goAsync race conditionMedium

Panic on closing already closed Go channel

Time: 0:00

BugFind the bug and fix the code

What it should do

Close channel without causing panics on double close. Example: safeCloseChannel(true) -> "closed"

What happens instead

panic: close of closed channel

package main

import "fmt"

func safeCloseChannel(alreadyClosed bool) string {
	ch := make(chan int)
	if alreadyClosed {
		close(ch)
	}
	close(ch)
	return "closed"
}

func main() {
	fmt.Println(safeCloseChannel(true))
}

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

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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.

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package main import "fmt" func safeCloseChannel(alreadyClosed bool) string { ch := make(chan int) if alreadyClosed { close(ch) } close(ch) return "closed" } func main() { fmt.Println(safeCloseChannel(true)) }

Panic on closing already closed Go channel

What it should do

What happens instead

More async and race conditions to practise

Panic on closing already closed Go channel

What it should do

What happens instead

More async and race conditions to practise