RFR: 8325340: Add ASCII fast-path to Data-/ObjectInputStream.readUTF

[Chen Liang]

On Tue, 6 Feb 2024 16:17:21 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> Adding a fast-path for ASCII-only modified UTF-8 strings deserialied via Data- and ObjectInputStream
> 
> Testing: tier1-3

src/java.base/share/classes/java/io/ObjectInputStream.java line 3688:

> 3686:                         // avoid a redundant scan
> 3687:                         String utf = new String(buf, pos, (int)utflen, StandardCharsets.ISO_8859_1);
> 3688:                         pos += (int)utflen;

Suggestion:

                        String utf = new String(buf, pos, ascii, StandardCharsets.ISO_8859_1);
                        pos += ascii;

Redundant casts

src/java.base/share/classes/java/io/ObjectInputStream.java line 3746:

> 3744:             int avail = Math.min(end - pos, CHAR_BUF_SIZE);
> 3745:             // stop short of last char unless all of utf bytes in buffer
> 3746:             int stop = start + ((utflen > avail) ? avail - 2 : (int) utflen);

Though reading LV instead of getfield is an improvement, we probably prefer to keep this patch cleaner.

src/java.base/share/classes/java/nio/charset/Charset.java line 682:

> 680:                 else
> 681:                     defaultCharset = sun.nio.cs.UTF_8.INSTANCE;
> 682:                 Charset.forName("UTF-8");

Redundant debug code?

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PR Review Comment: https://git.openjdk.org/jdk/pull/17734#discussion_r1480387150
PR Review Comment: https://git.openjdk.org/jdk/pull/17734#discussion_r1480389129
PR Review Comment: https://git.openjdk.org/jdk/pull/17734#discussion_r1480391246