RFR: 8339699: Optimize DataOutputStream writeUTF [v3]

[Chen Liang]

On Sat, 7 Sep 2024 08:51:25 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> PR #20772 introduced an optimization for writeUTF, which can also be used in DataOutputStream::writeUTF.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   reduce JDKUTF#utflen codeSize

src/java.base/share/classes/java/io/ObjectOutputStream.java line 2014:

> 2012:         }
> 2013: 
> 2014:         void writeUTF(String str, int stroff) throws IOException {

Can we move this to be near `writeUTFInternal` and make this `private` as they are closely related? This should also be renamed to indicate this is internal, like `writeMoreUtf` to avoid misuse.

src/java.base/share/classes/jdk/internal/classfile/impl/BufWriterImpl.java line 182:

> 180: 
> 181:         for (int i = countNonZeroAscii; i < strlen;) {
> 182:             offset = JDKUTF.putChar(elems, offset, str.charAt(i++));

Can we put this `++` in for loop instead of the statement here?

src/java.base/share/classes/jdk/internal/util/JDKUTF.java line 35:

> 33:  * @since 24
> 34:  */
> 35: public abstract class JDKUTF {

Can we name this class `ModifiedUtf`? `JDKUTF` looks like a constant field name, and this format is part of Java Platform instead of just JDK.

src/java.base/share/classes/jdk/internal/util/JDKUTF.java line 37:

> 35: public abstract class JDKUTF {
> 36:     @ForceInline
> 37:     public static int putChar(byte[] buf, int offset, char c) {

Do you think we can just move the loop here, like:

public static int putChars(byte[] buf, int offset, String str, int strStart, int strEnd) {
    for (int i = strStart; i < strEnd; i++) {
        offset = putChar(buf, offset, str.charAt(i);
    }
}

We can even unroll putChar in the loop.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/20886#discussion_r1759191218
PR Review Comment: https://git.openjdk.org/jdk/pull/20886#discussion_r1759175406
PR Review Comment: https://git.openjdk.org/jdk/pull/20886#discussion_r1759172395
PR Review Comment: https://git.openjdk.org/jdk/pull/20886#discussion_r1759205885