request {nanonext}

Request over Context (RPC Client for Req/Rep Protocol)

Description

Implements a caller/client for the req node of the req/rep protocol. Sends data to the rep node (executor/server) and returns an Aio, which can be called for the value when required.

A signalling version of the function takes a ‘conditionVariable’ as an additional argument and signals it when the async receive is complete.

Usage

request(
  context,
  data,
  send_mode = c("serial", "raw", "next"),
  recv_mode = c("serial", "character", "complex", "double", "integer", "logical",
    "numeric", "raw", "string"),
  timeout = NULL
)

request_signal(
  context,
  data,
  cv,
  send_mode = c("serial", "raw", "next"),
  recv_mode = c("serial", "character", "complex", "double", "integer", "logical",
    "numeric", "raw", "string"),
  timeout = NULL
)

Arguments

context

a Context.

data

an object (if send_mode = ‘raw’, a vector).

send_mode

[default 'serial'] character value or integer equivalent - one of ‘serial’ (1L) to send serialised R objects, ‘raw’ (2L) to send atomic vectors of any type as a raw byte vector, or ‘next’ (3L) - see ‘Send Modes’ section below.

recv_mode

[default 'serial'] character value or integer equivalent - one of ‘serial’ (1L), ‘character’ (2L), ‘complex’ (3L), ‘double’ (4L), ‘integer’ (5L), ‘logical’ (6L), ‘numeric’ (7L), ‘raw’ (8L), or ‘string’ (9L). The default ‘serial’ means a serialised R object; for the other modes, received bytes are converted into the respective mode. ‘string’ is a faster option for length one character vectors.

timeout

[default NULL] integer value in milliseconds or NULL, which applies a socket-specific default, usually the same as no timeout.

cv

For the signalling version: a ‘conditionVariable’ to signal when the async receive is complete.

Details

Sending the request and receiving the result are both performed async, hence the function will return immediately with a ‘recvAio’ object. Access the return value at $data.

This is designed so that the process on the server can run concurrently without blocking the client.

Optionally use call_aio on the ‘recvAio’ to call (and wait for) the result.

If an error occured in the server process, a nul byte 00 will be received. This allows an error to be easily distinguished from a NULL return value. is_nul_byte can be used to test for a nul byte.

It is recommended to use a new context for each request to ensure consistent state tracking. For safety, the context used for the request is closed when all references to the returned ‘recvAio’ are removed and the object is garbage collected.

For the signalling version: when the receive is complete, the supplied ‘conditionVariable’ is signalled by incrementing its value by 1. This happens asynchronously and independently of the R execution thread.

Value

A ‘recvAio’ (object of class ‘recvAio’) (invisibly).

Send Modes

The default mode ‘serial’ sends serialised R objects to ensure perfect reproducibility within R. When receiving, the corresponding mode ‘serial’ should be used.

Mode ‘raw’ sends atomic vectors of any type as a raw byte vector, and must be used when interfacing with external applications or raw system sockets, where R serialization is not in use. When receiving, the mode corresponding to the vector sent should be used.

Mode ‘next’ sends serialised R objects, with native extensions enabled by next_config. This configures custom serialization and unserialization functions for reference objects. When receiving, mode ‘serial’ should be used as ‘next’ sends are fully compatible.

Examples

# works if req and rep are running in parallel in different processes

# req <- socket("req", listen = "tcp://127.0.0.1:6546")
# rep <- socket("rep", dial = "tcp://127.0.0.1:6546")

# reply(.context(rep), execute = function(x) x + 1, timeout = 50)
# aio <- request(.context(req), data = 2022)
# aio$data

# close(req)
# close(rep)

# Signalling a condition variable

# req <- socket("req", listen = "tcp://127.0.0.1:6546")
# ctxq <- context(req)
# cv <- cv()
# aio <- request_signal(ctxq, data = 2022, cv = cv)
# until(cv, 10L)
# close(req)

# The following should be run in another process
# rep <- socket("rep", dial = "tcp://127.0.0.1:6546")
# ctxp <- context(rep)
# reply(ctxp, execute = function(x) x + 1)
# close(rep)