Go: What is the difference between goroutine and thread?

Goroutine — lightweight concurrency primitive. Thread — OS-level execution unit.

Memory:

• Goroutine: 2KB stack (dynamic growth).
• Thread: 1-8MB stack (fixed).

Scheduling:

• Goroutine: Go runtime (cooperative).
• Thread: OS kernel (preemptive).

Cost:

• Goroutine: ~2µs to create.
• Thread: ~10-100µs to create.

1// Efficient goroutine usage
2func fanOut(items []Item) []Result {
3    results := make([]Result, len(items))
4    var wg sync.WaitGroup
5    for i, item := range items {
6        wg.Add(1)
7        go func(i int, item Item) {
8            defer wg.Done()
9            results[i] = process(item)
10        }(i, item)
11    }
12    wg.Wait()
13    return results
14}

When to use goroutines:

• I/O-bound concurrency.
• Background tasks.

When to use threads:

• Cgo interop.
• Thread-local storage.

Common mistakes:

• Not synchronizing completion.
• Closure variable capture.
• Assuming goroutines are parallel.
• Creating too many without backpressure.
• Using runtime.LockOSThread() unnecessarily.