Refactor FastThreadLocal to simplify TLV management

Motivation:

When Netty runs in a managed environment such as web application server,
Netty needs to provide an explicit way to remove the thread-local
variables it created to prevent class loader leaks.

FastThreadLocal uses different execution paths for storing a
thread-local variable depending on the type of the current thread.
It increases the complexity of thread-local removal.

Modifications:

- Moved FastThreadLocal and FastThreadLocalThread out of the internal
  package so that a user can use it.
- FastThreadLocal now keeps track of all thread local variables it has
  initialized, and calling FastThreadLocal.removeAll() will remove all
  thread-local variables of the caller thread.
- Added FastThreadLocal.size() for diagnostics and tests
- Introduce InternalThreadLocalMap which is a mixture of hard-wired
  thread local variable fields and extensible indexed variables
- FastThreadLocal now uses InternalThreadLocalMap to implement a
  thread-local variable.
- Added ThreadDeathWatcher.unwatch() so that PooledByteBufAllocator
  tells it to stop watching when its thread-local cache has been freed
  by FastThreadLocal.removeAll().
- Added FastThreadLocalTest to ensure that removeAll() works
- Added microbenchmark for FastThreadLocal and JDK ThreadLocal
- Upgraded to JMH 0.9

Result:

- A user can remove all thread-local variables Netty created, as long as
  he or she did not exit from the current thread. (Note that there's no
  way to remove a thread-local variable from outside of the thread.)
- FastThreadLocal exposes more useful operations such as isSet() because
  we always implement a thread local variable via InternalThreadLocalMap
  instead of falling back to JDK ThreadLocal.
- FastThreadLocalBenchmark shows that this change improves the
  performance of FastThreadLocal even more.

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

@@ -17,6 +17,10 @@
 package io.netty.buffer;
 
 
+import io.netty.util.ThreadDeathWatcher;
+import io.netty.util.internal.logging.InternalLogger;
+import io.netty.util.internal.logging.InternalLoggerFactory;
+
 import java.nio.ByteBuffer;
 
 /**
@@ -26,6 +30,9 @@
  * 480222803919">Scalable memory allocation using jemalloc</a>.
  */
 final class PoolThreadCache {
+
+    private static final InternalLogger logger = InternalLoggerFactory.getInstance(PoolThreadCache.class);
+
     final PoolArena<byte[]> heapArena;
     final PoolArena<ByteBuffer> directArena;
 
@@ -44,6 +51,14 @@ final class PoolThreadCache {
 
     private int allocations;
 
+    private final Thread thread = Thread.currentThread();
+    private final Runnable freeTask = new Runnable() {
+        @Override
+        public void run() {
+            free0();
+        }
+    };
+
     // TODO: Test if adding padding helps under contention
     //private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
 
@@ -90,6 +105,10 @@ final class PoolThreadCache {
             normalHeapCaches = null;
             numShiftsNormalHeap = -1;
         }
+
+        // The thread-local cache will keep a list of pooled buffers which must be returned to
+        // the pool when the thread is not alive anymore.
+        ThreadDeathWatcher.watch(thread, freeTask);
     }
 
     private static <T> SubPageMemoryRegionCache<T>[] createSubPageCaches(int cacheSize, int numCaches) {
@@ -192,13 +211,22 @@ boolean add(PoolArena<?> area, PoolChunk chunk, long handle, int normCapacity) {
     /**
      *  Should be called if the Thread that uses this cache is about to exist to release resources out of the cache
      */
-    int free() {
-        return free(tinySubPageDirectCaches) +
+    void free() {
+        ThreadDeathWatcher.unwatch(thread, freeTask);
+        free0();
+    }
+
+    private void free0() {
+        int numFreed = free(tinySubPageDirectCaches) +
                 free(smallSubPageDirectCaches) +
                 free(normalDirectCaches) +
                 free(tinySubPageHeapCaches) +
                 free(smallSubPageHeapCaches) +
                 free(normalHeapCaches);
+
+        if (numFreed > 0 && logger.isDebugEnabled()) {
+            logger.debug("Freed {} thread-local buffer(s) from thread: {}", numFreed, thread.getName());
+        }
     }
 
     private static int free(MemoryRegionCache<?>[] caches) {

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

@@ -16,8 +16,7 @@
 
 package io.netty.buffer;
 
-import io.netty.util.ThreadDeathWatcher;
-import io.netty.util.internal.FastThreadLocal;
+import io.netty.util.concurrent.FastThreadLocal;
 import io.netty.util.internal.PlatformDependent;
 import io.netty.util.internal.SystemPropertyUtil;
 import io.netty.util.internal.logging.InternalLogger;
@@ -277,24 +276,14 @@ protected PoolThreadCache initialValue() {
                 directArena = null;
             }
 
-            final PoolThreadCache cache = new PoolThreadCache(
+            return new PoolThreadCache(
                     heapArena, directArena, tinyCacheSize, smallCacheSize, normalCacheSize,
                     DEFAULT_MAX_CACHED_BUFFER_CAPACITY, DEFAULT_CACHE_TRIM_INTERVAL);
+        }
 
-            // The thread-local cache will keep a list of pooled buffers which must be returned to
-            // the pool when the thread is not alive anymore.
-            final Thread thread = Thread.currentThread();
-            ThreadDeathWatcher.watch(thread, new Runnable() {
-                @Override
-                public void run() {
-                    int numFreed = cache.free();
-                    if (logger.isDebugEnabled()) {
-                        logger.debug("Freed {} thread-local buffer(s) from thread: {}", numFreed, thread.getName());
-                    }
-                }
-            });
-
-            return cache;
+        @Override
+        protected void onRemoval(PoolThreadCache value) {
+            value.free();
         }
     }
 

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

@@ -42,7 +42,7 @@ public static String encode(Cookie cookie) {
             throw new NullPointerException("cookie");
         }
 
-        StringBuilder buf = buffer.get();
+        StringBuilder buf = stringBuilder();
         encode(buf, cookie);
         return stripTrailingSeparator(buf);
     }
@@ -52,7 +52,7 @@ public static String encode(Cookie... cookies) {
             throw new NullPointerException("cookies");
         }
 
-        StringBuilder buf = buffer.get();
+        StringBuilder buf = stringBuilder();
         for (Cookie c: cookies) {
             if (c == null) {
                 break;
@@ -68,7 +68,7 @@ public static String encode(Iterable<Cookie> cookies) {
             throw new NullPointerException("cookies");
         }
 
-        StringBuilder buf = buffer.get();
+        StringBuilder buf = stringBuilder();
         for (Cookie c: cookies) {
             if (c == null) {
                 break;

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

@@ -16,23 +16,13 @@
 package io.netty.handler.codec.http;
 
 
-import io.netty.util.internal.FastThreadLocal;
+import io.netty.util.internal.InternalThreadLocalMap;
 
 final class CookieEncoderUtil {
 
-    static final ThreadLocal<StringBuilder> buffer = new FastThreadLocal<StringBuilder>() {
-        @Override
-        public StringBuilder get() {
-            StringBuilder buf = super.get();
-            buf.setLength(0);
-            return buf;
-        }
-
-        @Override
-        protected StringBuilder initialValue() {
-            return new StringBuilder(512);
-        }
-    };
+    static StringBuilder stringBuilder() {
+        return InternalThreadLocalMap.get().stringBuilder();
+    }
 
     static String stripTrailingSeparator(StringBuilder buf) {
         if (buf.length() > 0) {

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

@@ -15,7 +15,7 @@
  */
 package io.netty.handler.codec.http;
 
-import io.netty.util.internal.FastThreadLocal;
+import io.netty.util.concurrent.FastThreadLocal;
 
 import java.text.ParsePosition;
 import java.text.SimpleDateFormat;
@@ -39,7 +39,7 @@ final class HttpHeaderDateFormat extends SimpleDateFormat {
     private final SimpleDateFormat format1 = new HttpHeaderDateFormatObsolete1();
     private final SimpleDateFormat format2 = new HttpHeaderDateFormatObsolete2();
 
-    private static final ThreadLocal<HttpHeaderDateFormat> dateFormatThreadLocal =
+    private static final FastThreadLocal<HttpHeaderDateFormat> dateFormatThreadLocal =
             new FastThreadLocal<HttpHeaderDateFormat>() {
                 @Override
                 protected HttpHeaderDateFormat initialValue() {

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

@@ -47,7 +47,7 @@ public static String encode(Cookie cookie) {
             throw new NullPointerException("cookie");
         }
 
-        StringBuilder buf = buffer.get();
+        StringBuilder buf = stringBuilder();
 
         add(buf, cookie.getName(), cookie.getValue());
 

codec/src/main/java/io/netty/handler/codec/DefaultTextHeaders.java

@@ -16,7 +16,7 @@
 
 package io.netty.handler.codec;
 
-import io.netty.util.internal.FastThreadLocal;
+import io.netty.util.concurrent.FastThreadLocal;
 import io.netty.util.internal.PlatformDependent;
 
 import java.text.DateFormat;
@@ -769,7 +769,7 @@ public void remove() {
     static final class HttpHeaderDateFormat {
 
         private static final ParsePosition parsePos = new ParsePosition(0);
-        private static final ThreadLocal<HttpHeaderDateFormat> dateFormatThreadLocal =
+        private static final FastThreadLocal<HttpHeaderDateFormat> dateFormatThreadLocal =
                 new FastThreadLocal<HttpHeaderDateFormat>() {
                     @Override
                     protected HttpHeaderDateFormat initialValue() {

codec/src/main/java/io/netty/handler/codec/marshalling/ThreadLocalMarshallerProvider.java

@@ -17,7 +17,7 @@
 
 import io.netty.channel.ChannelHandlerContext;
 
-import io.netty.util.internal.FastThreadLocal;
+import io.netty.util.concurrent.FastThreadLocal;
 import org.jboss.marshalling.Marshaller;
 import org.jboss.marshalling.MarshallerFactory;
 import org.jboss.marshalling.MarshallingConfiguration;
@@ -28,7 +28,7 @@
  * many small {@link Object}'s and your actual Thread count is not to big
  */
 public class ThreadLocalMarshallerProvider implements MarshallerProvider {
-    private final ThreadLocal<Marshaller> marshallers = new FastThreadLocal<Marshaller>();
+    private final FastThreadLocal<Marshaller> marshallers = new FastThreadLocal<Marshaller>();
 
     private final MarshallerFactory factory;
     private final MarshallingConfiguration config;

codec/src/main/java/io/netty/handler/codec/marshalling/ThreadLocalUnmarshallerProvider.java

@@ -17,7 +17,7 @@
 
 import io.netty.channel.ChannelHandlerContext;
 
-import io.netty.util.internal.FastThreadLocal;
+import io.netty.util.concurrent.FastThreadLocal;
 import org.jboss.marshalling.MarshallerFactory;
 import org.jboss.marshalling.MarshallingConfiguration;
 import org.jboss.marshalling.Unmarshaller;
@@ -28,7 +28,7 @@
  * many small {@link Object}'s.
  */
 public class ThreadLocalUnmarshallerProvider implements UnmarshallerProvider {
-    private final ThreadLocal<Unmarshaller> unmarshallers = new FastThreadLocal<Unmarshaller>();
+    private final FastThreadLocal<Unmarshaller> unmarshallers = new FastThreadLocal<Unmarshaller>();
 
     private final MarshallerFactory factory;
     private final MarshallingConfiguration config;

common/src/main/java/io/netty/util/CharsetUtil.java

@@ -15,13 +15,12 @@
  */
 package io.netty.util;
 
-import io.netty.util.internal.FastThreadLocal;
+import io.netty.util.internal.InternalThreadLocalMap;
 
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetDecoder;
 import java.nio.charset.CharsetEncoder;
 import java.nio.charset.CodingErrorAction;
-import java.util.IdentityHashMap;
 import java.util.Map;
 
 /**
@@ -62,22 +61,6 @@ public final class CharsetUtil {
      */
     public static final Charset US_ASCII = Charset.forName("US-ASCII");
 
-    private static final ThreadLocal<Map<Charset, CharsetEncoder>> encoders =
-        new FastThreadLocal<Map<Charset, CharsetEncoder>>() {
-            @Override
-            protected Map<Charset, CharsetEncoder> initialValue() {
-                return new IdentityHashMap<Charset, CharsetEncoder>();
-            }
-        };
-
-    private static final ThreadLocal<Map<Charset, CharsetDecoder>> decoders =
-        new FastThreadLocal<Map<Charset, CharsetDecoder>>() {
-            @Override
-            protected Map<Charset, CharsetDecoder> initialValue() {
-                return new IdentityHashMap<Charset, CharsetDecoder>();
-            }
-        };
-
     /**
      * Returns a cached thread-local {@link CharsetEncoder} for the specified
      * <tt>charset</tt>.
@@ -87,7 +70,7 @@ public static CharsetEncoder getEncoder(Charset charset) {
             throw new NullPointerException("charset");
         }
 
-        Map<Charset, CharsetEncoder> map = encoders.get();
+        Map<Charset, CharsetEncoder> map = InternalThreadLocalMap.get().charsetEncoderCache();
         CharsetEncoder e = map.get(charset);
         if (e != null) {
             e.reset();
@@ -112,7 +95,7 @@ public static CharsetDecoder getDecoder(Charset charset) {
             throw new NullPointerException("charset");
         }
 
-        Map<Charset, CharsetDecoder> map = decoders.get();
+        Map<Charset, CharsetDecoder> map = InternalThreadLocalMap.get().charsetDecoderCache();
         CharsetDecoder d = map.get(charset);
         if (d != null) {
             d.reset();

common/src/main/java/io/netty/util/Recycler.java

@@ -16,15 +16,14 @@
 
 package io.netty.util;
 
+import io.netty.util.concurrent.FastThreadLocal;
 import io.netty.util.internal.SystemPropertyUtil;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
 import java.util.IdentityHashMap;
 import java.util.Map;
 
-import io.netty.util.internal.FastThreadLocal;
-
 /**
  * Light-weight object pool based on a thread-local stack.
  *
@@ -56,7 +55,7 @@ public abstract class Recycler<T> {
     }
 
     private final int maxCapacity;
-    private final ThreadLocal<Stack<T>> threadLocal = new FastThreadLocal<Stack<T>>() {
+    private final FastThreadLocal<Stack<T>> threadLocal = new FastThreadLocal<Stack<T>>() {
         @Override
         protected Stack<T> initialValue() {
             return new Stack<T>(Recycler.this, Thread.currentThread(), maxCapacity);
@@ -67,7 +66,7 @@ protected Recycler() {
         this(DEFAULT_MAX_CAPACITY);
     }
 
-    public Recycler(int maxCapacity) {
+    protected Recycler(int maxCapacity) {
         this.maxCapacity = Math.max(0, maxCapacity);
     }