Create a heartbeat instance

Create a heartbeat instance

Create a heartbeat instance

Details

Create a heartbeat instance. This can be used by running obj$start() which will reset the TTL (Time To Live) on key every period seconds (don't set this too high). If the R process dies, then the key will expire after 3 * period seconds (or set expire) and another application can tell that this R instance has died.

Methods

Public methods

• rrq_heartbeat$new()

• rrq_heartbeat$is_running()

• rrq_heartbeat$start()

• rrq_heartbeat$stop()

• rrq_heartbeat$format()

---

Method new()

Create a heartbeat object

Usage

rrq_heartbeat$new(
  key,
  period,
  expire = 3 * period,
  value = expire,
  config = NULL,
  start = TRUE,
  timeout = 10
)

Arguments

key

Key to use. Once the heartbeat starts it will create this key and set it to expire after expiry seconds.

period

Timeout period (in seconds)

expire

Key expiry time (in seconds)

value

Value to store in the key. By default it stores the expiry time, so the time since last heartbeat can be computed. This will be converted to character with as.character before saving into Redis

config

Configuration parameters passed through to redux::redis_config. Provide as either a named list or a redis_config object. This allows host, port, password, db, etc all to be set.

start

Should the heartbeat be started immediately?

timeout

Time, in seconds, to wait for the heartbeat to appear. It should generally appear very quickly (within a second unless your connection is very slow) so this can be generally left alone.

---

Method is_running()

Report if heartbeat process is running. This will be TRUE if the process has been started and has not stopped.

Usage

rrq_heartbeat$is_running()

---

Method start()

Start the heartbeat process. An error will be thrown if it is already running.

Usage

rrq_heartbeat$start()

---

Method stop()

Stop the heartbeat process

Usage

rrq_heartbeat$stop(wait = TRUE)

Arguments

wait

Logical, indicating if we should wait until the heartbeat process terminates (should take only a fraction of a second)

---

Method format()

Format method, used by R6 to nicely print the object

Usage

rrq_heartbeat$format(...)

Arguments

...

Additional arguments, currently ignored

Examples

if (redux::redis_available()) {
  rand_str <- function() {
    paste(sample(letters, 20, TRUE), collapse = "")
  }
  key <- sprintf("rrq:heartbeat:%s", rand_str())
  h <- rrq::rrq_heartbeat$new(key, 1, expire = 2)
  con <- redux::hiredis()

  # The heartbeat key exists
  con$EXISTS(key)

  # And has an expiry of less than 2000ms
  con$PTTL(key)

  # We can manually stop the heartbeat, and 2s later the key will
  # stop existing
  h$stop()

  Sys.sleep(2)
  con$EXISTS(key) # 0

  # This is required to close any processes opened by this
  # example, normally you would not need this.
  processx:::supervisor_kill()
}