HHVM 是 Facebook 推出的用来执行 PHP 代码的虚拟机，它是一个 PHP 的 JIT(Just-In-Time) 编译器，同时具有产生快速代码和即时编译的优点。
HHVM 3.27.1 和 3.24.8 都是针对所在系列的 bug 修复版本，更新内容如下：
3.27.1
- Fix stability issues when async if HHVM is linked against libevent2
- Fix overly-strict parameter type variance for implementations of abstract methods
- Fix as-you-type formatting when using recent versions of Nuclide
- Fix formatting of comments that include tabs
- Support debugging xbox requests
- Regression: Support “{$$foo}” in PHP files
- Regression: Support closures in anonymous classes
- Regression: Fix typechecker hangs/crashes if there are many if (Shape::keyExists())refinements
- Regression: Remove special meanings of some Hack keywords when file is PHP
- Autocomplete: Remove ‘namespace fallback’ behavior for functions, which is no longer part of Hack
- Autocomplete: Don’t trigger autocomplete after colons in case statements in namespaces
- Autocomplete: Don’t trigger autocomplete after user attributes
3.24.8
- Fix stability issues when using async if HHVM is linked against libevent2
- Fix overly-strict parameter type variance for implementations of abstract methods
