Preference data

Which answer is better, and why

Coding and agent-behavior comparisons chosen to test judgment, not just correctness: sometimes the longer answer is wrong, sometimes caution is the wrong call, and one pair is a genuine tie that should not be forced.

12 pairs
10 clear, 2 slight or tie
Agent safety and honesty cases
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A counter shared by goroutines

pref-06

Prompt

Is this Go code safe?

var count int
for i := 0; i < 100; i++ {
    go func() { count++ }()
}
fmt.Println(count)

Response A

No, two problems: 1. count++ from many goroutines is a data race (go run -race reports it); increments can be lost. 2. main prints before the goroutines finish.

var count int64
var wg sync.WaitGroup
for i := 0; i < 100; i++ {
    wg.Add(1)
    go func() { defer wg.Done(); atomic.AddInt64(&count, 1) }()
}
wg.Wait()
fmt.Println(count) // 100

Response B

Yes. The Go scheduler runs goroutines one at a time on a single thread, so count++ is effectively atomic and you will get 100.

Expert judgment

Prefers response AClear preference

B is wrong on both counts: Go runs goroutines in parallel across threads, and the program may print before they finish. A finds both bugs and fixes them with atomic and WaitGroup.