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AUGUST 22, 2018 #MEETUP @PHPUGDD

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github.com/hollodotme @hollodotme EXECUTIVE PRODUCER holger woltersdorf

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github.com/hollodotme @hollodotme@phpc.social EXECUTIVE PRODUCER holger woltersdorf

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CHAPTER 1: GENERATORS @hollodotme

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FITZ'PLANATION The heart of a generator function is the yield keyword. 
 In its simplest form, a yield statement looks much like a return statement, except that instead of stopping execution of the function and returning, yield instead provides a value to the code looping over the generator and pauses execution of the generator function. php.net @hollodotme

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FITZ'PLANATION BOY, WHAT THE HELL ARE YOU TALKING ABOUT? @hollodotme

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JEMMA'LOC function generate() { yield 1; } $generator = generate(); echo 'Type: ', gettype($generator), PHP_EOL; echo 'Class: ', get_class($generator), PHP_EOL; echo 'Is ', (is_callable($generator) ? 'callable' : 'not callable'), PHP_EOL; $generatorClone = clone $generator; @hollodotme

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JEMMA'LOC function generate() { yield 1; } $generator = generate(); echo 'Type: ', gettype($generator), PHP_EOL; echo 'Class: ', get_class($generator), PHP_EOL; echo 'Is ', (is_callable($generator) ? 'callable' : 'not callable'), PHP_EOL; $generatorClone = clone $generator; — Type: object Class: Generator Is not callable Fatal error: Uncaught Error: Trying to clone an uncloneable object of class Generator @hollodotme

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JEMMA'LOC function range( int $start, int $limit ) : array { $elements = []; for ( $i = $start; $i !<= $limit; $i!++ ) { $elements[] = $i; } return $elements; } # vs. function xrange( int $start, int $limit ) : Generator { for ( $i = $start; $i !<= $limit; $i!++ ) { yield $i; } } @hollodotme

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JEMMA'LOC foreach ( range( 1, 10000 ) as $i ) { print $i . '.'; } # 2 MiB foreach ( range( 1, 100000 ) as $i ) { print $i . '.'; } # 6 MiB foreach ( range( 1, 1000000 ) as $i ) { print $i . '.'; } # 34 MiB @hollodotme

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JEMMA'LOC foreach ( xrange( 1, 10000 ) as $i ) { print $i . '.'; } # 2 MiB foreach ( xrange( 1, 100000 ) as $i ) { print $i . '.'; } # 2 MiB foreach ( xrange( 1, 1000000 ) as $i ) { print $i . '.'; } # 2 MiB @hollodotme

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JEMMA'LOC # OPCODES OF RANGE() ~$ php -d vld.active=1 -d vld.execute=0 -f range.func.php number of ops: 22 compiled vars: !0 = $start, !1 = $limit, !2 = $step, !3 = $elements, !4 = $i # OPCODES OF XRANGE() ~$ php -d vld.active=1 -d vld.execute=0 -f xrange.func.php number of ops: 16 compiled vars: !0 = $start, !1 = $limit, !2 = $step, !3 = $i @hollodotme

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JEMMA'LOC function generate() { print 'generate - start' . PHP_EOL; for ( $i = 1; $i !<= 5; $i!++ ) { print 'generate - yielding!!...' . PHP_EOL; yield $i; print 'generate - continued' . PHP_EOL; } print 'generate - end' . PHP_EOL; } $generator = generate(); print 'Generator created' . PHP_EOL; while ( $generator!->valid() ) { print 'Loop gets current value' . PHP_EOL; print $generator!->current() . PHP_EOL; $generator!->next(); } @hollodotme

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JEMMA'LOC function generate() { print 'generate - start' . PHP_EOL; for ( $i = 1; $i !<= 5; $i!++ ) { print 'generate - yielding!!...' . PHP_EOL; yield $i; print 'generate - continued' . PHP_EOL; } print 'generate - end' . PHP_EOL; } $generator = generate(); print 'Generator created' . PHP_EOL; while ( $generator!->valid() ) { print 'Loop gets current value' . PHP_EOL; print $generator!->current() . PHP_EOL; $generator!->next(); } Generator created generate - start generate - yielding!!... Loop gets current value 1 generate - continued generate - yielding!!... Loop gets current value 2 generate - continued generate - yielding!!... Loop gets current value 3 generate - continued generate - yielding!!... Loop gets current value 4 generate - continued generate - yielding!!... Loop gets current value 5 generate - continued generate - end @hollodotme

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JEMMA'LOC function generate() { print 'generate - start' . PHP_EOL; for ( $i = 1; $i !<= 5; $i!++ ) { print 'generate - yielding!!...' . PHP_EOL; yield $i; print 'generate - continued' . PHP_EOL; } print 'generate - end' . PHP_EOL; } $generator = generate(); print 'Generator created' . PHP_EOL; while ( $generator!->valid() ) { print 'Loop gets current value' . PHP_EOL; print $generator!->current() . PHP_EOL; $generator!->next(); } Generator created generate - start generate - yielding!!... Loop gets current value 1 generate - continued generate - yielding!!... Loop gets current value 2 generate - continued generate - yielding!!... Loop gets current value 3 generate - continued generate - yielding!!... Loop gets current value 4 generate - continued generate - yielding!!... Loop gets current value 5 generate - continued generate - end @hollodotme

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JEMMA'LOC function generate() { print 'generate - start' . PHP_EOL; for ( $i = 1; $i !<= 5; $i!++ ) { print 'generate - yielding!!...' . PHP_EOL; yield $i; print 'generate - continued' . PHP_EOL; } print 'generate - end' . PHP_EOL; } $generator = generate(); print 'Generator created' . PHP_EOL; while ( $generator!->valid() ) { print 'Loop gets current value' . PHP_EOL; print $generator!->current() . PHP_EOL; $generator!->next(); } Generator created generate - start generate - yielding!!... Loop gets current value 1 generate - continued generate - yielding!!... Loop gets current value 2 generate - continued generate - yielding!!... Loop gets current value 3 generate - continued generate - yielding!!... Loop gets current value 4 generate - continued generate - yielding!!... Loop gets current value 5 generate - continued generate - end @hollodotme

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JEMMA'LOC function generate() { print 'generate - start' . PHP_EOL; for ( $i = 1; $i !<= 5; $i!++ ) { print 'generate - yielding!!...' . PHP_EOL; yield $i; print 'generate - continued' . PHP_EOL; } print 'generate - end' . PHP_EOL; } $generator = generate(); print 'Generator created' . PHP_EOL; while ( $generator!->valid() ) { print 'Loop gets current value' . PHP_EOL; print $generator!->current() . PHP_EOL; $generator!->next(); } Generator created generate - start generate - yielding!!... Loop gets current value 1 generate - continued generate - yielding!!... Loop gets current value 2 generate - continued generate - yielding!!... Loop gets current value 3 generate - continued generate - yielding!!... Loop gets current value 4 generate - continued generate - yielding!!... Loop gets current value 5 generate - continued generate - end @hollodotme

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JEMMA'LOC function generate() { print 'generate - start' . PHP_EOL; for ( $i = 1; $i !<= 5; $i!++ ) { print 'generate - yielding!!...' . PHP_EOL; yield $i; print 'generate - continued' . PHP_EOL; } print 'generate - end' . PHP_EOL; } $generator = generate(); print 'Generator created' . PHP_EOL; while ( $generator!->valid() ) { print 'Loop gets current value' . PHP_EOL; print $generator!->current() . PHP_EOL; $generator!->next(); } Generator created generate - start generate - yielding!!... Loop gets current value 1 generate - continued generate - yielding!!... Loop gets current value 2 generate - continued generate - yielding!!... Loop gets current value 3 generate - continued generate - yielding!!... Loop gets current value 4 generate - continued generate - yielding!!... Loop gets current value 5 generate - continued generate - end @hollodotme

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AND… GENERATORS IMPLEMENT IT… @hollodotme

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AND… GENERATORS IMPLEMENT IT… ITE… @hollodotme

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AND… GENERATORS IMPLEMENT IT… ITE… ITERATOR! @hollodotme

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FITZ'PLANATION The primary advantage of generators is their simplicity. Much less boilerplate code has to be written compared to implementing an Iterator class, and the code is generally much more readable. php.net @hollodotme

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JEMMA'LOC $generator = xrange( 1, 100 ); while ( $generator!->valid() ) { echo $generator!->current() . '.'; $generator!->next(); } # The Iterator interface interface Iterator extends Traversable { public function current(); public function next(); public function key(); public function valid(); public function rewind(); } @hollodotme

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OH… GOOD TO SEE SOMETHING FAMILIAR
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 SOMETHING I CAN COUNT ON! @hollodotme

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BUT YOU CAN’T, PHIL. @hollodotme

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IT’S NOT COUNTABLE! @hollodotme

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JEMMA'LOC $generator = xrange( 1, 100 ); count($generator); — PHP Warning: count(): Parameter must be an array or an object that implements Countable @hollodotme

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FITZ'PLANATION A generator is a highly dynamic construct with an iterator API, but an unknown number of elements. It’s not a data structure like an array or a common object. hw @hollodotme

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JEMMA'LOC $generator = xrange( 1, 100 ); $count = count( iterator_to_array( $generator ) ); echo 'Count: ', $count, PHP_EOL; $count = 0; foreach ( $generator as $item ) { $count!++; } echo 'Count: ', $count, PHP_EOL; @hollodotme

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JEMMA'LOC $generator = xrange( 1, 100 ); $count = count( iterator_to_array( $generator ) ); echo 'Count: ', $count, PHP_EOL; $count = 0; foreach ( $generator as $item ) { $count!++; } echo 'Count: ', $count, PHP_EOL; — Count: 100 Exception: Cannot traverse an already closed generator @hollodotme

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JEMMA'LOC $generator = xrange( 1, 100 ); $count = count( iterator_to_array( $generator ) ); echo 'Count: ', $count, PHP_EOL; $generator!->rewind(); $count = 0; foreach ( $generator as $item ) { $count!++; } echo 'Count: ', $count, PHP_EOL; @hollodotme

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JEMMA'LOC $generator = xrange( 1, 100 ); $count = count( iterator_to_array( $generator ) ); echo 'Count: ', $count, PHP_EOL; $generator!->rewind(); $count = 0; foreach ( $generator as $item ) { $count!++; } echo 'Count: ', $count, PHP_EOL; — Count: 100 Exception: Cannot rewind a generator that was already run @hollodotme

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What the F***?! @hollodotme

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FITZ'PLANATION […] generators are forward-only iterators, and cannot be rewound once iteration has started. This also means that the same generator can't be iterated over multiple times: the generator will need to be rebuilt by calling the generator function again. php.net @hollodotme

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YOU KNOW, IT'S LIKE ... @hollodotme

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GONE. @hollodotme

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JEMMA'LOC $generator = xrange( 1, 100 ); $count = count( iterator_to_array( $generator ) ); echo 'Count: ', $count, PHP_EOL; # Create new generator $generator = xrange( 1, 100 ); $count = 0; foreach ( $generator as $item ) { $count!++; } echo 'Count: ', $count, PHP_EOL; — Count: 100 Count: 100 @hollodotme

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YIELD FROM … @hollodotme

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JEMMA'LOC function countToTen() : Generator { yield 1; for ( $i = 2; $i < 4; $i!++ ) { yield $i; } yield from [4, 5]; yield from json_decode( '[6,7]' ); yield from eightNine(); yield 10; } function eightNine() : Generator { yield '8 ' !=> 9; } foreach ( countToTen() as $key !=> $number ) print (is_string($key) ? $key : '') . $number . ' '; @hollodotme

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JEMMA'LOC function countToTen() : Generator { yield 1; for ( $i = 2; $i < 4; $i!++ ) { yield $i; } yield from [4, 5]; yield from json_decode( '[6,7]' ); yield from eightNine(); yield 10; } function eightNine() : Generator { yield '8 ' !=> 9; } foreach ( countToTen() as $key !=> $number ) print (is_string($key) ? $key : '') . $number . ' '; — 1 2 3 4 5 6 7 8 9 10 @hollodotme

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YIELD ASS=>OC @hollodotme

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JEMMA'LOC function gen() { $key = new stdClass(); $key!->property = 'I am an object!'; yield $key !=> '& I am a simple string!'; } $generator = gen(); echo $generator!->key()!->property, ' ', $generator!->current(); @hollodotme

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JEMMA'LOC function gen() { $key = new stdClass(); $key!->property = 'I am an object!'; yield $key !=> '& I am a simple string!'; } $generator = gen(); echo $generator!->key()!->property, ' ', $generator!->current(); — I am an object! & I am a simple string! @hollodotme

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JEMMA'LOC $key = new stdClass(); $key!->property = 'I am an object!'; $array = [$key !=> '& I am a simple string.']; echo key($array)!->property, ' ', current($array); @hollodotme

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JEMMA'LOC $key = new stdClass(); $key!->property = 'I am an object!'; $array = [$key !=> '& I am a simple string.']; echo key($array)!->property, ' ', current($array); — PHP Warning: Illegal offset type in line 4 PHP Notice: Trying to get property 'property' of non-object in line 6 NO OUTPUT!!! @hollodotme

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YIELD & RETURN @hollodotme

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JEMMA'LOC function genFibonacci( int $loops ) : Generator { $fibonacci = ''; for ( $i = 0; $i < $loops; $i!++ ) { yield $i; $fibonacci !.= round( pow( (sqrt( 5 ) + 1) / 2, $i ) / sqrt( 5 ) ); } return $fibonacci; } $generator = genFibonacci( 10 ); while ( $generator!->valid() ) { print $generator!->current(); $generator!->next(); } print PHP_EOL . 'Fibonacci: ' . $generator!->getReturn() . PHP_EOL; @hollodotme

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JEMMA'LOC function genFibonacci( int $loops ) : Generator { $fibonacci = ''; for ( $i = 0; $i < $loops; $i!++ ) { yield $i; $fibonacci !.= round( pow( (sqrt( 5 ) + 1) / 2, $i ) / sqrt( 5 ) ); } return $fibonacci; } $generator = genFibonacci( 10 ); while ( $generator!->valid() ) { print $generator!->current(); $generator!->next(); } print PHP_EOL . 'Fibonacci: ' . $generator!->getReturn() . PHP_EOL; @hollodotme

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JEMMA'LOC function genFibonacci( int $loops ) : Generator { $fibonacci = ''; for ( $i = 0; $i < $loops; $i!++ ) { yield $i; $fibonacci !.= round( pow( (sqrt( 5 ) + 1) / 2, $i ) / sqrt( 5 ) ); } return $fibonacci; } $generator = genFibonacci( 10 ); while ( $generator!->valid() ) { print $generator!->current(); $generator!->next(); } print PHP_EOL . 'Fibonacci: ' . $generator!->getReturn() . PHP_EOL; — 0123456789 Fibonacci: 0112358132134 @hollodotme

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PSA: PHP >=7.0 ONLY @hollodotme

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UPGRADE YOUR STUFF! @hollodotme

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SERIOUSLY @hollodotme

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RECAP • A yield in a function or method always creates a Generator object • yield can provide a value to the caller of the Generator and pauses execution of its local context • Generator implements the Iterator interface, but can be consumed only once and forward-only • Generator can return a value when its execution stops @hollodotme

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THIS IS A NICE CAR! @hollodotme

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Mack, 
 CAN WE MAKE IT FLY? @hollodotme

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CHAPTER 2: COROUTINES @hollodotme

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FITZ'PLANATION Coroutines and concurrency are largely orthogonal. Coroutines are a general control structure whereby flow control is cooperatively passed between two different routines without returning. stackoverflow.com @hollodotme

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JEMMA'LOC function queue( PDO $pdo ) : Generator { $pdo!->query( 'CREATE TABLE queue (message TEXT)' ); $statement = $pdo!->prepare( 'INSERT INTO queue (message) VALUES (:message)' ); while ( true ) { $message = yield; $statement!->execute( ['message' !=> $message] ); print 'Sent: ' . $message . PHP_EOL; } } $queue = queue( new PDO( 'sqlite!::memory:' ) ); $queue!->send( 'Foo' ); $queue!->send( 'Bar' ); @hollodotme

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JEMMA'LOC function queue( PDO $pdo ) : Generator { $pdo!->query( 'CREATE TABLE queue (message TEXT)' ); $statement = $pdo!->prepare( 'INSERT INTO queue (message) VALUES (:message)' ); while ( true ) { $message = yield; $statement!->execute( ['message' !=> $message] ); print 'Sent: ' . $message . PHP_EOL; } } $queue = queue( new PDO( 'sqlite!::memory:' ) ); $queue!->send( 'Foo' ); $queue!->send( 'Bar' ); @hollodotme

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JEMMA'LOC function queue( PDO $pdo ) : Generator { $pdo!->query( 'CREATE TABLE queue (message TEXT)' ); $statement = $pdo!->prepare( 'INSERT INTO queue (message) VALUES (:message)' ); while ( true ) { $message = yield; $statement!->execute( ['message' !=> $message] ); print 'Sent: ' . $message . PHP_EOL; } } $queue = queue( new PDO( 'sqlite!::memory:' ) ); $queue!->send( 'Foo' ); $queue!->send( 'Bar' ); — Sent: Foo Sent: Bar @hollodotme

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JEMMA'LOC function queue( PDO $pdo ) : Generator { $pdo!->query( 'CREATE TABLE queue (message TEXT)' ); $statement = $pdo!->prepare( 'INSERT INTO queue (message) VALUES (:message)' ); $counter = 0; while ( true ) { $message = yield $counter!++; $statement!->execute( ['message' !=> $message] ); print 'Sent: ' . $message; } } $queue = queue( new PDO( 'sqlite!::memory:' ) ); $queue!->send( 'Foo' ); print ' (' . $queue!->current() . ')' . PHP_EOL; $queue!->send( 'Bar' ); print ' (' . $queue!->current() . ')' . PHP_EOL; @hollodotme

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JEMMA'LOC function queue( PDO $pdo ) : Generator { $pdo!->query( 'CREATE TABLE queue (message TEXT)' ); $statement = $pdo!->prepare( 'INSERT INTO queue (message) VALUES (:message)' ); $counter = 0; while ( true ) { $message = yield $counter!++; $statement!->execute( ['message' !=> $message] ); print 'Sent: ' . $message; } } $queue = queue( new PDO( 'sqlite!::memory:' ) ); $queue!->send( 'Foo' ); print ' (' . $queue!->current() . ')' . PHP_EOL; $queue!->send( 'Bar' ); print ' (' . $queue!->current() . ')' . PHP_EOL; @hollodotme

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JEMMA'LOC Sent: Foo (1) Sent: Bar (2) @hollodotme

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@hollodotme

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WHAT HAPPENED TO ZERO? @hollodotme

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JEMMA'LOC Sent: Foo (1) Sent: Bar (2) — $queue = queue( new PDO( 'sqlite!::memory:' ) ); print 'Hidden first value: ' . $queue!->current() . PHP_EOL; $queue!->send( 'Foo' ); print ' (' . $queue!->current() . ')' . PHP_EOL; $queue!->send( 'Bar' ); print ' (' . $queue!->current() . ')' . PHP_EOL; @hollodotme

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JEMMA'LOC Sent: Foo (1) Sent: Bar (2) — $queue = queue( new PDO( 'sqlite!::memory:' ) ); print 'Hidden first value: ' . $queue!->current() . PHP_EOL; $queue!->send( 'Foo' ); print ' (' . $queue!->current() . ')' . PHP_EOL; $queue!->send( 'Bar' ); print ' (' . $queue!->current() . ')' . PHP_EOL; — Hidden first value: 0 Sent: Foo (1) Sent: Bar (2) @hollodotme

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JEMMA'LOC function gen() { yield 'foo'; yield 'bar'; } $gen = gen(); print $gen!->send( '' ) . PHP_EOL; @hollodotme

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JEMMA'LOC function gen() { yield 'foo'; yield 'bar'; } $gen = gen(); print $gen!->send( '' ) . PHP_EOL; — bar @hollodotme

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JEMMA'LOC function gen() { yield 'foo'; yield 'bar'; } $gen = gen(); $gen!->rewind(); print $gen!->send( '' ) . PHP_EOL; @hollodotme

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JEMMA'LOC function gen() { yield 'foo'; yield 'bar'; } $gen = gen(); $gen!->rewind(); print $gen!->send( '' ) . PHP_EOL; — bar @hollodotme

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JEMMA'LOC function gen() { yield 'foo'; yield 'bar'; } $gen = gen(); $gen!->rewind(); # can be omitted print $gen!->current() . PHP_EOL; print $gen!->send( '' ) . PHP_EOL; @hollodotme

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JEMMA'LOC function gen() { yield 'foo'; yield 'bar'; } $gen = gen(); $gen!->rewind(); # can be omitted print $gen!->current() . PHP_EOL; print $gen!->send( '' ) . PHP_EOL; — foo bar @hollodotme

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JEMMA'LOC function gen() { yield 'foo'; yield 'bar'; } $gen = gen(); $gen!->rewind(); # can be omitted print $gen!->current() . PHP_EOL; print $gen!->send( '' ) . PHP_EOL; — foo bar COPY THAT. @hollodotme

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JEMMA'LOC interface Traversable { # Marker interface, cannot be implemented directly } interface Iterator extends Traversable { public function rewind() : void; public function key(); public function current(); public function next() : void; public function valid() : bool; } interface Generator extends Iterator { public function getReturn(); public function send( $value ) : void; public function throw( Throwable $throwable ) : void; public function !__wakeup() : void; } @hollodotme

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JEMMA'LOC interface Traversable { # Marker interface, cannot be implemented directly } interface Iterator extends Traversable { public function rewind() : void; public function key(); public function current(); public function next() : void; public function valid() : bool; } interface Generator extends Iterator { public function getReturn(); public function send( $value ) : void; public function throw( Throwable $throwable ) : void; public function !__wakeup() : void; } @hollodotme

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JEMMA'LOC function gen() { yield 1; } $generator = gen(); $generator!->!__wakeup(); @hollodotme

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JEMMA'LOC function gen() { yield 1; } $generator = gen(); $generator!->!__wakeup(); — PHP Fatal error: Uncaught Exception: Unserialization of 'Generator' is not allowed @hollodotme

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JEMMA'LOC function gen() { yield 1; } $generator = gen(); $generator!->!__wakeup(); — PHP Fatal error: Uncaught Exception: Unserialization of 'Generator' is not allowed @hollodotme DON’T!

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JEMMA'LOC function gen() : Generator { while ( true ) { try { echo "\n", yield; } catch ( LogicException $e ) { echo 'Exception: ' . $e!->getMessage(); } } } $generator = gen(); $generator!->send( 'Hello ' ); $generator!->throw( new LogicException( 'Raised inside the generator.' ) ); $generator!->send( 'World' ); $generator!->send( 'of tomorrow' ); @hollodotme

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JEMMA'LOC function gen() : Generator { while ( true ) { try { echo "\n", yield; } catch ( LogicException $e ) { echo 'Exception: ' . $e!->getMessage(); } } } $generator = gen(); $generator!->send( 'Hello ' ); $generator!->throw( new LogicException( 'Raised inside the generator.' ) ); $generator!->send( 'World' ); $generator!->send( 'of tomorrow' ); — Hello Exception: Raised inside the generator. World of tomorrow @hollodotme

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JEMMA'LOC function gen() : Generator { while ( true ) { try { echo "\n", yield; } catch ( RuntimeException $e ) { echo $e!->getMessage(); break; } } } $generator = gen(); $generator!->send( 'Hello ' ); $generator!->send( 'World' ); $generator!->throw( new RuntimeException( 'Stopping coroutine.' ) ); $generator!->send( 'of tomorrow' ); @hollodotme

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JEMMA'LOC function gen() : Generator { while ( true ) { try { echo "\n", yield; } catch ( RuntimeException $e ) { echo $e!->getMessage(); break; } } } $generator = gen(); $generator!->send( 'Hello ' ); $generator!->send( 'World' ); $generator!->throw( new RuntimeException( 'Stopping coroutine.' ) ); $generator!->send( 'of tomorrow' ); — Hello World Stopping coroutine. @hollodotme

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RECAP • Through yield a value can be sent to the generator to continue its execution • Through yield an exception can be raised in a generator • yield provides first and receives second • You can start a generator by calling any of its Iterator methods • rewind ignores the first provided value @hollodotme

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TAHITI? @hollodotme

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CHAPTER 3: COOPERATIVE MULTITASKING @hollodotme

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FITZ'PLANATION Co-operative multitasking, also k n o w n a s n o n - p r e e m p t i v e multitasking, is a style of computer multitasking in which the operating system never initiates a context switch from a running process to another process. Instead, processes voluntarily yield control periodically or when idle or logically blocked in order to enable multiple applications to be run concurrently. wikipedia.org @hollodotme

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THE FRAMEWORK (Task Scheduler) AGENTS OF YIELD (Coroutines) SystemCalls (Hooks into the Coroutines) Ammunition (Limits)

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final class TheFramework { private $backup, $agents = []; public function !__construct() { $this!->backup = new SplQueue(); } public function newAgent( string $agentName, Generator $coroutine ) : void { $agent = new Agent( $agentName, $coroutine ); $this!->agents[ $agentName ] = $agent; $this!->sendToBattle( $agent ); } public function sendToBattle( Agent $task ) : void { $this!->backup!->enqueue( $task ); } public function fight() : void { while ( !$this!->backup!->isEmpty() ) { $agent = $this!->backup!->dequeue(); $retval = $agent!->fight(); if ( $retval instanceof SystemCall ) { $retval( $agent, $this ); continue; } if ( $agent!->outOfMunitions() ) { unset( $this!->agents[ $agent!->getName() ] ); continue; } $this!->sendToBattle( $agent ); } } } @hollodotme

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final class Agent { private $name, $coroutine, $sendValue; private $beforeFirstYield = true; public function !__construct( string $name, Generator $coroutine ) { $this!->name = $name; $this!->coroutine = $coroutine; } public function getName() : string { return $this!->name; } public function setSendValue( $sendValue ) : void { $this!->sendValue = $sendValue; } public function fight() { if ( $this!->beforeFirstYield ) { $this!->beforeFirstYield = false; return $this!->coroutine!->current(); } $retval = $this!->coroutine!->send( $this!->sendValue ); $this!->sendValue = null; return $retval; } public function outOfMunitions() : bool { return !$this!->coroutine!->valid(); } } @hollodotme

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final class SystemCall { private $callback; public function !__construct( callable $callback ) { $this!->callback = $callback; } public function !__invoke( Agent $agent, TheFramework $battleGround ) { $callback = $this!->callback; return $callback( $agent, $battleGround ); } } @hollodotme

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# System call corouting function getAgentName() { return new SystemCall( function ( Agent $agent, TheFramework $battleGround ) { $agent!->setSendValue( $agent!->getName() ); $battleGround!->sendToBattle( $agent ); } ); } # Agent of yield function agent( $shots ) { $agentName = yield getAgentName(); for ( $i = 1; $i !<= $shots; !++$i ) { print "Agent {$agentName} fires shot {$i}." . PHP_EOL; yield; } print "Agent {$agentName} is out of munitions." . PHP_EOL; } @hollodotme

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THE FINAL BATTLE @hollodotme

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$battleGround = new TheFramework(); $battleGround!->newAgent( 'Coulson', agent( 12 ) ); $battleGround!->newAgent( 'Mack', agent( 5 ) ); $battleGround!->fight(); print 'Game Over' . PHP_EOL; @hollodotme

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$battleGround = new TheFramework(); $battleGround!->newAgent( 'Coulson', agent( 12 ) ); $battleGround!->newAgent( 'Mack', agent( 5 ) ); $battleGround!->fight(); print 'Game Over' . PHP_EOL; @hollodotme Agent Coulson fires shot 1. Agent Mack fires shot 1. Agent Coulson fires shot 2. Agent Mack fires shot 2. Agent Coulson fires shot 3. Agent Mack fires shot 3. Agent Coulson fires shot 4. Agent Mack fires shot 4. Agent Coulson fires shot 5. Agent Mack fires shot 5. Agent Coulson fires shot 6. Agent Mack is out of munitions. Agent Coulson fires shot 7. Agent Coulson fires shot 8. Agent Coulson fires shot 9. Agent Coulson fires shot 10. Agent Coulson fires shot 11. Agent Coulson fires shot 12. Agent Coulson is out of munitions. Game Over

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FITZ'PLANATION When I first heard about all this 
 I f o u n d t h i s co n ce p t to t a l l y awesome and that’s what motivated me to implement it in PHP. At the same time I find coroutines really scary. There is a thin line between awesome code and a total mess and I think coroutines sit exactly on that line. It’s hard for me to say whether writing async code in the way outlined is really beneficial. Nikita Popov @hollodotme THE REAL FITZ

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THE END @hollodotme

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github.com/hollodotme @hollodotme THANK YOU! holger woltersdorf

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RESOURCES • PHP Generator Documentation: https://secure.php.net/manual/en/language.generators.php • VLD extension for PHP: https://derickrethans.nl/projects.html#vld • «Introduction to generators» by Niklas Keller: https://blog.kelunik.com/2017/09/14/an-introduction-to-generators-in-php.html • PHP 5.5 migration guide: https://secure.php.net/manual/en/migration55.new-features.php • «Cooperative multitasking using coroutines (in PHP!)» by Nikita Popov
 https://nikic.github.io/2012/12/22/Cooperative-multitasking-using-coroutines-in-PHP.html • Repo with executable code of this talk:
 https://github.com/hollodotme/talk-preps/tree/master/agents-of-yield • Definition of Coroutines on Stack Overflow:
 https://stackoverflow.com/questions/553704/what-is-a-coroutine • Definition of Cooperative Multitasking on wikipedia.org: 
 https://en.wikipedia.org/wiki/Cooperative_multitasking @hollodotme