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authorRaimo Niskanen <[email protected]>2016-02-25 16:02:59 +0100
committerRaimo Niskanen <[email protected]>2016-02-26 10:20:52 +0100
commitcea77ca09be156669c657592bebf6efc9d5cfaee (patch)
treec1a8bbf56b5a8719552a068ca1224acf1dfbab64 /lib/stdlib
parent63b291070d5522b5b116c8fe158497ee55149656 (diff)
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Write a simple example in the reference manual
Diffstat (limited to 'lib/stdlib')
-rw-r--r--lib/stdlib/doc/src/gen_statem.xml188
1 files changed, 144 insertions, 44 deletions
diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml
index 4af6732e7c..d50b88c561 100644
--- a/lib/stdlib/doc/src/gen_statem.xml
+++ b/lib/stdlib/doc/src/gen_statem.xml
@@ -91,7 +91,7 @@ erlang:'!' -----> Module:StateName/3
in a <c>gen_statem</c> is the callback function that is called
for all events in this state, and is selected depending on
<seealso marker="#type-callback_mode">callback_mode</seealso>
- that the implementation specifies during <c>gen_statem</c> init.
+ that the implementation specifies when the the server starts.
</p>
<p>
When
@@ -103,7 +103,8 @@ erlang:'!' -----> Module:StateName/3
</seealso>.
This gathers all code for a specific state
in one function and hence dispatches on state first.
- Note that in this mode the callback function
+ Note that in this mode the fact that there is
+ a mandatory callback function
<seealso marker="#Module:terminate/3">
<c>Module:terminate/3</c>
</seealso> makes the state name <c>terminate</c> unusable.
@@ -115,9 +116,8 @@ erlang:'!' -----> Module:StateName/3
<seealso marker="#Module:handle_event/4">
<c>Module:handle_event/4</c>
</seealso>.
- This makes it easy to dispatch on state or on event as
- you like but you will have to implement it.
- Also be careful about which events you handle in which
+ This makes it easy to dispatch on state or on event as you desire.
+ Be careful about which events you handle in which
states so you do not accidentally postpone one event
forever creating an infinite busy loop.
</p>
@@ -132,9 +132,9 @@ erlang:'!' -----> Module:StateName/3
</p>
<p>
The <c>gen_statem</c> event queue model is sufficient
- to emulate the normal process message queue and selective receive
- with postponing an event corresponding to not matching
- it in a receive statement and changing states corresponding
+ to emulate the normal process message queue with selective receive.
+ Postponing an event corresponds to not matching it
+ in a receive statement and changing states corresponds
to entering a new receive statement.
</p>
<p>
@@ -149,8 +149,8 @@ erlang:'!' -----> Module:StateName/3
<seealso marker="#type-event_type">
<c>event_type()</c> <c>internal</c>
</seealso>
- that can be used for such events making it impossible
- to mistake for an external event.
+ that can be used for such events making them impossible
+ to mistake for external events.
</p>
<p>
Inserting an event replaces the trick of calling your own
@@ -165,7 +165,7 @@ erlang:'!' -----> Module:StateName/3
<p>
See the type
<seealso marker="#type-transition_option">
- <c>transition_option()</c>.
+ <c>transition_option()</c>
</seealso>
for the details of a state transition.
</p>
@@ -192,7 +192,7 @@ erlang:'!' -----> Module:StateName/3
</seealso>) if a
<seealso marker="#state_function">state function</seealso> or
<seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
- specifies <c>'hibernate'</c> in the returned
+ specifies <c>hibernate</c> in the returned
<seealso marker="#type-action"><c>Actions</c></seealso>
list. This might be useful if the server is expected to be idle
for a long time. However use this feature with care
@@ -202,6 +202,99 @@ erlang:'!' -----> Module:StateName/3
</p>
</description>
+ <section>
+ <title>EXAMPLE</title>
+ <p>
+ This example shows a simple pushbutton model
+ for a toggling pushbutton implemented with
+ <seealso marker="#type-callback_mode">
+ callback_mode()
+ </seealso>
+ <c>state_functions</c>.
+ You can push the button and it replies if it went on or off,
+ and you can ask for a count of how many times it has been
+ pushed to on.
+ </p>
+ <p>This is the complete callback module file <c>pushbutton.erl</c>:</p>
+ <code type="erl">
+-module(pushbutton).
+-behaviour(gen_statem).
+
+-export([start/0,push/0,get_count/0,stop/0]).
+-export([terminate/3,code_change/4,init/1]).
+-export([on/3,off/3]).
+
+name() -> pushbutton_statem. % The registered server name
+
+%% API. This example uses a registered name name()
+%% and does not link to the caller.
+start() ->
+ gen_statem:start({local,name()}, ?MODULE, [], []).
+push() ->
+ gen_statem:call(name(), push).
+get_count() ->
+ gen_statem:call(name(), get_count).
+stop() ->
+ gen_statem:stop(name()).
+
+%% Mandatory callback functions
+terminate(_Reason, _State, _Data) ->
+ void.
+code_change(_Vsn, State, Data, _Extra) ->
+ {ok,{State,Data}}.
+init([]) ->
+ %% Set the callback mode and initial state + data.
+ %% Data is used only as a counter.
+ State = off, Data = 0,
+ {state_functions,State,Data}.
+
+
+%%% State functions
+
+off({call,Caller}, push, Data) ->
+ %% Go to 'on', increment count and reply
+ %% that the resulting status is 'on'
+ {next_state,on,Data+1,[{reply,Caller,on}]};
+off(EventType, EventContent, Data) ->
+ handle_event(EventType, EventContent, Data).
+
+on({call,Caller}, push, Data) ->
+ %% Go to 'off' and reply that the resulting status is 'off'
+ {next_state,off,Data,[{reply,Caller,off}]};
+on(EventType, EventContent, Data) ->
+ handle_event(EventType, EventContent, Data).
+
+%% Handle events common to all states
+handle_event({call,Caller}, get_count, Data) ->
+ %% Reply with the current count
+ {keep_state,Data,[{reply,Caller,Data}]};
+handle_event(_, _, Data) ->
+ %% Ignore all other events
+ {keep_state,Data}.
+ </code>
+ <p>And this is a shell session when running it:</p>
+ <pre>
+1> pushbutton:start().
+{ok,&lt;0.36.0>}
+2> pushbutton:get_count().
+0
+3> pushbutton:push().
+on
+4> pushbutton:get_count().
+1
+5> pushbutton:push().
+off
+6> pushbutton:get_count().
+1
+7> pushbutton:stop().
+ok
+8> pushbutton:push().
+** exception exit: {noproc,{gen_statem,call,[pushbutton_statem,push,infinity]}}
+ in function gen:do_for_proc/2 (gen.erl, line 261)
+ in call from gen_statem:call/3 (gen_statem.erl, line 386)
+ </pre>
+ </section>
+
<datatypes>
<datatype>
<name name="server_name" />
@@ -327,7 +420,7 @@ erlang:'!' -----> Module:StateName/3
<seealso marker="#type-callback_mode">
callback_mode
</seealso>
- is <c>state_functions</c>, which is the default,
+ is <c>state_functions</c>,
the state has to be of this type.
</p>
</desc>
@@ -353,11 +446,14 @@ erlang:'!' -----> Module:StateName/3
<p>
External events are of 3 different type:
<c>{call,<anno>Caller</anno>}</c>, <c>cast</c> or <c>info</c>.
- Calls (synchronous) and casts (asynchronous)
+ <seealso marker="#call/2">Calls</seealso>
+ (synchronous) and
+ <seealso marker="#cast/2">casts</seealso>
originate from the corresponding API functions.
For calls the event contain whom to reply to.
- Type <c>info</c> originates from normal messages sent
- to the <c>gen_statem</c> process.
+ Type <c>info</c> originates from
+ regular process messages sent
+ to the <c>gen_statem</c>.
It is also possible for the state machine
implementation to insert events to itself,
in particular of types
@@ -421,7 +517,8 @@ erlang:'!' -----> Module:StateName/3
<p>
Transition options may be set by
<seealso marker="#type-action">actions</seealso>
- and they modify how the state transition is done:
+ and they modify some details below in how
+ the state transition is done:
</p>
<list type="ordered">
<item>
@@ -430,12 +527,12 @@ erlang:'!' -----> Module:StateName/3
are processed in order of appearance.
</item>
<item>
- If the
+ If
<seealso marker="#type-postpone">
- <c>transition_option()</c>
+ <c>postpone()</c>
</seealso>
- <seealso marker="#type-postpone"><c>postpone</c></seealso>
- is <c>true</c> the current event is postponed.
+ is <c>true</c>
+ the current event is postponed.
</item>
<item>
If the state changes the queue of incoming events
@@ -450,15 +547,16 @@ erlang:'!' -----> Module:StateName/3
all other events.
</item>
<item>
- If the
- <seealso marker="#type-postpone">
- <c>transition_option()</c>
- </seealso>
+ If a
<seealso marker="#type-state_timeout">
- <c>timeout</c>
+ <em><c>state_timeout()</c></em>
+ </seealso>
+ is set through
+ <seealso marker="#type-action">
+ <c>action() timeout</c>
</seealso>
- is set a state timer may be started or a timeout zero event
- may be enqueued as the newest incoming that is the last
+ a state timer may be started or a timeout zero event
+ may be enqueued as the newest incoming, that is the last
to process before going into <c>receive</c> for new events.
</item>
<item>
@@ -466,7 +564,12 @@ erlang:'!' -----> Module:StateName/3
<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>
- or hibernation (if the option <c>hibernate</c> is <c>true</c>)
+ or hibernation
+ (if
+ <seealso marker="#type-hibernate">
+ <c>hibernate()</c>
+ </seealso>
+ is <c>true</c>)
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>
@@ -518,7 +621,7 @@ erlang:'!' -----> Module:StateName/3
Also note that it is not possible nor needed
to cancel this timeout using the
<seealso marker="#type-action">
- <c>action() cancel_timer</c>.
+ <c>action() cancel_timer</c>
</seealso>
since this timeout is cancelled automatically by any other event.
</p>
@@ -538,25 +641,22 @@ erlang:'!' -----> Module:StateName/3
<p>
Actions are executed in the containing list order.
The order matters for some actions such as <c>next_event</c>
- and <c>reply_action()</c>. The order can in peculiar cases
- matter for <c>remove_event</c> with
- <c><anno>EventPredicate</anno></c> versus other
- event removal actions.
+ and <c>reply_action()</c>.
</p>
<p>
- The order also matters for actions that set
+ Actions that set
<seealso marker="#type-transition_option">
transition options
</seealso>
- since setting an option overrides any previous
- of the same kind, so the last in the containing list wins.
+ overrides any previous of the same kind,
+ so the last in the containing list wins.
</p>
<taglist>
<tag><c>postpone</c></tag>
<item>
Set the
<seealso marker="#type-transition_option">
- <c>transition_option() postpone</c>
+ <c>transition_option() postpone()</c>
</seealso>
for this state transition.
This action is ignored when returned from
@@ -569,7 +669,7 @@ erlang:'!' -----> Module:StateName/3
<item>
Set the
<seealso marker="#type-transition_option">
- <c>transition_option() hibernate</c>
+ <c>transition_option() hibernate()</c>
</seealso>
for this state transition.
</item>
@@ -577,7 +677,7 @@ erlang:'!' -----> Module:StateName/3
<item>
Set the
<seealso marker="#type-transition_option">
- <c>transition_option() timeout</c>
+ <c>transition_option() state_timeout()</c>
</seealso>
to <c><anno>Time</anno></c> with the
<c>EventContent</c> as <c><anno>Msg</anno></c>
@@ -594,7 +694,7 @@ erlang:'!' -----> Module:StateName/3
All <c>next_event</c> actions
in the containing list are buffered and inserted
after the actions have been done
- so the first in the list will be the first to process.
+ so that the first in the list will be the first to process.
An event of type
<seealso marker="#type-event_type">
<c>internal</c>
@@ -612,7 +712,7 @@ erlang:'!' -----> Module:StateName/3
and <c>postpone</c> events in the same actions list
does not get into the event queue until after all actions
has been done so you can not remove an event that you insert
- in the same actions list. Make up your mind!
+ with the same actions list. Make up your mind!
</item>
<tag><c>cancel_timer</c></tag>
<item>
@@ -622,7 +722,7 @@ erlang:'!' -----> Module:StateName/3
</seealso>
with <c><anno>TimerRef</anno></c>,
clean the process message queue from any late timeout message,
- and removes any late timeout message
+ and remove any late timeout message
from the <c>gen_statem</c> event queue using
<c>{remove_event,<anno>EventPredicate</anno>}</c> above.
This is a convenience function that saves quite some
@@ -639,7 +739,7 @@ erlang:'!' -----> Module:StateName/3
</item>
<tag><c>unlink</c></tag>
<item>
- Like <c>{cancel_timer,_}</c> above but for
+ Like <c>cancel_timer</c> above but for
<seealso marker="erts:erlang#unlink/1">
<c>unlink/1</c>
</seealso>