Use ByteBuf#isAccessible() in more places (#10506)

Motivation

ByteBuf has an isAccessible method which was introduced as part of ref
counting optimizations but there are some places still doing
accessibility checks by accessing the volatile refCnt() directly.

Modifications

- Have PooledNonRetained(Duplicate|Sliced)ByteBuf#isAccessible() use
their refcount delegate's isAccessible() method
- Add static isAccessible(buf) and ensureAccessible(buf) methods to
ByteBufUtil
(since ByteBuf#isAccessible() is package-private)
- Adjust DefaultByteBufHolder and similar classes to use these methods
rather than access refCnt() directly

Result

- More efficient accessibility checks in more places

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

@@ -33,6 +33,10 @@ public abstract class AbstractDerivedByteBuf extends AbstractByteBuf {
 
     @Override
     final boolean isAccessible() {
+        return isAccessible0();
+    }
+
+    boolean isAccessible0() {
         return unwrap().isAccessible();
     }
 

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

@@ -16,7 +16,6 @@
 
 package io.netty.buffer;
 
-import io.netty.util.ReferenceCounted;
 import io.netty.util.internal.ObjectPool.Handle;
 
 import java.nio.ByteBuffer;
@@ -158,13 +157,18 @@ abstract class AbstractPooledDerivedByteBuf extends AbstractReferenceCountedByte
     }
 
     private static final class PooledNonRetainedDuplicateByteBuf extends UnpooledDuplicatedByteBuf {
-        private final ReferenceCounted referenceCountDelegate;
+        private final ByteBuf referenceCountDelegate;
 
-        PooledNonRetainedDuplicateByteBuf(ReferenceCounted referenceCountDelegate, AbstractByteBuf buffer) {
+        PooledNonRetainedDuplicateByteBuf(ByteBuf referenceCountDelegate, AbstractByteBuf buffer) {
             super(buffer);
             this.referenceCountDelegate = referenceCountDelegate;
         }
 
+        @Override
+        boolean isAccessible0() {
+            return referenceCountDelegate.isAccessible();
+        }
+
         @Override
         int refCnt0() {
             return referenceCountDelegate.refCnt();
@@ -234,14 +238,19 @@ abstract class AbstractPooledDerivedByteBuf extends AbstractReferenceCountedByte
     }
 
     private static final class PooledNonRetainedSlicedByteBuf extends UnpooledSlicedByteBuf {
-        private final ReferenceCounted referenceCountDelegate;
+        private final ByteBuf referenceCountDelegate;
 
-        PooledNonRetainedSlicedByteBuf(ReferenceCounted referenceCountDelegate,
+        PooledNonRetainedSlicedByteBuf(ByteBuf referenceCountDelegate,
                                        AbstractByteBuf buffer, int index, int length) {
             super(buffer, index, length);
             this.referenceCountDelegate = referenceCountDelegate;
         }
 
+        @Override
+        boolean isAccessible0() {
+            return referenceCountDelegate.isAccessible();
+        }
+
         @Override
         int refCnt0() {
             return referenceCountDelegate.refCnt();

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

@@ -18,6 +18,7 @@ package io.netty.buffer;
 import io.netty.util.AsciiString;
 import io.netty.util.ByteProcessor;
 import io.netty.util.CharsetUtil;
+import io.netty.util.IllegalReferenceCountException;
 import io.netty.util.concurrent.FastThreadLocal;
 import io.netty.util.internal.MathUtil;
 import io.netty.util.internal.ObjectPool;
@@ -107,6 +108,24 @@ public final class ByteBufUtil {
             : PlatformDependent.allocateUninitializedArray(minLength);
     }
 
+    /**
+     * @return whether the specified buffer has a nonzero ref count
+     */
+    public static boolean isAccessible(ByteBuf buffer) {
+        return buffer.isAccessible();
+    }
+
+    /**
+     * @throws IllegalReferenceCountException if the buffer has a zero ref count
+     * @return the passed in buffer
+     */
+    public static ByteBuf ensureAccessible(ByteBuf buffer) {
+        if (!buffer.isAccessible()) {
+            throw new IllegalReferenceCountException(buffer.refCnt());
+        }
+        return buffer;
+    }
+
     /**
      * Returns a <a href="http://en.wikipedia.org/wiki/Hex_dump">hex dump</a>
      * of the specified buffer's readable bytes.

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

@@ -17,7 +17,6 @@ package io.netty.buffer;
 
 import static java.util.Objects.requireNonNull;
 
-import io.netty.util.IllegalReferenceCountException;
 import io.netty.util.internal.StringUtil;
 
 /**
@@ -35,10 +34,7 @@ public class DefaultByteBufHolder implements ByteBufHolder {
 
     @Override
     public ByteBuf content() {
-        if (data.refCnt() <= 0) {
-            throw new IllegalReferenceCountException(data.refCnt());
-        }
-        return data;
+        return ByteBufUtil.ensureAccessible(data);
     }
 
     /**

codec-http/src/main/java/io/netty/handler/codec/http/DefaultFullHttpRequest.java

@@ -16,6 +16,7 @@
 package io.netty.handler.codec.http;
 
 import io.netty.buffer.ByteBuf;
+import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.Unpooled;
 import io.netty.util.IllegalReferenceCountException;
 import static java.util.Objects.requireNonNull;
@@ -152,7 +153,7 @@ public class DefaultFullHttpRequest extends DefaultHttpRequest implements FullHt
     public int hashCode() {
         int hash = this.hash;
         if (hash == 0) {
-            if (content().refCnt() != 0) {
+            if (ByteBufUtil.isAccessible(content())) {
                 try {
                     hash = 31 + content().hashCode();
                 } catch (IllegalReferenceCountException ignored) {

codec-http/src/main/java/io/netty/handler/codec/http/DefaultFullHttpResponse.java

@@ -16,6 +16,7 @@
 package io.netty.handler.codec.http;
 
 import io.netty.buffer.ByteBuf;
+import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.Unpooled;
 import io.netty.util.IllegalReferenceCountException;
 
@@ -159,7 +160,7 @@ public class DefaultFullHttpResponse extends DefaultHttpResponse implements Full
     public int hashCode() {
         int hash = this.hash;
         if (hash == 0) {
-            if (content().refCnt() != 0) {
+            if (ByteBufUtil.isAccessible(content())) {
                 try {
                     hash = 31 + content().hashCode();
                 } catch (IllegalReferenceCountException ignored) {

codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2DataFrame.java

@@ -16,8 +16,8 @@
 package io.netty.handler.codec.http2;
 
 import io.netty.buffer.ByteBuf;
+import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.Unpooled;
-import io.netty.util.IllegalReferenceCountException;
 import io.netty.util.internal.StringUtil;
 import io.netty.util.internal.UnstableApi;
 
@@ -104,10 +104,7 @@ public final class DefaultHttp2DataFrame extends AbstractHttp2StreamFrame implem
 
     @Override
     public ByteBuf content() {
-        if (content.refCnt() <= 0) {
-            throw new IllegalReferenceCountException(content.refCnt());
-        }
-        return content;
+        return ByteBufUtil.ensureAccessible(content);
     }
 
     @Override

codec-mqtt/src/main/java/io/netty/handler/codec/mqtt/MqttPublishMessage.java

@@ -18,7 +18,7 @@ package io.netty.handler.codec.mqtt;
 
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufHolder;
-import io.netty.util.IllegalReferenceCountException;
+import io.netty.buffer.ByteBufUtil;
 
 /**
  * See <a href="http://public.dhe.ibm.com/software/dw/webservices/ws-mqtt/mqtt-v3r1.html#publish">MQTTV3.1/publish</a>
@@ -44,11 +44,7 @@ public class MqttPublishMessage extends MqttMessage implements ByteBufHolder {
 
     @Override
     public ByteBuf content() {
-        final ByteBuf data = (ByteBuf) super.payload();
-        if (data.refCnt() <= 0) {
-            throw new IllegalReferenceCountException(data.refCnt());
-        }
-        return data;
+        return ByteBufUtil.ensureAccessible((ByteBuf) super.payload());
     }
 
     @Override