生成器委托

简单地翻译官方文档的描述：

PHP7中，通过生成器委托(yield from)，可以将其他生成器、可迭代的对象、数组委托给外层生成器。外层的生成器会先顺序 yield 委托出来的值，然后继续 yield 本身中定义的值。

利用 yield from 可以方便我们编写比较清晰生成器嵌套，而代码嵌套调用是编写复杂系统所必需的。

上例子：

function echoTimes($msg, $max) {

for ($i = 1; $i <= $max; ++$i) {

echo "$msg iteration $i\n";

yield;

}

}

function task() {

yield from echoTimes('foo', 10); // print foo ten times

echo "---\n";

yield from echoTimes('bar', 5); // print bar five times

}

foreach (task() as $item) {

;

}

以上将输出：

foo iteration 1

foo iteration 2

foo iteration 3

foo iteration 4

foo iteration 5

foo iteration 6

foo iteration 7

foo iteration 8

foo iteration 9

foo iteration 10

---

bar iteration 1

bar iteration 2

bar iteration 3

bar iteration 4

bar iteration 5

自然，内部生成器也可以接受它的父生成器发送的信息或者异常，因为 yield from 为父子生成器建立一个双向的通道。不多说，上例子：

function echoMsg($msg) {

while (true) {

$i = yield;

if($i === null){

break;

}

if(!is_numeric($i)){

throw new Exception("Hoo! must give me a number");

}

echo "$msg iteration $i\n";

}

}

function task2() {

yield from echoMsg('foo');

echo "---\n";

yield from echoMsg('bar');

}

$gen = task2();

foreach (range(1,10) as $num) {

$gen->send($num);

}

$gen->send(null);

foreach (range(1,5) as $num) {

$gen->send($num);

}

//$gen->send("hello world"); //try it ,gay

输出和上个例子是一样的。

生成器返回值

如果生成器被迭代完成，或者运行到 return 关键字，是会给这个生成器返回值的。

可以有两种方法获取这个返回值：

使用 $ret = Generator::getReturn() 方法。

使用 $ret = yield from Generator() 表达式。

上例子：

function echoTimes($msg, $max) {

for ($i = 1; $i <= $max; ++$i) {

echo "$msg iteration $i\n";

yield;

}

return "$msg the end value : $i\n";

}

function task() {

$end = yield from echoTimes('foo', 10);

echo $end;

$gen = echoTimes('bar', 5);

yield from $gen;

echo $gen->getReturn();

}

foreach (task() as $item) {

;

}

输出结果就不贴了，想必大家都猜到。

可以看到 yield from 和 return 结合使得 yield 的写法更像平时我们写的同步模式的代码了，毕竟，这就是 PHP 出生成器特性的原因之一呀。

一个非阻塞的web服务器

时间回到2015年，鸟哥博客上转载的一篇《 在PHP中使用协程实现多任务调度》。文章介绍了PHP5 的迭代生成器，协程，并实现了一个简单的非阻塞 web 服务器。(链接见文末引用)

现在我们利用 PHP7 中的这两个新特性重写这个 web 服务器，只需要 100 多行代码。

代码如下：

class CoSocket

{

protected $masterCoSocket = null;

public $socket;

protected $handleCallback;

public $streamPoolRead = [];

public $streamPoolWrite = [];

public function __construct($socket, CoSocket $master = null)

{

$this->socket = $socket;

$this->masterCoSocket = $master ?? $this;

}

public function accept()

{

$isSelect = yield from $this->onRead();

$acceptS = null;

if ($isSelect && $as = stream_socket_accept($this->socket, 0)) {

$acceptS = new CoSocket($as, $this);

}

return $acceptS;

}

public function read($size)

{

yield from $this->onRead();

yield ($data = fread($this->socket, $size));

return $data;

}

public function write($string)

{

yield from $this->onWriter();

yield fwrite($this->socket, $string);

}

public function close()

{

unset($this->masterCoSocket->streamPoolRead[(int)$this->socket]);

unset($this->masterCoSocket->streamPoolWrite[(int)$this->socket]);

yield ($success = @fclose($this->socket));

return $success;

}

public function onRead($timeout = null)

{

$this->masterCoSocket->streamPoolRead[(int)$this->socket] = $this->socket;

$pool = $this->masterCoSocket->streamPoolRead;

$rSocks = [];

$wSocks = $eSocks = null;

foreach ($pool as $item) {

$rSocks[] = $item;

}

yield ($num = stream_select($rSocks, $wSocks, $eSocks, $timeout));

return $num;

}

public function onWriter($timeout = null)

{

$this->masterCoSocket->streamPoolWrite[(int)$this->socket] = $this->socket;

$pool = $this->masterCoSocket->streamPoolRead;

$wSocks = [];

$rSocks = $eSocks = null;

foreach ($pool as $item) {

$wSocks[] = $item;

}

yield ($num = stream_select($rSocks, $wSocks, $eSocks, $timeout));

return $num;

}

public function onRequest()

{

/** @var self $socket */

$socket = yield from $this->accept();

if (empty($socket)) {

return false;

}

$data = yield from $socket->read(8192);

$response = call_user_func($this->handleCallback, $data);

yield from $socket->write($response);

return yield from $socket->close();

}

public static function start($port, callable $callback)

{

echo "Starting server at port $port...\n";

$socket = @stream_socket_server("tcp://0.0.0.0:$port", $errNo, $errStr);

if (!$socket) throw new Exception($errStr, $errNo);

stream_set_blocking($socket, 0);

$coSocket = new self($socket);

$coSocket->handleCallback = $callback;

function gen($coSocket)

{

/** @var self $coSocket */

while (true) yield from $coSocket->onRequest();

}

foreach (gen($coSocket) as $item){};

}

}

CoSocket::start(8000, function ($data) {

$response = <<

HTTP/1.1 200 OK

Content-Type: text/plain

Content-Length: 12

Connection: close

hello world!

RES;

return $response;

});

参考资料