PHP下的异步尝试四：PHP版的Promise

其他 2018-11-16 16:37:52 阅读次数: 0

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

  1. PHP下的异步尝试一：初识生成器
  2. PHP下的异步尝试二：初识协程
  3. PHP下的异步尝试三：协程的PHP版thunkify自动执行器
  4. PHP下的异步尝试四：PHP版的Promise
  5. 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

猜你喜欢

转载自www.cnblogs.com/lalalagq/p/9970006.html
今日推荐
火速冲上 GitHub 热榜 —— 开源编程语言、框架哪有这么可爱？
北京人形机器人创新中心发布全球首个纯电驱拟人奔跑的全尺寸人形机器人“天工”
LFOSSA 源来如此公开课 | 掌握云原生未来：CNCF 认证全面攻略与备考秘籍
国产云输入法——仅华为无云端数据上传安全问题
开源日报 | 工业开源项目OGG 1.0；姐姐，你要和我一起配置火狐吗；苹果AI遥遥落后？Fedora 40
开放签电子签章：停止新增，优化体验，前进更进（五一假期前工作）
开源日报 | 中学生开源前端动画引擎；全球首个Llama3 8B中文版开源模型；联想电脑恐出局；Linus讽刺AI炒作
周排行
浏览器对同一域名进行请求的最大并发连接数
React Hook之自定义Hook
【转】MyBatis缓存机制
-Java-泛型
自动化测试常用脚本-发送邮件
LeetCode#859: Buddy Strings
java、Python处理字符串
第二篇の博客
Hadoop伪分布式环境安装
SQL Server进阶（十一）临时表、表变量
每日归档
更多
2024-04-27(56)
2024-04-26(39)
2024-04-25(22)
2024-04-24(36)
2024-04-23(26)
2024-04-22(39)
2024-04-21(0)
2024-04-20(6)
2024-04-19(5)
2024-04-18(0)

代码天地 © 2018 codetd.com

境外服务器   最新电视剧2022