java 9 multithreaded HTTP client doesn't work correctly

Question

I'm trying to convert the following sequential code to a multithreaded code but the results don't sound reasonable to me.

package com.net;

import jdk.incubator.http.HttpClient;
import jdk.incubator.http.HttpRequest;
import jdk.incubator.http.HttpResponse;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class Req {

    HttpClient client = HttpClient.newHttpClient();

    private String getResource(String someUrl) {
        String body = "";
        try {
            URI url = new URI(someUrl);
            HttpRequest request = HttpRequest.newBuilder()
                    .uri(url).GET().build();
            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandler.asString());
            body = response.body();
        } catch (URISyntaxException e) {
            System.out.println("URL " + someUrl + "is not valid");
        } catch (IOException | InterruptedException e) {
            System.out.println(e.getMessage());
        }
        return body;
    }


    public static void main(String[] args){

        String[] topIranianSites = {
                "https://www.aparat.com/",
                "http://www.varzesh3.com/",
                "http://namnak.com/",
                "http://www.telewebion.com/",
                "https://divar.ir/",
                "https://www.ninisite.com/",
                "https://www.blogfa.com/",
                "http://www.namasha.com/",
                "http://www.yjc.ir/"
        };

        Req singleThreadReq = new Req();
        float totalElapsedTime = 0F;

        for (String site : topIranianSites){
            long fetchStartTime = System.currentTimeMillis();
            String html = singleThreadReq.getResource(site);
            float elapsed = (float) (System.currentTimeMillis() - fetchStartTime) / 1000;

            Document doc = Jsoup.parse(html);
            System.out.println("It took " + elapsed + " seconds to fetch " + site + " with title " + doc.title());
            totalElapsedTime += elapsed;
        }

        System.out.println("Total Elapsed Time: " + totalElapsedTime + "\nTotal Number of sites: " + topIranianSites.length);

    }
}

This is the output

WARNING: Using incubator modules: jdk.incubator.httpclient
It took 2.622 seconds to fetch https://www.aparat.com/ with title آپارات - سرویس اشتراک ویدیو
It took 0.455 seconds to fetch http://www.varzesh3.com/ with title 
It took 0.521 seconds to fetch http://namnak.com/ with title نمناک
It took 2.172 seconds to fetch http://www.telewebion.com/ with title تلوبیون | مرجع پخش زنده و دانلود فیلم ، سریال و سایر برنامه های تلویزیون
General SSLEngine problem
It took 0.229 seconds to fetch https://divar.ir/ with title 
It took 1.769 seconds to fetch https://www.ninisite.com/ with title نی نی سایت | راهنمای بارداری و بچه داری
Received fatal alert: handshake_failure
It took 0.382 seconds to fetch https://www.blogfa.com/ with title 
It took 2.641 seconds to fetch http://www.namasha.com/ with title نماشا - سرویس رایگان اشتراک ویدیو
It took 0.503 seconds to fetch http://www.yjc.ir/ with title 
Total Elapsed Time: 11.294001
Total Number of sites: 9

From the sequential output I guess the correct multithreaded code should take about 2.8 seconds to fetch all 9 sites. But my implementation of multithreaded code takes more

package com.net;

import jdk.incubator.http.HttpClient;
import jdk.incubator.http.HttpRequest;
import jdk.incubator.http.HttpResponse;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class ReqThreaded implements Runnable {

    class Site {
        String url;
        String title;
        float fetchTime;
    }

    private HttpClient client = HttpClient.newHttpClient();

    private Thread[] threadPool;
    private String[] rawSites;
    private Site[] sitesArr;
    private int sitesDone = 0;
    long startTime = System.currentTimeMillis();
    float totalElapsed = 0F;

    public ReqThreaded(String[] sites) {
        threadPool = new Thread[sites.length];
        sitesArr = new Site[sites.length];
        rawSites = sites;

        for (int i = 0; i < sites.length; i++) {
            startThread(i);
        }

        while (sitesDone < sites.length) {
            try {
                Thread.sleep(1000);
                totalElapsed = (float) (System.currentTimeMillis() - startTime) / 1000;
                System.out.print("\rElapsed time: " + totalElapsed + "Sites Done: " + sitesDone);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        System.out.println("\n\nStatistics:\n\n");

        for (Site someSite : sitesArr) {
            System.out.println("URL " + someSite.url + "\nTitle: " + someSite.title + "\nFetch Time: " + someSite.fetchTime + "\n\n");
        }

    }

    private void startThread(int i) {
        if (threadPool[i] == null) {
            threadPool[i] = new Thread(this);
            threadPool[i].start();
        }
    }


    private String getResource(String someUrl) {
        String body = "";
        try {
            URI url = new URI(someUrl);
            HttpRequest request = HttpRequest.newBuilder()
                    .uri(url).GET().build();
            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandler.asString());
            body = response.body();
        } catch (URISyntaxException e) {
            System.out.println("URL " + someUrl + "is not valid");
        } catch (IOException | InterruptedException e) {
            System.out.println(e.getMessage());
        }
        return body;
    }


    @Override
    public void run() {
        Thread thisThread = Thread.currentThread();
        int sitesIndex = 0;

        for (int j = 0; j < threadPool.length; j++) {
            if (thisThread == threadPool[j]) {
                sitesIndex = j;
            }
        }
        long fetchStartTime = System.currentTimeMillis();
        String html = getResource(rawSites[sitesIndex]);
        float elapsed = (float) (System.currentTimeMillis() - fetchStartTime) / 1000;
        sitesDone++;
        Document doc = Jsoup.parse(html);
        sitesArr[sitesIndex] = new Site();
        sitesArr[sitesIndex].url = rawSites[sitesIndex];
        sitesArr[sitesIndex].title = doc.title();
        sitesArr[sitesIndex].fetchTime = elapsed;
    }

    public static void main(String[] args) {

        String[] topIranianSites = {
                "https://www.aparat.com/",
                "http://www.varzesh3.com/",
                "http://namnak.com/",
                "http://www.telewebion.com/",
                "https://divar.ir/",
                "https://www.ninisite.com/",
                "https://www.blogfa.com/",
                "http://www.namasha.com/",
                "http://www.yjc.ir/"
        };

        new ReqThreaded(topIranianSites);

    }
}

This is the output of multithreaded code. Both Total time and fetch time for each url seems incorrect. I think something is blocking here or some kind of race condition. What's wrong here?

WARNING: Using incubator modules: jdk.incubator.httpclient
General SSLEngine problem
Received fatal alert: handshake_failure
Elapsed time: 7.068Sites Done: 9

Statistics:


URL https://www.aparat.com/
Title: آپارات - سرویس اشتراک ویدیو
Fetch Time: 4.808


URL http://www.varzesh3.com/
Title: 
Fetch Time: 5.904


URL http://namnak.com/
Title: نمناک
Fetch Time: 1.056


URL http://www.telewebion.com/
Title: تلوبیون | مرجع پخش زنده و دانلود فیلم ، سریال و سایر برنامه های تلویزیون
Fetch Time: 6.569


URL https://divar.ir/
Title: 
Fetch Time: 0.53


URL https://www.ninisite.com/
Title: نی نی سایت | راهنمای بارداری و بچه داری
Fetch Time: 4.287


URL https://www.blogfa.com/
Title: 
Fetch Time: 0.767


URL http://www.namasha.com/
Title: نماشا - سرویس رایگان اشتراک ویدیو
Fetch Time: 4.539


URL http://www.yjc.ir/
Title: 
Fetch Time: 0.836

Answer 1

I fixed some obvious errors in class ReqThreaded like improper synchronization, moved method run() into class Site, and made result printing identical to that in the single-threaded variant. Thread pool was not used, for each request a separate thread was created.

The result is as follows:

Received fatal alert: handshake_failure
It took 0.263 seconds to fetch https://www.blogfa.com/ with title 
General SSLEngine problem
It took 0.491 seconds to fetch https://divar.ir/ with title 
It took 1.02 seconds to fetch http://www.yjc.ir/ with title 
It took 1.056 seconds to fetch http://www.telewebion.com/ with title تلوبیون | مرجع پخش زنده و دانلود فیلم ، سریال و سایر برنامه های تلویزیون
It took 1.262 seconds to fetch https://www.ninisite.com/ with title نی نی سایت | راهنمای بارداری و بچه داری
It took 1.411 seconds to fetch http://namnak.com/ with title نمناک
It took 1.608 seconds to fetch http://www.varzesh3.com/ with title ورزش سه :: صفحه اصلی
It took 2.221 seconds to fetch http://www.namasha.com/ with title نماشا - سرویس رایگان اشتراک ویدیو
It took 2.247 seconds to fetch https://www.aparat.com/ with title آپارات - سرویس اشتراک ویدیو
Elapsed time: 2.253
Sites Done: 9
Process finished with exit code 0

That is, total time is only slightly bigger than the longest time to get result from a site.

Multithreading works!

Modified code is as follows:

import jdk.incubator.http.HttpClient;
import jdk.incubator.http.HttpRequest;
import jdk.incubator.http.HttpResponse;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.concurrent.CountDownLatch;

public class ReqThreaded {

class Site implements Runnable {
    final String url;
    String title;
    float fetchTime;

    Site(String url) {
        this.url = url;
    }

    @Override
    public void run() {
        long fetchStartTime = System.currentTimeMillis();
        String html = getResource(url);
        float elapsed = (float) (System.currentTimeMillis() - fetchStartTime) / 1000;
        Document doc = Jsoup.parse(html);
        title = doc.title();
        fetchTime = elapsed;
        System.out.println("It took " + fetchTime + " seconds to fetch " + url + " with title " + title);
        sitesDone.countDown();
    }
}

private HttpClient client = HttpClient.newHttpClient();

private CountDownLatch sitesDone;

public ReqThreaded(String[] sites) throws InterruptedException {
    int siteNumber = sites.length;
    sitesDone = new CountDownLatch(siteNumber);
    long startTime = System.currentTimeMillis();

    for (int i = 0; i < siteNumber; i++) {
        Runnable site = new Site(sites[i]);
        Thread thread = new Thread(site);
        thread.start();
    }

    sitesDone.await();
    float totalElapsed = (float) (System.currentTimeMillis() - startTime) / 1000;
    System.out.print("\rElapsed time: " + totalElapsed + "\nSites Done: " + siteNumber);
}

private String getResource(String someUrl) {
    String body = "";
    try {
        URI url = new URI(someUrl);
        HttpRequest request = HttpRequest.newBuilder()
                .uri(url).GET().build();
        HttpResponse<String> response = client.send(request, HttpResponse.BodyHandler.asString());
        body = response.body();
    } catch (URISyntaxException e) {
        System.out.println("URL " + someUrl + "is not valid");
    } catch (IOException | InterruptedException e) {
        System.out.println(e.getMessage());
    }
    return body;
}

public static void main(String[] args) throws InterruptedException {

    String[] topIranianSites = {
            "https://www.aparat.com/",
            "http://www.varzesh3.com/",
            "http://namnak.com/",
            "http://www.telewebion.com/",
            "https://divar.ir/",
            "https://www.ninisite.com/",
            "https://www.blogfa.com/",
            "http://www.namasha.com/",
            "http://www.yjc.ir/"
    };

    new ReqThreaded(topIranianSites);

}
}

That is:

• never run the same method of the same object on different threads simultaneously

• never exchange information between threads via plain variables. Use only specialized facilities. Here I used CountDownLatch, to signal the end of each thread. If I want to return some information to the main thread, I'd use BlockingQueue instead.