PHP下的异步尝试四：PHP版的Promise
PHP下的异步尝试系列
如果你还不太了解PHP下的生成器和协程，你可以根据下面目录翻阅
- PHP下的异步尝试一：初识生成器
- PHP下的异步尝试二：初识协程
- PHP下的异步尝试三：协程的PHP版thunkify自动执行器
- PHP下的异步尝试四：PHP版的Promise
- PHP下的异步尝试五：PHP版的Promise的继续完善
Promise 实现
代码结构
│ │ autoload.php
│ │ promise1.php
│ │ promise2.php
│ │ promise3.php
│ │ promise4.php
│ │ promise5.php
│ │
│ └─classes
│ Promise1.php
│ Promise2.php
│ Promise3.php
│ Promise4.php
│ Promise5.php
│ PromiseState.php
尝试一 (Promise基础)
classess/PromiseState.php
final class PromiseState
{
const PENDING = 'pending';
const FULFILLED = 'fulfilled';
const REJECTED = 'rejected';
}
classess/Promise1.php
// 尝试一
class Promise1
{
private $value;
private $reason;
private $state;
public function __construct(\Closure $func = null)
{
$this->state = PromiseState::PENDING;
$func([$this, 'resolve'], [$this, 'reject']);
}
/**
* 执行回调方法里的resolve绑定的方法
* @param null $value
*/
public function resolve($value = null)
{
// 回调执行resolve传参的值，赋值给result
$this->value = $value;
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::FULFILLED;
}
}
public function reject($reason = null)
{
// 回调执行resolve传参的值，赋值给result
$this->reason = $reason;
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::REJECTED;
}
}
public function getState()
{
return $this->state;
}
public function getValue()
{
return $this->value;
}
public function getReason()
{
return $this->reason;
}
}
promise1.php
require "autoload.php";
$promise = new Promise1(function($resolve, $reject) {
$resolve("打印我");
});
var_dump($promise->getState());
var_dump($promise->getValue());
结果：
string(9) "fulfilled"
string(9) "打印我"
结论或问题：
我们在这里建构了最基础的Promise模型
尝试二 (增加链式then)
classess/Promise2.php
<?php
// 尝试二 （增加链式then）
class Promise2
{
private $value;
private $reason;
private $state;
public function __construct(\Closure $func = null)
{
$this->state = PromiseState::PENDING;
$func([$this, 'resolve'], [$this, 'reject']);
}
public function then(\Closure $onFulfilled = null, \Closure $onRejected = null)
{
// 如果状态是fulfilled，直接回调执行并传参value
if ($this->state == PromiseState::FULFILLED) {
$onFulfilled($this->value);
}
// 如果状态是rejected，直接回调执行并传参reason
if ($this->state == PromiseState::REJECTED) {
$onRejected($this->reason);
}
// 返回对象自身，实现链式调用
return $this;
}
/**
* 执行回调方法里的resolve绑定的方法
* 本状态只能从pending->fulfilled
* @param null $value
*/
public function resolve($value = null)
{
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::FULFILLED;
$this->value = $value;
}
}
/**
* 执行回调方法里的rejected绑定的方法
* 本状态只能从pending->rejected
* @param null $reason
*/
public function reject($reason = null)
{
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::REJECTED;
$this->reason = $reason;
}
}
public function getState()
{
return $this->state;
}
public function getValue()
{
return $this->value;
}
public function getReason()
{
return $this->reason;
}
}
promise2.php
<?php
require "autoload.php";
$promise = new Promise2(function($resolve, $reject) {
$resolve("打印我");
});
$promise->then(function ($value) {
var_dump($value);
}, function ($reason) {
var_dump($reason);
})->then(function ($value) {
var_dump($value);
}, function ($reason) {
var_dump($reason);
});
结果：
string(9) "打印我"
string(9) "打印我"
结论或问题：
我们实现了链式then方法
如果我们的构造里的回调是异步执行的话，那么状态在没有变成fulfilled之前，我们then里的回调方法就永远没法执行
尝试三（真正的链式then）
classess/Promise3.php
// 解决思路：我们肯定要把then传入的回调，放到Promise构造里回调代码执行完后resolve调用后改变了state状态后再调用，所以我们必须存储到一个地方并方便后续调用
// 我们需要改造then、resolve和reject方法
class Promise3
{
private $value;
private $reason;
private $state;
private $fulfilledCallbacks = [];
private $rejectedCallbacks = [];
public function __construct(\Closure $func = null)
{
$this->state = PromiseState::PENDING;
$func([$this, 'resolve'], [$this, 'reject']);
}
public function then(\Closure $onFulfilled = null, \Closure $onRejected = null)
{
// 如果是异步回调，状态未变化之前，then的回调方法压入相应的数组方便后续调用
if ($this->state == PromiseState::PENDING) {
$this->fulfilledCallbacks[] = static function() use ($onFulfilled, $value){
$onFulfilled($this->value);
};
$this->rejectedCallbacks[] = static function() use ($onRejected, $reason){
$onRejected($this->reason);
};
}
// 如果状态是fulfilled，直接回调执行并传参value
if ($this->state == PromiseState::FULFILLED) {
$onFulfilled($this->value);
}
// 如果状态是rejected，直接回调执行并传参reason
if ($this->state == PromiseState::REJECTED) {
$onRejected($this->reason);
}
// 返回对象自身，实现链式调用
return $this;
}
/**
* 执行回调方法里的resolve绑定的方法
* 本状态只能从pending->fulfilled
* @param null $value
*/
public function resolve($value = null)
{
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::FULFILLED;
$this->value = $value;
array_walk($this->fulfilledCallbacks, function ($callback) {
$callback();
});
}
}
/**
* 执行回调方法里的rejected绑定的方法
* 本状态只能从pending->rejected
* @param null $reason
*/
public function reject($reason = null)
{
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::REJECTED;
$this->reason = $reason;
}
}
public function getState()
{
return $this->state;
}
public function getValue()
{
return $this->value;
}
public function getReason()
{
return $this->reason;
}
}
promise3.php
require "autoload.php";
$promise = new Promise3(function($resolve, $reject) {
$resolve("打印我");
});
$promise->then(function ($value) {
var_dump($value);
}, function ($reason) {
var_dump($reason);
})->then(function ($value) {
var_dump($value);
}, function ($reason) {
var_dump($reason);
});
结果：
string(9) "打印我"
string(9) "打印我"
结论或问题：
我们这次基本实现了真正的链式then方法
不过在Promise/A+里规范，要求then返回每次都要求是一个新的Promise对象
then方法成功执行，相当于返回一个实例一个Promise回调里执行resolve方法，resolve值为then里return的值
then方法执行失败或出错，相当于返回一个实例一个Promise回调里执行rejected方法，rejected值为then里return的值
尝试四（then返回pormise对象, 并传递上一次的结果给下一个Promise对象）
classess/Promise4.php
class Promise4
{
private $value;
private $reason;
private $state;
private $fulfilledCallbacks = [];
private $rejectedCallbacks = [];
public function __construct(\Closure $func = null)
{
$this->state = PromiseState::PENDING;
$func([$this, 'resolve'], [$this, 'reject']);
}
public function then(\Closure $onFulfilled = null, \Closure $onRejected = null)
{
$thenPromise = new Promise4(function ($reslove, $reject) use (&$thenPromise, $onFulfilled, $onRejected) {
//$this 代表的当前的Promise对象，不要混淆了
// 如果是异步回调，状态未变化之前，then的回调方法压入相应的数组方便后续调用
if ($this->state == PromiseState::PENDING) {
$this->fulfilledCallbacks[] = static function() use ($thenPromise, $onFulfilled, $reslove, $reject){
$value = $onFulfilled($this->value);
$this->resolvePromise($thenPromise, $value, $reslove, $reject);
};
$this->rejectedCallbacks[] = static function() use ($thenPromise, $onRejected, $reslove, $reject){
$reason = $onRejected($this->reason);
$this->resolvePromise($thenPromise, $reason, $reslove, $reject);
};
}
// 如果状态是fulfilled，直接回调执行并传参value
if ($this->state == PromiseState::FULFILLED) {
$value = $onFulfilled($this->value);
$this->resolvePromise($thenPromise, $value, $reslove, $reject);
}
// 如果状态是rejected，直接回调执行并传参reason
if ($this->state == PromiseState::REJECTED) {
$reason = $onRejected($this->reason);
$this->resolvePromise($thenPromise, $reason, $reslove, $reject);
}
});
// 返回对象自身，实现链式调用
return $thenPromise;
}
/**
* 解决Pormise链式then传递
* 可参考 [Promises/A+]2.3 [https://promisesaplus.com/#the-promise-resolution-procedure]
* @param $thenPromise
* @param $x $x为thenable对象
* @param $resolve
* @param $reject
*/
private function resolvePromise($thenPromise, $x, $resolve, $reject)
{
$called = false;
if ($thenPromise === $x) {
return $reject(new \Exception('循环引用'));
}
if ( is_object($x) && method_exists($x, 'then')) {
$resolveCb = function ($value) use($thenPromise, $resolve, $reject, $called) {
if ($called) return ;
$called = true;
// 成功值y有可能还是promise或者是具有then方法等，再次resolvePromise，直到成功值为基本类型或者非thenable
$this->resolvePromise($thenPromise, $value, $resolve, $reject);
};
$rejectCb = function($reason) use($thenPromise, $resolve, $reject, $called) {
if ($called) return ;
$called = true;
$reject($reason);
};
call_user_func_array([$x, 'then'], [$resolveCb, $rejectCb]);
} else {
if ($called) return ;
$called = true;
$resolve($x);
}
}
/**
* 执行回调方法里的resolve绑定的方法
* 本状态只能从pending->fulfilled
* @param null $value
*/
public function resolve($value = null)
{
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::FULFILLED;
$this->value = $value;
array_walk($this->fulfilledCallbacks, function ($callback) {
$callback();
});
}
}
/**
* 执行回调方法里的rejected绑定的方法
* 本状态只能从pending->rejected
* @param null $reason
*/
public function reject($reason = null)
{
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::REJECTED;
$this->reason = $reason;
}
}
public function getState()
{
return $this->state;
}
public function getValue()
{
return $this->value;
}
public function getReason()
{
return $this->reason;
}
}
promise4.php
require "autoload.php";
$promise1 = new Promise4(function($resolve, $reject) {
$resolve("打印我");
});
$promise2 = $promise1->then(function ($value) {
var_dump($value);
return "promise2";
}, function ($reason) {
var_dump($reason);
});
$promise3 = $promise2->then(function ($value) {
var_dump($value);
return new Promise4(function($resolve, $reject) {
$resolve("promise3");
});
}, function ($reason) {
var_dump($reason);
});
$promise4 = $promise3->then(function ($value) {
var_dump($value);
return "promise4";
}, function ($reason) {
var_dump($reason);
});
var_dump($promise4);
结果：
string(9) "打印我"
string(8) "promise2"
string(8) "promise3"
object(Promise4)#15 (5) {
["value":"Promise4":private]=>
string(8) "promise4"
["reason":"Promise4":private]=>
NULL
["state":"Promise4":private]=>
string(9) "fulfilled"
["fulfilledCallbacks":"Promise4":private]=>
array(0) {
}
["rejectedCallbacks":"Promise4":private]=>
array(0) {
}
}
结论或问题：
一个基本的Pormise，不过我们上面都是基于成功fulfilled状态的实现
下面我们来增加错误捕获
尝试五（错误捕获）
classess/Promise5.php
class Promise5
{
private $value;
private $reason;
private $state;
private $fulfilledCallbacks = [];
private $rejectedCallbacks = [];
public function __construct(\Closure $func = null)
{
$this->state = PromiseState::PENDING;
$func([$this, 'resolve'], [$this, 'reject']);
}
public function then(\Closure $onFulfilled = null, \Closure $onRejected = null)
{
// 此处作用是兼容then方法的以下四种参数变化，catchError就是第二种情况
// 1. then($onFulfilled, null)
// 2. then(null, $onRejected)
// 3. then(null, null)
// 4. then($onFulfilled, $onRejected)
$onFulfilled = is_callable($onFulfilled) ? $onFulfilled : function ($value) {return $value;};
$onRejected = is_callable($onRejected) ? $onRejected : function ($reason) {throw $reason;};
$thenPromise = new Promise5(function ($reslove, $reject) use (&$thenPromise, $onFulfilled, $onRejected) {
//$this 代表的当前的Promise对象，不要混淆了
// 如果是异步回调，状态未变化之前，then的回调方法压入相应的数组方便后续调用
if ($this->state == PromiseState::PENDING) {
$this->fulfilledCallbacks[] = static function() use ($thenPromise, $onFulfilled, $reslove, $reject){
try {
$value = $onFulfilled($this->value);
$this->resolvePromise($thenPromise, $value, $reslove, $reject);
} catch (\Exception $e) {
$reject($e);
}
};
$this->rejectedCallbacks[] = static function() use ($thenPromise, $onRejected, $reslove, $reject){
try {
$reason = $onRejected($this->reason);
$this->resolvePromise($thenPromise, $reason, $reslove, $reject);
} catch (\Exception $e) {
$reject($e);
}
};
}
// 如果状态是fulfilled，直接回调执行并传参value
if ($this->state == PromiseState::FULFILLED) {
try {
$value = $onFulfilled($this->value);
$this->resolvePromise($thenPromise, $value, $reslove, $reject);
} catch (\Exception $e) {
$reject($e);
}
}
// 如果状态是rejected，直接回调执行并传参reason
if ($this->state == PromiseState::REJECTED) {
try {
$reason = $onRejected($this->reason);
$this->resolvePromise($thenPromise, $reason, $reslove, $reject);
} catch (\Exception $e) {
$reject($e);
}
}
});
// 返回对象自身，实现链式调用
return $thenPromise;
}
public function catchError($onRejected)
{
return $this->then(null, $onRejected);
}
/**
* 解决Pormise链式then传递
* 可参考 [Promises/A+]2.3 [https://promisesaplus.com/#the-promise-resolution-procedure]
* @param $thenPromise
* @param $x $x为thenable对象
* @param $resolve
* @param $reject
*/
private function resolvePromise($thenPromise, $x, $resolve, $reject)
{
$called = false;
if ($thenPromise === $x) {
return $reject(new \Exception('循环引用'));
}
if ( is_object($x) && method_exists($x, 'then')) {
try {
$resolveCb = function ($value) use ($thenPromise, $resolve, $reject, $called) {
if ($called) return;
$called = true;
// 成功值y有可能还是promise或者是具有then方法等，再次resolvePromise，直到成功值为基本类型或者非thenable
$this->resolvePromise($thenPromise, $value, $resolve, $reject);
};
$rejectCb = function ($reason) use ($thenPromise, $resolve, $reject, $called) {
if ($called) return;
$called = true;
$reject($reason);
};
call_user_func_array([$x, 'then'], [$resolveCb, $rejectCb]);
} catch (\Exception $e) {
if ($called) return ;
$called = true;
$reject($e);
}
} else {
if ($called) return ;
$called = true;
$resolve($x);
}
}
/**
* 执行回调方法里的resolve绑定的方法
* 本状态只能从pending->fulfilled
* @param null $value
*/
public function resolve($value = null)
{
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::FULFILLED;
$this->value = $value;
array_walk($this->fulfilledCallbacks, function ($callback) {
$callback(); //因为回调本身携带了作用于，所以直接调用，无法参数
});
}
}
/**
* 执行回调方法里的rejected绑定的方法
* 本状态只能从pending->rejected
* @param null $reason
*/
public function reject($reason = null)
{
if ($this->state == PromiseState::PENDING) {
$this->state = PromiseState::REJECTED;
$this->reason = $reason;
array_walk($this->rejectedCallbacks, function ($callback) {
$callback(); //因为回调本身携带了作用于，所以直接调用，无法参数
});
}
}
public function getState()
{
return $this->state;
}
public function getValue()
{
return $this->value;
}
public function getReason()
{
return $this->reason;
}
}
promise5.php
require "autoload.php";
$promise1 = new Promise5(function($resolve, $reject) {
$resolve("打印我");
});
$promise2 = $promise1->then(function ($value) {
var_dump($value);
throw new \Exception("promise2 error");
return "promise2";
}, function ($reason) {
var_dump($reason->getMessage());
return "promise3 error return";
});
//我们可以简写then方法，只传入$onFulfilled方法，然后错误会自己冒泡方式到下一个catchError或then里处理。
//$promise3 = $promise2->then(function ($value) {
// var_dump($value);
// return new Promise5(function($resolve, $reject) {
// $resolve("promise3");
// });
//})->catchError(function ($reason) {
// var_dump($reason->getMessage());
// return "promise3 error return";
//});
$promise3 = $promise2->then(function ($value) {
var_dump($value);
return new Promise5(function($resolve, $reject) {
$resolve("promise3");
});
}, function ($reason) {
var_dump($reason->getMessage());
return "promise3 error return";
});
$promise4 = $promise3->then(function ($value) {
var_dump($value);
return "promise4";
}, function ($reason) {
echo $reason->getMessage();
});
var_dump($promise4);
结果：
string(9) "打印我"
string(14) "promise2 error"
string(21) "promise3 error return"
object(Promise4)#10 (5) {
["value":"Promise4":private]=>
string(8) "promise4"
["reason":"Promise4":private]=>
NULL
["state":"Promise4":private]=>
string(9) "fulfilled"
["fulfilledCallbacks":"Promise4":private]=>
array(0) {
}
["rejectedCallbacks":"Promise4":private]=>
array(0) {
}
}
结论或问题：
这里我们基础实现了一个可以用于生产环境的Promise
后续我们会接续完善这个Promise的特有方法，比如：finally, all, race, resolve, reject等
后续再介绍用Promise实现的自动执行器等
附录参考
Promises/A+
Promises/A+ 中文
Promise 对象 - ECMAScript 6 入门 阮一峰
原文地址：https://segmentfault.com/a/1190000016564649
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