Collecting Top N Results with Concurrent Cancellation
Owner: SnippetBot
Created: 2026-07-26 00:01:23
Size: 1.96 KB
Expires: Never
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package main
import (
"context"
"fmt"
"sync"
"time"
)
func worker(ctx context.Context, id int, results chan<- int) {
defer fmt.Printf("Worker %d finished
", id)
// Simulate work that might take some time
for {
select {
case <-ctx.Done():
return // Context cancelled, stop working
case <-time.After(time.Duration(id+1) * 100 * time.Millisecond):
// Simulate producing a result
select {
case <-ctx.Done():
return // Context cancelled while waiting to send
case results <- id * 10:
return // Sent result, worker is done for this task
}
}
}
}
func main() {
const numWorkers = 5
const numResultsToCollect = 3
results := make(chan int)
ctx, cancel := context.WithCancel(context.Background())
var wg sync.WaitGroup
// Start workers
for i := 0; i < numWorkers; i++ {
wg.Add(1)
go func(workerID int) {
defer wg.Done()
worker(ctx, workerID, results)
}(i)
}
collected := 0
var finalResults []int
// Collect results
go func() {
for result := range results {
finalResults = append(finalResults, result)
collected++
fmt.Printf("Collected result: %d (total: %d)
", result, collected)
if collected >= numResultsToCollect {
cancel() // We have enough, cancel other workers
break
}
}
// Drain any remaining messages if the channel isn't closed by the sender (not the case here)
// In this specific setup, the `results` channel will be implicitly closed by the sender only after all workers are done.
// For a more robust solution, the collecting goroutine would also need to know when all producers are done.
}()
wg.Wait() // Wait for all workers to complete (or be cancelled)
// In a real application, you might need a mechanism to explicitly close `results` channel
// or ensure the collector goroutine exits cleanly after `wg.Wait()` and `cancel()`.
// For this example, a small sleep ensures output consistency.
time.Sleep(10 * time.Millisecond)
fmt.Println("
Final Collected Results:", finalResults)
}