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<em>[Rate limiting](http://en.wikipedia.org/wiki/Rate_limiting)</em> is an important mechanism for controlling resource utilization and maintaining quality of service. Go elegantly supports rate limiting with goroutines, channels, and [tickers](tickers).

	package main

	import (
	"fmt"
	"time"
	)

	func main() {

First we'll look at basic rate limiting. Suppose we want to limit our handling of incoming requests. We'll serve these requests off a channel of the same name.	requests := make(chan int, 5)
	for i := 1; i <= 5; i++ {
	requests <- i
	}
	close(requests)

This `limiter` channel will receive a value every 200 milliseconds. This is the regulator in our rate limiting scheme.	limiter := time.Tick(200 * time.Millisecond)

By blocking on a receive from the `limiter` channel before serving each request, we limit ourselves to 1 request every 200 milliseconds.	for req := range requests {
	<-limiter
	fmt.Println("request", req, time.Now())	request 1 2020-10-21 16:53:50.395291385 +0000 UTC m=+0.200203008 request 2 2020-10-21 16:53:50.599166533 +0000 UTC m=+0.404078122 request 3 2020-10-21 16:53:50.795310384 +0000 UTC m=+0.600222016 request 4 2020-10-21 16:53:50.995286879 +0000 UTC m=+0.800198499 request 5 2020-10-21 16:53:51.195267593 +0000 UTC m=+1.000179165
	}	request 1 2020-10-21 16:53:51.835344603 +0000 UTC m=+0.200172935 request 2 2020-10-21 16:53:52.035349525 +0000 UTC m=+0.400177860 request 3 2020-10-21 16:53:52.235373114 +0000 UTC m=+0.600201456 request 4 2020-10-21 16:53:52.435425931 +0000 UTC m=+0.800254255 request 5 2020-10-21 16:53:52.635358659 +0000 UTC m=+1.000186981

We may want to allow short bursts of requests in our rate limiting scheme while preserving the overall rate limit. We can accomplish this by buffering our limiter channel. This `burstyLimiter` channel will allow bursts of up to 3 events.	burstyLimiter := make(chan time.Time, 3)

Fill up the channel to represent allowed bursting.	for i := 0; i < 3; i++ {
	burstyLimiter <- time.Now()	request 1 2020-10-21 16:54:02.816778941 +0000 UTC m=+0.200206237 request 2 2020-10-21 16:54:03.016775311 +0000 UTC m=+0.400202600 request 3 2020-10-21 16:54:03.216763927 +0000 UTC m=+0.600191169 request 4 2020-10-21 16:54:03.416764574 +0000 UTC m=+0.800191909 request 5 2020-10-21 16:54:03.616744823 +0000 UTC m=+1.000172050
	}	request 1 2020-10-21 16:54:04.232918831 +0000 UTC m=+0.200280371 request 2 2020-10-21 16:54:04.432997938 +0000 UTC m=+0.400359770 request 3 2020-10-21 16:54:04.632931045 +0000 UTC m=+0.600292602 request 4 2020-10-21 16:54:04.832919318 +0000 UTC m=+0.800280921 request 5 2020-10-21 16:54:05.032891925 +0000 UTC m=+1.000253479

Every 200 milliseconds we'll try to add a new value to `burstyLimiter`, up to its limit of 3.	go func() {
	for t := range time.Tick(200 * time.Millisecond) {
	burstyLimiter <- t
	}
	}()	request 1 2020-10-21 16:54:10.176046549 +0000 UTC m=+0.200179195 request 2 2020-10-21 16:54:10.376067042 +0000 UTC m=+0.400199627 request 3 2020-10-21 16:54:10.576063101 +0000 UTC m=+0.600195898 request 4 2020-10-21 16:54:10.776036879 +0000 UTC m=+0.800169467 request 5 2020-10-21 16:54:10.976052867 +0000 UTC m=+1.000185446

Now simulate 5 more incoming requests. The first 3 of these will benefit from the burst capability of `burstyLimiter`.	burstyRequests := make(chan int, 5)
	for i := 1; i <= 5; i++ {
	burstyRequests <- i	request 1 2020-10-21 16:54:17.828242725 +0000 UTC m=+0.200199154 request 2 2020-10-21 16:54:18.028291874 +0000 UTC m=+0.400248385 request 3 2020-10-21 16:54:18.228258219 +0000 UTC m=+0.600214720 request 4 2020-10-21 16:54:18.428244427 +0000 UTC m=+0.800200934 request 5 2020-10-21 16:54:18.628256684 +0000 UTC m=+1.000213216
	}	request 1 2020-10-21 16:54:19.233902539 +0000 UTC m=+0.200206278 request 2 2020-10-21 16:54:19.433884891 +0000 UTC m=+0.400188622 request 3 2020-10-21 16:54:19.633922697 +0000 UTC m=+0.600226519 request 4 2020-10-21 16:54:19.83391026 +0000 UTC m=+0.800213976 request 5 2020-10-21 16:54:20.033891067 +0000 UTC m=+1.000194793
	close(burstyRequests)	request 1 2020-10-21 16:54:20.668442616 +0000 UTC m=+0.200238556 request 2 2020-10-21 16:54:20.868384667 +0000 UTC m=+0.400180641 request 3 2020-10-21 16:54:21.068404615 +0000 UTC m=+0.600200562 request 4 2020-10-21 16:54:21.268510532 +0000 UTC m=+0.800306470 request 5 2020-10-21 16:54:21.468431947 +0000 UTC m=+1.000227939
	for req := range burstyRequests {
	<-burstyLimiter
	fmt.Println("request", req, time.Now())	request 1 2020-10-21 16:54:22.678544517 +0000 UTC m=+0.200264505 request 2 2020-10-21 16:54:22.878521123 +0000 UTC m=+0.400240991 request 3 2020-10-21 16:54:23.07852738 +0000 UTC m=+0.600247293 request 4 2020-10-21 16:54:23.278523098 +0000 UTC m=+0.800242968 request 5 2020-10-21 16:54:23.478542539 +0000 UTC m=+1.000262515 request 1 2020-10-21 16:54:23.47859248 +0000 UTC m=+1.000312349 request 2 2020-10-21 16:54:23.478600138 +0000 UTC m=+1.000320005 request 3 2020-10-21 16:54:23.478614967 +0000 UTC m=+1.000334841 request 4 2020-10-21 16:54:23.678733121 +0000 UTC m=+1.200453007 request 5 2020-10-21 16:54:23.878721299 +0000 UTC m=+1.400441217
	}	request 1 2020-10-21 16:54:24.470811399 +0000 UTC m=+0.200246254 request 2 2020-10-21 16:54:24.670758827 +0000 UTC m=+0.400193482 request 3 2020-10-21 16:54:24.871167288 +0000 UTC m=+0.600601913 request 4 2020-10-21 16:54:25.070775841 +0000 UTC m=+0.800210554 request 5 2020-10-21 16:54:25.270805827 +0000 UTC m=+1.000240505 request 1 2020-10-21 16:54:25.270854384 +0000 UTC m=+1.000289018 request 2 2020-10-21 16:54:25.270859646 +0000 UTC m=+1.000294273 request 3 2020-10-21 16:54:25.270863497 +0000 UTC m=+1.000298116 request 4 2020-10-21 16:54:25.470974975 +0000 UTC m=+1.200409608 request 5 2020-10-21 16:54:25.67116232 +0000 UTC m=+1.400596974
	}	request 1 2020-10-21 16:54:26.271738531 +0000 UTC m=+0.200278269 request 2 2020-10-21 16:54:26.471727684 +0000 UTC m=+0.400267456 request 3 2020-10-21 16:54:26.671712201 +0000 UTC m=+0.600251980 request 4 2020-10-21 16:54:26.871703296 +0000 UTC m=+0.800243237 request 5 2020-10-21 16:54:27.071760433 +0000 UTC m=+1.000300158 request 1 2020-10-21 16:54:27.071817886 +0000 UTC m=+1.000357577 request 2 2020-10-21 16:54:27.071835043 +0000 UTC m=+1.000374733 request 3 2020-10-21 16:54:27.071840685 +0000 UTC m=+1.000380381 request 4 2020-10-21 16:54:27.271919949 +0000 UTC m=+1.200459667 request 5 2020-10-21 16:54:27.471947605 +0000 UTC m=+1.400487336

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