constants_curl_multi_setopt

CURLMOPT_CHUNK_LENGTH_PENALTY_SIZE (int)
Specifies the chunk length threshold for pipelining in bytes. Available as of PHP 7.0.7 and cURL 7.30.0

CURLMOPT_CONTENT_LENGTH_PENALTY_SIZE (int)
Specifies the size threshold for pipelining penalty in bytes. Available as of PHP 7.0.7 and cURL 7.30.0

CURLMOPT_MAXCONNECTS (int)
Specifies the maximum amount of simultaneously open connections that libcurl may cache. By default the size will be enlarged to fit four times the number of handles added via curl_multi_add_handle. When the cache is full, curl closes the oldest one in the cache to prevent the number of open connections from increasing. Available as of cURL 7.16.3.

CURLMOPT_MAX_CONCURRENT_STREAMS (int)
Specifies the maximum number of concurrent streams for connections that cURL should support on connections using HTTP/2. Valid values range from 1 to 2147483647 (2^31 - 1). The value passed here would be honored based on other system resources properties. Default is 100. Available as of PHP 8.2.0 and cURL 7.67.0.

CURLMOPT_MAX_HOST_CONNECTIONS (int)
Specifies the maximum number of connections to a single host. Available as of PHP 7.0.7 and cURL 7.30.0

CURLMOPT_MAX_PIPELINE_LENGTH (int)
Specifies the maximum number of requests in a pipeline. Available as of PHP 7.0.7 and cURL 7.30.0

CURLMOPT_MAX_TOTAL_CONNECTIONS (int)
Specifies the maximum number of simultaneously open connections. Available as of PHP 7.0.7 and cURL 7.30.0

CURLMOPT_PIPELINING (int)
Pass 1 to enable or 0 to disable. Enabling pipelining on a multi handle will make it attempt to perform HTTP Pipelining as far as possible for transfers using this handle. This means that adding a second request that can use an already existing connection will "pipe" the second request on the same connection. As of cURL 7.43.0, the value is a bitmask, and passing 2 will try to multiplex the new transfer over an existing HTTP/2 connection. Passing 3 instructs cURL to ask for pipelining and multiplexing independently of each other. As of cURL 7.62.0, setting the pipelining bit has no effect. Instead of integer literals, the CURLPIPE_* constants can also be used. Available as of cURL 7.16.0.

CURLMOPT_PUSHFUNCTION (int)
Pass a callable that will be registered to handle server pushes and should have the following signature: int<pushfunction> resource``parent_ch resource``pushed_ch array``headers

The push function is supposed to return either CURL_PUSH_OK if it can handle the push, or CURL_PUSH_DENY to reject it. Available as of PHP 7.1.0 and cURL 7.44.0