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NAME
rpc - Remote Procedure Call services.
DESCRIPTION
This module contains services 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.
Note:
rpc:call() and friends makes it quite hard to distinguish between successful results,
raised exceptions, and other errors. This cannot be changed due to compatibility reasons.
As of OTP 23, a new module erpc was introduced in order to provide an API that makes it
possible to distingush between the different results. The erpc module provides a subset
(however, the central subset) of the functionality available in the rpc module. The erpc
implementation also provides a more scalable implementation with better performance than
the original rpc implementation. However, since the introduction of erpc, the rpc module
implements large parts of its central functionality using erpc, so the rpc module wont not
suffer scalability wise and performance wise compared to erpc.
DATA TYPES
key()
Opaque value returned by async_call/4.
EXPORTS
abcast(Name, Msg) -> abcast
Types:
Name = atom()
Msg = term()
Equivalent to abcast([node()|nodes()], Name, Msg).
abcast(Nodes, Name, Msg) -> abcast
Types:
Nodes = [node()]
Name = atom()
Msg = term()
Broadcasts the message Msg asynchronously to the registered process Name on the
specified nodes.
async_call(Node, Module, Function, Args) -> Key
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Key = key()
Implements call streams with promises, a type of RPC that does not suspend the
caller until the result is finished. Instead, a key is returned, which can be used
later to collect the value. The key can be viewed as a promise to deliver the
answer.
In this case, the key Key is returned, which can be used in a subsequent call to
yield/1 or nb_yield/1,2 to retrieve the value of evaluating apply(Module, Function,
Args) on node Node.
Note:
If you want the ability to distinguish between results, you may want to consider
using the erpc:send_request() function from the erpc module instead. This also
gives you the ability retrieve the results in other useful ways.
Note:
yield/1 and nb_yield/1,2 must be called by the same process from which this
function was made otherwise they will never yield correctly.
Note:
You cannot make any assumptions about the process that will perform the apply(). It
may be an rpc server, another server, or a freshly spawned process.
block_call(Node, Module, Function, Args) -> Res | {badrpc, Reason}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Res = Reason = term()
The same as calling rpc:block_call(Node, Module, Function, Args, infinity).
block_call(Node, Module, Function, Args, Timeout) ->
Res | {badrpc, Reason}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Res = Reason = term()
Timeout = 0..4294967295 | infinity
The same as calling rpc:call(Node, Module, Function, Args, Timeout) with the
exception that it also blocks other rpc:block_call() operations from executing
concurrently on the node Node.
Warning:
Note that it also blocks other operations than just rpc:block_call() operations, so
use it with care.
call(Node, Module, Function, Args) -> Res | {badrpc, Reason}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Res = Reason = term()
Evaluates apply(Module, Function, Args) on node Node and returns the corresponding
value Res, or {badrpc, Reason} if the call fails. The same as calling
rpc:call(Node, Module, Function, Args, infinity).
call(Node, Module, Function, Args, Timeout) ->
Res | {badrpc, Reason}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Res = Reason = term()
Timeout = 0..4294967295 | infinity
Evaluates apply(Module, Function, Args) on node Node and returns the corresponding
value Res, or {badrpc, Reason} if the call fails. Timeout is a time-out value in
milliseconds. If the call times out, Reason is timeout.
If the reply arrives after the call times out, no message contaminates the caller's
message queue.
Note:
If you want the ability to distinguish between results, you may want to consider
using the erpc:call() function from the erpc module instead.
Note:
Here follows the details of what exactly is returned.
{badrpc, Reason} will be returned in the following circumstances:
* The called function fails with an exit exception.
* The called function fails with an error exception.
* The called function returns a term that matches {'EXIT', _}.
* The called function throws a term that matches {'EXIT', _}.
Res is returned in the following circumstances:
* The called function returns normally with a term that does not match
{'EXIT',_}.
* The called function throws a term that does not match {'EXIT',_}.
Note:
You cannot make any assumptions about the process that will perform the apply(). It
may be the calling process itself, an rpc server, another server, or a freshly
spawned process.
cast(Node, Module, Function, Args) -> true
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Evaluates apply(Module, Function, Args) on node Node. No response is delivered and
the calling process is not suspended until the evaluation is complete, as is the
case with call/4,5.
Note:
You cannot make any assumptions about the process that will perform the apply(). It
may be an rpc server, another server, or a freshly spawned process.
eval_everywhere(Module, Function, Args) -> abcast
Types:
Module = module()
Function = atom()
Args = [term()]
Equivalent to eval_everywhere([node()|nodes()], Module, Function, Args).
eval_everywhere(Nodes, Module, Function, Args) -> abcast
Types:
Nodes = [node()]
Module = module()
Function = atom()
Args = [term()]
Evaluates apply(Module, Function, Args) on the specified nodes. No answers are
collected.
multi_server_call(Name, Msg) -> {Replies, BadNodes}
Types:
Name = atom()
Msg = term()
Replies = [Reply :: term()]
BadNodes = [node()]
Equivalent to multi_server_call([node()|nodes()], Name, Msg).
multi_server_call(Nodes, Name, Msg) -> {Replies, BadNodes}
Types:
Nodes = [node()]
Name = atom()
Msg = term()
Replies = [Reply :: term()]
BadNodes = [node()]
Can be used when interacting with servers called Name on the specified nodes. It is
assumed that the servers receive messages in the format {From, Msg} and reply using
From ! {Name, Node, Reply}, where Node is the name of the node where the server is
located. The function returns {Replies, BadNodes}, where Replies is a list of all
Reply values, and BadNodes is one of the following:
* A list of the nodes that do not exist
* A list of the nodes where the server does not exist
* A list of the nodes where the server terminated before sending any reply.
multicall(Module, Function, Args) -> {ResL, BadNodes}
Types:
Module = module()
Function = atom()
Args = [term()]
ResL = [Res :: term() | {badrpc, Reason :: term()}]
BadNodes = [node()]
Equivalent to multicall([node()|nodes()], Module, Function, Args, infinity).
multicall(Nodes, Module, Function, Args) -> {ResL, BadNodes}
Types:
Nodes = [node()]
Module = module()
Function = atom()
Args = [term()]
ResL = [Res :: term() | {badrpc, Reason :: term()}]
BadNodes = [node()]
Equivalent to multicall(Nodes, Module, Function, Args, infinity).
multicall(Module, Function, Args, Timeout) -> {ResL, BadNodes}
Types:
Module = module()
Function = atom()
Args = [term()]
Timeout = 0..4294967295 | infinity
ResL = [Res :: term() | {badrpc, Reason :: term()}]
BadNodes = [node()]
Equivalent to multicall([node()|nodes()], Module, Function, Args, Timeout).
multicall(Nodes, Module, Function, Args, Timeout) ->
{ResL, BadNodes}
Types:
Nodes = [node()]
Module = module()
Function = atom()
Args = [term()]
Timeout = 0..4294967295 | infinity
ResL = [Res :: term() | {badrpc, Reason :: term()}]
BadNodes = [node()]
In contrast to an RPC, a multicall is an RPC that is sent concurrently from one
client to multiple servers. This is useful for collecting 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.
The function evaluates apply(Module, Function, Args) on the specified nodes and
collects the answers. It returns {ResL, BadNodes}, where BadNodes is a list of the
nodes that do not exist, and ResL is a list of the return values, or {badrpc,
Reason} for failing calls. Timeout is a time (integer) in milliseconds, or
infinity.
The following example is useful when new object code is to be loaded on all nodes
in the network, and indicates some side effects that RPCs can produce:
%% 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, File, Bin]),
%% and then maybe check the ResL list.
Note:
If you want the ability to distinguish between results, you may want to consider
using the erpc:multicall() function from the erpc module instead.
Note:
You cannot make any assumptions about the process that will perform the apply(). It
may be the calling process itself, an rpc server, another server, or a freshly
spawned process.
nb_yield(Key) -> {value, Val} | timeout
Types:
Key = key()
Val = (Res :: term()) | {badrpc, Reason :: term()}
Equivalent to nb_yield(Key, 0).
nb_yield(Key, Timeout) -> {value, Val} | timeout
Types:
Key = key()
Timeout = 0..4294967295 | infinity
Val = (Res :: term()) | {badrpc, Reason :: term()}
Non-blocking version of yield/1. It returns the tuple {value, Val} when the
computation is finished, or timeout when Timeout milliseconds has elapsed.
See the note in call/4 for more details of Val.
Note:
This function must be called by the same process from which async_call/4 was made
otherwise it will only return timeout.
parallel_eval(FuncCalls) -> ResL
Types:
FuncCalls = [{Module, Function, Args}]
Module = module()
Function = atom()
Args = ResL = [term()]
Evaluates, for every tuple in FuncCalls, apply(Module, Function, Args) on some node
in the network. Returns the list of return values, in the same order as in
FuncCalls.
pinfo(Pid) -> [{Item, Info}] | undefined
Types:
Pid = pid()
Item = atom()
Info = term()
Location transparent version of the BIF erlang:process_info/1 in ERTS.
pinfo(Pid, Item) -> {Item, Info} | undefined | []
pinfo(Pid, ItemList) -> [{Item, Info}] | undefined | []
Types:
Pid = pid()
Item = atom()
ItemList = [Item]
Info = term()
Location transparent version of the BIF erlang:process_info/2 in ERTS.
pmap(FuncSpec, ExtraArgs, List1) -> List2
Types:
FuncSpec = {Module, Function}
Module = module()
Function = atom()
ExtraArgs = [term()]
List1 = [Elem :: term()]
List2 = [term()]
Evaluates apply(Module, Function, [Elem|ExtraArgs]) for every element Elem in
List1, in parallel. Returns the list of return values, in the same order as in
List1.
sbcast(Name, Msg) -> {GoodNodes, BadNodes}
Types:
Name = atom()
Msg = term()
GoodNodes = BadNodes = [node()]
Equivalent to sbcast([node()|nodes()], Name, Msg).
sbcast(Nodes, Name, Msg) -> {GoodNodes, BadNodes}
Types:
Name = atom()
Msg = term()
Nodes = GoodNodes = BadNodes = [node()]
Broadcasts the message Msg synchronously to the registered process Name on the
specified nodes.
Returns {GoodNodes, BadNodes}, where GoodNodes is the list of nodes that have Name
as a registered process.
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 processed the message.
Any further messages sent to the servers, after this function has returned, are
received by all servers after this message.
server_call(Node, Name, ReplyWrapper, Msg) ->
Reply | {error, Reason}
Types:
Node = node()
Name = atom()
ReplyWrapper = Msg = Reply = term()
Reason = nodedown
Can be used when interacting with a server called Name on node Node. It is assumed
that the server receives messages in the format {From, Msg} and replies using From
! {ReplyWrapper, Node, Reply}. 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.
The function returns the answer Reply as produced by the server Name, or {error,
Reason}.
yield(Key) -> Res | {badrpc, Reason}
Types:
Key = key()
Res = Reason = term()
Returns the promised answer from a previous async_call/4. If the answer is
available, it is returned immediately. Otherwise, the calling process is suspended
until the answer arrives from Node.
Note:
This function must be called by the same process from which async_call/4 was made
otherwise it will never return.
See the note in call/4 for more details of the return value.