New threadLocal provides more performance. (#1745)

* SerializerFactory 获取Serializer时，锁住整个hashmap，导致整个过程被block

* 单元测试。保证一个class只有一个serializer和deserializer。单线程和多线程测试

* 增加线程数 50 模拟多个线程来获取serializer和deserializer

* 当cores线程数全都使用的情况下，默认线程池会把任务放入到队列中。队列满则再创建线程（总数不会超过Max线程数）
增强线程池：在请求量阶段性出现高峰时使用
特性：cores线程全部使用的情况下，优先创建线程（总数不会超过max），当max个线程全都在忙的情况下，才将任务放入队列。请求量下降时，线程池会自动维持cores个线程，多余的线程退出。

* 当cores线程数全都使用的情况下，默认线程池会把任务放入到队列中。队列满则再创建线程（总数不会超过Max线程数）
增强线程池：在请求量阶段性出现高峰时使用
特性：cores线程全部使用的情况下，优先创建线程（总数不会超过max），当max个线程全都在忙的情况下，才将任务放入队列。请求量下降时，线程池会自动维持cores个线程，多余的线程退出。

* 补全单元测试，测试扩展是否生效

* 错误命名

* 增加@OverRide注解
long 初始化赋值时，小写l改为大写L防止误读

* 修复单元测试

* remove enhanced

* remove enhanced

* Faster ThreadLocal impl in internal use
* Used in RpcContext`s LOCAL field.
* Faster get than the traditional ThreadLocal

* add License

* fix ci failed

* fix ci failed

* fix ci failed

* fix ci failed

* fix ci failed

* remove author info

* fix destroy method

* fix bug at method size.

dubbo-common/src/main/java/com/alibaba/dubbo/common/threadlocal/InternalThread.java

@@ -0,0 +1,73 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.alibaba.dubbo.common.threadlocal;
+
+/**
+ * InternalThread
+ */
+public class InternalThread extends Thread {
+
+    private InternalThreadLocalMap threadLocalMap;
+
+    public InternalThread() {
+    }
+
+    public InternalThread(Runnable target) {
+        super(target);
+    }
+
+    public InternalThread(ThreadGroup group, Runnable target) {
+        super(group, target);
+    }
+
+    public InternalThread(String name) {
+        super(name);
+    }
+
+    public InternalThread(ThreadGroup group, String name) {
+        super(group, name);
+    }
+
+    public InternalThread(Runnable target, String name) {
+        super(target, name);
+    }
+
+    public InternalThread(ThreadGroup group, Runnable target, String name) {
+        super(group, target, name);
+    }
+
+    public InternalThread(ThreadGroup group, Runnable target, String name, long stackSize) {
+        super(group, target, name, stackSize);
+    }
+
+    /**
+     * Returns the internal data structure that keeps the threadLocal variables bound to this thread.
+     * Note that this method is for internal use only, and thus is subject to change at any time.
+     */
+    public final InternalThreadLocalMap threadLocalMap() {
+        return threadLocalMap;
+    }
+
+    /**
+     * Sets the internal data structure that keeps the threadLocal variables bound to this thread.
+     * Note that this method is for internal use only, and thus is subject to change at any time.
+     */
+    public final void setThreadLocalMap(InternalThreadLocalMap threadLocalMap) {
+        this.threadLocalMap = threadLocalMap;
+    }
+}

dubbo-common/src/main/java/com/alibaba/dubbo/common/threadlocal/InternalThreadLocal.java

@@ -0,0 +1,197 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.alibaba.dubbo.common.threadlocal;
+
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.Set;
+
+/**
+ * InternalThreadLocal
+ * A special variant of {@link ThreadLocal} that yields higher access performance when accessed from a
+ * {@link InternalThread}.
+ * <p></p>
+ * Internally, a {@link InternalThread} uses a constant index in an array, instead of using hash code and hash table,
+ * to look for a variable.  Although seemingly very subtle, it yields slight performance advantage over using a hash
+ * table, and it is useful when accessed frequently.
+ * <p></p>
+ * This design is learning from {@see io.netty.util.concurrent.FastThreadLocal} which is in Netty.
+ */
+public class InternalThreadLocal<V> {
+
+    private static final int variablesToRemoveIndex = InternalThreadLocalMap.nextVariableIndex();
+
+    private final int index;
+
+    public InternalThreadLocal() {
+        index = InternalThreadLocalMap.nextVariableIndex();
+    }
+
+    /**
+     * Removes all {@link InternalThreadLocal} variables bound to the current thread.  This operation is useful when you
+     * are in a container environment, and you don't want to leave the thread local variables in the threads you do not
+     * manage.
+     */
+    @SuppressWarnings("unchecked")
+    public static void removeAll() {
+        InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.getIfSet();
+        if (threadLocalMap == null) {
+            return;
+        }
+
+        try {
+            Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex);
+            if (v != null && v != InternalThreadLocalMap.UNSET) {
+                Set<InternalThreadLocal<?>> variablesToRemove = (Set<InternalThreadLocal<?>>) v;
+                for (InternalThreadLocal<?> tlv : variablesToRemove) {
+                    tlv.remove(threadLocalMap);
+                }
+            }
+        } finally {
+            InternalThreadLocalMap.remove();
+        }
+    }
+
+    /**
+     * Returns the number of thread local variables bound to the current thread.
+     */
+    public static int size() {
+        InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.getIfSet();
+        if (threadLocalMap == null) {
+            return 0;
+        } else {
+            return threadLocalMap.size();
+        }
+    }
+
+    public static void destroy() {
+        InternalThreadLocalMap.destroy();
+    }
+
+    @SuppressWarnings("unchecked")
+    private static void addToVariablesToRemove(InternalThreadLocalMap threadLocalMap, InternalThreadLocal<?> variable) {
+        Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex);
+        Set<InternalThreadLocal<?>> variablesToRemove;
+        if (v == InternalThreadLocalMap.UNSET || v == null) {
+            variablesToRemove = Collections.newSetFromMap(new IdentityHashMap<InternalThreadLocal<?>, Boolean>());
+            threadLocalMap.setIndexedVariable(variablesToRemoveIndex, variablesToRemove);
+        } else {
+            variablesToRemove = (Set<InternalThreadLocal<?>>) v;
+        }
+
+        variablesToRemove.add(variable);
+    }
+
+    @SuppressWarnings("unchecked")
+    private static void removeFromVariablesToRemove(InternalThreadLocalMap threadLocalMap, InternalThreadLocal<?> variable) {
+
+        Object v = threadLocalMap.indexedVariable(variablesToRemoveIndex);
+
+        if (v == InternalThreadLocalMap.UNSET || v == null) {
+            return;
+        }
+
+        Set<InternalThreadLocal<?>> variablesToRemove = (Set<InternalThreadLocal<?>>) v;
+        variablesToRemove.remove(variable);
+    }
+
+    /**
+     * Returns the current value for the current thread
+     */
+    @SuppressWarnings("unchecked")
+    public final V get() {
+        InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.get();
+        Object v = threadLocalMap.indexedVariable(index);
+        if (v != InternalThreadLocalMap.UNSET) {
+            return (V) v;
+        }
+
+        return initialize(threadLocalMap);
+    }
+
+    private V initialize(InternalThreadLocalMap threadLocalMap) {
+        V v = null;
+        try {
+            v = initialValue();
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+
+        threadLocalMap.setIndexedVariable(index, v);
+        addToVariablesToRemove(threadLocalMap, this);
+        return v;
+    }
+
+    /**
+     * Sets the value for the current thread.
+     */
+    public final void set(V value) {
+        if (value == null || value == InternalThreadLocalMap.UNSET) {
+            remove();
+        } else {
+            InternalThreadLocalMap threadLocalMap = InternalThreadLocalMap.get();
+            if (threadLocalMap.setIndexedVariable(index, value)) {
+                addToVariablesToRemove(threadLocalMap, this);
+            }
+        }
+    }
+
+    /**
+     * Sets the value to uninitialized; a proceeding call to get() will trigger a call to initialValue().
+     */
+    @SuppressWarnings("unchecked")
+    public final void remove() {
+        remove(InternalThreadLocalMap.getIfSet());
+    }
+
+    /**
+     * Sets the value to uninitialized for the specified thread local map;
+     * a proceeding call to get() will trigger a call to initialValue().
+     * The specified thread local map must be for the current thread.
+     */
+    @SuppressWarnings("unchecked")
+    public final void remove(InternalThreadLocalMap threadLocalMap) {
+        if (threadLocalMap == null) {
+            return;
+        }
+
+        Object v = threadLocalMap.removeIndexedVariable(index);
+        removeFromVariablesToRemove(threadLocalMap, this);
+
+        if (v != InternalThreadLocalMap.UNSET) {
+            try {
+                onRemoval((V) v);
+            } catch (Exception e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+
+    /**
+     * Returns the initial value for this thread-local variable.
+     */
+    protected V initialValue() throws Exception {
+        return null;
+    }
+
+    /**
+     * Invoked when this thread local variable is removed by {@link #remove()}.
+     */
+    protected void onRemoval(@SuppressWarnings("unused") V value) throws Exception {
+    }
+}