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Bounded Parallel Get Requests in Golang
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| package main | |
| import ( | |
| "fmt" | |
| "net/http" | |
| "sort" | |
| "time" | |
| ) | |
| // a struct to hold the result from each request including an index | |
| // which can be used for sorting the results after they come in | |
| type result struct { | |
| index int | |
| res http.Response | |
| err error | |
| } | |
| // boundedParallelGet sends requests in parallel but only up to a certain | |
| // limit, and furthermore it's only parallel up to the amount of CPUs but | |
| // is always concurrent up to the concurrency limit | |
| func boundedParallelGet(urls []string, concurrencyLimit int) []result { | |
| // this buffered channel will block at the concurrency limit | |
| semaphoreChan := make(chan struct{}, concurrencyLimit) | |
| // this channel will not block and collect the http request results | |
| resultChan := make(chan *result) | |
| // keen an index and loop through every url we will send a request to | |
| for i, url := range urls { | |
| // start a go routine with the index and url in a closure | |
| go func(i int, url string) { | |
| // this sends an empty struct into the semaphoreChan which | |
| // is basically saying add one to the limit, but when the | |
| // limit has been reached block until there is room | |
| semaphoreChan <- struct{}{} | |
| // send the request and put the response in a result struct | |
| // along with the index so we can sort them later along with | |
| // any error that might have occoured | |
| res, err := http.Get(url) | |
| result := &result{i, *res, err} | |
| // now send the result struct through the resultChan so we | |
| // can get the results without being able to return them | |
| resultChan <- result | |
| // once we're done it's we read from the semaphoreChan which | |
| // has the effect of removing one from the limit and allowing | |
| // another goroutine to start | |
| <-semaphoreChan | |
| }(i, url) | |
| } | |
| // make a slice to hold the results we're expecting | |
| var results []result | |
| // start listening for any results over the resultChan | |
| for { | |
| // once we've got a result append it to the result slice | |
| result := <-resultChan | |
| results = append(results, *result) | |
| // if we've reached the expected amount of urls then stop | |
| if len(results) == len(urls) { | |
| break | |
| } | |
| } | |
| // let's sort these results real quick | |
| sort.Slice(results, func(i, j int) bool { | |
| return results[i].index < results[j].index | |
| }) | |
| return results | |
| } | |
| // send a bunch of requests and time how long they take | |
| func benchmarkBoundedParallelRequests(urls []string, concurrency int) string { | |
| boundedParallelTimeStart := time.Now() | |
| results := boundedParallelGet(urls, concurrency) | |
| seconds := time.Since(boundedParallelTimeStart).Seconds() | |
| tmplate := "%d bounded parallel requests: %d/%d in %v" | |
| return fmt.Sprintf(tmplate, concurrency, len(results), len(urls), seconds) | |
| } | |
| func main() { | |
| // let's make a slice of URLs to send requets to | |
| var urls []string | |
| for i := 0; i < 100; i++ { | |
| urls = append(urls, "http://httpbin.org/get") | |
| } | |
| // and now let's compare different concurrency limits | |
| fmt.Println(benchmarkBoundedParallelRequests(urls, 5)) | |
| fmt.Println(benchmarkBoundedParallelRequests(urls, 10)) | |
| fmt.Println(benchmarkBoundedParallelRequests(urls, 25)) | |
| fmt.Println(benchmarkBoundedParallelRequests(urls, 50)) | |
| fmt.Println(benchmarkBoundedParallelRequests(urls, 75)) | |
| fmt.Println(benchmarkBoundedParallelRequests(urls, 100)) | |
| // and you should see something like the following printed | |
| // depending on how fast your computer and internet is | |
| // 5 bounded parallel requests: 100/100 in 5.533223255 | |
| // 10 bounded parallel requests: 100/100 in 2.5115351219999997 | |
| // 25 bounded parallel requests: 100/100 in 1.189462884 | |
| // 50 bounded parallel requests: 100/100 in 1.17430002 | |
| // 75 bounded parallel requests: 100/100 in 1.001383863 | |
| // 100 bounded parallel requests: 100/100 in 1.3769354 | |
| } |
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