如何在安普中正确地把闭包变成承诺？

Question

我在学安非他语。我想转换同步调用异步调用使用事件循环在安普。我的示例代码使用file_get_contents作为示例阻塞调用。

使用sync调用，它看起来如下所示：

$uris = [
    "https://google.com/",
    "https://github.com/",
    "https://stackoverflow.com/",
];

$results = [];
foreach ($uris as $uri) {
    var_dump("fetching $uri..");
    $results[$uri] = file_get_contents($uri);
    var_dump("done fetching $uri.");
}

foreach ($results as $uri => $result) {
    var_dump("uri : $uri");
    var_dump("result : " . strlen($result));
}

和输出：

string(30) "fetching https://google.com/.."
string(34) "done fetching https://google.com/."
string(30) "fetching https://github.com/.."
string(34) "done fetching https://github.com/."
string(37) "fetching https://stackoverflow.com/.."
string(41) "done fetching https://stackoverflow.com/."
string(25) "uri : https://google.com/"
string(14) "result : 48092"
string(25) "uri : https://github.com/"
string(14) "result : 65749"
string(32) "uri : https://stackoverflow.com/"
string(15) "result : 260394"

我知道有artax会在异步模式下打电话。但是，我想学习如何正确地将阻塞代码转换为异步并发代码(而不是并行代码)。我已经成功地使用amp并行实现了它。

我相信如果我在amp中成功地在异步中实现它，正确的输出将是这样的：

string(30) "fetching https://google.com/.."
string(30) "fetching https://github.com/.."
string(37) "fetching https://stackoverflow.com/.."
string(34) "done fetching https://google.com/."
string(34) "done fetching https://github.com/."
string(41) "done fetching https://stackoverflow.com/."
string(25) "uri : https://google.com/"
string(14) "result : 48124"
string(25) "uri : https://github.com/"
string(14) "result : 65749"
string(32) "uri : https://stackoverflow.com/"
string(15) "result : 260107"

我试过使用下面的代码：

<?php
require __DIR__ . '/vendor/autoload.php';

use Amp\Loop;
use function Amp\call;

Loop::run(function () {
    $uris = [
        "https://google.com/",
        "https://github.com/",
        "https://stackoverflow.com/",
    ];

    foreach ($uris as $uri) {
        $promises[$uri] = call(function () use ($uri) {
            var_dump("fetching $uri..");
            $result = file_get_contents($uri);
            var_dump("done fetching $uri.");
            yield $result;
        });
    }

    $responses = yield $promises;

    foreach ($responses as $uri => $result) {
        var_dump("uri : $uri");
        var_dump("result : " . strlen($result));
    }
});

它给出的不是我预期的结果，而是这个错误：

string(30) "fetching https://google.com/.."
string(34) "done fetching https://google.com/."
string(30) "fetching https://github.com/.."
string(34) "done fetching https://github.com/."
string(37) "fetching https://stackoverflow.com/.."
string(41) "done fetching https://stackoverflow.com/."
PHP Fatal error:  Uncaught Amp\InvalidYieldError: Unexpected yield; Expected an instance of Amp\Promise or React\Promise\PromiseInterface or an array of such instances; string yielded at key 0 on line 20 

结果似乎也是同步运行，而不是异步运行。

我应该如何正确地做这件事？

Answer 1

你需要使用一个非阻塞实现你所使用的函数。file_get_contents被阻塞。例如，您可以在amphp/file中找到非阻塞实现。如果您将file_get_contents替换为Amp\File\get，它应该会按预期工作。