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<HTML>
<HEAD>
<!-- refpage -->
<TITLE>gen_event</TITLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF">
<CENTER>
<A HREF="http://www.erlang.se"><IMG BORDER=0 ALT="[Erlang Systems]" SRC="min_head.gif"></A>
<H1>gen_event</H1>
</CENTER>
<H3>MODULE</H3>
<UL>
gen_event</UL>
<H3>MODULE SUMMARY</H3>
<UL>
Generic Event Handling Behaviour</UL>
<H3>DESCRIPTION</H3>
<UL>
<P>A behaviour module for implementing event handling functionality.
The OTP event handling model consists of a generic event manager
process with an arbitrary number of event handlers which are added and
deleted dynamically.<P> An event manager implemented using this module will have a standard
set of interface functions and include functionality for tracing and
error reporting. It will also fit into an OTP supervision tree.
Refer to <STRONG>OTP Design Principles</STRONG> for more information.<P>Each event handler is implemented as a callback module exporting
a pre-defined set of functions. The relationship between the behaviour
functions and the callback functions can be illustrated as follows:<PRE>gen_event module Callback module
--------------- -------------
gen_event:start -----> -
gen_event:add_handler
gen_event:add_suphandler -----> Module:init/1
gen_event:notify
gen_event:sync_notify -----> Module:handle_event/2
gen_event:call -----> Module:handle_call/2
- -----> Module:handle_info/2
gen_event:delete_handler -----> Module:terminate/2
gen_event:swap_handler
gen_event:swap_sup_handler -----> Module1:terminate/2
Module2:init/1
gen_event:which_handlers -----> -
gen_event:stop -----> Module:terminate/2
- -----> Module:code_change/3
</PRE>
<P>Since each event handler is one callback module, an event manager
will have several callback modules which are added and deleted
dynamically. Therefore <CODE>gen_event</CODE> is more tolerant of callback
module errors than the other behaviours. If a callback function for
an installed event handler fails with <CODE>Reason</CODE>, or returns a
bad value <CODE>Term</CODE>, the event manager will not fail. It will delete
the event handler by calling the callback function
<CODE>Module:terminate/2</CODE> (see below), giving as argument
<CODE>{error,{'EXIT',Reason}}</CODE> or <CODE>{error,Term}</CODE>, respectively.
No other event handler will be affected.<P>The <CODE>sys</CODE> module can be used for debugging an event manager.<P>Note that an event manager <STRONG>does</STRONG> trap exit signals
automatically.
<P>Unless otherwise stated, all functions in this module fail if
the specified event manager does not exist or if bad arguments are
given.</UL>
<H3>EXPORTS</H3>
<P><A NAME="start%0"><STRONG><CODE>start() -> Result</CODE></STRONG></A><BR>
<A NAME="start%1"><STRONG><CODE>start(EventMgrName) -> Result</CODE></STRONG></A><BR>
<A NAME="start_link%0"><STRONG><CODE>start_link() -> Result</CODE></STRONG></A><BR>
<A NAME="start_link%1"><STRONG><CODE>start_link(EventMgrName) -> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgrName = {local,Name} | {global,Name}</CODE></STRONG><BR>
<STRONG><CODE> Name = atom()</CODE></STRONG><BR>
<STRONG><CODE>Result = {ok,Pid} | {error,{already_started,Pid}}</CODE></STRONG><BR>
<STRONG><CODE> Pid = pid()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Creates an event manager.<P>An event manager started using <CODE>start_link</CODE> is linked to
the calling process. This function must be used if the event
manager is included in a supervision tree. An event manager started
using <CODE>start</CODE> is not linked to the calling process.<P>If <CODE>EventMgrName={local,Name}</CODE>, the event manager is
registered locally as <CODE>Name</CODE> using <CODE>register/2</CODE>.
If <CODE>EventMgrName={global,Name}</CODE>, the event manager is
registered globally as <CODE>Name</CODE> using
<CODE>global:register_name/2</CODE>. If no name is provided, the event
manager is not registered.<P>If the event manager is successfully created the function
returns <CODE>{ok,Pid}</CODE>, where <CODE>Pid</CODE> is the pid of the event
manager. If there already exists a process with the specified
<CODE>EventMgrName</CODE> the function returns
<CODE>{error,{already_started,Pid}}</CODE>, where <CODE>Pid</CODE> is the pid
of that process.</UL>
<P><A NAME="add_handler%3"><STRONG><CODE>add_handler(EventMgrRef, Handler, Args) -> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgr = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE> Name = Node = atom()</CODE></STRONG><BR>
<STRONG><CODE>Handler = Module | {Module,Id}</CODE></STRONG><BR>
<STRONG><CODE> Module = atom()</CODE></STRONG><BR>
<STRONG><CODE> Id = term()</CODE></STRONG><BR>
<STRONG><CODE>Args = term()</CODE></STRONG><BR>
<STRONG><CODE>Result = ok | {'EXIT',Reason} | term()</CODE></STRONG><BR>
<STRONG><CODE> Reason = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Adds a new event handler to the event manager <CODE>EventMgrRef</CODE>.
The event manager will call <CODE>Module:init/1</CODE> to initiate
the event handler and its internal state.<P><CODE>EventMgrRef</CODE> can be:<P><UL>
<LI>the pid,</LI><BR>
<LI><CODE>Name</CODE>, if the event manager is locally registered,
</LI><BR>
<LI><CODE>{Name,Node}</CODE>, if the event manager is locally
registered at another node, or</LI><BR>
<LI><CODE>{global,Name}</CODE>, if the event manager is globally
registered.</LI><BR>
</UL>
<P><CODE>Handler</CODE> is the name of the callback module <CODE>Module</CODE> or
a tuple <CODE>{Module,Id}</CODE>, where <CODE>Id</CODE> is any term.
The <CODE>{Module,Id}</CODE> representation makes it possible to
identify a specific event handler when there are several event
handlers using the same callback module.<P><CODE>Args</CODE> is an arbitrary term which is passed as the argument
to <CODE>Module:init/1</CODE>.<P>If <CODE>Module:init/1</CODE> returns a correct value, the event
manager adds the event handler and this function returns
<CODE>ok</CODE>. If <CODE>Module:init/1</CODE> fails with <CODE>Reason</CODE> or
returns an unexpected value <CODE>Term</CODE>, the event handler is
ignored and this function returns <CODE>{'EXIT',Reason}</CODE> or
<CODE>Term</CODE>, respectively.</UL>
<P><A NAME="add_sup_handler%3"><STRONG><CODE>add_sup_handler(EventMgrRef, Handler, Args) -> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgr = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE> Name = Node = atom()</CODE></STRONG><BR>
<STRONG><CODE>Handler = Module | {Module,Id}</CODE></STRONG><BR>
<STRONG><CODE> Module = atom()</CODE></STRONG><BR>
<STRONG><CODE> Id = term()</CODE></STRONG><BR>
<STRONG><CODE>Args = term()</CODE></STRONG><BR>
<STRONG><CODE>Result = ok | {'EXIT',Reason} | term()</CODE></STRONG><BR>
<STRONG><CODE> Reason = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Adds a new event handler in the same way as <CODE>add_handler/3</CODE>
but will also supervise the connection between the event handler
and the calling process.<P><UL>
<LI>If the calling process later terminates with <CODE>Reason</CODE>,
the event manager will delete the event handler by calling
<CODE>Module:terminate/2</CODE> with <CODE>{stop,Reason}</CODE> as argument.
</LI><BR>
<LI>If the event handler later is deleted, the event manager
sends a message<CODE>{gen_event_EXIT,Handler,Reason}</CODE> to
the calling process. <CODE>Reason</CODE> is one of the following:
<UL>
<LI> <CODE>normal</CODE>, if the event handler has been removed due to a
call to <CODE>delete_handler/3</CODE>, or <CODE>remove_handler</CODE>
has been returned by a callback function (see below).
</LI><BR>
<LI> <CODE>shutdown</CODE>, if the event handler has been removed
because the event manager is terminating.
</LI><BR>
<LI> <CODE>{swapped,NewHandler,Pid}</CODE>, if the process <CODE>Pid</CODE>
has replaced the event handler with another event handler
<CODE>NewHandler</CODE> using a call to <CODE>swap_handler/3</CODE> or
<CODE>swap_sup_handler/3</CODE>.
</LI><BR>
<LI> a term, if the event handler is removed due to an error.
Which term depends on the error.
</LI><BR>
</UL>
</LI><BR>
</UL>
<P>See <CODE>add_handler/3</CODE> for a description of the arguments
and return values.</UL>
<P><A NAME="notify%2"><STRONG><CODE>notify(EventMgrRef, Event) -> ok</CODE></STRONG></A><BR>
<A NAME="sync_notify%2"><STRONG><CODE>sync_notify(EventMgrRef, Event) -> ok</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgrRef = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE> Name = Node = atom()</CODE></STRONG><BR>
<STRONG><CODE>Event = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Sends an event notification to the event manager
<CODE>EventMgrRef</CODE>. The event manager will call
<CODE>Module:handle_event/2</CODE> for each installed event handler to
handle the event.<P><CODE>notify</CODE> is asynchronous and will return immediately after
the event notification has been sent. <CODE>sync_notify</CODE> is
synchronous in the sense that it will return <CODE>ok</CODE> after
the event has been handled by all event handlers.<P>See <CODE>add_handler/3</CODE> for a description of <CODE>EventMgrRef</CODE>.
<P><CODE>Event</CODE> is an arbitrary term which is passed as one of
the arguments to <CODE>Module:handle_event/2</CODE>.<P><CODE>notify</CODE> will not fail even if the specified event manager
does not exist, unless it is specified as <CODE>Name</CODE>.
</UL>
<P><A NAME="call%3"><STRONG><CODE>call(EventMgrRef, Handler, Request) -> Result</CODE></STRONG></A><BR>
<A NAME="call%4"><STRONG><CODE>call(EventMgrRef, Handler, Request, Timeout) -> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgrRef = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE> Name = Node = atom()</CODE></STRONG><BR>
<STRONG><CODE>Handler = Module | {Module,Id}</CODE></STRONG><BR>
<STRONG><CODE> Module = atom()</CODE></STRONG><BR>
<STRONG><CODE> Id = term()</CODE></STRONG><BR>
<STRONG><CODE>Request = term()</CODE></STRONG><BR>
<STRONG><CODE>Timeout = int()>0 | infinity</CODE></STRONG><BR>
<STRONG><CODE>Result = Reply | {error,Error}</CODE></STRONG><BR>
<STRONG><CODE> Reply = term()</CODE></STRONG><BR>
<STRONG><CODE> Error = bad_module | {'EXIT',Reason} | term()</CODE></STRONG><BR>
<STRONG><CODE>  Reason = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Makes a synchronous call to the event handler <CODE>Handler</CODE>
installed in the event manager <CODE>EventMgrRef</CODE> by sending a
request and waiting until a reply arrives or a timeout occurs.
The event manager will call <CODE>Module:handle_call/2</CODE> to handle
the request.<P>See <CODE>add_handler/3</CODE> for a description of <CODE>EventMgrRef</CODE>
and <CODE>Handler</CODE>.<P><CODE>Request</CODE> is an arbitrary term which is passed as one of
the arguments to <CODE>Module:handle_call/2</CODE>.<P><CODE>Timeout</CODE> is an integer greater than zero which specifies
how many milliseconds to wait for a reply, or the atom
<CODE>infinity</CODE> to wait indefinitely. Default value is 5000.
If no reply is received within the specified time, the function
call fails.<P>The return value <CODE>Reply</CODE> is defined in the return value of
<CODE>Module:handle_call/2</CODE>. If the specified event handler is not
installed, the function returns <CODE>{error,bad_module}</CODE>. If
the callback function fails with <CODE>Reason</CODE> or returns an
unexpected value <CODE>Term</CODE>, this function returns
<CODE>{error,{'EXIT',Reason}}</CODE> or <CODE>{error,Term}</CODE>,
respectively.</UL>
<P><A NAME="delete_handler%3"><STRONG><CODE>delete_handler(EventMgrRef, Handler, Args) -> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgrRef = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE> Name = Node = atom()</CODE></STRONG><BR>
<STRONG><CODE>Handler = Module | {Module,Id}</CODE></STRONG><BR>
<STRONG><CODE> Module = atom()</CODE></STRONG><BR>
<STRONG><CODE> Id = term()</CODE></STRONG><BR>
<STRONG><CODE>Args = term()</CODE></STRONG><BR>
<STRONG><CODE>Result = term() | {error,module_not_found} | {'EXIT',Reason}</CODE></STRONG><BR>
<STRONG><CODE> Reason = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Deletes an event handler from the event manager
<CODE>EventMgrRef</CODE>. The event manager will call
<CODE>Module:terminate/2</CODE> to terminate the event handler.<P>See <CODE>add_handler/3</CODE> for a description of <CODE>EventMgrRef</CODE>
and <CODE>Handler</CODE>.<P><CODE>Args</CODE> is an arbitrary term which is passed as one of
the arguments to <CODE>Module:terminate/2</CODE>.<P>The return value is the return value of <CODE>Module:terminate/2</CODE>.
If the specified event handler is not installed, the function
returns <CODE>{error,module_not_found}</CODE>. If the callback function
fails with <CODE>Reason</CODE>, the function returns
<CODE>{'EXIT',Reason}</CODE>.</UL>
<P><A NAME="swap_handler%5"><STRONG><CODE>swap_handler(EventMgrRef, {Handler1,Args1}, {Handler2,Args2})
-> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgrRef = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE> Name = Node = atom()</CODE></STRONG><BR>
<STRONG><CODE>Handler1 = Handler2 = Module | {Module,Id}</CODE></STRONG><BR>
<STRONG><CODE> Module = atom()</CODE></STRONG><BR>
<STRONG><CODE> Id = term()</CODE></STRONG><BR>
<STRONG><CODE>Args1 = Args2 = term()</CODE></STRONG><BR>
<STRONG><CODE>Result = ok | {error,Error}</CODE></STRONG><BR>
<STRONG><CODE> Error = {'EXIT',Reason} | term()</CODE></STRONG><BR>
<STRONG><CODE>  Reason = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Replaces an old event handler with a new event handler in
the event manager <CODE>EventMgrRef</CODE>.<P>See <CODE>add_handler/3</CODE> for a description of the arguments.<P>First the old event handler <CODE>Handler1</CODE> is deleted.
The event manager calls <CODE>Module1:terminate(Args1, ...)</CODE>,
where <CODE>Module1</CODE> is the callback module of <CODE>Handler1</CODE>,
and collects the return value.<P>Then the new event handler <CODE>Handler2</CODE> is added and initiated
by calling <CODE>Module2:init({Args2,Term})</CODE>, where <CODE>Module2</CODE>
is the callback module of <CODE>Handler2</CODE> and <CODE>Term</CODE>
the return value of <CODE>Module1:terminate/2</CODE>. This makes it
possible to transfer information from <CODE>Handler1</CODE> to
<CODE>Handler2</CODE>.<P>The new handler will be added even if the the specified old event
handler is not installed in which case <CODE>Term=error</CODE>, or if
<CODE>Module1:terminate/2</CODE> fails with <CODE>Reason</CODE> in which case
<CODE>Term={'EXIT',Reason}</CODE>.
The old handler will be deleted even if <CODE>Module2:init/1</CODE>
fails.<P>If there was a supervised connection between <CODE>Handler1</CODE> and
a process <CODE>Pid</CODE>, there will be a supervised connection
between <CODE>Handler2</CODE> and <CODE>Pid</CODE> instead.<P>If <CODE>Module2:init/1</CODE> returns a correct value, this function
returns <CODE>ok</CODE>. If <CODE>Module2:init/1</CODE> fails with
<CODE>Reason</CODE> or returns an unexpected value <CODE>Term</CODE>, this
this function returns <CODE>{error,{'EXIT',Reason}}</CODE> or
<CODE>{error,Term}</CODE>, respectively.</UL>
<P><A NAME="swap_sup_handler%5"><STRONG><CODE>swap_sup_handler(EventMgrRef, {Handler1,Args1}, {Handler2,Args2})
-> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgrRef = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE> Name = Node = atom()</CODE></STRONG><BR>
<STRONG><CODE>Handler1 = Handler 2 = Module | {Module,Id}</CODE></STRONG><BR>
<STRONG><CODE> Module = atom()</CODE></STRONG><BR>
<STRONG><CODE> Id = term()</CODE></STRONG><BR>
<STRONG><CODE>Args1 = Args2 = term()</CODE></STRONG><BR>
<STRONG><CODE>Result = ok | {error,Error}</CODE></STRONG><BR>
<STRONG><CODE> Error = {'EXIT',Reason} | term()</CODE></STRONG><BR>
<STRONG><CODE>  Reason = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Replaces an event handler in the event manager <CODE>EventMgrRef</CODE>
in the same way as <CODE>swap_handler/3</CODE> but will also supervise
the connection between <CODE>Handler2</CODE> and the calling process.<P>See <CODE>swap_handler/3</CODE> for a description of the arguments
and return values.</UL>
<P><A NAME="which_handlers%1"><STRONG><CODE>which_handlers(EventMgrRef) -> [Handler]</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgrRef = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE> Name = Node = atom()</CODE></STRONG><BR>
<STRONG><CODE>Handler = Module | {Module,Id}</CODE></STRONG><BR>
<STRONG><CODE> Module = atom()</CODE></STRONG><BR>
<STRONG><CODE> Id = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Returns a list of all event handlers installed in the event
manager <CODE>EventMgrRef</CODE>.<P>See <CODE>add_handler/3</CODE> for a description of <CODE>EventMgrRef</CODE>
and <CODE>Handler</CODE>.</UL>
<P><A NAME="stop%1"><STRONG><CODE>stop(EventMgrRef) -> ok</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>EventMgrRef = Name | {Name,Node} | {global,Name} | pid()</CODE></STRONG><BR>
<STRONG><CODE>Name = Node = atom()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Terminates the event manager <CODE>EventMgrRef</CODE>. Before
terminating, the event manager will call
<CODE>Module:terminate(stop,...)</CODE> for each installed event
handler.<P>See <CODE>add_handler/3</CODE> for a description of the argument.</UL>
<H3>CALLBACK FUNCTIONS</H3>
<UL>
<P>The following functions should be exported from a <CODE>gen_event</CODE>
callback module.</UL>
<H3>EXPORTS</H3>
<P><A NAME="Module:init%1"><STRONG><CODE>Module:init(InitArgs) -> {ok,State}</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>InitArgs = Args | {Args,Term}</CODE></STRONG><BR>
<STRONG><CODE> Args = Term = term()</CODE></STRONG><BR>
<STRONG><CODE>State = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Whenever a new event handler is added to an event manager,
this function is called to initialize the event handler.<P>If the event handler is added due to a call to
<CODE>gen_event:add_handler/3</CODE> or
<CODE>gen_event:add_sup_handler/3</CODE>, <CODE>InitArgs</CODE> is
the <CODE>Args</CODE> argument of these functions.<P>If the event handler is replacing another event handler due to
a call to <CODE>gen_event:swap_handler/3</CODE> or
<CODE>gen_event:swap_sup_handler/3</CODE>, or due to a <CODE>swap</CODE>
return tuple from one of the other callback functions,
<CODE>InitArgs</CODE> is a tuple <CODE>{Args,Term}</CODE> where <CODE>Args</CODE> is
the argument provided in the function call/return tuple and
<CODE>Term</CODE> is the result of terminating the old event handler,
see <CODE>gen_event:swap_handler/3</CODE>.<P>The function should return <CODE>{ok,State}</CODE> where <CODE>State</CODE>
is the initial internal state of the event handler.</UL>
<P><A NAME="Module:handle_event%2"><STRONG><CODE>Module:handle_event(Event, State) -> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Event = term()</CODE></STRONG><BR>
<STRONG><CODE>State = term()</CODE></STRONG><BR>
<STRONG><CODE>Result = {ok,NewState}</CODE></STRONG><BR>
<STRONG><CODE> | {swap_handler,Args1,NewState,Handler2,Args2} |
remove_handler</CODE></STRONG><BR>
<STRONG><CODE> NewState = term()</CODE></STRONG><BR>
<STRONG><CODE> Args1 = Args2 = term()</CODE></STRONG><BR>
<STRONG><CODE> Handler2 = Module2 | {Module2,Id}</CODE></STRONG><BR>
<STRONG><CODE>  Module2 = atom()</CODE></STRONG><BR>
<STRONG><CODE>  Id = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Whenever an event manager receives an event sent using
<CODE>gen_event:notify/2</CODE> or <CODE>gen_event:sync_notify/2</CODE>, this
function is called for each installed event handler to handle
the event.<P><CODE>Event</CODE> is the <CODE>Event</CODE> argument of
<CODE>notify</CODE>/<CODE>sync_notify</CODE>.<P><CODE>State</CODE> is the internal state of the event handler.<P>If the function returns <CODE>{ok,NewState}</CODE> the event handler
will remain in the event manager with the possible updated
internal state <CODE>NewState</CODE>.<P>If the function returns
<CODE>{swap_handler,Args1,NewState,Handler2,Args2}</CODE> the event
handler will be replaced by <CODE>Handler2</CODE> by first calling
<CODE>Module:terminate(Args1,NewState)</CODE> and then
<CODE>Module2:init({Args2,Term})</CODE> where <CODE>Term</CODE> is the return
value of <CODE>Module:terminate/2</CODE>.
See <CODE>gen_event:swap_handler/3</CODE> for more information.<P>If the function returns <CODE>remove_handler</CODE> the event handler
will be deleted by calling
<CODE>Module:terminate(remove_handler,State)</CODE>.</UL>
<P><A NAME="Module:handle_call%2"><STRONG><CODE>Module:handle_call(Request, State) -> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Request = term()</CODE></STRONG><BR>
<STRONG><CODE>State = term()</CODE></STRONG><BR>
<STRONG><CODE>Result = {ok,Reply,NewState}</CODE></STRONG><BR>
<STRONG><CODE> | {swap_handler,Reply,Args1,NewState,Handler2,Args2}</CODE></STRONG><BR>
<STRONG><CODE> | {remove_handler, Reply}</CODE></STRONG><BR>
<STRONG><CODE> Reply = term()</CODE></STRONG><BR>
<STRONG><CODE> NewState = term()</CODE></STRONG><BR>
<STRONG><CODE> Args1 = Args2 = term()</CODE></STRONG><BR>
<STRONG><CODE> Handler2 = Module2 | {Module2,Id}</CODE></STRONG><BR>
<STRONG><CODE>  Module2 = atom()</CODE></STRONG><BR>
<STRONG><CODE>  Id = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Whenever an event manager receives a request sent using
<CODE>gen_event:call/3,4</CODE>, this function is called for
the specified event handler to handle the request.<P><CODE>Request</CODE> is the <CODE>Request</CODE> argument of <CODE>call</CODE>.<P><CODE>State</CODE> is the internal state of the event handler.<P>The return values are the same as for <CODE>handle_event/2</CODE>
except they also contain a term <CODE>Reply</CODE> which is the reply
given back to the client as the return value of <CODE>call</CODE>.</UL>
<P><A NAME="Module:handle_info%2"><STRONG><CODE>Module:handle_info(Info, State) -> Result</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Info = term()</CODE></STRONG><BR>
<STRONG><CODE>State = term()</CODE></STRONG><BR>
<STRONG><CODE>Result = {ok,NewState}</CODE></STRONG><BR>
<STRONG><CODE> | {swap_handler,Args1,NewState,Handler2,Args2} |
remove_handler</CODE></STRONG><BR>
<STRONG><CODE> NewState = term()</CODE></STRONG><BR>
<STRONG><CODE> Args1 = Args2 = term()</CODE></STRONG><BR>
<STRONG><CODE> Handler2 = Module2 | {Module2,Id}</CODE></STRONG><BR>
<STRONG><CODE>  Module2 = atom()</CODE></STRONG><BR>
<STRONG><CODE>  Id = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>This function is called for each installed event handler when
an event manager receives any other message than an event or
a synchronous request (or a system message).<P><CODE>Info</CODE> is the received message.<P>See <CODE>Module:handle_event/2</CODE> for a description of State
and possible return values.</UL>
<P><A NAME="Module:terminate%2"><STRONG><CODE>Module:terminate(Arg, State) -> term()</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Arg = Args | {stop,Reason} | stop | remove_handler</CODE></STRONG><BR>
<STRONG><CODE> | {error,{'EXIT',Reason}} | {error,Term}</CODE></STRONG><BR>
<STRONG><CODE> Args = Reason = Term = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Whenever an event handler is deleted from an event manager,
this function is called. It should be the opposite of
<CODE>Module:init/1</CODE> and do any necessary cleaning up.<P>If the event handler is deleted due to a call to
<CODE>gen_event:delete_handler</CODE>, <CODE>gen_event:swap_handler/3</CODE>
or <CODE>gen_event:swap_sup_handler/3</CODE>, <CODE>Arg</CODE> is
the <CODE>Args</CODE> argument of this function call.<P><CODE>Arg={stop,Reason}</CODE> if the event handler has a supervised
connection to a process which has terminated with reason
<CODE>Reason</CODE>.<P><CODE>Arg=stop</CODE> if the event handler is deleted because
the event manager is terminating.<P><CODE>Arg=remove_handler</CODE> if the event handler is deleted because
another callback function has returned <CODE>remove_handler</CODE> or
<CODE>{remove_handler,Reply}</CODE>.<P><CODE>Arg={error,Term}</CODE> if the event handler is deleted because
a callback function returned an unexpected value <CODE>Term</CODE>,
or <CODE>Arg={error,{'EXIT',Reason}}</CODE> if a callback function
failed.<P><CODE>State</CODE> is the internal state of the event handler.<P>The function may return any term. If the event handler is
deleted due to a call to <CODE>gen_event:delete_handler</CODE>,
the return value of that function will be the return value of this
function. If the event handler is to be replaced with another event
handler due to a swap, the return value will be passed to
the <CODE>init</CODE> function of the new event handler. Otherwise
the return value is ignored.</UL>
<P><A NAME="Module:code_change%3"><STRONG><CODE>Module:code_change(OldVsn, State, Extra) -> {ok, NewState}</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>OldVsn = undefined | term()</CODE></STRONG><BR>
<STRONG><CODE>State = NewState = term()</CODE></STRONG><BR>
<STRONG><CODE>Extra = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>This function is called for each installed event handler they
should update the internal state due to code replacement, i.e. when
the instruction
<CODE>{update,Module,Change,PrePurge,PostPurge,Modules</CODE> where
<CODE>Change={advanced,Extra}</CODE> has been given to the release
handler. See <STRONG>SASL User's Guide</STRONG> for more information.<P><CODE>OldVsn</CODE> is the <CODE>vsn</CODE> attribute of the old version of
the callback module <CODE>Module</CODE>, or <CODE>undefined</CODE> if no such
attribute is defined.<P><CODE>State</CODE> is the internal state of the event handler.<P><CODE>Extra</CODE> is the same as in the <CODE>{advanced,Extra}</CODE> part
of the update instruction.<P>The function should return <CODE>{ok,NewState}</CODE>, where
<CODE>NewState</CODE> is the updated internal state.</UL>
<H3>SEE ALSO</H3>
<UL>
<P>supervisor(3), sys(3)</UL>
<H3>AUTHORS</H3>
<UL>
Gunilla Hugosson - support@erlang.ericsson.se<BR>
</UL>
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