throttler.core — throttler 1.0.1

chan-throttler clj

(chan-throttler rate unit)

(chan-throttler rate unit bucket-size)

Returns a function that will take an input channel and return an output channel with the desired rate. Optionally acceps a bucket size for bursty channels.

If the throttling function returned here is used on more than one channel, they will all share the same token-bucket. This means their overall output rate combined will be equal to the provided rate. In other words, they will all share the alloted bandwith using statistical multiplexing.

See fn-throttler for an example that can trivially be extrapolated to chan-throttler.

fn-throttler clj

(fn-throttler rate unit)

(fn-throttler rate unit bucket-size)

Creates a function that will globally throttle multiple functions at the provided rate. The returned function accepts a function and produces an equivalent one that complies with the desired rate. If applied to many functions, the sum af all their invocations in a time interval will sum up to the goal average rate.

Example: ; create the function throttler (def slow-to-1-per-minute (fn-throttler 1 :minute)

; create slow versions of f1, f2 and f3
(def f1-slow (slow-to-1-per-minute f1)
(def f2-slow (slow-to-1-per-minute f2)
(def f3-slow (slow-to-1-per-minute f3)

; use them to do work. Their aggregate rate will be equal to 1
; call/minute
(f1-slow arg1 arg2) ; => result, t = 0
(f2-slow)           ; => result, t = 1 minute
(f3-slow arg)       ; => result, t = 2 minutes

The combined rate of f1-slow, f2-slow and f3-slow will be equal to 'rate'. This does not mean that the rate of each is 1/3rd of 'rate'; if only f1-slow is being called then its throughput will be close to rate. Or, if one of the functions is being called from multiple threads then it'll get a greater share of the total bandwith.

In other words, the functions will use statistical multiplexing to cap the allotted bandwidth.

pipe clj macro

(pipe from to)

Pipes an element from the from channel and supplies it to the to channel. The to channel will be closed when the from channel closes. Must be called within a go block.

throttle-chan clj

(throttle-chan c rate unit)

(throttle-chan c rate unit bucket-size)

Takes a write channel, a goal rate and a unit and returns a read channel. Messages written to the input channel can be read from the throttled output channel at a rate that will be at most the provided goal rate.

Optionally takes a bucket size, which will correspond to the maximum number of burst messages.

As an example, the channel produced by calling:

(throttle-chan (chan) 1 :second 9)

Will transmit 1 message/second on average but can transmit up to 10 messages on a single second (9 burst messages + 1 message/second).

Note that after the burst messages have been consumed they have to be refilled in a quiescent period at the provided rate, so the overall goal rate is not affected in the long term.

The throttled channel will be closed when the input channel closes.

throttle-fn clj

(throttle-fn f rate unit)

(throttle-fn f rate unit bucket-size)

Takes a function, a goal rate and a time unit and returns a function that is equivalent to the original but that will have a maximum throughput of 'rate'.

Optionally accepts a burst rate, in which case the resulting function will behave like a bursty channel. See throttle-chan for details.