RFR: 8300236: Use VarHandle access in Data(Input | Output)Stream classes

[Roger Riggs]

On Wed, 18 Jan 2023 16:34:57 GMT, Per Minborg <pminborg at openjdk.org> wrote:

> This PR proposes using a performance optimization using a new supported API for operations similar to those found in `java.io.Bits`

src/java.base/share/classes/java/io/ObjectStreamClass.java line 2486:

> 2484:                 );
> 2485:             } catch (NoSuchMethodException | IllegalAccessException e) {
> 2486:                 throw new InternalError("Can't lookup BigEndian.getXXX", e);

BigEndian -> ByteArrayAccess

src/java.base/share/classes/jdk/internal/util/access/ByteArrayAccess.java line 26:

> 24:  */
> 25: 
> 26: package jdk.internal.util.access;

This is pretty deep; I'd drop the final "access". The package name `jdk.internal.util` is fine.

src/java.base/share/classes/jdk/internal/util/access/ByteArrayAccess.java line 60:

> 58:     /*
> 59:      * Methods for unpacking primitive values from byte arrays starting at
> 60:      * a given offsets.

Typo: "a given offsets".

src/java.base/share/classes/jdk/internal/util/access/ByteArrayAccess.java line 64:

> 62: 
> 63:     /**
> 64:      * Gets a {@code boolean} from the provided {@code array} at the given {@code offset}.

This could use the concise javadoc tag that provides both the first line and @return value.  For example,
`{@return Returns a {@code boolean} from the provided {@code array} at the given {@code offset}}`

src/java.base/share/classes/jdk/internal/util/access/ByteArrayAccess.java line 69:

> 67:      * @param offset where extraction in the array should begin
> 68:      * @return a {@code boolean} from the array
> 69:      * @throws NullPointerException      if the provided {@code array} is {@code null}

With the class level statement about throwing NullPointer, the @throws is not necessary in each method.

src/java.base/share/classes/jdk/internal/util/access/ByteArrayAccess.java line 614:

> 612:     /*
> 613:      * Methods for packing primitive values into byte arrays starting at offset zero.
> 614:      */

Is the only advantage to the zero offset versions in the API. 
Is there any performance difference?

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PR: https://git.openjdk.org/jdk/pull/12076