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Diffstat (limited to 'system/doc/design_principles/statem.xml')
| -rw-r--r-- | system/doc/design_principles/statem.xml | 21 |
1 files changed, 16 insertions, 5 deletions
diff --git a/system/doc/design_principles/statem.xml b/system/doc/design_principles/statem.xml index 65daeac782..02754bd23d 100644 --- a/system/doc/design_principles/statem.xml +++ b/system/doc/design_principles/statem.xml @@ -90,7 +90,7 @@ State(S) x Event(E) -> Actions(A), State(S')</pre> <pre> StateName(EventType, EventContent, Data) -> .. code for actions here ... - {next_state, StateName', Data'}.</pre> + {next_state, NewStateName, NewData}.</pre> <p> In the mode <c>handle_event_function</c> there is only one Erlang function that implements all state transition rules: @@ -612,7 +612,7 @@ stop() -> An example of event postponing comes in later in this chapter. See the <seealso marker="stdlib:gen_statem#type-action"> - documentation + reference manual </seealso> for details. You can for example actually reply to several callers and generate multiple next events to handle. @@ -735,7 +735,8 @@ open(cast, {button,_}, Data) -> <c>erlang:cancel_timer(Tref)</c>. </seealso> Note that a timeout message can not arrive after this, - unless you have postponed it before (why on earth one would do that). + unless you have postponed it (see the next section) before, + so make sure you do not accidentally postpone such messages. </p> <p> Another way to cancel a timer is to not cancel it, @@ -838,14 +839,24 @@ do_unlock() -> to implicitly postpone any events to the <c>locked</c> state. </p> <p> + A selective receive can not be used from a <c>gen_statem</c> + behaviour just as for any <c>gen_*</c> behavior + since the receive statement is within the <c>gen_*</c> engine itself. + It has to be there because all + <seealso marker="stdlib:sys"><c>sys</c></seealso> + compatible behaviours must respond to system messages and therefore + do that in their engine receive loop, + passing non-system messages to the callback module. + </p> + <p> The <seealso marker="stdlib:gen_statem#type-action"> state transition action </seealso> <c>postpone</c> is designed to be able to model - selective receive. Selective receive implicitly postpones + selective receives. A selective receive implicitly postpones any not received events, but the <c>postpone</c> - state transition action explicitly postpones a received event. + state transition action explicitly postpones one received event. </p> <p> Other than that both mechanisms have got the same theoretical |