goAsync race conditionMedium

Select default branch starves channel communication

Time: 0:00

BugFind the bug and fix the code

What it should do

Receive value from channel if available, or return fallback. Example: receiveOrFallback(42) -> 42

What happens instead

Select drops into default immediately before buffered channel item is read

package main

import "fmt"

func receiveOrFallback(val int) int {
	ch := make(chan int, 1)
	ch <- val
	// Non-blocking select with immediate default
	select {
	case <-ch:
		// Succeeded
	default:
		return -1
	}
	return val
}

func main() {
	fmt.Println(receiveOrFallback(42))
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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Hint 3

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This bug belongs to the async and race conditions pattern

A missing await, unbuffered channel deadlocks, ConcurrentModificationException, and data races under load.

Learn the async and race conditions pattern Step through your own code

<iframe src="https://trybughunt.com/embed/06ea4ef2-ebbd-4d8a-baa8-b241b179d41e" title="Debugging challenge: Select default branch starves channel communication" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe> <p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/06ea4ef2-ebbd-4d8a-baa8-b241b179d41e">TryBugHunt</a></p>

package main import "fmt" func receiveOrFallback(val int) int { ch := make(chan int, 1) ch <- val // Non-blocking select with immediate default select { case <-ch: // Succeeded default: return -1 } return val } func main() { fmt.Println(receiveOrFallback(42)) }

Select default branch starves channel communication

What it should do

What happens instead

More async and race conditions to practise

Select default branch starves channel communication

What it should do

What happens instead

More async and race conditions to practise