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-rw-r--r--lib/stdlib/doc/src/gen_statem.xml71
1 files changed, 44 insertions, 27 deletions
diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml
index c21398d64d..adca3673be 100644
--- a/lib/stdlib/doc/src/gen_statem.xml
+++ b/lib/stdlib/doc/src/gen_statem.xml
@@ -32,8 +32,9 @@
<modulesummary>Generic State Machine Behaviour</modulesummary>
<description>
<p>
- A behaviour module for implementing a state machine.
- Two callback modes are supported. One for a finite state
+ A behaviour module for implementing a state machine. Two
+ <seealso marker="#type-callback_mode"><em>callback modes</em></seealso>
+ are supported. One for a finite state
machine like <seealso marker="gen_fsm">gen_fsm</seealso>
that requires the state to be an atom and use that state as
the name of the callback function for a particular state,
@@ -89,13 +90,13 @@ erlang:'!' -----> Module:StateName/3
The "<em>state function</em>" for a specific
<seealso marker="#type-state">state</seealso>
in a <c>gen_statem</c> is the callback function that is called
- for all events in this state, and is selected depending on
- <seealso marker="#type-callback_mode">callback_mode</seealso>
+ for all events in this state, and is selected depending on which
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
that the implementation specifies when the the server starts.
</p>
<p>
- When
- <seealso marker="#type-callback_mode">callback_mode</seealso>
+ When the
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
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">
@@ -110,7 +111,8 @@ erlang:'!' -----> Module:StateName/3
</seealso> makes the state name <c>terminate</c> unusable.
</p>
<p>
- When <seealso marker="#type-callback_mode">callback_mode</seealso>
+ When the
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
is <c>handle_event_function</c> the state can be any term
and the state function name is
<seealso marker="#Module:handle_event/4">
@@ -208,9 +210,7 @@ erlang:'!' -----> Module:StateName/3
<p>
This example shows a simple pushbutton model
for a toggling pushbutton implemented with
- <seealso marker="#type-callback_mode">
- callback_mode()
- </seealso>
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
<c>state_functions</c>.
You can push the button and it replies if it went on or off,
and you can ask for a count of how many times it has been
@@ -226,6 +226,7 @@ erlang:'!' -----> Module:StateName/3
-export([on/3,off/3]).
name() -> pushbutton_statem. % The registered server name
+callback_mode() -> state_functions.
%% API. This example uses a registered name name()
%% and does not link to the caller.
@@ -242,12 +243,12 @@ stop() ->
terminate(_Reason, _State, _Data) ->
void.
code_change(_Vsn, State, Data, _Extra) ->
- {ok,State,Data}.
+ {callback_mode(),State,Data}.
init([]) ->
%% Set the callback mode and initial state + data.
%% Data is used only as a counter.
State = off, Data = 0,
- {state_functions,State,Data}.
+ {callback_mode(),State,Data}.
%%% State functions
@@ -297,9 +298,7 @@ ok
<p>
And just to compare styles here is the same example using
- <seealso marker="#type-callback_mode">
- <c>callback_mode</c>
- </seealso>
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
<c>state_functions</c>, or rather here is code to replace
from the <c>init/1</c> function of the <c>pushbutton.erl</c>
example file above:
@@ -453,10 +452,8 @@ handle_event(_, _, State, Data) ->
<name name="state_name" />
<desc>
<p>
- If
- <seealso marker="#type-callback_mode">
- callback_mode
- </seealso>
+ If the
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
is <c>state_functions</c>,
the state has to be of this type.
</p>
@@ -499,7 +496,7 @@ handle_event(_, _, State, Data) ->
<name name="callback_mode" />
<desc>
<p>
- The <c>callback_mode</c> is selected when starting the
+ The <em>callback mode</em> is selected when starting the
<c>gen_statem</c> using the return value from
<seealso marker="#Module:init/1">Module:init/1</seealso>
or when calling
@@ -1277,7 +1274,7 @@ handle_event(_, _, State, Data) ->
return <c>{CallbackMode,State,Data}</c> or
<c>{CallbackMode,State,Data,Actions}</c>.
<c>CallbackMode</c> selects the
- <seealso marker="#type-callback_mode">callback_mode()</seealso>.
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>.
of the <c>gen_statem</c>.
<c>State</c> is the initial
<seealso marker="#type-state">state()</seealso>
@@ -1344,8 +1341,8 @@ handle_event(_, _, State, Data) ->
Whenever a <c>gen_statem</c> receives an event from
<seealso marker="#call/2">call/2</seealso>,
<seealso marker="#cast/2">cast/2</seealso> or
- as a normal process message one of these functions is called.
- If <seealso marker="#type-callback_mode">callback_mode</seealso>
+ as a normal process message one of these functions is called. If
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
is <c>state_functions</c> then <c>Module:StateName/3</c> is called,
and if it is <c>handle_event_function</c>
then <c>Module:handle_event/4</c> is called.
@@ -1468,7 +1465,11 @@ handle_event(_, _, State, Data) ->
<v>&nbsp;&nbsp;Vsn = term()</v>
<v>OldState = NewState = term()</v>
<v>Extra = term()</v>
- <v>Result = {ok,NewState,NewData} | Reason</v>
+ <v>Result = {NewCallbackMode,NewState,NewData} | Reason</v>
+ <v>
+ NewCallbackMode =
+ <seealso marker="#type-callback_mode">callback_mode()</seealso>
+ </v>
<v>
OldState = NewState =
<seealso marker="#type-state">state()</seealso>
@@ -1484,8 +1485,9 @@ handle_event(_, _, State, Data) ->
This function is called by a <c>gen_statem</c> when it should
update its internal state during a release upgrade/downgrade,
that is when the instruction <c>{update,Module,Change,...}</c>
- where <c>Change={advanced,Extra}</c> is given in
- the <c>appup</c> file. See
+ where <c>Change={advanced,Extra}</c> is given in the
+ <seealso marker="sasl:appup"><c>appup</c></seealso>
+ file. See
<seealso marker="doc/design_principles:release_handling#instr">
OTP Design Principles
</seealso>
@@ -1499,6 +1501,21 @@ handle_event(_, _, State, Data) ->
<c>Module</c>. If no such attribute is defined, the version
is the checksum of the BEAM file.
</p>
+ <note>
+ <p>
+ If you would dare to change
+ <seealso marker="#type-callback_mode"><em>callback mode</em></seealso>
+ during release upgrade/downgrade, the upgrade is no problem
+ since the new code surely knows what <em>callback mode</em>
+ it needs, but for a downgrade this function will have to
+ know from the <c>Extra</c> argument that comes from the
+ <seealso marker="sasl:appup"><c>appup</c></seealso>
+ file what <em>callback mode</em> the old code did use.
+ It may also be possible to figure this out
+ from the <c>{down,Vsn}</c> argument since <c>Vsn</c>
+ in effect defines the old callback module version.
+ </p>
+ </note>
<p>
<c>OldState</c> and <c>OldData</c> is the internal state
of the <c>gen_statem</c>.
@@ -1510,7 +1527,7 @@ handle_event(_, _, State, Data) ->
<p>
If successful, the function shall return the updated
internal state in an
- <c>{ok,NewState,NewData}</c> tuple.
+ <c>{NewCallbackMode,NewState,NewData}</c> tuple.
</p>
<p>
If the function returns <c>Reason</c>, the ongoing