Taking advantage of TCP Loopback fast path in Windows

[Kirk Shoop (MS OPEN TECH)]

My memory is that setting it on the socket before calling listen did not work. However, we will try again and verify.

Thanks,
Kirk

Software Design Engineer
Microsoft Open Technologies, Inc.

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From: Alan Bateman [mailto:Alan.Bateman at oracle.com]
Sent: Wednesday, September 24, 2014 11:06 AM
To: Kirk Shoop (MS OPEN TECH); Martin Sawicki (MS OPEN TECH); net-dev at openjdk.java.net
Cc: Valery Kopylov (Akvelon); nio-dev
Subject: Re: Taking advantage of TCP Loopback fast path in Windows

On 24/09/2014 16:58, Kirk Shoop (MS OPEN TECH) wrote:
SIO_LOOPBACK_FAST_PATH must be set on the socket passed to accept.

The way I think about this is the socket instance passed to listen represents the port while the socket instance passed to accept represents a single TCP stream. SIO_LOOPBACK_FAST_PATH has no effect when applied to a port, but does have an effect when applied to a TCP stream.

Given that we are open to suggestions for a better organization of the code to set SIO_LOOPBACK_FAST_PATH on the sockets passed to accept.


Taking ServerSocketChannel has an example then you are setting SIO_LOOPBACK_FAST_PATH over and over on the same socket and it's not clear to me that this is needed. My reading of the SIO_LOOPBACK_FAST_PATH page is that it just needs to be set once on the listener and the socket corresponding to each of the subsequently accepted connections will use the fast path. Perhaps my reading is incorrect and you mean that accept will reset the setting after it accepts a connection?

The AsynchronouServerSocketChannel case is clearly a bit different as it needs to create the SOCKET in advance before the connection is accepted but in that case it will still create the SOCKET via Net.socket0.

One thing that isn't clear to me from the document is whether it is possible to enable SIO_LOOPBACK_FAST_PATH before calling listen. If that is allowed then I think you should be able to just set the option in Net.c socket0 and it should work for all NIO usages.

-Alan
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