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

[Jaikiran Pai]

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.

src/java.net.http/share/classes/jdk/internal/net/http/Http2Connection.java line 1037:

> 1035:         } else {
> 1036:             // Start timer if property present and not already created
> 1037:             synchronized (this) {

I think we can avoid this `synchronized` block every time we close a non-final stream, by slightly changing this code to something like:


final Optional<Duration> idleTimeoutDuration = client().idleConnectionTimeout();
if (idleTimeoutDuration.isPresent()) {
  synchronized(this) {
    // idleConnectionTimerEvent is always accessed within a synchronized block
    if (streams.isEmpty() && idleConnectionTimeoutEvent == null) {
      idleConnectionTimeoutEvent = idleTimeoutDuration.map(IdleConnectionTimeoutEvent::new).get();
      client().registerTimer(idleConnectionTimeoutEvent);
    }
  }
}

This would avoid the `synchronized` block when no idle timeout is configured.

src/java.net.http/share/classes/jdk/internal/net/http/Http2Connection.java line 1222:

> 1220:                 if (idleConnectionTimeoutEvent != null) {
> 1221:                     client().cancelTimer(idleConnectionTimeoutEvent);
> 1222:                     System.err.println("Http2Connection: Timer Event Cancelled");

I suspect this is a left over `System.err` message?

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