On Fri, 2 Jul 2021 06:20:29 GMT, Markus KARG <github.com+1701815+mk...@openjdk.org> wrote:
>> This PR-*draft* is **work in progress** and an invitation to discuss a >> possible solution for issue >> [JDK-8265891](https://bugs.openjdk.java.net/browse/JDK-8265891). It is *not >> yet* intended for a final review. >> >> As proposed in JDK-8265891, this PR provides an implementation for >> `Channels.newInputStream().transferTo()` which provide superior performance >> compared to the current implementation. The changes are: >> * 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 more JRE heap in the fallback case when no NIO is possible (still >> only KiBs, hence mostl ynegligible even on SBCs) to better perform on modern >> hardware / fast I/O devides. >> >> 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. So this PoC proofs that >> it makes sense to finalize this work and turn it into an actual OpenJDK >> contribution. >> >> I encourage everybody to discuss this draft: >> * Are there valid arguments for *not* doing this change? >> * Is there a *better* way to improve performance of >> `Channels.newInputStream().transferTo()`? >> * How to go on from here: What is missing to get this ready for an actual >> review? > > Markus KARG has refreshed the contents of this pull request, and previous > commits have been removed. The incremental views will show differences > compared to the previous content of the PR. I cloned the `InputStream/TransferTo` test in a way which uses providers, but when started to implement the providers I noticed that a huge amount of *empty* source code is needed just to make the compiler happy: `FileChannel` already has dozens of abstract methods I have to override but they never will be used by any of the tests... Having that said, it would be good if I would be allowed to spare us thousands of useless codelines: * May I just implement the `content()` test or do you insist on me really implementing *all* the tests found in `InputStream/TransferTo` for *each* of the overloaded `transferTo` implementations? * May I use a mocking framework to actually just provide *partial* implementations of the channels, or do you insist on me actually overloading *all* methods of *all* channels in actual Java source code just for the sake of making the compiler happy? While I understand the necessity of tests, and while I am convinced that the performance benefit outweighs the weeks of work this would imply just for adding all those test code, I actually like to propose that I only cover the `content()` tests plus using Mockito, so we would have 80% of the benefit for 20% of the coding costs. WDYT? ------------- PR: https://git.openjdk.java.net/jdk/pull/4263
