Apache HttpClient CoreConnectionPNames.CONNECTION_TIMEOUT什么都不做？

Question

在参数CoreConnectionPNames.CONNECTION_TIMEOUT设置为1的情况下，我从HttpClient得到了奇怪的行为。我本以为HttpGet请求会失败，抛出连接超时异常，但它们还是成功了。这似乎不合理，因为它实际上意味着TCP握手在不到1毫秒内完成。

在这个pom.xml中可以看到，我使用的httpclient版本是

    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.0.1</version>
        <type>jar</type>
    </dependency>

代码如下：

import java.io.IOException;
import java.util.Random;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.params.CoreConnectionPNames;
import org.apache.http.util.EntityUtils;
import org.apache.log4j.Logger;

public class TestNodeAliveness {
    private static Logger log = Logger.getLogger(TestNodeAliveness.class);

    public static boolean nodeBIT(String elasticIP) throws ClientProtocolException, IOException {
        try {
            HttpClient client = new DefaultHttpClient();

            // The time it takes to open TCP connection.
            client.getParams().setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, 1);

            // Timeout when server does not send data.
            client.getParams().setParameter(CoreConnectionPNames.SO_TIMEOUT, 5000);

            // Some tuning that is not required for bit tests.
            client.getParams().setParameter(CoreConnectionPNames.STALE_CONNECTION_CHECK, false);
            client.getParams().setParameter(CoreConnectionPNames.TCP_NODELAY, true);


            HttpUriRequest request = new HttpGet("http://" + elasticIP);
            HttpResponse response = client.execute(request);

            HttpEntity entity = response.getEntity();
            if(entity == null) { 
                return false;
            } else {
                System.out.println(EntityUtils.toString(entity));
            }

            // Close just in case.
            request.abort();

        } catch (Throwable e) {
            log.warn("BIT Test failed for " + elasticIP);
            e.printStackTrace();

            return false;
        }

        return true;
    }


    public static void main(String[] args) throws ClientProtocolException, IOException {
        nodeBIT("google.com?cant_cache_this=" + (new Random()).nextInt());
    }
}

这怎麽可能？谢谢。

Answer 1

在我使用过的所有JVM中，超时的有效粒度大约是15-30ms。即使超时设置为单套接字I/O和connect请求，如果它们花费的时间少于15-30ms，通常也会成功。

Answer 2

如果您设置HttpGet的超时，而不是HttpClient，它似乎工作得更好。

    HttpGet httpget = new HttpGet("http://www.apache.org/");

    RequestConfig Default = RequestConfig.DEFAULT;

    RequestConfig requestConfig = RequestConfig.copy(Default)
            .setSocketTimeout(5000)
            .setConnectTimeout(5000)
            .setConnectionRequestTimeout(5000)
            .build();
    httpget.setConfig(requestConfig);