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44 ” cURL Extension operate unpredictably in a threaded environment such as Windo ws Server or *NIX running a threaded Apache MPM such as worker. If you are using the HTTP streams wrapper or either of the PHP -based HTTP client libraries co vered in this chapter and you have access to install software on your server, you may want to install a local DNS caching daemon to impro ve performance. Try nscd or dnsmasq on *NIX. W riting DNS caching into your o wn client will be co vered in a later chapter on writing your o wn HTTP client. T imeouts CURLOPT_CONNECTTIMEOUT is a maximum amount of time in seconds to which a connection attempt will be restricted for a cURL operation. It can be set to 0 to disable this limit, but this is inadvisable in a production environment. N ote that this time includes DNS lookups. F or environments where the DNS server in use or the web server hosting the target application is not particularly responsive, it may be necessary to increase the value of this setting. CURLOPT_TIMEOUT is a maximum amount of time in seconds to which the execution of individual cURL extension function calls will be limited. N ote that the value for this setting should include the value for CURLOPT_CONNECTTIMEOUT. In other words, CURLOPT_CONNECTTIMEOUT is a segment of the time represented by CURLOPT_TIMEOUT, so the value of the latter should be greater than the value of the former. R equest P ooling Because it is written C, the cURL extension has one feature that cannot be replicated exactly in libraries written in PHP: the ability to run multiple requests in parallel. What this means is that multiple requests can be pro vided to cURL all at once and, rather than waiting for a response to be received for the first request before mo ving on to sending the second, all requests will be sent and processed as responses are returned. This can significantly shorten the time required to collectively complete all the requests. H o wever, care should be taken not to o verload a single host with requests when using this feature.
cURL Extension ” 45 $ch1 = curl_init(’http://localhost.example/resource1’); curl_setopt($ch1, CURLOPT_RETURNTRANSFER, true); /* other curl_setopt calls */ $ch2 = curl_init(’http://localhost.example/resource2’); curl_setopt($ch2, CURLOPT_RETURNTRANSFER, true); /* other curl_setopt calls */ $mh = curl_multi_init(); curl_multi_add_handle($mh, $ch1); curl_multi_add_handle($mh, $ch2); $running = null; do { curl_multi_exec($mh, $running); } while ($running > 0); $ch1_response = curl_multi_getcontent($ch1); $ch2_response = curl_multi_getcontent($ch2); curl_multi_remove_handle($mh, $ch1); curl_close($ch1); curl_multi_remove_handle($mh, $ch2); curl_close($ch2); curl_multi_close($mh); ?> • Two cURL session handles $ch1 and $ch2 are initialized and configured normally. N ote that more than two can be used in this type of operation; two merely satisfy the purpose of this example. • A cURL multi handle $mh is initialized and the two session handles are added to it. • A loop is used in conjunction with the flag $running to repeatedly check (i.e. poll) the multi handle for completion of all contained operations. • curl_multi_getcontent is used on the two session handles to get the response bodies of each.
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