RFR: 8306374: (bf) Improve performance of DirectCharBuffer::append(CharSequence[,int,int])

[Brian Burkhalter]

On Wed, 19 Apr 2023 00:29:14 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

> Use `getChars()` to copy characters to an intermediate local `char[]` array and then `putArray()` to copy the chars into the buffer itself.

Appending a sequence of 32768 characters gave the following results:

**Before**

Benchmark                                         Mode  Cnt      Score      Error  Units
CharBufferAppend.appendStringBufferToDirect      thrpt   10  42746.409 ±  436.898  ops/s
CharBufferAppend.appendStringBuilderToDirect     thrpt   10  39007.579 ±  934.130  ops/s
CharBufferAppend.appendStringToDirect            thrpt   10  47820.006 ± 1142.298  ops/s
CharBufferAppend.appendSubStringBufferToDirect   thrpt   10  79981.671 ± 2248.619  ops/s
CharBufferAppend.appendSubStringBuilderToDirect  thrpt   10  82032.943 ±  890.607  ops/s
CharBufferAppend.appendSubStringToDirect         thrpt   10  80458.162 ± 1396.552  ops/s

**After**

Benchmark                                         Mode  Cnt       Score      Error  Units
CharBufferAppend.appendStringBufferToDirect      thrpt   10   41448.953 ± 1176.265  ops/s
CharBufferAppend.appendStringBuilderToDirect     thrpt   10  317041.262 ± 4242.432  ops/s
CharBufferAppend.appendStringToDirect            thrpt   10   47376.189 ±  479.143  ops/s
CharBufferAppend.appendSubStringBufferToDirect   thrpt   10  551124.908 ± 4773.753  ops/s
CharBufferAppend.appendSubStringBuilderToDirect  thrpt   10  616143.045 ± 9020.091  ops/s
CharBufferAppend.appendSubStringToDirect         thrpt   10  605963.509 ± 6222.007  ops/s

Throughput is either effectively unchanged or increased by a factor of 6 to 8.

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PR Comment: https://git.openjdk.org/jdk/pull/13522#issuecomment-1513952917