RFR: 8294696 - BufferedInputStream.transferTo should drain buffer when mark set [v5]

[Markus KARG]

On Mon, 31 Oct 2022 09:52:06 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> > **TL;DR:** Your optimization is now contained in this PR and outperforms the previous code. Nevertheless I plead for Alternative C (double buffering) instead, which is even faster but much simpler.

> You had dismissed this previously so it's useful to have results now to compare. I agree it's much simpler, it can probably use Arrays.copyOfRange too.

Sorry for that. Unless I actually tested, I was unaware how slow Alternative B actually is (in fact it was quite surprising that `Arrays.fill` apparently is implemented in pure Java while `System.arraycopy` is native). So let's go on with Alternative C + `Arrays.copyOfRange`! :-)

> For the results, can you say what the underlying input stream is and what the target output stream is? Also it would be useful to get a baseline. I suspect you have that, it's just not pasted in the table above.

The underlying input stream is `ByteArrayInputStream` wrapping 1 MB byte array, the output stream is `ByteArrayOutputStream`. So the test is not I/O-bound, hence it is clearly focusing on the actual difference Alternatives B/C. Yes, I do have a baseline. It is the original code without *any* safety against poisoning and leaking and the numbers are shown below. I have not published it before, because they are not perfectly comparable: A Windows Update happened after the above runs, and before this run, and my laptop feels to behave somewhat different since then. Sorry for that, but I had no time to repeat the full four hours test suite, and I think the numbers are good enough for our decision pro Alternative C. 

Benchmark                                            (bufSize)  (posPercent)   Mode  Cnt        Score       Error  Units
BufferedInputStreamTransferToPerformance.transferTo       8192             0  thrpt   25     4197,126 ┬▒   627,973  ops/s
BufferedInputStreamTransferToPerformance.transferTo       8192            10  thrpt   25     2615,802 ┬▒   251,678  ops/s
BufferedInputStreamTransferToPerformance.transferTo       8192            90  thrpt   25     3140,941 ┬▒   575,787  ops/s
BufferedInputStreamTransferToPerformance.transferTo       8192           100  thrpt   25     4603,691 ┬▒    12,127  ops/s
BufferedInputStreamTransferToPerformance.transferTo    1048576             0  thrpt   25     3539,737 ┬▒    59,913  ops/s
BufferedInputStreamTransferToPerformance.transferTo    1048576            10  thrpt   25     4790,750 ┬▒    63,090  ops/s
BufferedInputStreamTransferToPerformance.transferTo    1048576            90  thrpt   25    43273,624 ┬▒  1784,369  ops/s
BufferedInputStreamTransferToPerformance.transferTo    1048576           100  thrpt   25  1693553,210 ┬▒ 21249,108  ops/s

-------------

PR: https://git.openjdk.org/jdk/pull/10525