How to correctly use sync.Cond?

Question

I\'m having trouble figuring out how to correctly use sync.Cond. From what I can tell, a race condition exists between locking the Locker and invoking the condition\'s Wait meth

Answer 1

I finally discovered a way to do this and it doesn't involve sync.Cond at all - just the mutex.

type Task struct {
    m       sync.Mutex
    headers http.Header
}

func NewTask() *Task {
    t := &Task{}
    t.m.Lock()
    go func() {
        defer t.m.Unlock()
        // ...do stuff...
    }()
    return t
}

func (t *Task) WaitFor() http.Header {
    t.m.Lock()
    defer t.m.Unlock()
    return t.headers
}

How does this work?

The mutex is locked at the beginning of the task, ensuring that anything calling WaitFor() will block. Once the headers are available and the mutex unlocked by the goroutine, each call to WaitFor() will execute one at a time. All future calls (even after the goroutine ends) will have no problem locking the mutex, since it will always be left unlocked.