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? ------------- Commit messages: - Draft: Correctly positioning channel in case of exception - Draft: Corrected try-catch block - Draft: Moving I/O ops into the for statement block - Draft: Replaced custom bounds check by Objects.checkFromIndexSize() - Draft: Replaced casting by pattern matching for instanceof - Draft: Replacing var by actual type - Draft: Hiding ChannelOutputStream from the API - Draft: Removing final everywhere but kept only for constants - Draft: Using Thread-Local Buffer Cache - Draft: Increased DEFAULT_BUFFER_SIZE - ... and 1 more: https://git.openjdk.java.net/jdk/compare/66274320...ed49098a Changes: https://git.openjdk.java.net/jdk/pull/4263/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4263&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8265891 Stats: 286 lines in 4 files changed: 205 ins; 76 del; 5 mod Patch: https://git.openjdk.java.net/jdk/pull/4263.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/4263/head:pull/4263 PR: https://git.openjdk.java.net/jdk/pull/4263
