[Java] Avoid setting buffer reference if same buffer to avoid the write barrier.

Author: mjpt777

build.gradle

@@ -702,7 +702,7 @@ task generateIrCodecs {
  dependsOn 'generateJavaIrCodecs', 'generateCppIrCodecs', 'generateGolangIrCodecs'
 }
 
-task runBenchmarks(type: Exec) {
+task runJavaBenchmarks(type: Exec) {
  commandLine 'java',
  '-Dagrona.disable.bounds.checks=true',
  '-jar', 'sbe-benchmarks/build/libs/sbe-benchmarks.jar',

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -352,7 +352,10 @@ private void generateGroupDecoderClassHeader(
  indent + " final %s parentMessage, final %s buffer)\n" +
  indent + " {\n" +
  indent + " this.parentMessage = parentMessage;\n" +
- indent + " this.buffer = buffer;\n" +
+ indent + " if (buffer != this.buffer)\n" +
+ indent + " {\n" +
+ indent + " this.buffer = buffer;\n" +
+ indent + " }\n" +
  indent + " dimensions.wrap(buffer, parentMessage.limit());\n" +
  indent + " blockLength = (int)dimensions.blockLength();\n" +
  indent + " count = (int)dimensions.numInGroup();\n" +
@@ -444,7 +447,10 @@ private void generateGroupEncoderClassHeader(
  ind + " throw new IllegalArgumentException(\"count outside allowed range: count=\" + count);\n" +
  ind + " }\n\n" +
  ind + " this.parentMessage = parentMessage;\n" +
- ind + " this.buffer = buffer;\n" +
+ ind + " if (buffer != this.buffer)\n" +
+ ind + " {\n" +
+ ind + " this.buffer = buffer;\n" +
+ ind + " }\n" +
  ind + " dimensions.wrap(buffer, parentMessage.limit());\n" +
  ind + " dimensions.blockLength((%5$s)%6$d);\n" +
  ind + " dimensions.numInGroup((%7$s)count);\n" +
@@ -2236,7 +2242,10 @@ private CharSequence generateFixedFlyweightCode(
  " private %3$s buffer;\n\n" +
  " public %1$s wrap(final %3$s buffer, final int offset)\n" +
  " {\n" +
- " this.buffer = buffer;\n" +
+ " if (buffer != this.buffer)\n" +
+ " {\n" +
+ " this.buffer = buffer;\n" +
+ " }\n" +
  " this.offset = offset;\n\n" +
  " return this;\n" +
  " }\n\n" +
@@ -2276,7 +2285,10 @@ private CharSequence generateDecoderFlyweightCode(final String className, final
  " public %1$s wrap(\n" +
  " final %2$s buffer, final int offset, final int actingBlockLength, final int actingVersion)\n" +
  " {\n" +
- " this.buffer = buffer;\n" +
+ " if (buffer != this.buffer)\n" +
+ " {\n" +
+ " this.buffer = buffer;\n" +
+ " }\n" +
  " this.offset = offset;\n" +
  " this.actingBlockLength = actingBlockLength;\n" +
  " this.actingVersion = actingVersion;\n" +
@@ -2381,7 +2393,10 @@ private CharSequence generateEncoderFlyweightCode(final String className, final
  final String wrapMethod = String.format(
  " public %1$s wrap(final %2$s buffer, final int offset)\n" +
  " {\n" +
- " this.buffer = buffer;\n" +
+ " if (buffer != this.buffer)\n" +
+ " {\n" +
+ " this.buffer = buffer;\n" +
+ " }\n" +
  " this.offset = offset;\n" +
  " limit(offset + BLOCK_LENGTH);\n\n" +
  " return this;\n" +