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

[Michael McMahon]

On Tue, 6 Sep 2022 13:56:15 GMT, Conor Cleary <ccleary 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.

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