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Version 2.15

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# rpc

### MODULE

rpc

### MODULE SUMMARY

Remote Procedure Call Services

### DESCRIPTION

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.

### DATA TYPES

key()

As returned by async_call/4.

### EXPORTS

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 the node Node and returns the corresponding value Res, or {badrpc, Reason} if the call fails.

call(Node, Module, Function, Args, Timeout) ->
Res | {badrpc, Reason}

Types:

Node = node()
Module = module()
Function = atom()
Args = [term()]
Res = Reason = term()
Timeout = timeout()

Evaluates apply(Module, Function, Args) on the node Node and returns the corresponding value Res, or {badrpc, Reason} if the call fails. Timeout is a timeout value in milliseconds. If the call times out, Reason is timeout.

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 call/4 at the caller's end.

block_call(Node, Module, Function, Args) -> Res | {badrpc, Reason}

Types:

Node = node()
Module = module()
Function = atom()
Args = [term()]
Res = Reason = term()

Like call/4, but the RPC server at Node 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.

block_call(Node, Module, Function, Args, Timeout) ->
Res | {badrpc, Reason}

Types:

Node = node()
Module = module()
Function = atom()
Args = [term()]
Res = Reason = term()
Timeout = timeout()

Like block_call/4, but with a timeout value in the same manner as call/5.

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 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.

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 the node Node.

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.

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 = timeout()
Val = (Res :: term()) | {badrpc, Reason :: term()}

This is a non-blocking version of yield/1. It returns the tuple {value, Val} when the computation has finished, or timeout when Timeout milliseconds has elapsed.

multicall(Module, Function, Args) -> {ResL, BadNodes}

Types:

Module = module()
Function = atom()
Args = ResL = [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 = ResL = [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 = timeout()
ResL = [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 = timeout()
ResL = [term()]
BadNodes = [node()]

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.

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 terminated or timed out during computation, and ResL is a list of the return values. 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 also indicates some side effects RPCs may 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, Bin, File,]),

    %% and then maybe check the ResL list.

cast(Node, Module, Function, Args) -> true

Types:

Node = node()
Module = module()
Function = atom()
Args = [term()]

Evaluates apply(Module, Function, Args) on the 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.

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.

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.

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 which 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 actually processed the message.

Any further messages sent to the servers, after this function has returned, will be 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

This function can be used when interacting with a server called Name at 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}.

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()]

This function 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 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.

safe_multi_server_call(Name, Msg) -> {Replies, BadNodes}
safe_multi_server_call(Nodes, Name, Msg) -> {Replies, BadNodes}

Types:

Nodes = [node()]
Name = atom()
Msg = term()
Replies = [Reply :: term()]
BadNodes = [node()]

Warning

This function is deprecated. Use multi_server_call/2,3 instead.

In Erlang/OTP R6B and earlier releases, multi_server_call/2,3 could not handle the case where the remote node exists, but there is no server called Name. 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.

parallel_eval(FuncCalls) -> ResL

Types:

FuncCalls = [{Module, Function, Args}]
Module = module()
Function = atom()
Args = ResL = [term()]

For every tuple in FuncCalls, evaluates apply(Module, Function, Args) on some node in the network. Returns the list of return values, in the same order as in FuncCalls.

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.

pinfo(Pid) -> [{Item, Info}] | undefined

Types:

Pid = pid()
Item = atom()
Info = term()

Location transparent version of the BIF process_info/1.

pinfo(Pid, Item) -> {Item, Info} | undefined | []

Types:

Pid = pid()
Item = atom()
Info = term()

Location transparent version of the BIF process_info/2.