recv_aio {nanonext}

Receive Async

Description

Receive data asynchronously over a connection (Socket, Context or Stream).

Usage

recv_aio(
  con,
  mode = c("serial", "character", "complex", "double", "integer", "logical", "numeric",
    "raw", "string"),
  timeout = NULL,
  cv = NULL,
  n = 65536L
)

Arguments

con

a Socket, Context or Stream.

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. For Streams, ‘serial’ is not an option and the default is ‘character’.

timeout

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

cv

(optional) a ‘conditionVariable’ to signal when the async receive is complete.

n

[default 65536L] applicable to Streams only, the maximum number of bytes to receive. Can be an over-estimate, but note that a buffer of this size is reserved.

Details

Async receive is always non-blocking and returns a ‘recvAio’ immediately.

For a ‘recvAio’, the received message is available at $data. An ‘unresolved’ logical NA is returned if the async operation is yet to complete.

To wait for the async operation to complete and retrieve the received message, use call_aio on the returned ‘recvAio’ object.

Alternatively, to stop the async operation, use stop_aio.

In case of an error, an integer ‘errorValue’ is returned (to be distiguishable from an integer message value). This can be checked using is_error_value.

If an error occurred in unserialization or conversion of the message data to the specified mode, a raw vector will be returned instead to allow recovery (accompanied by a warning).

Value

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

Signalling

By supplying a ‘conditionVariable’, when the receive is complete, the ‘conditionVariable’ is signalled by incrementing its value by 1. This happens asynchronously and independently of the R execution thread.

Examples

s1 <- socket("pair", listen = "inproc://nanonext")
s2 <- socket("pair", dial = "inproc://nanonext")

res <- send_aio(s1, data.frame(a = 1, b = 2), timeout = 100)
msg <- recv_aio(s2, timeout = 100)
msg
msg$data

res <- send_aio(s1, c(1.1, 2.2, 3.3), mode = "raw", timeout = 100)
msg <- recv_aio(s2, mode = "double", timeout = 100)
msg
msg$data

res <- send_aio(s1, "example message", mode = "raw", timeout = 100)
msg <- recv_aio(s2, mode = "character", timeout = 100)
call_aio(msg)
msg$data

close(s1)
close(s2)

# Signalling a condition variable

s1 <- socket("pair", listen = "tcp://127.0.0.1:6546")
cv <- cv()
msg <- recv_aio(s1, timeout = 100, cv = cv)
until(cv, 10L)
msg$data
close(s1)

# in another process in parallel
s2 <- socket("pair", dial = "tcp://127.0.0.1:6546")
res <- send_aio(s2, c(1.1, 2.2, 3.3), mode = "raw", timeout = 100)
close(s2)