postgresWaitForNotify: Wait for and return any notifications that return within...

In RPostgres: C++ Interface to PostgreSQL

Wait for and return any notifications that return within timeout

Description

Once you subscribe to notifications with LISTEN, use this to wait for responses on each channel.

Usage

postgresWaitForNotify(conn, timeout = 1)

Arguments

conn	a PqConnection object, produced by DBI::dbConnect()
timeout	How long to wait, in seconds. Default 1

Value

If a notification was available, a list of:

channel

Name of channel

pid

PID of notifying server process

payload

Content of notification

If no notifications are available, return NULL

Examples

library(DBI)
library(callr)

# listen for messages on the grapevine
db_listen <- dbConnect(RPostgres::Postgres())
dbExecute(db_listen, "LISTEN grapevine")

# Start another process, which sends a message after a delay
rp <- r_bg(function() {
  library(DBI)
  Sys.sleep(0.3)
  db_notify <- dbConnect(RPostgres::Postgres())
  dbExecute(db_notify, "NOTIFY grapevine, 'psst'")
  dbDisconnect(db_notify)
})

# Sleep until we get the message
n <- NULL
while (is.null(n)) {
  n <- RPostgres::postgresWaitForNotify(db_listen, 60)
}
stopifnot(n$payload == 'psst')

# Tidy up
rp$wait()
dbDisconnect(db_listen)

RPostgres documentation built on Oct. 23, 2023, 1:06 a.m.