PHPUnder The Hood

What Is PHP?● An Easy To Learn Language?

○ Sure!● A Simple Language?

○ Usually● A Well Designed Language?

○ HA!● An Effective Language!

○ Absolutely!

PHP Is...

Dynamically Typed

$a = 1;$b = "a";

PHP Is...

Weak Typed

1 + "1b" == 2

PHP Is...

Implementation Defined

ImplementationsMain:

C-PHP: www.php.netAlt:

HipHop - FacebookRoadsend - CompilerPhalanger - .NETPHP Compiler - CompilerPHPPHP - PHP

Interesting Note:C-PHP Requires PHP To Compile!

PHP Is...

Compiled

PHP Is...

DynamicallyCompiled

On-Demand

It All Starts With TheSAPI

SAPI● Server API● "Starts" PHP and issues request(s)● Common SAPIs:

○ CLI○ CGI (and FastCGI)○ mod_php○ FPM○ etc...

Execution Pipeline

Execution PipelineStart Up

Request

Shut Down

SAPI

Execution PipelineStart Up

Request

Shut Down

SAPIConfig Init

Engine Init

Module Init

Zend/zend.c

PHPPHP/PHP.php

Execution PipelineStart Up

Request

Shut Down

SAPI

Module Shutdown

EngineShutdown

Zend/zend.c

Execution PipelineStart Up

Request

Shut Down

SAPI

Request Init

Compile Code

Execute Code

Request Shutdown

Compiler PipelineLexer

Lexer Step● C-PHP

○ Tokenizes using RE2C○ Produces Array of Tokens

● PHPPHP○ Uses core tokenizer (or emulative)○ PHPParser Powered

Zend/zend_language_scanner.l

PHPParser/Lexer/Emulative.php

Compiler PipelineLexer

Parser

Parse Step● C-PHP

○ Directly Generates OPCode Array○ BISON Powered

● PHPPHP○ Generates AST Structure○ PHPParser Powered

Zend/zend_language_parser.y

Compiler PipelineLexer

Parser

Compiler

Compile Step● C-PHP

○ Compiled Directly During Parse○ Single Pass Compilation

● PHPPHP○ Recurses Over AST○ Single Pass (for now)○

PHPPHP/Engine/Compiler.php

Compiler PipelineLexer

Parser

Compiler

OpCode

OpCodes● A Series of Operations

○ Just like Assembler Opcodes○ Represent "units of functionality"

● Designed to run on Virtual Machine○ Zend Engine○ Or PHPPHP!

$a = 1;$b = 2;echo $a + $b;

Notice Anything?

What If We Cached The OpCodes?

We Can Cache!● Given the compiler is Idempodent

○ (has no side-effects)○ (hint: it's not)

● OpCodes are really Pointers○ Swizzling!!!

In Other Words

OpCode CachingIs Hard!

Time To Execute!

Zend/zend_vm_execute.h

PHPPHP/Engine/Executor.php

Executor Pipeline

OpCode

Is Return?No Yes

Return

But What Are We Executing?

Zend/zend_vm_execute.h

Interesting Note:vm_execute.h

Is Generated By PHP

PHPPHP/Engine/OpLines/Add.php

Variables!

Zend/zend.h

PHPPHP/Engine/Zval/Value.php

Ref-Counting● RefCount + References

○ Allows Copy-On-Write● Variable Is "Deleted" When

RefCount = 0

● Enables Primitive Garbage Collection○ Circular GC is also implemented

That's All There Is To It!

Let's Look At An Example

$a = 1;$b = 2;var_dump( $a + $b);

line # op return operands----------------------------------- 2 0 ASSIGN !0, 1 3 1 ASSIGN !1, 2 6 2 ADD ~2 !0, !1 3 SEND_VAL ~2 4 DO_FCALL 'var_dump' 5 RETURN 1

[0] => PHPPHP\Engine\OpLines\Assign[1] => PHPPHP\Engine\OpLines\Assign[2] => PHPPHP\Engine\OpLines\Add[3] => PHPPHP\Engine\OpLines\InitFCallByName[4] => PHPPHP\Engine\OpLines\Send[5] => PHPPHP\Engine\OpLines\FunctionCall[6] => PHPPHP\Engine\OpLines\ReturnOp

[0] => PHPPHP\Engine\OpLines\Assign Object (

[op1] => PHPPHP\Engine\Zval\Ptr Object (

[zval:protected] => PHPPHP\Engine\Zval\Variable Object (

[name:protected] => PHPPHP\Engine\Zval\Ptr Object (

[zval:protected] => PHPPHP\Engine\Zval\Value Object (

[value:protected] => a

[refcount:protected] => 1

[isRef:protected] =>

[dtorFunc:protected] =>

)

)

[class:protected] =>

[zval:protected] =>

[executor:protected] =>

[scope] => 1

)

)

[op2] => PHPPHP\Engine\Zval\Ptr Object (

[zval:protected] => PHPPHP\Engine\Zval\Value Object (

[value:protected] => 1

[refcount:protected] => 1

[isRef:protected] =>

[dtorFunc:protected] =>

)

)

[result] =>

[lineno] => 2

)

PHPPHP/Engine/OpLines/Assign.php

PHPPHP/Engine/OpLines/Add.php

PHPPHP/Engine/OpLines/InitFCallByName.php

PHPPHP/Engine/OpLines/Send.php

PHPPHP/Engine/OpLines/FunctionCall.php

There's A Ton More

Get Involved!

More Info● github.com/php/php-src● lxr.php.net● github.com/ircmaxell/PHPPHP

● Reference Series○ wiki.php.net○ blog.ircmaxell.com

■ PHP Internals Series

Anthony FerraraJoind.in/8443

@ircmaxellblog.ircmaxell.comircmaxell@php.netyoutube.com/ircmaxell