Panic when trying to use uninitialized or deleted Pigosat objects

[wkschwartz]

Based on justinfx/pigosat@a755660. Open to suggestions about how to test 35d2c7f.

[wkschwartz]

35d2c7f is wrong. The whole point of p.isReady() is to check whether p is nil, and thus if the lock can be accessed. Perhaps we should lock inside p.isReady(), have one for reading and one for read/write.

func (p *Pigosat) readyRead() (unlock func()) {
    // No race here because the pointer p cannot magically change if it's nil.
    if p == nil {
        return nil
    }
    p.lock.RLock()
    if p.p == nil {
        p.lock.RUnlock()
        return nil
    }
    return p.lock.RUnlock
}

Then it's used like

func (p *Pigosat) Print(file *os.File) error {
    unlock := readyRead()
    if unlock == nil {
        return nil
    }
    defer unlock()
    // ...
}

[wkschwartz]

The real issue is that having default return values for when p is nil or already deleted just doesn't make sense. Better to panic for such a hard-to-achieve programming error.