealso marker="sys#get_status/1"><c>sys:get_status/1,2</c></seealso> @@ -1494,20 +1961,21 @@ handle_event(_, _, State, Data) -> printed in log files. Another use is to hide sensitive data from being written to the error log. </p> - <p> - This function can use - <seealso marker="erts:erlang#throw/1"><c>erlang:throw/1</c></seealso> - to return <c>Status</c>. - </p> </desc> </func> <func> + <name>Module:StateName(enter, OldState, Data) -> + StateEnterResult(StateName) + </name> <name>Module:StateName(EventType, EventContent, Data) -> StateFunctionResult </name> - <name>Module:handle_event(EventType, EventContent, - State, Data) -> HandleEventResult + <name>Module:handle_event(enter, OldState, State, Data) -> + StateEnterResult(State) + </name> + <name>Module:handle_event(EventType, EventContent, State, Data) -> + HandleEventResult </name> <fsummary>Handle an event.</fsummary> <type> @@ -1525,12 +1993,20 @@ handle_event(_, _, State, Data) -> <seealso marker="#type-data">data()</seealso> </v> <v> + StateEnterResult(StateName) = + <seealso marker="#type-state_enter_result">state_enter_result(StateName)</seealso> + </v> + <v> StateFunctionResult = - <seealso marker="#type-state_function_result">state_function_result()</seealso> + <seealso marker="#type-event_handler_result">event_handler_result</seealso>(<seealso marker="#type-state_name">state_name()</seealso>) + </v> + <v> + StateEnterResult(State) = + <seealso marker="#type-state_enter_result">state_enter_result(State)</seealso> </v> <v> HandleEventResult = - <seealso marker="#type-handle_event_result">handle_event_result()</seealso> + <seealso marker="#type-event_handler_result">event_handler_result</seealso>(<seealso marker="#type-state">state()</seealso>) </v> </type> <desc> @@ -1549,7 +2025,7 @@ handle_event(_, _, State, Data) -> <seealso marker="#type-event_type"><c>{call,From}</c></seealso>, the caller waits for a reply. The reply can be sent from this or from any other - <seealso marker="#state_function">state function</seealso> + <seealso marker="#state callback">state callback</seealso> by returning with <c>{reply,From,Reply}</c> in <seealso marker="#type-action"><c>Actions</c></seealso>, in <seealso marker="#type-reply_action"><c>Replies</c></seealso>, @@ -1573,9 +2049,41 @@ handle_event(_, _, State, Data) -> see <seealso marker="#type-action"><c>action()</c></seealso>. </p> <p> - These functions can use - <seealso marker="erts:erlang#throw/1"><c>erlang:throw/1</c></seealso>, - to return the result. + When the <c>gen_statem</c> runs with + <seealso marker="#type-state_enter">state enter calls</seealso>, + these functions are also called with arguments + <c>(enter, OldState, ...)</c> whenever the state changes. + In this case there are some restrictions on the + <seealso marker="#type-enter_action">actions</seealso> + that may be returned: + <seealso marker="#type-postpone"><c>postpone()</c></seealso> + is not allowed since a <em>state enter call</em> is not + an event so there is no event to postpone, and + <seealso marker="#type-action"><c>{next_event,_,_}</c></seealso> + is not allowed since using <em>state enter calls</em> + should not affect how events are consumed and produced. + You may also not change states from this call. + Should you return <c>{next_state,NextState, ...}</c> + with <c>NextState =/= State</c> the <c>gen_statem</c> crashes. + It is possible to use <c>{repeat_state, ...}</c>, + <c>{repeat_state_and_data,_}</c> or + <c>repeat_state_and_data</c> but all of them makes little + sense since you immediately will be called again with a new + <em>state enter call</em> making this just a weird way + of looping, and there are better ways to loop in Erlang. + You are advised to use <c>{keep_state,...}</c>, + <c>{keep_state_and_data,_}</c> or + <c>keep_state_and_data</c> since you can not change states + from a <em>state enter call</em> anyway. + </p> + <p> + Note the fact that you can use + <seealso marker="erts:erlang#throw/1"><c>throw</c></seealso> + to return the result, which can be useful. + For example to bail out with <c>throw(keep_state_and_data)</c> + from deep within complex code that can not + return <c>{next_state,State,Data}</c> because + <c>State</c> or <c>Data</c> is no longer in scope. </p> </desc> </func> @@ -1590,6 +2098,11 @@ handle_event(_, _, State, Data) -> <v>Ignored = term()</v> </type> <desc> + <note> + <p>This callback is optional, so callback modules need not + export it. The <c>gen_statem</c> module provides a default + implementation without cleanup.</p> + </note> <p> This function is called by a <c>gen_statem</c> when it is about to terminate. It is to be the opposite of @@ -1648,11 +2161,6 @@ handle_event(_, _, State, Data) -> and an error report is issued using <seealso marker="kernel:error_logger#format/2"><c>error_logger:format/2</c></seealso>. </p> - <p> - This function can use - <seealso marker="erts:erlang#throw/1"><c>erlang:throw/1</c></seealso> - to return <c>Ignored</c>, which is ignored anyway. - </p> </desc> </func> </funcs> |