| HHVM | |
|---|---|
 | |
| Developer | Meta Platforms |
| Initial release | December 9, 2011; 14 years ago (2011-12-09)[1] |
| Stable release | |
| Written in | PHP,C++,[3]OCaml[4][a] andRust[5] |
| License | PHP License andZend License[6] |
| Website | hhvm |
| Repository | |
HipHop Virtual Machine (HHVM) is anopen-source virtual machine based onjust-in-time (JIT) compilation that serves as an execution engine for theHack programming language. By using the principle of JIT compilation, Hack code is first transformed into intermediateHipHop bytecode (HHBC), which is then dynamically translated intox86-64machine code, optimized, and natively executed.[7][8] This contrasts with PHP's usualinterpreted execution, in which theZend Engine transforms PHPsource code intoopcodes that serve as a form ofbytecode, and executes the opcodes directly on the Zend Engine's virtualCPU.[9]
HHVM is developed byMeta, with the project's source code hosted onGitHub;[10] it is licensed under the terms of thePHP License andZend License.[1][6]
HHVM was created as the successor to theHipHop for PHP (HPHPc) PHP execution engine, which is a PHP-to-C++transpiler also created by Facebook.[11][12] Based on the gained experience and aiming to solve issues introduced by HPHPc, Meta decided in early 2010 to create a JIT-based PHPvirtual machine. Issues associated with HPHPc included reaching aplateau for further performance improvements, a fundamental inability to support all features of the PHP language, and difficulties arising from specific time- and resource-consuming development and deployment processes.[11] In Q1 2013, the production version of the facebook.com website stopped using HPHPc and switched to HHVM.
Following the JIT compilation principle, HHVM first converts the executed code into anintermediate language, the high-levelbytecode HHBC. HHBC is a bytecode format created specifically for HHVM, appropriate for consumption by bothinterpreters and just-in-time compilers. Next, HHVM dynamically ("just-in-time") translates the HHBC into x86-64 machine code,optimized through dynamic analysis of the translated bytecode. Finally, it executes the x86-64 machine code.[1][11][13] As a result, HHVM has certain similarities to the virtual machines used by other programming languages, including theCommon Language Runtime (CLR, for theC# language) andJava virtual machine (JVM, for theJava language).
HHVM brings many benefits in comparison with HPHPc. HHVM uses the same execution engine when deployed in both production and development environments, while supporting integration between the execution engine and theHPHPddebugger in both environment types; as a result, maintainingHPHPi (HipHop interpreter) separately as a development utility is no longer needed as it was the case with HPHPc. HHVM also eliminates the lengthybuilds required by HPHPc to run programs, resulting in much simpler development and deployment processes than it was the case with HPHPc.[1] Finally, versions of HHVM before 4.0 have almost complete support for the entire PHP language (as defined by the official implementation of PHP version 5.4), including the support for thecreate_function() andeval() constructs, which was impossible with HPHPc.[14][15]
Together with HHVM 3.0,[16] Meta also releasedHack, a derivative of PHP[17][18] that allows programmers to use bothdynamic typing andstatic typing (a concept also known asgradual typing), and allowstypes to be specified forfunctionarguments, functionreturn values, andclass properties. However, Hack does not provide completebackward compatibility since it removes several PHP features, such as thegoto statement and dynamicvariable names.[19][20][21][22]
In September 2017, it was announced that version 3.30 would be the last version of HHVM to officially support PHP, and that HHVM will only support Hack going forward.[23] This was due to differences and incompatibilities in PHP 7.[24] HHVM 4.0, released in February 2019, was the first version without support for PHP.[25]
As a process virtual machine that provides the execution environment, HHVM has the ability to use live type information to produce more efficientnative code, leading to a higher web serverthroughput and lowerlatency. In Q4 2012, the execution of facebook.com'ssource code on HHVM achieved performance parity with HPHPc,[11] and in December 2013 HPHPc was even surpassed by around 15%.[26]
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