CURLMOPT_MAX_PIPELINE_LENGTH (3) - Linux Man Pages
CURLMOPT_MAX_PIPELINE_LENGTH: maximum number of requests in a pipeline
NAMECURLMOPT_MAX_PIPELINE_LENGTH - maximum number of requests in a pipeline
DESCRIPTIONPass a long. The set max number will be used as the maximum amount of outstanding requests in a pipelined connection. Only used if pipelining is enabled.
When this limit is reached, libcurl will use another connection to the same host (see CURLMOPT_MAX_HOST_CONNECTIONS(3)), or queue the request until one of the pipelines to the host is ready to accept a request. Thus, the total number of requests in-flight is CURLMOPT_MAX_HOST_CONNECTIONS(3) * CURLMOPT_MAX_PIPELINE_LENGTH(3).