RFR: 8278268 - (ch) InputStream returned by Channels.newInputStream should have fast path for FileChannel targets [v16]

[Markus KARG]

On Sun, 10 Jul 2022 09:50:02 GMT, Markus KARG <duke at openjdk.org> wrote:

>> Markus KARG has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - separate test class for each large file test
>>  - Base class only contains utilities and helpers
>>  - Renamed AbstractTransferTo to TransferToBase as it is not abstract
>
> Please keep this PR open; I will continune work on it soon.

> @mkarg Do you have any benchmarks/results for the change?

@AlanBateman It needed several months, but finally I found the time to provide the requested performance numbers:

TransferToPerformance.inputStreamLoop    104857  thrpt   25  20557.862 ± 1539.845  ops/s
TransferToPerformance.transferFrom       104857  thrpt   25  22093.131 ± 1178.483  ops/s

TransferToPerformance.inputStreamLoop   1048576  thrpt   25   2366.391 ±  189.846  ops/s
TransferToPerformance.transferFrom      1048576  thrpt   25   2553.160 ±   43.617  ops/s

TransferToPerformance.inputStreamLoop  10485760  thrpt   25    197.128 ±    8.086  ops/s
TransferToPerformance.transferFrom     10485760  thrpt   25    202.492 ±    6.436  ops/s

These numbers undoubtedly proof that `transferFrom` is *always faster* than `InputStream::transferTo`'s original loop, for *all* tested stream lengths.

> @mkarg I'm asking because FileChannel transferTo is implemented (where possible) on sendfile/equivalent so fast for the file -> socket and file -> file cases. The changes in this PR make use of FileChannel transferFrom so may not be significantly better than the default implementation.

@AlanBateman The existing cases only covered file-to-something, while the current PR optimizes the reverse something-to-file way. As the above numbers proof that (why ever) `transferFrom` is *always faster* than the original loop of `InputStream::transferTo`, I will continue work on this PR ASAP.

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PR: https://git.openjdk.org/jdk/pull/6711