HttpServer performance issue / improvement

[Robert Engels]

I added a new test specifically to address this issue. Ran fine on osx without changes - long duration (failure) on Linux without the fix. 

> On Apr 8, 2024, at 4:01 AM, Jaikiran Pai <jai.forums2013 at gmail.com> wrote:
> 
> Recently on AIX the same change was needed to address the test time outs in the test/jdk/com/sun/net/httpserver/simpleserver/StressDirListings.java test - https://github.com/openjdk/jdk/pull/17363
> 
> -Jaikiran
> 
>> On 08/04/24 1:50 pm, Daniel Jeliński wrote:
>> Hi Robert,
>> If you are on Linux, see test/jdk/java/net/vthread/HttpALot.java. That
>> test was recently modified to add -Dsun.net.httpserver.nodelay=true
>> [1], because it took forever to complete on LInux machines. On other
>> OSes the problem is not visible in existing tests.
>> Cheers,
>> Daniel
>> 
>> [1] https://github.com/openjdk/jdk/pull/10504
>> 
>> sob., 6 kwi 2024 o 00:37 robert engels <rengels at ix.netcom.com> napisał(a):
>>> Hi Daniel,
>>> 
>>> I think I have a solution that would work. I will try to get a PR together. Do you know if there is an existing test case the demonstrates the issue? - if not, I will start with that.
>>> 
>>> Robert
>>> 
>>>> On Apr 4, 2024, at 9:44 AM, Daniel Jeliński <djelinski1 at gmail.com> wrote:
>>> 
>>> Hi Robert,
>>> Thanks for bringing this up! We are aware of the issue, it's tracked under https://bugs.openjdk.org/browse/JDK-6968351.
>>> 
>>> If you have an idea for a proper fix that doesn't add too much complexity, please open a PR, and we'll be happy to help.
>>> Cheers,
>>> Daniel
>>> 
>>> czw., 4 kwi 2024, 14:55 użytkownik Robert Engels <rengels at ix.netcom.com> napisał:
>>>> 
>>>> When doing some testing on github.com/robaho/httpserver - which is a fork of the jdk http server, I discovered a significant performance issue.
>>>> 
>>>> When an http connection is in ‘keep-alive’ - the default for http 1.1 - the headers are “flushed” here https://github.com/openjdk/jdk21/blob/890adb6410dab4606a4f26a942aed02fb2f55387/src/jdk.httpserver/share/classes/sun/net/httpserver/ExchangeImpl.java#L281
>>>> 
>>>> This means that after the handler runs and it sends data - e.g. /hello sends “hello” on the connection, the connection will stall due to the Nagel algorithm - usually incurring a 50 ms delay. The stall occurs since the client will not see the expected data until after the delay, so it is unable to send the next (when reusing the same connection/HttpClient).
>>>> 
>>>> You can set the TCP_NODELAY on the server to work-around this, but a better solution would be to override the flush() on the BufferedOutputStream to not flush() the underlying connection - i.e. only write the buffered bytes, or rework it a bit to only flush when there is no content to send.
>>>>