At the moment PHP doesn't allow serializing closures. I needed a unobtrusive solution to passing closures to child processes, which are invoked later when the child process has completed the task.
Here's a quick release. I've been doing a lot of scraping work lately and of course use a cURL class. There's plenty of cURL classes out there, and here's another. I plan on evolving the class (joining multicurl into curl) and taking advantage of PHP 5.3 lambdas.