Method acquire

onecache/pool.go:167–227

Acquire is used to get a connection that is pooled or to return a new connection

(addr net.Addr)

// Acquire is used to get a connection that is pooled or to return a new
// connection
func (p *connPool) acquire(addr net.Addr) (*conn, error) {
	// Check to see if there's a pooled connection available. This is up
	// here since it should the the vastly more common case than the rest
	// of the code here.
	p.Lock()
	s := addr.String()
	c := p.pool[s]
	if c != nil {
		c.markForUse()
		p.Unlock()
		return c, nil
	}

	// If not (while we are still locked), set up the throttling structure
	// for this address, which will make everyone else wait until our
	// attempt is done.
	var wait chan struct{}
	var ok bool
	if wait, ok = p.limiter[addr.String()]; !ok {
		wait = make(chan struct{})
		p.limiter[addr.String()] = wait
	}
	isLeadThread := !ok
	p.Unlock()

	// If we are the lead thread, make the new connection and then wake
	// everybody else up to see if we got it.
	if isLeadThread {
		c, err := p.getNewConn(addr)
		p.Lock()
		delete(p.limiter, addr.String())
		close(wait)
		if err != nil {
			p.Unlock()
			return nil, err
		}

		p.pool[addr.String()] = c
		p.Unlock()
		return c, nil
	}

	// Otherwise, wait for the lead thread to attempt the connection
	// and use what's in the pool at that point.
	select {
	case <-p.shutdownCh:
		return nil, fmt.Errorf("rpc error: shutdown")
	case <-wait:
	}

	// See if the lead thread was able to get us a connection.
	p.Lock()
	if c := p.pool[addr.String()]; c != nil {
		c.markForUse()
		p.Unlock()
		return c, nil
	}