postgresWaitForNotify: 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

Run this code

# NOT RUN {
# For running the examples on systems without PostgreSQL connection:
if (postgresHasDefault()) {
    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)
}
# }

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