Joe Watkins has a post to his site talking about polyfills and pthreads and some feedback he received during his work on the extension that allows for multi-threaded handling in PHP.
Recently a fellow githubber opened an issue for pthreads, they are writing a static analysis suite for PHP, and are attempting to integrate pthreads into their code. First thing to say is, I don't know where that will lead him. But it does give him the problem that a lot of environments don't have pthreads available, and or they aren't using a thread safe interpreter.
In the issue, he made the suggestion that we have a compatibility layer, a polyfill. I confess, this had never occurred to me before. Not only does it solve his problem but it actually serves as a useful tool ... I shall explain.
He starts by answering a question he's gotten a lot during his work on pthreads: "what's a good use case for threading?" Instead he answers a question that follows the intent a bit more: "What kind of code lends itself to threading?" He talks about units of work and separation of responsibility and how it "avoids synchronization" that could be caused by unforeseen circumstances. He instead recommends that, for most applications, true multi-threading probably isn't needed and a polyfill that simulates the functionality is probably good enough.