Method popIdle

internal/pool/pool.go:1140–1200

()

}

func (p *ConnPool) popIdle() (*Conn, error) {
	if p.closed() {
		return nil, ErrClosed
	}
	defer p.checkMinIdleConns()

	n := len(p.idleConns)
	if n == 0 {
		return nil, nil
	}

	var cn *Conn
	attempts := 0

	maxAttempts := min(popAttempts, n)
	for attempts < maxAttempts {
		if len(p.idleConns) == 0 {
			return nil, nil
		}

		if p.cfg.PoolFIFO {
			cn = p.idleConns[0]
			copy(p.idleConns, p.idleConns[1:])
			p.idleConns = p.idleConns[:len(p.idleConns)-1]
		} else {
			idx := len(p.idleConns) - 1
			cn = p.idleConns[idx]
			p.idleConns = p.idleConns[:idx]
		}
		attempts++

		// Hot path optimization: try IDLE → IN_USE or CREATED → IN_USE transition
		// Using inline TryAcquire() method for better performance (avoids pointer dereference)
		if cn.TryAcquire() {
			// Successfully acquired the connection
			p.idleConnsLen.Add(-1)
			break
		}

		// Connection is in UNUSABLE, INITIALIZING, or other state - skip it

		// Connection is not in a valid state (might be UNUSABLE for handoff/re-auth, INITIALIZING, etc.)
		// Put it back in the pool and try the next one
		if p.cfg.PoolFIFO {
			// FIFO: put at end (will be picked up last since we pop from front)
			p.idleConns = append(p.idleConns, cn)
		} else {
			// LIFO: put at beginning (will be picked up last since we pop from end)
			p.idleConns = append([]*Conn{cn}, p.idleConns...)
		}
		cn = nil
	}

	// If we exhausted all attempts without finding a usable connection, return nil
	if attempts > 1 && attempts >= maxAttempts && int32(attempts) >= p.poolSize.Load() {
		internal.Logger.Printf(context.Background(), "redis: connection pool: failed to get a usable connection after %d attempts", attempts)
		return nil, nil
	}