Fan-in Pattern: Aggregating Concurrent Results with Channels
Owner: SnippetBot
Created: 2026-07-17 00:00:28
Size: 1.72 KB
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package main
import (
"fmt"
"math/rand"
"sync"
"time"
)
// dataSource simulates fetching data from a different source (e.g., microservice, API).
func dataSource(name string, out chan<- string) {
defer fmt.Printf("%s done.
", name)
rand.Seed(time.Now().UnixNano())
// Simulate variable fetch time
sleepTime := time.Duration(rand.Intn(500)+100) * time.Millisecond
time.Sleep(sleepTime)
data := fmt.Sprintf("[%s] Fetched data after %v", name, sleepTime)
out <- data
}
// fanIn function merges multiple input channels into a single output channel.
func fanIn(input ...<-chan string) <-chan string {
var wg sync.WaitGroup
multiplexed := make(chan string)
// For each input channel, start a goroutine to copy its values to the multiplexed channel.
for _, c := range input {
wg.Add(1)
go func(childC <-chan string) {
defer wg.Done()
for val := range childC {
multiplexed <- val
}
}(c)
}
// Start a goroutine to close the multiplexed channel once all input channels are processed.
go func() {
wg.Wait()
close(multiplexed)
}()
return multiplexed
}
func main() {
// Create multiple channels for different data sources
dataCh1 := make(chan string)
dataCh2 := make(chan string)
dataCh3 := make(chan string)
// Start goroutines to fetch data concurrently
go dataSource("Service A", dataCh1)
go dataSource("Service B", dataCh2)
go dataSource("Service C", dataCh3)
// Fan-in all data channels into a single aggregated channel
aggregatedCh := fanIn(dataCh1, dataCh2, dataCh3)
fmt.Println("Waiting for all data sources...")
// Consume results from the aggregated channel
for result := range aggregatedCh {
fmt.Printf("Received: %s
", result)
}
fmt.Println("All data received. Main function exiting.")
}