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-rw-r--r--system/doc/design_principles/statem.xml84
1 files changed, 48 insertions, 36 deletions
diff --git a/system/doc/design_principles/statem.xml b/system/doc/design_principles/statem.xml
index aea623851a..f785ca9650 100644
--- a/system/doc/design_principles/statem.xml
+++ b/system/doc/design_principles/statem.xml
@@ -52,7 +52,7 @@
<section>
<title>Event-Driven State Machines</title>
<p>
- Established Automata theory does not deal much with
+ Established Automata Theory does not deal much with
how a state transition is triggered,
but assumes that the output is a function
of the input (and the state) and that they are
@@ -226,11 +226,10 @@ 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]).
--export([init/1,terminate/3,code_change/4]).
+-export([init/1,callback_mode/0,terminate/3,code_change/4]).
-export([locked/3,open/3]).
start_link(Code) ->
@@ -242,7 +241,10 @@ button(Digit) ->
init(Code) ->
do_lock(),
Data = #{code => Code, remaining => Code},
- {?CALLBACK_MODE,locked,Data}.
+ {ok,locked,Data}.
+
+callback_mode() ->
+ state_functions.
locked(
cast, {button,Digit},
@@ -273,7 +275,7 @@ terminate(_Reason, State, _Data) ->
State =/= locked andalso do_lock(),
ok.
code_change(_Vsn, State, Data, _Extra) ->
- {?CALLBACK_MODE,State,Data}.
+ {ok,State,Data}.
]]></code>
<p>The code is explained in the next sections.</p>
</section>
@@ -343,14 +345,8 @@ start_link(Code) ->
<p>
If name registration succeeds, the new <c>gen_statem</c> process
calls callback function <c>code_lock:init(Code)</c>.
- This function is expected to return <c>{CallbackMode,State,Data}</c>,
- 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 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>,
+ This function is expected to return <c>{ok,State,Data}</c>,
+ where <c>State</c> is the initial state of the <c>gen_statem</c>,
in this case <c>locked</c>; assuming that 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>
@@ -359,11 +355,12 @@ start_link(Code) ->
that stores the remaining correct button sequence
(the same as the <c>code</c> to begin with).
</p>
+
<code type="erl"><![CDATA[
init(Code) ->
do_lock(),
Data = #{code => Code, remaining => Code},
- {?CALLBACK_MODE,locked,Data}.
+ {ok,locked,Data}.
]]></code>
<p>Function
<seealso marker="stdlib:gen_statem#start_link/3"><c>gen_statem:start_link</c></seealso>
@@ -380,6 +377,21 @@ init(Code) ->
can be used to start a standalone <c>gen_statem</c>, that is,
a <c>gen_statem</c> that is not part of a supervision tree.
</p>
+
+ <code type="erl"><![CDATA[
+callback_mode() ->
+ state_functions.
+ ]]></code>
+ <p>
+ Function
+ <seealso marker="stdlib:gen_statem#Module:callback_mode/0"><c>Module:callback_mode/0</c></seealso>
+ selects the
+ <seealso marker="#callback_modes"><c>CallbackMode</c></seealso>
+ for the callback module, in this case
+ <seealso marker="stdlib:gen_statem#type-callback_mode"><c>state_functions</c></seealso>.
+ That is, each state has got its own handler function.
+ </p>
+
</section>
<!-- =================================================================== -->
@@ -533,12 +545,11 @@ handle_event({call,From}, code_length, #{code := Code} = Data) ->
</p>
<code type="erl"><![CDATA[
...
--define(CALLBACK_MODE, handle_event_function).
-
-...
-export([handle_event/4]).
...
+callback_mode() ->
+ handle_event_function.
handle_event(cast, {button,Digit}, State, #{code := Code} = Data) ->
case State of
@@ -597,7 +608,7 @@ init(Args) ->
callback function <c>terminate(shutdown, State, Data)</c>.
</p>
<p>
- In the following example, function <c>terminate/3</c>
+ In this example, function <c>terminate/3</c>
locks the door if it is open, so we do not accidentally leave the door
open when the supervision tree terminates:
</p>
@@ -962,16 +973,13 @@ do_unlock() ->
</p>
<code type="erl"><![CDATA[
...
--define(CALLBACK_MODE, state_functions).
-
-...
-
init(Code) ->
process_flag(trap_exit, true),
Data = #{code => Code},
- enter(?CALLBACK_MODE, locked, Data).
+ enter(ok, locked, Data).
-...
+callback_mode() ->
+ state_functions.
locked(internal, enter, _Data) ->
do_lock(),
@@ -1027,11 +1035,10 @@ 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]).
--export([init/1,terminate/3,code_change/4]).
+-export([init/1,callback_mode/0,terminate/3,code_change/4]).
-export([locked/3,open/3]).
start_link(Code) ->
@@ -1047,7 +1054,10 @@ code_length() ->
init(Code) ->
process_flag(trap_exit, true),
Data = #{code => Code},
- enter(?CALLBACK_MODE, locked, Data).
+ enter(ok, locked, Data).
+
+callback_mode() ->
+ state_functions.
locked(internal, enter, #{code := Code} = Data) ->
do_lock(),
@@ -1091,7 +1101,7 @@ terminate(_Reason, State, _Data) ->
State =/= locked andalso do_lock(),
ok.
code_change(_Vsn, State, Data, _Extra) ->
- {?CALLBACK_MODE,State,Data}.
+ {ok,State,Data}.
]]></code>
</section>
@@ -1106,12 +1116,11 @@ code_change(_Vsn, State, Data, _Extra) ->
</p>
<code type="erl"><![CDATA[
...
--define(CALLBACK_MODE, handle_event_function).
-
-...
-export([handle_event/4]).
...
+callback_mode() ->
+ handle_event_function.
%% State: locked
handle_event(internal, enter, locked, #{code := Code} = Data) ->
@@ -1208,7 +1217,8 @@ format_status(Opt, [_PDict,State,Data]) ->
<seealso marker="stdlib:gen_statem#Module:format_status/2"><c>Module:format_status/2</c></seealso>
function. If you do not, a default implementation is used that
does the same as this example function without filtering
- the <c>Data</c> term, that is, <c>StateData = {State,Data}</c>.
+ the <c>Data</c> term, that is, <c>StateData = {State,Data}</c>,
+ in this example containing sensitive information.
</p>
</section>
@@ -1273,11 +1283,10 @@ format_status(Opt, [_PDict,State,Data]) ->
-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]).
--export([init/1,terminate/3,code_change/4,format_status/2]).
+-export([init/1,callback_mode/0,terminate/3,code_change/4,format_status/2]).
-export([handle_event/4]).
start_link(Code, LockButton) ->
@@ -1296,7 +1305,10 @@ set_lock_button(LockButton) ->
init({Code,LockButton}) ->
process_flag(trap_exit, true),
Data = #{code => Code, remaining => undefined, timer => undefined},
- enter(?CALLBACK_MODE, {locked,LockButton}, Data, []).
+ enter(ok, {locked,LockButton}, Data, []).
+
+callback_mode() ->
+ handle_event_function.
handle_event(
{call,From}, {set_lock_button,NewLockButton},
@@ -1366,7 +1378,7 @@ terminate(_Reason, State, _Data) ->
State =/= locked andalso do_lock(),
ok.
code_change(_Vsn, State, Data, _Extra) ->
- {?CALLBACK_MODE,State,Data}.
+ {ok,State,Data}.
format_status(Opt, [_PDict,State,Data]) ->
StateData =
{State,
generated by cgit v1.2.3 (git 2.25.1) at 2024-12-20 14:23:51 +0000