Thanks for taking the questions!
How extensively is Facebook using Hack at this point? Is it in production?
What has been the biggest learning/unlearning you've needed to do going from PHP to Hack?
How extensively is Facebook using Hack at this point? Is it in production?
What has been the biggest learning/unlearning you've needed to do going from PHP to Hack?
The biggest learning step for our engineering teams was to treat type errors from Hack as actual logic errors. We have a collection of "linters" that provide advice on code style and other nice-to-have factors. Some people (quite reasonably) initially thought of Hack errors as lint-like stuff that it was safe to ignore, when in fact they indicate real logical inconsistencies in code.
Interesting, thanks!
One followup: what has it been like from an ops perspective? Similar to PHP, or is there a better frame of reference?
HHVM is its own web server (although it supports FastCGI for easier use with existing infrastructure like nginx), and that's how we use it in production. It's hard to compare memory usage, except at scale, where it benefits from not having a whole bunch of interpreters (in different processes) running at the same time and some other benefits by using more appropriate types to store values through type inference.
On a webserver, that goes further since HHVM is single-process/multi-thread, whereas PHP (in its typical setup) is multi-process/single-thread. This cuts HHVM's memory overhead much further.
Yes, PHP can run multi-threaded, but it still has a number of instability issues in that mode.