Add parallel request example

examples/6-parallel-requests.php

@@ -0,0 +1,42 @@
+<?php
+
+use Amp\Artax\Response;
+use Amp\Loop;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+Loop::run(function () {
+    $uris = [
+        "https://google.com/",
+        "https://github.com/",
+        "https://stackoverflow.com/",
+    ];
+
+    // Instantiate the HTTP client
+    $client = new Amp\Artax\DefaultClient;
+
+    $requestHandler = function (string $uri) use ($client) {
+        /** @var Response $response */
+        $response = yield $client->request($uri);
+
+        return $response->getBody();
+    };
+
+    try {
+        $promises = [];
+
+        foreach ($uris as $uri) {
+            $promises[$uri] = Amp\call($requestHandler, $uri);
+        }
+
+        $bodies = yield $promises;
+
+        foreach ($bodies as $uri => $body) {
+            print $uri . " - " . \strlen($body) . " bytes" . PHP_EOL;
+        }
+    } catch (Amp\Artax\HttpException $error) {
+        // If something goes wrong Amp will throw the exception where the promise was yielded.
+        // The Client::request() method itself will never throw directly, but returns a promise.
+        echo $error;
+    }
+});