Suppress creation of SocksSocketImpl in SocketAdaptor's constructor

[David Holmes]

Probably better discussed on nio-dev list.

David

On 18/11/2011 6:22 PM, ÈöåÈ wrote:
> Hi all,
> 
> I'd like to propose the following change to JDK's sun.nio.ch.SocketAdaptor:
> 
> In OpenJDK 6, 7 and 8, sun.nio.ch.SocketAdaptor is used to adapt a SocketChannelImpl to a java.net.Socket.
> 
> A comment in the constructor of SocketAdaptor says "super will create a useless impl", but it actually doesn't have to. AFAICT the SocksSocketImpl instance created here really isn't used at all in SocketAdaptor, unless someone invokes non-public methods on java.net.Socket via reflection.
> 
> The attached patch is to get rid of creation of the useless SocksSocketImpl.
> 
> At a glance, creating a useless SocksSocketImpl for every SocketAdaptor seems innocent. But that's not the case when the allocation rate/heap memory pressure is high. SocksSocketImpl has a finalizer (inherited from PlainSocketImpl), and when:
> * old generation is large
> * there are a lot of ready-to-die SocksSocketImpl instances
> these instances can be queued up in the finalizer queue, which increases the heap pressure.
> 
> In one of our Hadoop NameNode nodes in production, excessive SocksSocketImpl instances had been causing frequent CMS collections + long reference processing pause. Using this patch helps side-steping the problem.
> 
> I don't have a bug ID for this yet. Could anyone kindly open a bug for this?
> 
> Regards,
> Kris Mok
> Software Engineer, Taobao (http://www.taobao.com)
> 
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