RFR: 8314774: Optimize URLEncoder

[Daniel Fuchs]

On Sat, 19 Aug 2023 20:57:27 GMT, Glavo <duke at openjdk.org> wrote:

> I mainly made these optimizations:
> 
> * Avoid allocating `StringBuilder` when there are no characters in the URL that need to be encoded;
> * Implement a fast path for UTF-8.
> 
> In addition to improving performance, these optimizations also reduce temporary objects:
> 
> * It no longer allocates any object when there are no characters in the URL that need to be encoded;
> * The initial size of StringBuilder is larger to avoid expansion as much as possible;
> * For UTF-8, the temporary `CharArrayWriter`, strings and byte arrays are no longer needed.
> 
> The results of the `URLEncodeDecode` benchmark:
> 
> 
> Before:
> Benchmark                       (count)  (maxLength)  (mySeed)  Mode  Cnt  Score   Error  Units
> URLEncodeDecode.testEncodeUTF8     1024         1024         3  avgt   15  5.587 ? 0.010  ms/op
> 
> After:
> Benchmark                       (count)  (maxLength)  (mySeed)  Mode  Cnt  Score   Error  Units
> URLEncodeDecode.testEncodeUTF8     1024         1024         3  avgt   15  3.582 ? 0.054  ms/op
> 
> 
> I also updated the tests to add more test cases.

The fast path that just returns the given string if ASCII-only and no encoding looks simple enough. I don't particularly like the idea of embedding the logic of encoding UTF-8 into that class though, that increases the complexity significantly, and Charset encoders are there for that. Also I don't understand the reason for changing BitSet into a boolean array - that seems gratuitous?

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PR Comment: https://git.openjdk.org/jdk/pull/15354#issuecomment-1690474419