RFR: 4926314: Optimize Reader.read(CharBuffer) [v7]

[Philippe Marschall]

On Wed, 17 Feb 2021 15:37:11 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Philippe Marschall has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Replace c-style array declarations
>>  - Share work buffer between #skip and #read
>
> src/java.base/share/classes/java/io/Reader.java line 221:
> 
>> 219:                     // if the last call to read returned -1 or the number of bytes
>> 220:                     // requested have been read then break
>> 221:                 } while (n >= 0 && remaining > 0);
> 
> The code for case that the char buffer has a backing array looks okay but I'm not sure about the direct buffer/other cases. One concern is that this is a read method, not a transferXXX method so we shouldn't be calling the underlying read several times. You'll see what I mean if you consider the scenario where you read < rem, then read again and the second read blocks or throws. I'l also concerned about "workBuffer" adding more per-stream footprint for cases where skip or read(CB) is used. Objects such as InputStreamReader are already a problem due to the underlying stream decoder.

Right. So you propose to revert the off-heap path to the current master? That would be fine with me. The original bug and my motivation was only about the backing array case, the rest crept in. That would certainly keep the risk and impact lower.

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PR: https://git.openjdk.java.net/jdk/pull/1915