Http Server apparently not handling async

[romeufcrosa]

Hi,

I'm trying to understand why I can't make an http server on top of react that can handle multiple concurrent requests.
Since the underlying socket server is async I don't understand why the http server that runs on top of it then can only process 1 request at a time?

Considering the following socket server:

$loop = React\EventLoop\Factory::create();

$i = 0;

$server = stream_socket_server("tcp://127.0.0.1:8080");
stream_set_blocking($server, 0);

$loop->addReadStream($server, function ($server) use ($loop, &$i) {
    $conn = stream_socket_accept($server);
    $data = "HTTP/1.1 200 OK\r\nContent-Length: 5\r\n\r\nHi ".$i."\n";
    $i++;
    $loop->addWriteStream($conn, function ($conn) use (&$data, $loop) {
        $written = fwrite($conn, $data);
        if ($written === strlen($data)) {
            fclose($conn);
            $loop->removeStream($conn);
        } else {
            $data = substr($data, $written);
        }
    });
});

When I run loadtest on this with concurrent requests, I get as response Hi X, where X is not always in sequence. Which is proof of it being asynchronous.

However take the following http server as example:

$i = 0;
$app = function ($request, $response) use (&$i) {
    $text = "This is request number $i.\n";
    $i++;
    $headers = array("Content-Type" => "text/plain");
    $response->writeHead(200, $headers);
    $response->end($text);
};
$loop = React\EventLoop\Factory::create();

$server = new React\Socket\Server($loop);
$http = new React\Http\Server($server);

$http->on("request", $app);
$socket->listen(8080, "0.0.0.0");
$loop->run();

This always returns This is request number X in sequence.
I'm wondering how I could make the http server handle concurrency, I assumed because socket was async that it would just work but apparently not.

Sorry if this is not really an issue, but it's been bugging me for days now and I had to turn here for help.

Thanks.

[clue]

Hi @romeufcrosa! I'm not sure I follow what you're trying to do and what your issue is, as it's a bit unclear what you're trying to achieve from the description you've posted.

Both snippets can in fact handle multiple requests concurrently. They are async in the sense of using non-blocking I/O under the hood, so that one request will never block another one. This does not imply that two request handlers will run in parallel (parallel != async). If you want to run multiple handlers at the same time, you may want to look into combinding this with forking or multithreading.

I hope this helps 👍

[romeufcrosa]

Hi Christian, Thanks for your response, I understand the difference between alternate (concurrent) and simultaneous (parallel) execution. I just found it weird that in 2 sequential curl requests, curl #2 would always wait for curl #1 to finish before being processed which is proof of non-concurrency, a true concurrent setup has to be able to make progress in multiple computations. By adding a for loop into those snippets above it was not able to make progress in X+N requests while request X was not completed, and as far as I know a for loop is not a blocking I/O operation. So I don't understand why it's behaving that way. I guess that combining this with pthreads would actually do what I want it to do. But I still don't think this is behaving as I understand it should be. Thanks.

…

On Tue, May 2, 2017 at 9:40 AM, Christian Lück ***@***.***> wrote: Hi @romeufcrosa <https://github.com/romeufcrosa>! I'm not sure I follow what you're trying to do and what your issue is, as it's a bit unclear what you're trying to achieve from the description you've posted. Both snippets can in fact handle multiple requests concurrently. They are async in the sense of using non-blocking I/O under the hood, so that one request will never block another one. This does not imply that two request handlers will run in parallel (parallel != async). If you want to run multiple handlers at the same time, you may want to look into combinding this with forking or multithreading. I hope this helps 👍 — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#172 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AELM8YQw1O9RoEeVuy3hWBaKaNlCV62Xks5r1uv4gaJpZM4NEkZj> .

-- Cumprimentos, Romeu Rosa

[clue]

I just found it weird that in 2 sequential curl requests, curl #2 would always wait for curl #1 to finish before being processed which is proof of non-concurrency, a true concurrent setup has to be able to make progress in multiple computations.

If I understand this right, than you're not actually having any issues with React's HTTP server or your HTTP client (curl), but actually with how you're using your HTTP client.

Running two curl requests sequentially implies that one has to wait for the other in this sequence. For example $ curl A; curl B will actually run the first request and only once it's ready start the second one. This is the very nature of a synchronous example.

If you want to run multiple curl requests in parallel, you can simply tell your shell to run multiple processes in the background with $ curl A &; curl B or use an async HTTP client such as https://github.com/reactphp/http-client.

I hope this helps 👍

[romeufcrosa]

Hi Christian, Sorry I should have been more explicit with how I'm running the curls, I'm running then in a bash script actually. #!/bin/bash for i in {1..20} do curl http://localhost:8080 & done As you can see this is not synchronous, and still it waits for *i* to be complete before *i*+1 is processed.

…

On Tue, May 2, 2017 at 11:52 AM, Christian Lück ***@***.***> wrote: I just found it weird that in 2 sequential curl requests, curl #2 <#2> would always wait for curl #1 <#1> to finish before being processed which is proof of non-concurrency, a true concurrent setup has to be able to make progress in multiple computations. If I understand this right, than you're not actually having any issues with React's HTTP server or your HTTP client (curl), but actually with how you're using your HTTP client. Running two curl requests *sequentially* implies that one has to wait for the other in this sequence. For example $ curl A; curl B will actually run the first request and only once it's ready start the second one. This is the very nature of a synchronous example. If you want to run multiple curl requests in parallel, you can simply tell your shell to run multiple processes in the background with $ curl A &; curl B or use an async HTTP client such as https://github.com/reactphp/ http-client. I hope this helps 👍 — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#172 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AELM8fRxRRg0jO46fHG2wZYAG2Rse9f9ks5r1wsLgaJpZM4NEkZj> .

-- Cumprimentos, Romeu Rosa

[clue]

What is exactly is "synchronous" or "waiting" here? :-)

You're still running a number of sub-processes and unless your OS scheduler has a good reason to decide otherwise, it may (or may not) execute these in the order they're started in. You may want to add some random delays to ensure some source of randomness, but other than that it's still unclear what you're trying to achieve.

Perhaps the following may also help you: https://serverfault.com/questions/456490/execute-curl-requests-in-parallel-in-bash and smi