RFR: 8288717: Add a means to close idle connections in HTTP/2 connection pool

[Daniel Fuchs]

On Tue, 27 Sep 2022 10:58:07 GMT, Michael McMahon <michaelm at openjdk.org> wrote:

>> **Issue**
>> When using HTTP/2 with the HttpClient, it can often be necessary to close an idle Http2 Connection before a server sends a GOAWAY frame. For example, a server or cloud based tool could close a TCP connection silently when it is idle for too long resulting in ConnectionResetException being thrown by the HttpClient.
>> 
>> **Proposed Solution**
>> A new system property, `jdk.httpclient.idleConnectionTimeout`, was added and is used to specify in Milliseconds how long an idle connection (idle connections are those which have no currently active streams) for the HttpClient before the connection is closed.
>
> I understand that the H2 connection cache is structured slightly differently to the HTTP/1 idle cache, but I agree that we should try to present the same view of idle connections across both HTTP/1 and H2. It seems like it should be possible to record a timestamp when the stream count on a connection goes to zero, and after a certain time close connections that exceed the current max idle time. In that situation, it would make sense to use the same property for both HTTP/1 and H2.

OK - thanks @Michael-Mc-Mahon  for taking a look. I accept that in the case of idle timeout, there is not much difference in behavior between HTTP/1.1 and HTTP/2 - the property in both cases defines how long the connection will remain open after last being used. I agree that in this case the same timeout value could legitimately be used to configure both pools. It's a bit unfortunate that it's named `keepAlive` rather than `idleTimeout` as `keepAlive` as a stronger HTTP/1.1 connotation - but that's not too bad. Should we also take this opportunity to revisit the default value (1200s is a long time?)

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PR: https://git.openjdk.org/jdk/pull/10183