RFR: JDK-8273038: ChannelInputStream.transferTo() uses FileChannel.transferTo(FileChannel) [v13]

[Alan Bateman]

On Tue, 7 Sep 2021 11:44:13 GMT, Markus KARG <github.com+1701815+mkarg at openjdk.org> wrote:

>> As proposed in JDK-8265891, this PR provides an implementation for `Channels.newInputStream().transferTo()` which provide superior performance compared to the current implementation. This PR is a spin-off from https://github.com/openjdk/jdk/pull/4263 and https://github.com/openjdk/jdk/pull/5179 and deliberately concentrates **only** on the case where both, source **and** target, are actually `FileChannel`s. Other types of channels will be discussed in future PRs.
>> 
>> * Prevents transfers through the JVM heap as much as possibly by offloading to deeper levels via NIO, hence allowing the operating system to optimize the transfer.
>> 
>> Using JMH I have benchmarked both, the original implementation and this implementation, and (depending on the used hardware and use case) performance change was approx. doubled performance. A rather similar approach in different use casse was recently implemented by https://github.com/openjdk/jdk/pull/5097 which was reported by even provide 5x performance (https://github.com/openjdk/jdk/pull/5097#issuecomment-897271997).
>
> Markus KARG has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Copyright (C) 2021 instead of 2014, 2021
>   
>   Signed-off-by: Markus Karg <markus at headcrashing.eu>

> Done with [1804aa0](https://github.com/openjdk/jdk/commit/1804aa00f34010a174301ac3d816de23806e179f).

Nearly there, it needs to be "2021," to avoid falling foul of scripts that check headers.

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PR: https://git.openjdk.java.net/jdk/pull/5209