Parallel cURL execution in PHP

cURL is a Swiss army knife of web content processing. Programmers use it for a number of things everyday. One interesting feature the cURL library offers that many programmers are unaware of is the parallel execution of requests.
curl has two major modes of request execution: ‘easy’ mode and the ‘multi’ mode. Most people use the ‘easy’ mode – in this mode when we issue multiple requests, the second request will not start until the first one is complete. This is known as synchronous execution, and this is the one we normally use. This means that if we have 100 requests to process, each will be processed in a linear manner, which could take a lot of time. This is where ‘multi’ mode comes to the rescue. In this mode all requests can be handled in parallel or asynchronously. And it can be quite handy and time saving on many occasions. The ‘multi’ or parallel mode is handled by the following curl functions:

curl_multi_init();
curl_multi_add_handle();
curl_multi_select();
curl_multi_exec();
curl_multi_getcontent();
curl_multi_info_read();
curl_multi_remove_handle();

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