RFR: 8246739: InputStream.skipNBytes could be implemented more efficiently

[Naoto Sato]

On Thu, 19 Nov 2020 19:29:43 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.

The code looks good. Should we also change the @implSpec, as it specifically describes how it works, i.e., calling no-arg read(), but the new impl calls read() with buffer.

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