Guzzle send()方法导致cURL错误

尝试使用Guzzle 5执行以下代码。

$client = new GuzzleClient(['defaults/headers/User-Agent' => static::$userAgentString]);
$request = $client->createRequest(static::$serviceRequestMethod, $url, $options); // Create signing request.
$signature = new Signature'Signature($this->accessKey, $this->secretKey);
$options = array_merge_recursive($options, ['query' => ['Signature' => $signature->signString($hash)]]);
$request = $client->createRequest(static::$serviceRequestMethod, $url, $options); // Create real request.
$response = $client->send($request);

当我在长时间运行的CLI进程中调用这行足够多次时，我得到以下错误，可以追溯到$response = $client->send($request);

cURL error 35: error:02001018:system library:fopen:Too many open files

点击后，服务器上的所有其他网页和命令都会崩溃，并出现同样的"打开的文件太多"错误。

下面是堆栈跟踪:

#0 /home/vagrant/code/example.com/vendor/guzzlehttp/guzzle/src/RequestFsm.php(104): GuzzleHttp'Exception'RequestException::wrapException(Object(GuzzleHttp'Message'Request), Object(GuzzleHttp'Ring'Exception'ConnectException))
#1 /home/vagrant/code/example.com/vendor/guzzlehttp/guzzle/src/RequestFsm.php(132): GuzzleHttp'RequestFsm->__invoke(Object(GuzzleHttp'Transaction))
#2 /home/vagrant/code/example.com/vendor/react/promise/src/FulfilledPromise.php(25): GuzzleHttp'RequestFsm->GuzzleHttp'{closure}(Array)
#3 /home/vagrant/code/example.com/vendor/guzzlehttp/ringphp/src/Future/CompletedFutureValue.php(55): React'Promise'FulfilledPromise->then(Object(Closure), NULL, NULL)
#4 /home/vagrant/code/example.com/vendor/guzzlehttp/guzzle/src/Message/FutureResponse.php(43): GuzzleHttp'Ring'Future'CompletedFutureValue->then(Object(Closure), NULL, NULL)
#5 /home/vagrant/code/example.com/vendor/guzzlehttp/guzzle/src/RequestFsm.php(135): GuzzleHttp'Message'FutureResponse::proxy(Object(GuzzleHttp'Ring'Future'CompletedFutureArray), Object(Closure))
#6 /home/vagrant/code/example.com/vendor/guzzlehttp/guzzle/src/Client.php(165): GuzzleHttp'RequestFsm->__invoke(Object(GuzzleHttp'Transaction))
#7 /home/vagrant/code/example.com/app/library/amazon/src/AWS.php(540): GuzzleHttp'Client->send(Object(GuzzleHttp'Message'Request))

我不知道通过Guzzle发送请求后是否需要显式地关闭资源。是我遗漏了什么，还是这是Guzzle的bug ?