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-rw-r--r--system/doc/design_principles/statem.xml87
1 files changed, 49 insertions, 38 deletions
diff --git a/system/doc/design_principles/statem.xml b/system/doc/design_principles/statem.xml
index 72aaafd780..27b9b7c761 100644
--- a/system/doc/design_principles/statem.xml
+++ b/system/doc/design_principles/statem.xml
@@ -90,11 +90,11 @@ State(S) x Event(E) -> Actions(A), State(S')</pre>
<marker id="callback_modes" />
<title>Callback Modes</title>
<p>
- The <c>gen_statem</c> behaviour supports two different
- <seealso marker="stdlib:gen_statem#type-action">
- callback modes.
+ The <c>gen_statem</c> behaviour supports two different callback modes.
+ In the mode
+ <seealso marker="stdlib:gen_statem#type-callback_mode">
+ <c>state_functions</c>,
</seealso>
- In the mode <c>state_functions</c>,
the state transition rules are written as a number of Erlang
functions, which conform to the following convention:
</p>
@@ -103,7 +103,11 @@ StateName(EventType, EventContent, Data) ->
.. code for actions here ...
{next_state, NewStateName, NewData}.</pre>
<p>
- In the mode <c>handle_event_function</c> there is only one
+ In the mode
+ <seealso marker="stdlib:gen_statem#type-callback_mode">
+ <c>handle_event_function</c>
+ </seealso>
+ there is only one
Erlang function that implements all state transition rules:
</p>
<pre>
@@ -125,9 +129,7 @@ handle_event(EventType, EventContent, State, Data) ->
<title>Choosing Callback Mode</title>
<p>
The two
- <seealso marker="stdlib:gen_statem#type-action">
- callback modes
- </seealso>
+ <seealso marker="#callback_modes">callback modes</seealso>
gives different possibilities
and restrictions, but one goal remains:
you want to handle all possible combinations of
@@ -186,7 +188,7 @@ handle_event(EventType, EventContent, State, Data) ->
<title>Example</title>
<p>
This is an example starting off as equivalent to the the example in the
- <seealso marker="fsm"><c>gen_fsm</c> behaviour </seealso>
+ <seealso marker="fsm"><c>gen_fsm</c> behaviour</seealso>
description. In later chapters additions and tweaks are made
using features in <c>gen_statem</c> that <c>gen_fsm</c> does not have.
At the end of this section you can find the example again
@@ -217,6 +219,7 @@ handle_event(EventType, EventContent, State, Data) ->
-module(code_lock).
-behaviour(gen_statem).
-define(NAME, code_lock).
+-define(CALLBACK_MODE, state_functions).
-export([start_link/1]).
-export([button/1]).
@@ -233,7 +236,7 @@ button(Digit) ->
init(Code) ->
do_lock(),
Data = #{code => Code, remaining => Code},
- {state_functions,locked,Data}.
+ {?CALLBACK_MODE,locked,Data}.
locked(
cast, {button,Digit},
@@ -264,7 +267,7 @@ terminate(_Reason, State, _Data) ->
State =/= locked andalso do_lock(),
ok.
code_change(_Vsn, State, Data, _Extra) ->
- {ok,State,Data}.
+ {?CALLBACK_MODE,State,Data}.
]]></code>
<p>The code is explained in the next sections.</p>
</section>
@@ -340,16 +343,20 @@ start_link(Code) ->
If name registration succeeds, the new <c>gen_statem</c> process
calls the callback function <c>code_lock:init(Code)</c>.
This function is expected to return <c>{CallbackMode,State,Data}</c>,
- where <c>CallbackMode</c> selects callback module state function
- mode, in this case <c>state_functions</c> that is each state
+ where
+ <seealso marker="#callback_modes">
+ <c>CallbackMode</c>
+ </seealso>
+ selects callback module state function mode, in this case
+ <seealso marker="stdlib:gen_statem#type-callback_mode">
+ <c>state_functions</c>
+ </seealso>
+ through the macro <c>?CALLBACK_MODE</c> that is; each state
has got its own handler function.
<c>State</c> is the initial state of the <c>gen_statem</c>,
in this case <c>locked</c>; assuming the door is locked to begin with.
<c>Data</c> is the internal server data of the <c>gen_statem</c>.
- Here the server data is a
- <seealso marker="stdlib:maps">
- map
- </seealso>
+ Here the server data is a <seealso marker="stdlib:maps">map</seealso>
with the key <c>code</c> that stores
the correct button sequence and the key <c>remaining</c>
that stores the remaining correct button sequence
@@ -359,7 +366,7 @@ start_link(Code) ->
init(Code) ->
do_lock(),
Data = #{code => Code, remaining => Code},
- {state_functions,locked,Data}.
+ {?CALLBACK_MODE,locked,Data}.
]]></code>
<p>
<seealso marker="stdlib:gen_statem#start_link/3">
@@ -536,13 +543,12 @@ handle_event({call,From}, code_length, #{code := Code} = Data) ->
</p>
<code type="erl"><![CDATA[
...
--export([handle_event/4]).
+-define(CALLBACK_MODE, state_functions).
...
+-export([handle_event/4]).
-init(Code) ->
- Data = #{code => Code, remaining => Code},
- {handle_event_function,locked,Data}.
+...
handle_event(cast, {button,Digit}, State, #{code := Code} = Data) ->
case State of
@@ -598,8 +604,8 @@ handle_event(timeout, _, open, Data) ->
<code type="erl"><![CDATA[
init(Args) ->
process_flag(trap_exit, true),
+ do_lock(),
...
- {CallbackMode,State,Data}.
]]></code>
<p>
In this example we let the <c>terminate/3</c> function
@@ -994,11 +1000,18 @@ do_unlock() ->
utilizing a helper function <c>enter/3</c> for state entry:
</p>
<code type="erl"><![CDATA[
+...
+-define(CALLBACK_MODE, state_functions).
+
+...
+
init(Code) ->
+ process_flag(trap_exit, true),
Data = #{code => Code},
- enter(state_functions, locked, Data).
+ enter(?CALLBACK_MODE, locked, Data).
...
+
locked(internal, enter, _Data) ->
do_lock(),
{keep_state,Data#{remaining => Code}};
@@ -1053,6 +1066,7 @@ enter(Tag, State, Data) ->
-module(code_lock).
-behaviour(gen_statem).
-define(NAME, code_lock_2).
+-define(CALLBACK_MODE, state_functions).
-export([start_link/1,stop/0]).
-export([button/1,code_length/0]).
@@ -1070,8 +1084,9 @@ code_length() ->
gen_statem:call(?NAME, code_length).
init(Code) ->
+ process_flag(trap_exit, true),
Data = #{code => Code},
- enter(state_functions, locked, Data).
+ enter(?CALLBACK_MODE, locked, Data).
locked(internal, enter, #{code := Code} = Data) ->
do_lock(),
@@ -1115,7 +1130,7 @@ terminate(_Reason, State, _Data) ->
State =/= locked andalso do_lock(),
ok.
code_change(_Vsn, State, Data, _Extra) ->
- {ok,State,Data}.
+ {?CALLBACK_MODE,State,Data}.
]]></code>
</section>
@@ -1129,14 +1144,10 @@ code_change(_Vsn, State, Data, _Extra) ->
</p>
<code type="erl"><![CDATA[
...
--export([handle_event/4]).
+-define(CALLBACK_MODE, handle_event_function).
...
-
-init(Code) ->
- process_flag(trap_exit, true),
- Data = #{code => Code},
- enter(handle_event_function, locked, Data).
+-export([handle_event/4]).
...
@@ -1185,11 +1196,10 @@ handle_event({call,From}, code_length, _State, #{code := Code}) ->
<section>
<title>Complex State</title>
<p>
- The
- <seealso marker="stdlib:gen_statem#type-action">
- callback mode
+ The callback mode
+ <seealso marker="stdlib:gen_statem#type-callback_mode">
+ <c>handle_event_function</c>
</seealso>
- <c>handle_event_function</c>
enables using a non-atom state as described in
<seealso marker="#callback_modes">
Callback Modes,
@@ -1245,6 +1255,7 @@ handle_event({call,From}, code_length, _State, #{code := Code}) ->
-module(code_lock).
-behaviour(gen_statem).
-define(NAME, code_lock_3).
+-define(CALLBACK_MODE, handle_event_function).
-export([start_link/2,stop/0]).
-export([button/1,code_length/0,set_lock_button/1]).
@@ -1267,7 +1278,7 @@ set_lock_button(LockButton) ->
init({Code,LockButton}) ->
process_flag(trap_exit, true),
Data = #{code => Code},
- enter(handle_event_function, {locked,LockButton}, Data, []).
+ enter(?CALLBACK_MODE, {locked,LockButton}, Data, []).
%% State: locked
handle_event(internal, enter, {locked,_}, #{code := Code} = Data) ->
@@ -1323,7 +1334,7 @@ terminate(_Reason, State, _Data) ->
State =/= locked andalso do_lock(),
ok.
code_change(_Vsn, State, Data, _Extra) ->
- {ok,State,Data}.
+ {?CALLBACK_MODE,State,Data}.
]]></code>
<p>
It may be an ill-fitting model for a physical code lock
generated by cgit v1.2.3 (git 2.25.1) at 2024-12-27 16:51:30 +0000