Somewhere in our program we have a connection counter leak.

There are no open connections, but AsyncHttpClient throws too many connections exception.

I cannot exactly reproduce the problem, but looking at the code I see at least one issue in function org.asynchttpclient.netty.request.NettyRequestSender#sendRequestWithNewChannel:

If RequestHostnameResolver.INSTANCE.resolve throws an exception after acquireChannelLock (for example, in asyncHandlerExtensions.onHostnameResolutionAttempt(name)), then counter is leaked.