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diff --git a/lib/stdlib/doc/src/gen_server.xml b/lib/stdlib/doc/src/gen_server.xml new file mode 100644 index 0000000000..8496802259 --- /dev/null +++ b/lib/stdlib/doc/src/gen_server.xml @@ -0,0 +1,612 @@ +<?xml version="1.0" encoding="latin1" ?> +<!DOCTYPE erlref SYSTEM "erlref.dtd"> + +<erlref> + <header> + <copyright> + <year>1996</year><year>2009</year> + <holder>Ericsson AB. All Rights Reserved.</holder> + </copyright> + <legalnotice> + The contents of this file are subject to the Erlang Public License, + Version 1.1, (the "License"); you may not use this file except in + compliance with the License. You should have received a copy of the + Erlang Public License along with this software. If not, it can be + retrieved online at http://www.erlang.org/. + + Software distributed under the License is distributed on an "AS IS" + basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See + the License for the specific language governing rights and limitations + under the License. + + </legalnotice> + + <title>gen_server</title> + <prepared></prepared> + <docno></docno> + <date></date> + <rev></rev> + </header> + <module>gen_server</module> + <modulesummary>Generic Server Behaviour</modulesummary> + <description> + <p>A behaviour module for implementing the server of a client-server + relation. A generic server process (gen_server) 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 + <seealso marker="doc/design_principles:gen_server_concepts">OTP Design Principles</seealso> for more information.</p> + <p>A gen_server assumes all specific parts to be located in 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:</p> + <pre> +gen_server module Callback module +----------------- --------------- +gen_server:start_link -----> Module:init/1 + +gen_server:call +gen_server:multi_call -----> Module:handle_call/3 + +gen_server:cast +gen_server:abcast -----> Module:handle_cast/2 + +- -----> Module:handle_info/2 + +- -----> Module:terminate/2 + +- -----> Module:code_change/3 </pre> + <p>If a callback function fails or returns a bad value, + the gen_server will terminate.</p> + <p>A gen_server handles system messages as documented in + <seealso marker="sys">sys(3)</seealso>. The <c>sys</c> module + can be used for debugging a gen_server.</p> + <p>Note that a gen_server does not trap exit signals automatically, + this must be explicitly initiated in the callback module.</p> + <p>Unless otherwise stated, all functions in this module fail if + the specified gen_server does not exist or if bad arguments are + given.</p> + + <p>The gen_server process can go into hibernation + (see <seealso marker="erts:erlang#erlang:hibernate/3">erlang(3)</seealso>) if a callback + function specifies <c>'hibernate'</c> instead of a timeout value. This + might be useful if the server is expected to be idle for a long + time. However this feature should be used with care as hibernation + implies at least two garbage collections (when hibernating and + shortly after waking up) and is not something you'd want to do + between each call to a busy server.</p> + + </description> + <funcs> + <func> + <name>start_link(Module, Args, Options) -> Result</name> + <name>start_link(ServerName, Module, Args, Options) -> Result</name> + <fsummary>Create a gen_server process in a supervision tree.</fsummary> + <type> + <v>ServerName = {local,Name} | {global,GlobalName}</v> + <v> Name = atom()</v> + <v> GlobalName = term()</v> + <v>Module = atom()</v> + <v>Args = term()</v> + <v>Options = [Option]</v> + <v> Option = {debug,Dbgs} | {timeout,Time} | {spawn_opt,SOpts}</v> + <v> Dbgs = [Dbg]</v> + <v> Dbg = trace | log | statistics | {log_to_file,FileName} | {install,{Func,FuncState}}</v> + <v> SOpts = [term()]</v> + <v>Result = {ok,Pid} | ignore | {error,Error}</v> + <v> Pid = pid()</v> + <v> Error = {already_started,Pid} | term()</v> + </type> + <desc> + <p>Creates a gen_server process as part of a supervision tree. + The function should be called, directly or indirectly, by + the supervisor. It will, among other things, ensure that + the gen_server is linked to the supervisor.</p> + <p>The gen_server process calls <c>Module:init/1</c> to + initialize. To ensure a synchronized start-up procedure, + <c>start_link/3,4</c> does not return until + <c>Module:init/1</c> has returned.</p> + <p>If <c>ServerName={local,Name}</c> the gen_server is + registered locally as <c>Name</c> using <c>register/2</c>. + If <c>ServerName={global,GlobalName}</c> the gen_server is + registered globally as <c>GlobalName</c> using + <c>global:register_name/2</c>. If no name is provided, + the gen_server is not registered.</p> + <p><c>Module</c> is the name of the callback module.</p> + <p><c>Args</c> is an arbitrary term which is passed as + the argument to <c>Module:init/1</c>.</p> + <p>If the option <c>{timeout,Time}</c> is present, + the gen_server is allowed to spend <c>Time</c> milliseconds + initializing or it will be terminated and the start function + will return <c>{error,timeout}</c>.</p> + <p>If the option <c>{debug,Dbgs}</c> is present, + the corresponding <c>sys</c> function will be called for each + item in <c>Dbgs</c>. See + <seealso marker="sys">sys(3)</seealso>.</p> + <p>If the option <c>{spawn_opt,SOpts}</c> is present, + <c>SOpts</c> will be passed as option list to + the <c>spawn_opt</c> BIF which is used to spawn + the gen_server. See + <seealso marker="erts:erlang#spawn_opt/2">erlang(3)</seealso>.</p> + <note> + <p>Using the spawn option <c>monitor</c> is currently not + allowed, but will cause the function to fail with reason + <c>badarg</c>.</p> + </note> + <p>If the gen_server is successfully created and initialized + the function returns <c>{ok,Pid}</c>, where <c>Pid</c> is + the pid of the gen_server. If there already exists a process + with the specified <c>ServerName</c> the function returns + <c>{error,{already_started,Pid}}</c>, where <c>Pid</c> is + the pid of that process.</p> + <p>If <c>Module:init/1</c> fails with <c>Reason</c>, + the function returns <c>{error,Reason}</c>. If + <c>Module:init/1</c> returns <c>{stop,Reason}</c> or + <c>ignore</c>, the process is terminated and the function + returns <c>{error,Reason}</c> or <c>ignore</c>, respectively.</p> + </desc> + </func> + <func> + <name>start(Module, Args, Options) -> Result</name> + <name>start(ServerName, Module, Args, Options) -> Result</name> + <fsummary>Create a stand-alone gen_server process.</fsummary> + <type> + <v>ServerName = {local,Name} | {global,GlobalName}</v> + <v> Name = atom()</v> + <v> GlobalName = term()</v> + <v>Module = atom()</v> + <v>Args = term()</v> + <v>Options = [Option]</v> + <v> Option = {debug,Dbgs} | {timeout,Time} | {spawn_opt,SOpts}</v> + <v> Dbgs = [Dbg]</v> + <v> Dbg = trace | log | statistics | {log_to_file,FileName} | {install,{Func,FuncState}}</v> + <v> SOpts = [term()]</v> + <v>Result = {ok,Pid} | ignore | {error,Error}</v> + <v> Pid = pid()</v> + <v> Error = {already_started,Pid} | term()</v> + </type> + <desc> + <p>Creates a stand-alone gen_server process, i.e. a gen_server + which is not part of a supervision tree and thus has no + supervisor.</p> + <p>See <seealso marker="#start_link/3">start_link/3,4</seealso> + for a description of arguments and return values.</p> + </desc> + </func> + <func> + <name>call(ServerRef, Request) -> Reply</name> + <name>call(ServerRef, Request, Timeout) -> Reply</name> + <fsummary>Make a synchronous call to a generic server.</fsummary> + <type> + <v>ServerRef = Name | {Name,Node} | {global,GlobalName} | pid()</v> + <v> Node = atom()</v> + <v> GlobalName = term()</v> + <v>Request = term()</v> + <v>Timeout = int()>0 | infinity</v> + <v>Reply = term()</v> + </type> + <desc> + <p>Makes a synchronous call to the gen_server <c>ServerRef</c> + by sending a request and waiting until a reply arrives or a + timeout occurs. The gen_server will call + <c>Module:handle_call/3</c> to handle the request.</p> + <p><c>ServerRef</c> can be:</p> + <list type="bulleted"> + <item>the pid,</item> + <item><c>Name</c>, if the gen_server is locally registered,</item> + <item><c>{Name,Node}</c>, if the gen_server is locally + registered at another node, or</item> + <item><c>{global,GlobalName}</c>, if the gen_server is + globally registered.</item> + </list> + <p><c>Request</c> is an arbitrary term which is passed as one of + the arguments to <c>Module:handle_call/3</c>.</p> + <p><c>Timeout</c> is an integer greater than zero which + specifies how many milliseconds to wait for a reply, or + the atom <c>infinity</c> to wait indefinitely. Default value + is 5000. If no reply is received within the specified time, + the function call fails. If the caller catches the failure + and continues running, and the server is just late with the reply, + it may arrive at any time later into the caller's message queue. + The caller must in this case be prepared for this + and discard any such garbage messages that are two element + tuples with a reference as the first element.</p> + <p>The return value <c>Reply</c> is defined in the return value + of <c>Module:handle_call/3</c>.</p> + <p>The call may fail for several reasons, including timeout and + the called gen_server dying before or during the call.</p> + <p>The ancient behaviour of sometimes consuming the server + exit message if the server died during the call while + linked to the client has been removed in OTP R12B/Erlang 5.6.</p> + </desc> + </func> + <func> + <name>multi_call(Name, Request) -> Result</name> + <name>multi_call(Nodes, Name, Request) -> Result</name> + <name>multi_call(Nodes, Name, Request, Timeout) -> Result</name> + <fsummary>Make a synchronous call to several generic servers.</fsummary> + <type> + <v>Nodes = [Node]</v> + <v> Node = atom()</v> + <v>Name = atom()</v> + <v>Request = term()</v> + <v>Timeout = int()>=0 | infinity</v> + <v>Result = {Replies,BadNodes}</v> + <v> Replies = [{Node,Reply}]</v> + <v> Reply = term()</v> + <v>BadNodes = [Node]</v> + </type> + <desc> + <p>Makes a synchronous call to all gen_servers locally + registered as <c>Name</c> at the specified nodes by first + sending a request to every node and then waiting for + the replies. The gen_servers will call + <c>Module:handle_call/3</c> to handle the request.</p> + <p>The function returns a tuple <c>{Replies,BadNodes}</c> where + <c>Replies</c> is a list of <c>{Node,Reply}</c> and + <c>BadNodes</c> is a list of node that either did not exist, + or where the gen_server <c>Name</c> did not exist or did not + reply.</p> + <p><c>Nodes</c> is a list of node names to which the request + should be sent. Default value is the list of all known nodes + <c>[node()|nodes()]</c>.</p> + <p><c>Name</c> is the locally registered name of each + gen_server.</p> + <p><c>Request</c> is an arbitrary term which is passed as one of + the arguments to <c>Module:handle_call/3</c>.</p> + <p><c>Timeout</c> is an integer greater than zero which + specifies how many milliseconds to wait for each reply, or + the atom <c>infinity</c> to wait indefinitely. Default value + is <c>infinity</c>. If no reply is received from a node within + the specified time, the node is added to <c>BadNodes</c>.</p> + <p>When a reply <c>Reply</c> is received from the gen_server at + a node <c>Node</c>, <c>{Node,Reply}</c> is added to + <c>Replies</c>. <c>Reply</c> is defined in the return value of + <c>Module:handle_call/3</c>.</p> + <warning> + <p>If one of the nodes is not capable of process monitors, + for example C or Java nodes, and the gen_server is not started + when the requests are sent, but starts within 2 seconds, + this function waits the whole <c>Timeout</c>, + which may be infinity.</p> + <p>This problem does not exist if all nodes are Erlang nodes.</p> + </warning> + <p>To avoid that late answers (after the timeout) pollutes + the caller's message queue, a middleman process is used to + do the actual calls. Late answers will then be discarded + when they arrive to a terminated process.</p> + </desc> + </func> + <func> + <name>cast(ServerRef, Request) -> ok</name> + <fsummary>Send an asynchronous request to a generic server.</fsummary> + <type> + <v>ServerRef = Name | {Name,Node} | {global,GlobalName} | pid()</v> + <v> Node = atom()</v> + <v> GlobalName = term()</v> + <v>Request = term()</v> + </type> + <desc> + <p>Sends an asynchronous request to the gen_server + <c>ServerRef</c> and returns <c>ok</c> immediately, ignoring + if the destination node or gen_server does not exist. + The gen_server will call <c>Module:handle_cast/2</c> to + handle the request.</p> + <p>See <seealso marker="#call/2">call/2,3</seealso> for a + description of <c>ServerRef</c>.</p> + <p><c>Request</c> is an arbitrary term which is passed as one + of the arguments to <c>Module:handle_cast/2</c>.</p> + </desc> + </func> + <func> + <name>abcast(Name, Request) -> abcast</name> + <name>abcast(Nodes, Name, Request) -> abcast</name> + <fsummary>Send an asynchronous request to several generic servers.</fsummary> + <type> + <v>Nodes = [Node]</v> + <v> Node = atom()</v> + <v>Name = atom()</v> + <v>Request = term()</v> + </type> + <desc> + <p>Sends an asynchronous request to the gen_servers locally + registered as <c>Name</c> at the specified nodes. The function + returns immediately and ignores nodes that do not exist, or + where the gen_server <c>Name</c> does not exist. + The gen_servers will call <c>Module:handle_cast/2</c> to + handle the request.</p> + <p>See + <seealso marker="#multi_call/2">multi_call/2,3,4</seealso> + for a description of the arguments.</p> + </desc> + </func> + <func> + <name>reply(Client, Reply) -> Result</name> + <fsummary>Send a reply to a client.</fsummary> + <type> + <v>Client - see below</v> + <v>Reply = term()</v> + <v>Result = term()</v> + </type> + <desc> + <p>This function can be used by a gen_server to explicitly send + a reply to a client that called <c>call/2,3</c> or + <c>multi_call/2,3,4</c>, when the reply cannot be defined in + the return value of <c>Module:handle_call/3</c>.</p> + <p><c>Client</c> must be the <c>From</c> argument provided to + the callback function. <c>Reply</c> is an arbitrary term, + which will be given back to the client as the return value of + <c>call/2,3</c> or <c>multi_call/2,3,4</c>.</p> + <p>The return value <c>Result</c> is not further defined, and + should always be ignored.</p> + </desc> + </func> + <func> + <name>enter_loop(Module, Options, State)</name> + <name>enter_loop(Module, Options, State, ServerName)</name> + <name>enter_loop(Module, Options, State, Timeout)</name> + <name>enter_loop(Module, Options, State, ServerName, Timeout)</name> + <fsummary>Enter the gen_server receive loop</fsummary> + <type> + <v>Module = atom()</v> + <v>Options = [Option]</v> + <v> Option = {debug,Dbgs}</v> + <v> Dbgs = [Dbg]</v> + <v> Dbg = trace | log | statistics</v> + <v> | {log_to_file,FileName} | {install,{Func,FuncState}}</v> + <v>State = term()</v> + <v>ServerName = {local,Name} | {global,GlobalName}</v> + <v> Name = atom()</v> + <v> GlobalName = term()</v> + <v>Timeout = int() | infinity</v> + </type> + <desc> + <p>Makes an existing process into a gen_server. Does not return, + instead the calling process will enter the gen_server receive + loop and become a gen_server process. The process + <em>must</em> have been started using one of the start + functions in <c>proc_lib</c>, see + <seealso marker="proc_lib">proc_lib(3)</seealso>. The user is + responsible for any initialization of the process, including + registering a name for it.</p> + <p>This function is useful when a more complex initialization + procedure is needed than the gen_server behaviour provides.</p> + <p><c>Module</c>, <c>Options</c> and <c>ServerName</c> have + the same meanings as when calling + <seealso marker="#start_link/3">gen_server:start[_link]/3,4</seealso>. + However, if <c>ServerName</c> is specified, the process must + have been registered accordingly <em>before</em> this function + is called.</p> + <p><c>State</c> and <c>Timeout</c> have the same meanings as in + the return value of + <seealso marker="#Moduleinit">Module:init/1</seealso>. + Also, the callback module <c>Module</c> does not need to + export an <c>init/1</c> function. </p> + <p>Failure: If the calling process was not started by a + <c>proc_lib</c> start function, or if it is not registered + according to <c>ServerName</c>.</p> + </desc> + </func> + </funcs> + + <section> + <title>CALLBACK FUNCTIONS</title> + <p>The following functions + should be exported from a <c>gen_server</c> callback module.</p> + </section> + <funcs> + <func> + <name>Module:init(Args) -> Result</name> + <fsummary>Initialize process and internal state.</fsummary> + <type> + <v>Args = term()</v> + <v>Result = {ok,State} | {ok,State,Timeout} | {ok,State,hibernate}</v> + <v> | {stop,Reason} | ignore</v> + <v> State = term()</v> + <v> Timeout = int()>=0 | infinity</v> + <v> Reason = term()</v> + </type> + <desc> + <marker id="Moduleinit"></marker> + <p>Whenever a gen_server is started using + <seealso marker="#start/3">gen_server:start/3,4</seealso> or + <seealso marker="#start_link/3">gen_server:start_link/3,4</seealso>, + this function is called by the new process to initialize.</p> + <p><c>Args</c> is the <c>Args</c> argument provided to the start + function.</p> + <p>If the initialization is successful, the function should + return <c>{ok,State}</c>, <c>{ok,State,Timeout}</c> or <c>{ok,State,hibernate}</c>, where + <c>State</c> is the internal state of the gen_server.</p> + <p>If an integer timeout value is provided, a timeout will occur + unless a request or a message is received within + <c>Timeout</c> milliseconds. A timeout is represented by + the atom <c>timeout</c> which should be handled by + the <c>handle_info/2</c> callback function. The atom + <c>infinity</c> can be used to wait indefinitely, this is + the default value.</p> + <p>If <c>hibernate</c> is specified instead of a timeout value, the process will go + into hibernation when waiting for the next message to arrive (by calling + <seealso marker="proc_lib#hibernate/3">proc_lib:hibernate/3</seealso>).</p> + <p>If something goes wrong during the initialization + the function should return <c>{stop,Reason}</c> where + <c>Reason</c> is any term, or <c>ignore</c>.</p> + </desc> + </func> + <func> + <name>Module:handle_call(Request, From, State) -> Result</name> + <fsummary>Handle a synchronous request.</fsummary> + <type> + <v>Request = term()</v> + <v>From = {pid(),Tag}</v> + <v>State = term()</v> + <v>Result = {reply,Reply,NewState} | {reply,Reply,NewState,Timeout}</v> + <v> | {reply,Reply,NewState,hibernate}</v> + <v> | {noreply,NewState} | {noreply,NewState,Timeout}</v> + <v> | {noreply,NewState,hibernate}</v> + <v> | {stop,Reason,Reply,NewState} | {stop,Reason,NewState}</v> + <v> Reply = term()</v> + <v> NewState = term()</v> + <v> Timeout = int()>=0 | infinity</v> + <v> Reason = term()</v> + </type> + <desc> + <p>Whenever a gen_server receives a request sent using + <seealso marker="#call/2">gen_server:call/2,3</seealso> or + <seealso marker="#multi_call/2">gen_server:multi_call/2,3,4</seealso>, + this function is called to handle the request.</p> + <p><c>Request</c> is the <c>Request</c> argument provided + to <c>call</c> or <c>multi_call</c>.</p> + <p><c>From</c> is a tuple <c>{Pid,Tag}</c> where <c>Pid</c> is + the pid of the client and <c>Tag</c> is a unique tag.</p> + <p><c>State</c> is the internal state of the gen_server.</p> + <p>If the function returns <c>{reply,Reply,NewState}</c>, + <c>{reply,Reply,NewState,Timeout}</c> or + <c>{reply,Reply,NewState,hibernate}</c>, <c>Reply</c> will be + given back to <c>From</c> as the return value of + <c>call/2,3</c> or included in the return value of + <c>multi_call/2,3,4</c>. The gen_server then continues + executing with the possibly updated internal state + <c>NewState</c>. See <c>Module:init/1</c> for a description + of <c>Timeout</c> and <c>hibernate</c>.</p> + <p>If the functions returns <c>{noreply,NewState}</c>, + <c>{noreply,NewState,Timeout}</c> or <c>{noreply,NewState,hibernate}</c>, + the gen_server will + continue executing with <c>NewState</c>. Any reply to + <c>From</c> must be given explicitly using + <seealso marker="#reply/2">gen_server:reply/2</seealso>.</p> + <p>If the function returns <c>{stop,Reason,Reply,NewState}</c>, + <c>Reply</c> will be given back to <c>From</c>. If + the function returns <c>{stop,Reason,NewState}</c>, any reply + to <c>From</c> must be given explicitly using + <c>gen_server:reply/2</c>. The gen_server will then call + <c>Module:terminate(Reason,NewState)</c> and terminate.</p> + </desc> + </func> + <func> + <name>Module:handle_cast(Request, State) -> Result</name> + <fsummary>Handle an asynchronous request.</fsummary> + <type> + <v>Request = term()</v> + <v>State = term()</v> + <v>Result = {noreply,NewState} | {noreply,NewState,Timeout}</v> + <v> | {noreply,NewState,hibernate}</v> + <v> | {stop,Reason,NewState}</v> + <v> NewState = term()</v> + <v> Timeout = int()>=0 | infinity</v> + <v> Reason = term()</v> + </type> + <desc> + <p>Whenever a gen_server receives a request sent using + <seealso marker="#cast/2">gen_server:cast/2</seealso> or + <seealso marker="#abcast/2">gen_server:abcast/2,3</seealso>, + this function is called to handle the request.</p> + <p>See <c>Module:handle_call/3</c> for a description of + the arguments and possible return values.</p> + </desc> + </func> + <func> + <name>Module:handle_info(Info, State) -> Result</name> + <fsummary>Handle an incoming message.</fsummary> + <type> + <v>Info = timeout | term()</v> + <v>State = term()</v> + <v>Result = {noreply,NewState} | {noreply,NewState,Timeout} </v> + <v> | {noreply,NewState,hibernate}</v> + <v> | {stop,Reason,NewState}</v> + <v> NewState = term()</v> + <v> Timeout = int()>=0 | infinity</v> + <v> Reason = normal | term()</v> + </type> + <desc> + <p>This function is called by a gen_server when a timeout + occurs or when it receives any other message than a + synchronous or asynchronous request (or a system message).</p> + <p><c>Info</c> is either the atom <c>timeout</c>, if a timeout + has occurred, or the received message.</p> + <p>See <c>Module:handle_call/3</c> for a description of + the other arguments and possible return values.</p> + </desc> + </func> + <func> + <name>Module:terminate(Reason, State)</name> + <fsummary>Clean up before termination.</fsummary> + <type> + <v>Reason = normal | shutdown | {shutdown,term()} | term()</v> + <v>State = term()</v> + </type> + <desc> + <p>This function is called by a gen_server when it is about to + terminate. It should be the opposite of <c>Module:init/1</c> + and do any necessary cleaning up. When it returns, + the gen_server terminates with <c>Reason</c>. The return + value is ignored.</p> + <p><c>Reason</c> is a term denoting the stop reason and + <c>State</c> is the internal state of the gen_server.</p> + <p><c>Reason</c> depends on why the gen_server is terminating. + If it is because another callback function has returned a + stop tuple <c>{stop,..}</c>, <c>Reason</c> will have + the value specified in that tuple. If it is due to a failure, + <c>Reason</c> is the error reason.</p> + <p>If the gen_server is part of a supervision tree and is + ordered by its supervisor to terminate, this function will be + called with <c>Reason=shutdown</c> if the following + conditions apply:</p> + <list type="bulleted"> + <item>the gen_server has been set to trap exit signals, and</item> + <item>the shutdown strategy as defined in the supervisor's + child specification is an integer timeout value, not + <c>brutal_kill</c>.</item> + </list> + <p>Even if the gen_server is <em>not</em> part of a supervision tree, + this function will be called if it receives an <c>'EXIT'</c> + message from its parent. <c>Reason</c> will be the same as in + the <c>'EXIT'</c> message.</p> + <p>Otherwise, the gen_server will be immediately terminated.</p> + <p>Note that for any other reason than <c>normal</c>, + <c>shutdown</c>, or <c>{shutdown,Term}</c> the gen_server is + assumed to terminate due to an error and + an error report is issued using + <seealso marker="kernel:error_logger#format/2">error_logger:format/2</seealso>.</p> + </desc> + </func> + <func> + <name>Module:code_change(OldVsn, State, Extra) -> {ok, NewState}</name> + <fsummary>Update the internal state during upgrade/downgrade.</fsummary> + <type> + <v>OldVsn = Vsn | {down, Vsn}</v> + <v> Vsn = term()</v> + <v>State = NewState = term()</v> + <v>Extra = term()</v> + </type> + <desc> + <p>This function is called by a gen_server when it should + update its internal state during a release upgrade/downgrade, + i.e. when the instruction <c>{update,Module,Change,...}</c> + where <c>Change={advanced,Extra}</c> is given in + the <c>appup</c> file. See + <seealso marker="doc/design_principles:release_handling#instr">OTP Design Principles</seealso> + for more information.</p> + <p>In the case of an upgrade, <c>OldVsn</c> is <c>Vsn</c>, and + in the case of a downgrade, <c>OldVsn</c> is + <c>{down,Vsn}</c>. <c>Vsn</c> is defined by the <c>vsn</c> + attribute(s) of the old version of the callback module + <c>Module</c>. If no such attribute is defined, the version + is the checksum of the BEAM file.</p> + <p><c>State</c> is the internal state of the gen_server.</p> + <p><c>Extra</c> is passed as-is from the <c>{advanced,Extra}</c> + part of the update instruction.</p> + <p>The function should return the updated internal state.</p> + </desc> + </func> + </funcs> + + <section> + <title>SEE ALSO</title> + <p><seealso marker="gen_event">gen_event(3)</seealso>, + <seealso marker="gen_fsm">gen_fsm(3)</seealso>, + <seealso marker="supervisor">supervisor(3)</seealso>, + <seealso marker="proc_lib">proc_lib(3)</seealso>, + <seealso marker="sys">sys(3)</seealso></p> + </section> +</erlref> + |