RFR: 8246739: InputStream.skipNBytes could be implemented more efficiently [v2]

[sergus13]

On Thu, 19 Nov 2020 20:20:17 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Please review this modification of `java.io.InputStream.skipNBytes(long)` to improve its performance when `skip(long)` skips fewer than the requested number of bytes. In the current implementation, `skip(long)` is invoked once and, if not enough bytes have been skipped, then `read()` is invoked for each of the remaining bytes to be skipped. The proposed implementation instead repeatedly invokes `skip(long)` until the requested number of bytes has been skipped, or an error condition is encountered. For cases where `skip(long)` skips fewer bytes than the number requested, the new version was measured to be up to more than one thousand times faster than the old version. When `skip(long)` actually skips the requested number of bytes, the performance difference is insignificant.
>
> Brian Burkhalter has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - 8246739: InputStream.skipNBytes could be implemented more efficiently
>  - 8246739: InputStream.skipNBytes could be implemented more efficiently

src/java.base/share/classes/java/io/InputStream.java line 607:

> 605:                 if (read() < 0) {
> 606:                     throw new EOFException();
> 607:                 }

Shouldn't we decrement "n" in case "read" returns non-negative value?

                if (read() < 0) {
                    throw new EOFException();
                } else {
                    n--;
                }
`

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PR: https://git.openjdk.java.net/jdk/pull/1329