When using http2 in okhttp, why multi requests to the same host didn't use just one connectoin

Question

I would like to test okhttp's http2 function. And I make multi requsts to same host in async style. But, I found that, it involved multi connections, since the protocol is h2, It should use just one connection, right? The code is below. Ah, I'm using okhttp2.5

public class Performance {
    private final OkHttpClient client = new OkHttpClient();
    private final Dispatcher dispatcher = new Dispatcher();
    private final int times = 20;

    public Performance(){
        dispatcher.setMaxRequestsPerHost(2);
        client.setDispatcher(dispatcher);

        // Configure the sslContext
        // MySSLSocketFactory mySSLSocketFactory = new MySSLSocketFactory();
        // client.setSslSocketFactory(mySSLSocketFactory);
        // client.setHostnameVerifier(new HostnameVerifier() {
        //     public boolean verify(String s, SSLSession sslSession) {
        //         return true;
        //     }
        // });
    }
    public void run()throws Exception{
        for(int i=0; i<times; i++) {
            Request request = new Request.Builder()
                .url("https://http2bin.org/delay/1")
                .build();
            client.newCall(request).enqueue(new Callback() {
                public void onFailure(Request request, IOException e) {
                    e.printStackTrace();
                }

                public void onResponse(Response response) throws IOException {
                    System.out.println(response.headers().get("OkHttp-Selected-Protocol"));
                }
            });
        }
    }
    public static void main(String[] args)throws Exception{
        Performance performance = new Performance();
        performance.run();
    }
}

Dacha

Please explain how do you know that your requests are going through more than one connection. – Allomorphism

I get the conclusion for these reasons: 1. when modify dispatcher's maxRequestsPerHost , result changes accordingly, and that's why I use the /delay/1 path for test. The maxRequestsPerHost means the number of connections or just the number of requests, despite that multi requests can be executed in just one connection? ; 2. I compare the performance with HTTP1.1 using other path like /get, it seems that there are no performance differences, no matter how many request I set. – Beanstalk

Can you confirm you're getting an HTTP/2 connection? Note that you'll need Jetty-ALPN on the desktop. – Roughspoken

Yes, I can. response.headers().get("OkHttp-Selected-Protocol") shows that the protocol used and I got h2. I already add Jetty-ALPN support using -Xbootclasspath/p:C:/Users/zfz/.m2/repository/org/mortbay/jetty/alpn/alpn-boot/8.1.4.v20150727/alpn-boot-8.1.4.v20150727.jar in VM options. – Beanstalk

Answer 1

There's a bug in OkHttp where multiple simultaneous requests each create their own socket connection, rather than coordinating a shared connection. This only happens when the connections are created simultaneously. Work around by yielding 500ms before the 2nd connection.

Roughspoken

If this bug exists, it means that in many circumstances my application won't benefit from HTTP/2's multiplexed features, right? Because if I want to wait 500ms to create the 2nd connection, may be using HTTP1.1 is enough. And, I do an experiment by add Thread.sleep(1000) after the client.newCall(reqeust).enqueue, it seems always using multi connections as before. – Beanstalk

Is the bug link right? I don't think it's relevant to this problem. Your bug description is related, however, I cannot work around it using sleep. Waiting for your help, thx~ – Beanstalk

Did they fix this bug in OKHttp3.0+? – Howzell

I wanted to know that too. Has this been fixed in 3.x yet? – Belding

Actually should be fixed now, though a related issue still needs attention. github.com/square/okhttp/pull/3207 – Roughspoken