Performance compared to PHP with APC opcode cache turned on:
- 30% less CPU time serving traffic in API usage (shorter requests pulling data from fewer sources)
- 50% less CPU time serving traffic in WEB page rendering usage
PHP, being a scripted language, has a certain amount of ‘non-magic’ code that looks and feels much like static code you might write in C/C++. This code and logic can be compiled down to very fast static function calls, static variable look-ups, static types. This is where HipHop’s performance gains come from. The ‘magic’ / dynamic features of PHP are much harder to optimize and run roughly as fast as they do on the Zend engine. Magic includes:
$$x = $$y;
eval($x . $y);
$$$$foo();
function foo($x) { include $x; }
There are some tricks that can be applied for this style of dynamic code, things like prehashing dynamic variable look-ups, efficient jump tables, etc.
“If the code has a lot of dynamicness it will execute at roughly the same speed.”
Transformation Process:
1. Static analysis
* Collect info on who declares what, dependencies
2. Type inference
* Pick most specific type for every variable possible
** C++ scalars string array, classes, object, and variant
* Type hints in code are analyzed
3. Code Generation
Facebook hand wrote the runtime libraries for string/array/object classes. Similar to Zend engine’s. They rewrote Zend engine because it primarily deals with variant types. In Hip-Hop there are special cases for static types made possible by type inference. Code for “what if this variable is an integer”, etc. Another reason to rewrtie the runtime is that once the whole runtime in C++ it should be easier to author extensions based on primitive C++/FaceBook types than their Zend engine, dynamic counter-parts.
“We want people to write PHP like they’re used to writing PHP.”
Supported magical PHP features:
- dynamic function call including call_user_func()
- dynamic object properties and methods
- dynamic variables, including extract()
- dynamic includes
- redeclared functions
- redeclared classes
- redeclared constance
- magic methods __toString(), __get(), __set(), __call()
Features not supported:
1. eval, create function, preg_replace /e
2. “if(function_exists(‘foo’){print ‘foo’;})
function foo() {}”
HipHop runs as one process with multiple threads. No downtimes during restarts (port takeover). Uses libevent internally.
In the next month the goal is to bring it up to speed with 5.2.12. After that the focus switches to PHP 5.3+. HipHop may potentially support some of the type suggestion and typing features that did not make the 5.3 cut.
