如何解决PHP异步编程的复杂性？GuzzlePromises助你构建流畅高效的应用

<code class="bash">composer require guzzlehttp/promises</code>

<pre class="brush:php;toolbar:false;">use GuzzleHttp\Promise\Promise;

// 模拟一个异步操作，例如一个耗时2秒的API请求
$apiCallPromise = new Promise(function () use (&$apiCallPromise) {
    // 假设这里是真正的异步I/O操作，例如通过非阻塞HTTP客户端发送请求
    // 为了演示，我们用sleep模拟延迟
    sleep(2); 
    $apiCallPromise->resolve('Data from API Service A');
});

echo "API请求已发出，程序继续执行...\n";

// 此时，apiCallPromise 处于 pending 状态

<pre class="brush:php;toolbar:false;">$apiCallPromise
    ->then(function ($value) {
        echo "API请求成功：{$value}\n";
        // 返回一个新的值，它将传递给下一个then
        return "Processed: " . $value;
    })
    ->then(function ($processedValue) {
        echo "进一步处理后的结果：{$processedValue}\n";
        // 这里可以返回另一个Promise，实现异步操作的嵌套
        // 例如：return anotherAsyncOperationPromise();
    })
    ->otherwise(function ($reason) { // 等同于 then(null, $onRejected)
        echo "API请求失败：{$reason}\n";
        // 可以选择抛出异常或返回一个值，以决定链的后续走向
        throw new \Exception("处理失败: " . $reason);
    });

<pre class="brush:php;toolbar:false;">use GuzzleHttp\Promise\Promise;

$promise = new Promise(function () use (&$promise) {
    // 模拟异步操作
    sleep(1);
    $promise->resolve('Hello, World!');
});

echo "开始等待Promise完成...\n";
try {
    $result = $promise->wait(); // 阻塞直到Promise完成
    echo "Promise完成，结果是：{$result}\n";
} catch (\Exception $e) {
    echo "Promise被拒绝：{$e->getMessage()}\n";
}

<pre class="brush:php;toolbar:false;">use GuzzleHttp\Promise\Promise;

$failingPromise = new Promise();
$failingPromise
    ->then(function ($value) {
        echo "不应该执行到这里\n";
    })
    ->then(null, function ($reason) { // 捕获前一个Promise的拒绝
        echo "捕获到错误：{$reason}\n";
        // 可以返回一个新值，使链条恢复正常
        return "错误已处理，继续执行";
    })
    ->then(function ($value) {
        echo "错误处理后，链条继续：{$value}\n";
    });

$failingPromise->reject('Something went wrong!');

<pre class="brush:php;toolbar:false;">use GuzzleHttp\Promise\Coroutine;
use GuzzleHttp\Promise\Promise;

function asyncOperation($value) {
    return new Promise(function () use (&$promise, $value) {
        sleep(1); // 模拟异步
        $promise->resolve("Processed: " . $value);
    });
}

$coroutine = Coroutine::of(function () {
    $result1 = yield asyncOperation('Initial Data');
    echo "Coroutine step 1: {$result1}\n";
    $result2 = yield asyncOperation($result1);
    echo "Coroutine step 2: {$result2}\n";
    return $result2 . " (Final)";
});

echo "开始执行协程...\n";
$finalResult = $coroutine->wait();
echo "协程完成，最终结果：{$finalResult}\n";