diff options
Diffstat (limited to 'lib/stdlib/doc/src')
| -rw-r--r-- | lib/stdlib/doc/src/gen_statem.xml | 66 |
1 files changed, 54 insertions, 12 deletions
diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml index 4708fc1301..90d2326954 100644 --- a/lib/stdlib/doc/src/gen_statem.xml +++ b/lib/stdlib/doc/src/gen_statem.xml @@ -35,10 +35,10 @@ A behaviour module for implementing a state machine. Two callback modes are supported. One for a finite state machine like <seealso marker="gen_fsm">gen_fsm</seealso> - that require the state to be an atom and use that state as + that requires the state to be an atom and use that state as the name of the callback function for a particular state, - and one without restriction on the state that use the same - callback function for all states. + and one without restriction on the state data type + that uses the same callback function for all states. </p> <p> A generic state machine process (<c>gen_statem</c>) implemented @@ -96,7 +96,7 @@ erlang:'!' -----> Module:StateName/3 <p> When <seealso marker="#type-callback_mode">callback_mode</seealso> - is <c>state_functions</c> the state has to be an atom and + is <c>state_functions</c>, the state has to be an atom and is used as the state function name. See <seealso marker="#Module:StateName/3"> <c>Module:StateName/3</c> @@ -127,8 +127,8 @@ erlang:'!' -----> Module:StateName/3 <seealso marker="#state_function">state function</seealso> in that order. The state function can postpone an event so it is not retried in the current state. - After a state change all enqueued events (including postponed) - are again presented to the state function. + After a state change all enqueued events (including postponed ones) + are presented again to the state function. </p> <p> The <c>gen_statem</c> event queue model is sufficient @@ -177,8 +177,10 @@ erlang:'!' -----> Module:StateName/3 </p> <p> Note that a <c>gen_statem</c> does not trap exit signals - automatically, this must be explicitly initiated by - the callback module. + automatically, this must be explicitly initiated in + the callback module (by calling + <seealso marker="erts:erlang#process_flag/2"> + <c>process_flag(trap_exit, true)</c></seealso>. </p> <p> Unless otherwise stated, all functions in this module fail if @@ -293,6 +295,42 @@ ok in function gen:do_for_proc/2 (gen.erl, line 261) in call from gen_statem:call/3 (gen_statem.erl, line 386) </pre> + + <p> + And just to compare styles here is the same example using + <seealso marker="#type-callback_mode"> + <c>callback_mode</c> + </seealso> + <c>state_functions</c>, or rather here is code to replace + from the <c>init/1</c> function of the <c>pushbutton</c> + example module 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}. + + +%%% Event handling + +handle_event({call,Caller}, push, off, Data) -> + %% Go to 'on', increment count and reply + %% that the resulting status is 'on' + {next_state,on,Data+1,[{reply,Caller,on}]}; +handle_event({call,Caller}, push, on, Data) -> + %% Go to 'off' and reply that the resulting status is 'off' + {next_state,off,Data,[{reply,Caller,off}]}; +%% +%% Event handling common to all states +handle_event({call,Caller}, get_count, State, Data) -> + %% Reply with the current count + {next_state,State,Data,[{reply,Caller,Data}]}; +handle_event(_, _, State, Data) -> + %% Ignore all other events + {next_state,State,Data}. + </code> </section> <datatypes> @@ -564,8 +602,8 @@ ok <desc> <p> If <c>true</c> postpone the current event and retry - it when the state changes that is: - <c>NextState =/= State</c>. + it when the state changes + (<c>NextState =/= State</c>). </p> </desc> </datatype> @@ -778,14 +816,18 @@ ok The <c>gen_statem</c> will keep the current state, or do a state transition to the current state if you like, set <c><anno>NewData</anno></c> - and execute all <c><anno>Actions</anno></c> + and execute all <c><anno>Actions</anno></c>. + This is the same as + <c>{next_state,CurrentState,<anno>NewData</anno>,<anno>Actions</anno>}</c>. </item> <tag><c>keep_state_and_data</c></tag> <item> The <c>gen_statem</c> will keep the current state or do a state transition to the current state if you like, keep the current server data, - and execute all <c><anno>Actions</anno></c> + and execute all <c><anno>Actions</anno></c>. + This is the same as + <c>{next_state,CurrentState,CurrentData,<anno>Actions</anno>}</c>. </item> </taglist> <p> |