RFR: Ensure vthread has connected to server [v2]

[Miao Zheng]

On Mon, 6 Sep 2021 11:14:09 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Thanks for your review.
>> Do I need remove this? I think the following is duplicated with the check of "server.connectionCount() == 0"
>> 
>>     // server should have accepted one connection
>>     if (server.connectionCount() != 1)
>>         throw new RuntimeException("Expected 1 HTTP connection");
>
> We should keep it to checks that only one connection is established. The details on this are in sun.net.www.http.HttpClient where it makes a decision on whether to retry the HTTP request when interrupted. In this case, it should not retry.

Got it. Thanks for your answer.
I have changed this PR on your suggestion.

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PR: https://git.openjdk.java.net/loom/pull/60