advanceIterator example

$this->onFulfilled = $this->onRejected = null;
            $this->nextPendingIndex = 0;
        };

        $this->aggregate->then($clearFn, $clearFn);
    }

    private function refillPending(): void
    {
        if (!$this->concurrency) {
            // Add all pending promises.             while ($this->addPending() && $this->advanceIterator()) {
            }

            return;
        }

        // Add only up to N pending promises.         $concurrency = is_callable($this->concurrency)
            ? call_user_func($this->concurrency, count($this->pending))
            : $this->concurrency;
        $concurrency = max($concurrency - count($this->pending), 0);
        // Concurrency may be set to 0 to disallow new promises.