diff options
Diffstat (limited to 'system/doc/design_principles')
| -rw-r--r-- | system/doc/design_principles/statem.xml | 90 |
1 files changed, 51 insertions, 39 deletions
diff --git a/system/doc/design_principles/statem.xml b/system/doc/design_principles/statem.xml index b63327291d..57e47431b8 100644 --- a/system/doc/design_principles/statem.xml +++ b/system/doc/design_principles/statem.xml @@ -33,7 +33,7 @@ <p> This section is to be read with the <seealso marker="stdlib:gen_statem"><c>gen_statem(3)</c></seealso> - manual page in <c>STDLIB</c>, where all interface functions and callback + manual page in STDLIB, where all interface functions and callback functions are described in detail. </p> <note> @@ -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> @@ -308,7 +310,7 @@ start_link(Code) -> as <c>{global,Name}</c>, then the <c>gen_statem</c> is registered using <seealso marker="kernel:global#register_name/2"><c>global:register_name/2</c></seealso> - in <c>Kernel</c>. + in Kernel. </p> </item> <item> @@ -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> @@ -755,7 +766,7 @@ stop() -> Suppose that we do not want a button to lock the door, instead we want to ignore button events in the <c>open</c> state. Then we start a timer when entering the <c>open</c> state - and waits for it to expire while ignoring button events: + and wait for it to expire while ignoring button events: </p> <code type="erl"><![CDATA[ ... @@ -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, |