<div class="__aliyun_email_body_block"><div  style="line-height:1.7;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#0070c0;"><div  style="clear:both;"><span >Should we allow use Unsafe or ByteArrayLittleEndian for trivial byte[] writes in core-libs？</span></div><div  style="clear:both;"><br ><div  style="clear:both;">There is already code that uses ByteArrayLittleEndian to improve performance, such as:</div><div  style="clear:both;">```java</div><div  style="clear:both;">package java.util;</div><div  style="clear:both;"><br ></div><div  style="clear:both;">class UUID {</div><div  style="clear:both;"> <span  style="color:#0070c0;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:.0px;text-transform:none;word-spacing:.0px;white-space:normal;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline;">   <span > </span></span>public String toString() {</div><div  style="clear:both;">     <span  style="color:#0070c0;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:.0px;text-transform:none;word-spacing:.0px;white-space:normal;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline;">   <span > </span></span>// ...</div><div  style="clear:both;">        ByteArrayLittleEndian.setInt(</div><div  style="clear:both;">                buf,</div><div  style="clear:both;">                9,</div><div  style="clear:both;">                HexDigits.packDigits(((int) msb) >> 24, ((int) msb) >> 16));</div><div  style="clear:both;">        // ...</div><div  style="clear:both;"> <span  style="color:#0070c0;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:.0px;text-transform:none;word-spacing:.0px;white-space:normal;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline;">   <span > </span></span>}</div><div  style="clear:both;">}</div><div  style="clear:both;">```</div><div  style="clear:both;"><br ></div><div  style="clear:both;">There are examples of using ByteArrayLittleEndian and then removing it because it caused the JVM to start slowly (we can use Unsafe.putShortUnaligned to solve the problem of slow JVM startup)</div><div  style="clear:both;">```java</div><div  style="clear:both;">package java.lang;</div><div  style="clear:both;">class StringLatin1 {</div><div  style="clear:both;">    private static void writeDigitPair(byte[] buf, int charPos, int value) {</div><div  style="clear:both;">        short pair = DecimalDigits.digitPair(value);</div><div  style="clear:both;">        // UNSAFE.putShortUnaligned(buf, ARRAY_BYTE_BASE_OFFSET + charPos, pair);</div><div  style="clear:both;">        buf[charPos] = (byte)(pair);</div><div  style="clear:both;">        buf[charPos + 1] = (byte)(pair >> 8);</div><div  style="clear:both;">    } </div><div  style="clear:both;">}</div><div  style="clear:both;">```</div><div  style="clear:both;"><br ></div><div  style="clear:both;">Here is an example in the PR Review is disagreeing with the use of ByteArrayLittleEndian</div><div  style="clear:both;"><a  href="https://github.com/openjdk/jdk/pull/15768" target="_blank">https://github.com/openjdk/jdk/pull/15768</a></div><div  style="clear:both;">```java</div><div  style="clear:both;">package java.util;</div><div  style="clear:both;">class HexFormat {</div><div  style="clear:both;"> <span  style="color:#0070c0;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:.0px;text-transform:none;word-spacing:.0px;white-space:normal;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline;">   <span > </span></span>String formatOptDelimiter(byte[] bytes, int fromIndex, int toIndex) {</div><div  style="clear:both;">     // ...</div><div  style="clear:both;">        short pair = HexDigits.digitPair(bytes[fromIndex + i], ucase);</div><div  style="clear:both;">        int pos = i * 2;</div><div  style="clear:both;">        rep[pos] = (byte)pair;</div><div  style="clear:both;">        rep[pos + 1] = (byte)(pair >>> 8);</div><div  style="clear:both;">        // ByteArrayLittleEndian.setShort(rep, pos, pair);</div><div  style="clear:both;"> <span  style="color:#0070c0;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:.0px;text-transform:none;word-spacing:.0px;white-space:normal;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline;">   <span > </span></span>}</div><div  style="clear:both;">}</div><div  style="clear:both;">```</div><div  style="clear:both;"><br ></div><div  style="clear:both;">This is another example of PR Review disagreeing with the use of ByteArrayLittleEndian.</div><div  style="clear:both;"><a  href="https://github.com/openjdk/jdk/pull/15990" target="_blank">https://github.com/openjdk/jdk/pull/15990</a></div><div  style="clear:both;">```java</div><div  style="clear:both;">package java.lang;</div><div  style="clear:both;">class AbstractStringBuilder {</div><div  style="clear:both;"> <span  style="color:#0070c0;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:.0px;text-transform:none;word-spacing:.0px;white-space:normal;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline;">   <span > </span></span>static final class Constants {</div><div  style="clear:both;">        static final int NULL_LATIN1;</div><div  style="clear:both;">        static final int NULL_UTF16;</div><div  style="clear:both;">        static {</div><div  style="clear:both;">            byte[] bytes4 = new byte[] {'t', 'r', 'u', 'e'};</div><div  style="clear:both;">            byte[] bytes8 = new byte[8];</div><div  style="clear:both;">            NULL_LATIN1 = ByteArrayLittleEndian.getInt(bytes4, 0);</div><div  style="clear:both;">            StringLatin1.inflate(bytes4, 0, bytes8, 0, 4);</div><div  style="clear:both;">            NULL_UTF16 = ByteArrayLittleEndian.getLong(bytes8, 0);</div><div  style="clear:both;">        }</div><div  style="clear:both;">    }</div><div  style="clear:both;"><br ></div><div  style="clear:both;">    private AbstractStringBuilder appendNull() {</div><div  style="clear:both;">        ensureCapacityInternal(count + 4);</div><div  style="clear:both;">        int count = this.count;</div><div  style="clear:both;">        byte[] val = this.value;</div><div  style="clear:both;">        if (isLatin1()) {</div><div  style="clear:both;">            ByteArrayLittleEndian.setInt(val, count, Constants.NULL_LATIN1);</div><div  style="clear:both;">        } else {</div><div  style="clear:both;">            ByteArrayLittleEndian.setLong(val, count << 1, Constants.NULL_UTF16);</div><div  style="clear:both;">        }</div><div  style="clear:both;">        this.count = count + 4;</div><div  style="clear:both;">        return this;</div><div  style="clear:both;">    }</div><div  style="clear:both;">}</div><div  style="clear:both;">```</div><div  style="clear:both;"><br ></div><span >In these examples, using Unsafe/ByteArrayLittleEndian significantly improves performance. If JIT automatic optimization is the best solution, but SuperWord Level Parallelism (SLP) does not currently support this optimization, what are our recommendations? <span >What scenarios cannot use Unsafe, and what scenarios cannot use ByteArrayLittleEndian?</span></span></div></div></div>