random_port(): more robust version

[HenrikBengtsson]

While I'm at it:

random_port() relies on "chance", i.e. it bets on a random port will be available:

> proffer::random_port
function (lower = 49152L, upper = 65355L) 
{
    sample(seq.int(from = lower, to = upper, by = 1L), size = 1L)
}

Suggestion

In R (>= 4.0.0) we can easily check if a port is available, e.g.

> parallelly:::canPortBeUsed
function (port) 
{
    port <- assertPort(port)
    ns <- asNamespace("parallel")
    if (!exists("serverSocket", envir = ns, mode = "function")) 
        return(NA)
    serverSocket <- get("serverSocket", envir = ns, mode = "function")
    suspendInterrupts <- get("suspendInterrupts", envir = asNamespace("base"), 
        mode = "function")
    suspendInterrupts({
        con <- tryCatch(serverSocket(port), error = identity)
    })
    free <- inherits(con, "connection")
    if (free) 
        close(con)
    free
}
<environment: namespace:parallelly>

So, you could use that technique to increase the chances for getting a port that's actually available. That's now parallelly::freePort() works.

[wlandau]

Thanks for such a helpful suggestion! Happy to invoke parallelly::freePort() directly on the ephemeral port range.