Creates a rate limiter.

• parameter rate

  Maximum number of promise resolutions per second, per channel.

• parameter max

  Maximum number of pending promises allowed at once, over all channels.

• parameter n

  Initial size of the internal channel hash table. This should be approximately the number of different channels that will be used.

Lwt_throttle.wait limiter channel returns a new promise associated with the given rate limiter and channel.

If the maximum number of pending promises for limiter has not been reached, the promise starts pending. It will be resolved with true at some future time, such that the rate limit of limiter is not exceeded, with respect to other promises in the same channel.

If the maximum number of pending promises has been reached, the returned promise is already resolved with false.