In a post to his site Colin O'Dell shows how he used the Blackfire.io service to optimize the colinodell/json5 package he created to parse JSON5 in PHP. Blackfire.io is a performance profiling service (from the folks behind Symfony) that shows where the pain points are in your code. They also have a "developer" plan that you can use to try out the service.
Back in November, I released colinodell/json5 - a JSON5 parser for PHP. It's essentially a drop-in replacement for PHP's json_decode() function, but it allows things like comments, trailing commas, and more.
Fast forward to this weekend when I received [a] bug report from a user named Antonio [about slowness in parsing large JSON documents]. Yikes! I always knew that a PHP-based implementation would be slower than PHP's native C implementation, but execution time measured in minutes was completely unacceptable!
So I fired up Blackfire (which I've previously used to optimize league/commonmark) and got to work.
He starts off by getting a baseline to work from, executing the parsing on a custom document he created (not quite as large as in the bug report but still large). After locating a few issues he then started in on the optimizations. The first was an issue with the use of mb_substr, the second was around the remainder of the document to parse and the last an optimization for a regular expression. The post ends with a few other micro-optimizations he also made to the package and a check to use json_decode for faster parsing and only kick in the JSON5 parsing when needed.