Minimize reference count checks in SlicedByteBuf

Motivation:

SlicedByteBuf did double reference count checking for various bulk operations, which affects performance.

Modifications:

- Add package private method to AbstractByteBuf that can be used to check indexes without check the reference count
- Use this new method in the bulk operation os SlicedByteBuf as the reference count checks take place on the wrapped buffer anyway
- Fix test-case to not try to read data that is out of the bounds of the buffer.

Result:

Better performance on bulk operations when using SlicedByteBuf (and sub-classes)

buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java

@@ -1106,6 +1106,10 @@ public abstract class AbstractByteBuf extends ByteBuf {
 
     protected final void checkIndex(int index, int fieldLength) {
         ensureAccessible();
+        checkIndex0(index, fieldLength);
+    }
+
+    final void checkIndex0(int index, int fieldLength) {
         if (isInvalid(index, fieldLength, capacity())) {
             throw new IndexOutOfBoundsException(String.format(
                     "index: %d, length: %d (expected: range(0, %d))", index, fieldLength, capacity()));

buffer/src/main/java/io/netty/buffer/SlicedByteBuf.java

@@ -148,33 +148,33 @@ public class SlicedByteBuf extends AbstractDerivedByteBuf {
 
     @Override
     public ByteBuf copy(int index, int length) {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         return buffer.copy(idx(index), length);
     }
 
     @Override
     public ByteBuf slice(int index, int length) {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         return buffer.slice(idx(index), length);
     }
 
     @Override
     public ByteBuf getBytes(int index, ByteBuf dst, int dstIndex, int length) {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         buffer.getBytes(idx(index), dst, dstIndex, length);
         return this;
     }
 
     @Override
     public ByteBuf getBytes(int index, byte[] dst, int dstIndex, int length) {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         buffer.getBytes(idx(index), dst, dstIndex, length);
         return this;
     }
 
     @Override
     public ByteBuf getBytes(int index, ByteBuffer dst) {
-        checkIndex(index, dst.remaining());
+        checkIndex0(index, dst.remaining());
         buffer.getBytes(idx(index), dst);
         return this;
     }
@@ -206,47 +206,47 @@ public class SlicedByteBuf extends AbstractDerivedByteBuf {
 
     @Override
     public ByteBuf setBytes(int index, byte[] src, int srcIndex, int length) {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         buffer.setBytes(idx(index), src, srcIndex, length);
         return this;
     }
 
     @Override
     public ByteBuf setBytes(int index, ByteBuf src, int srcIndex, int length) {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         buffer.setBytes(idx(index), src, srcIndex, length);
         return this;
     }
 
     @Override
     public ByteBuf setBytes(int index, ByteBuffer src) {
-        checkIndex(index, src.remaining());
+        checkIndex0(index, src.remaining());
         buffer.setBytes(idx(index), src);
         return this;
     }
 
     @Override
     public ByteBuf getBytes(int index, OutputStream out, int length) throws IOException {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         buffer.getBytes(idx(index), out, length);
         return this;
     }
 
     @Override
     public int getBytes(int index, GatheringByteChannel out, int length) throws IOException {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         return buffer.getBytes(idx(index), out, length);
     }
 
     @Override
     public int setBytes(int index, InputStream in, int length) throws IOException {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         return buffer.setBytes(idx(index), in, length);
     }
 
     @Override
     public int setBytes(int index, ScatteringByteChannel in, int length) throws IOException {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         return buffer.setBytes(idx(index), in, length);
     }
 
@@ -257,24 +257,24 @@ public class SlicedByteBuf extends AbstractDerivedByteBuf {
 
     @Override
     public ByteBuffer nioBuffer(int index, int length) {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         return buffer.nioBuffer(idx(index), length);
     }
 
     @Override
     public ByteBuffer[] nioBuffers(int index, int length) {
-        checkIndex(index, length);
+        checkIndex0(index, length);
         return buffer.nioBuffers(idx(index), length);
     }
 
     @Override
     public ByteBuffer internalNioBuffer(int index, int length) {
-        checkIndex(index, length);
         return nioBuffer(index, length);
     }
 
     @Override
     public int forEachByte(int index, int length, ByteProcessor processor) {
+        checkIndex0(index, length);
         int ret = buffer.forEachByte(idx(index), length, processor);
         if (ret >= adjustment) {
             return ret - adjustment;
@@ -285,6 +285,7 @@ public class SlicedByteBuf extends AbstractDerivedByteBuf {
 
     @Override
     public int forEachByteDesc(int index, int length, ByteProcessor processor) {
+        checkIndex0(index, length);
         int ret = buffer.forEachByteDesc(idx(index), length, processor);
         if (ret >= adjustment) {
             return ret - adjustment;

buffer/src/test/java/io/netty/buffer/AbstractByteBufTest.java

@@ -2043,7 +2043,7 @@ public abstract class AbstractByteBufTest {
 
     @Test(expected = IllegalReferenceCountException.class)
     public void testGetBytesAfterRelease() {
-        releasedBuffer().getBytes(0, releaseLater(buffer()));
+        releasedBuffer().getBytes(0, releaseLater(buffer(8)));
     }
 
     @Test(expected = IllegalReferenceCountException.class)