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<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<header>
<copyright>
<year>1996</year><year>2011</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
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</legalnotice>
<title>rpc</title>
<prepared>Claes Wikstrom</prepared>
<docno>1</docno>
<date>96-09-10</date>
<rev>A</rev>
</header>
<module>rpc</module>
<modulesummary>Remote Procedure Call Services</modulesummary>
<description>
<p>This module contains services which are similar to remote
procedure calls. It also contains broadcast facilities and
parallel evaluators. A remote procedure call is a method to call
a function on a remote node and collect the answer. It is used
for collecting information on a remote node, or for running a
function with some specific side effects on the remote node.</p>
</description>
<datatypes>
<datatype>
<name name="key"/>
<desc>
<p>As returned by <seealso marker="#async_call/4">
<c>async_call/4</c>.</seealso></p>
</desc>
</datatype>
</datatypes>
<funcs>
<func>
<name name="call" arity="4"/>
<fsummary>Evaluate a function call on a node</fsummary>
<desc>
<p>Evaluates <c>apply(<anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c> on the node
<c><anno>Node</anno></c> and returns the corresponding value <c><anno>Res</anno></c>, or
<c>{badrpc, <anno>Reason</anno>}</c> if the call fails.</p>
</desc>
</func>
<func>
<name name="call" arity="5"/>
<fsummary>Evaluate a function call on a node</fsummary>
<desc>
<p>Evaluates <c>apply(<anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c> on the node
<c><anno>Node</anno></c> and returns the corresponding value <c><anno>Res</anno></c>, or
<c>{badrpc, <anno>Reason</anno>}</c> if the call fails. <c><anno>Timeout</anno></c> is
a timeout value in milliseconds. If the call times out,
<c><anno>Reason</anno></c> is <c>timeout</c>.</p>
<p>If the reply arrives after the call times out, no message
will contaminate the caller's message queue, since this
function spawns off a middleman process to act as (a void)
destination for such an orphan reply. This feature also makes
this function more expensive than <c>call/4</c> at
the caller's end.</p>
</desc>
</func>
<func>
<name name="block_call" arity="4"/>
<fsummary>Evaluate a function call on a node in the RPC server's context</fsummary>
<desc>
<p>Like <c>call/4</c>, but the RPC server at <c><anno>Node</anno></c> does
not create a separate process to handle the call. Thus,
this function can be used if the intention of the call is to
block the RPC server from any other incoming requests until
the request has been handled. The function can also be used
for efficiency reasons when very small fast functions are
evaluated, for example BIFs that are guaranteed not to
suspend.</p>
</desc>
</func>
<func>
<name name="block_call" arity="5"/>
<fsummary>Evaluate a function call on a node in the RPC server's context</fsummary>
<desc>
<p>Like <c>block_call/4</c>, but with a timeout value in
the same manner as <c>call/5</c>.</p>
</desc>
</func>
<func>
<name name="async_call" arity="4"/>
<fsummary>Evaluate a function call on a node, asynchronous version</fsummary>
<desc>
<p>Implements <em>call streams with promises</em>, a type of
RPC which does not suspend the caller until the result is
finished. Instead, a key is returned which can be used at a
later stage to collect the value. The key can be viewed as a
promise to deliver the answer.</p>
<p>In this case, the key <c><anno>Key</anno></c> is returned, which can be
used in a subsequent call to <c>yield/1</c> or
<c>nb_yield/1,2</c> to retrieve the value of evaluating
<c>apply(<anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c> on the node <c><anno>Node</anno></c>.</p>
</desc>
</func>
<func>
<name name="yield" arity="1"/>
<fsummary>Deliver the result of evaluating a function call on a node (blocking)</fsummary>
<desc>
<p>Returns the promised answer from a previous
<c>async_call/4</c>. If the answer is available, it is
returned immediately. Otherwise, the calling process is
suspended until the answer arrives from <c>Node</c>.</p>
</desc>
</func>
<func>
<name name="nb_yield" arity="1"/>
<fsummary>Deliver the result of evaluating a function call on a node (non-blocking)</fsummary>
<desc>
<p>Equivalent to <c>nb_yield(<anno>Key</anno>, 0)</c>.</p>
</desc>
</func>
<func>
<name name="nb_yield" arity="2"/>
<fsummary>Deliver the result of evaluating a function call on a node (non-blocking)</fsummary>
<desc>
<p>This is a non-blocking version of <c>yield/1</c>. It returns
the tuple <c>{value, <anno>Val</anno>}</c> when the computation has
finished, or <c>timeout</c> when <c><anno>Timeout</anno></c> milliseconds
has elapsed.</p>
</desc>
</func>
<func>
<name name="multicall" arity="3"/>
<fsummary>Evaluate a function call on a number of nodes</fsummary>
<desc>
<p>Equivalent to <c>multicall([node()|nodes()], <anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>, infinity)</c>.</p>
</desc>
</func>
<func>
<name name="multicall" arity="4" clause_i="1"/>
<fsummary>Evaluate a function call on a number of nodes</fsummary>
<desc>
<p>Equivalent to <c>multicall(<anno>Nodes</anno>, <anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>, infinity)</c>.</p>
</desc>
</func>
<func>
<name name="multicall" arity="4" clause_i="2"/>
<fsummary>Evaluate a function call on a number of nodes</fsummary>
<desc>
<p>Equivalent to <c>multicall([node()|nodes()], <anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>, <anno>Timeout</anno>)</c>.</p>
</desc>
</func>
<func>
<name name="multicall" arity="5"/>
<fsummary>Evaluate a function call on a number of nodes</fsummary>
<desc>
<p>In contrast to an RPC, a multicall is an RPC which is sent
concurrently from one client to multiple servers. This is
useful for collecting some information from a set of nodes,
or for calling a function on a set of nodes to achieve some
side effects. It is semantically the same as iteratively
making a series of RPCs on all the nodes, but the multicall
is faster as all the requests are sent at the same time
and are collected one by one as they come back.</p>
<p>The function evaluates <c>apply(<anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c>
on the specified nodes and collects the answers. It returns
<c>{<anno>ResL</anno>, <anno>BadNodes</anno>}</c>, where <c><anno>BadNodes</anno></c> is a list
of the nodes that terminated or timed out during computation,
and <c><anno>ResL</anno></c> is a list of the return values.
<c><anno>Timeout</anno></c> is a time (integer) in milliseconds, or
<c>infinity</c>.</p>
<p>The following example is useful when new object code is to
be loaded on all nodes in the network, and also indicates
some side effects RPCs may produce:</p>
<code type="none">
%% Find object code for module Mod
{Mod, Bin, File} = code:get_object_code(Mod),
%% and load it on all nodes including this one
{ResL, _} = rpc:multicall(code, load_binary, [Mod, Bin, File,]),
%% and then maybe check the ResL list.</code>
</desc>
</func>
<func>
<name name="cast" arity="4"/>
<fsummary>Run a function on a node ignoring the result</fsummary>
<desc>
<p>Evaluates <c>apply(<anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c> on the node
<c><anno>Node</anno></c>. No response is delivered and the calling
process is not suspended until the evaluation is complete, as
is the case with <c>call/4,5</c>.</p>
</desc>
</func>
<func>
<name name="eval_everywhere" arity="3"/>
<fsummary>Run a function on all nodes, ignoring the result</fsummary>
<desc>
<p>Equivalent to <c>eval_everywhere([node()|nodes()], <anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c>.</p>
</desc>
</func>
<func>
<name name="eval_everywhere" arity="4"/>
<fsummary>Run a function on specific nodes, ignoring the result</fsummary>
<desc>
<p>Evaluates <c>apply(<anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c> on
the specified nodes. No answers are collected.</p>
</desc>
</func>
<func>
<name name="abcast" arity="2"/>
<fsummary>Broadcast a message asynchronously to a registered process on all nodes</fsummary>
<desc>
<p>Equivalent to <c>abcast([node()|nodes()], <anno>Name</anno>, <anno>Msg</anno>)</c>.</p>
</desc>
</func>
<func>
<name name="abcast" arity="3"/>
<fsummary>Broadcast a message asynchronously to a registered process on specific nodes</fsummary>
<desc>
<p>Broadcasts the message <c><anno>Msg</anno></c> asynchronously to
the registered process <c><anno>Name</anno></c> on the specified nodes.</p>
</desc>
</func>
<func>
<name name="sbcast" arity="2"/>
<fsummary>Broadcast a message synchronously to a registered process on all nodes</fsummary>
<desc>
<p>Equivalent to <c>sbcast([node()|nodes()], <anno>Name</anno>, <anno>Msg</anno>)</c>.</p>
</desc>
</func>
<func>
<name name="sbcast" arity="3"/>
<fsummary>Broadcast a message synchronously to a registered process on specific nodes</fsummary>
<desc>
<p>Broadcasts the message <c><anno>Msg</anno></c> synchronously to
the registered process <c><anno>Name</anno></c> on the specified nodes.</p>
<p>Returns <c>{<anno>GoodNodes</anno>, <anno>BadNodes</anno>}</c>, where <c><anno>GoodNodes</anno></c>
is the list of nodes which have <c><anno>Name</anno></c> as a registered
process.</p>
<p>The function is synchronous in the sense that it is known
that all servers have received the message when the call
returns. It is not possible to know that the servers have
actually processed the message.</p>
<p>Any further messages sent to the servers, after this
function has returned, will be received by all servers after
this message.</p>
</desc>
</func>
<func>
<name name="server_call" arity="4"/>
<fsummary>Interact with a server on a node</fsummary>
<desc>
<p>This function can be used when interacting with a server
called <c><anno>Name</anno></c> at node <c><anno>Node</anno></c>. It is assumed that
the server receives messages in the format
<c>{From, <anno>Msg</anno>}</c> and replies using <c>From ! {<anno>ReplyWrapper</anno>, <anno>Node</anno>, <anno>Reply</anno>}</c>. This function makes such
a server call and ensures that the entire call is packed into
an atomic transaction which either succeeds or fails. It
never hangs, unless the server itself hangs.</p>
<p>The function returns the answer <c><anno>Reply</anno></c> as produced by
the server <c><anno>Name</anno></c>, or <c>{error, <anno>Reason</anno>}</c>.</p>
</desc>
</func>
<func>
<name name="multi_server_call" arity="2"/>
<fsummary>Interact with the servers on a number of nodes</fsummary>
<desc>
<p>Equivalent to <c>multi_server_call([node()|nodes()], <anno>Name</anno>, <anno>Msg</anno>)</c>.</p>
</desc>
</func>
<func>
<name name="multi_server_call" arity="3"/>
<fsummary>Interact with the servers on a number of nodes</fsummary>
<desc>
<p>This function can be used when interacting with servers
called <c><anno>Name</anno></c> on the specified nodes. It is assumed that
the servers receive messages in the format <c>{From, <anno>Msg</anno>}</c>
and reply using <c>From ! {<anno>Name</anno>, Node, <anno>Reply</anno>}</c>, where
<c>Node</c> is the name of the node where the server is
located. The function returns <c>{<anno>Replies</anno>, <anno>BadNodes</anno>}</c>,
where <c><anno>Replies</anno></c> is a list of all <c><anno>Reply</anno></c> values and
<c><anno>BadNodes</anno></c> is a list of the nodes which did not exist, or
where the server did not exist, or where the server terminated
before sending any reply.</p>
</desc>
</func>
<func>
<name name="safe_multi_server_call" arity="2"/>
<name name="safe_multi_server_call" arity="3"/>
<fsummary>Interact with the servers on a number of nodes (deprecated)</fsummary>
<desc>
<warning>
<p>This function is deprecated. Use
<c>multi_server_call/2,3</c> instead.</p>
</warning>
<p>In Erlang/OTP R6B and earlier releases,
<c>multi_server_call/2,3</c> could not handle the case
where the remote node exists, but there is no server called
<c><anno>Name</anno></c>. Instead this function had to be used. In
Erlang/OTP R7B and later releases, however, the functions are
equivalent, except for this function being slightly slower.</p>
</desc>
</func>
<func>
<name name="parallel_eval" arity="1"/>
<fsummary>Evaluate several function calls on all nodes in parallel</fsummary>
<desc>
<p>For every tuple in <c><anno>FuncCalls</anno></c>, evaluates
<c>apply(<anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c> on some node in
the network. Returns the list of return values, in the same
order as in <c><anno>FuncCalls</anno></c>.</p>
</desc>
</func>
<func>
<name name="pmap" arity="3"/>
<fsummary>Parallell evaluation of mapping a function over a list </fsummary>
<desc>
<p>Evaluates <c>apply(<anno>Module</anno>, <anno>Function</anno>, [<anno>Elem</anno>|<anno>ExtraArgs</anno>])</c>,
for every element <c><anno>Elem</anno></c> in <c><anno>List1</anno></c>, in parallel.
Returns the list of return values, in the same order as in
<c><anno>List1</anno></c>.</p>
</desc>
</func>
<func>
<name name="pinfo" arity="1"/>
<fsummary>Information about a process</fsummary>
<desc>
<p>Location transparent version of the BIF
<seealso marker="erts:erlang#process_info/1">
<c>process_info/1</c></seealso>.</p>
</desc>
</func>
<func>
<name name="pinfo" arity="2"/>
<fsummary>Information about a process</fsummary>
<desc>
<p>Location transparent version of the BIF
<seealso marker="erts:erlang#process_info/2">
<c>process_info/2</c></seealso>.</p>
</desc>
</func>
</funcs>
</erlref>
