base2. Atomic原子操作，Types类型转换

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AtomicIntegerT模板类图

数据成员：

volatile T value_：一个T类型的value_

成员函数：

AtomicIntegerT()：默认构造函数，令value_=0
T get()：返回value_，原子性操作
T getAndAdd(T x)：先获取后加x，返回value_，之后把value_+x，原子性操作
T addAndGet(T x)：先加后获取x，返回value_+x，原子性操作
T incrementAndGet()：自增1，先增后获取，返回value_+1
T decrementAndGet()：自减1，先减后获取，返回value_-1
void add(T x)：先获取后加，返回value_，之后把value_+x
void increment()：自增1，先增后获取，返回value_+1
void decrement()：自减1，先减后获取，返回value_-1
T getAndSet(T newValue)：返回原来的value_，并将其设置为newValue

Atomic.h

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)#ifndef MUDUO_BASE_ATOMIC_H
#define MUDUO_BASE_ATOMIC_H#include <boost/noncopyable.hpp>
#include <stdint.h>namespace muduo
{namespace detail
{
template<typename T>
class AtomicIntegerT : boost::noncopyable
{public:AtomicIntegerT(): value_(0){}//noncopyable的另一种实现方式是把拷贝构造函数和赋值运算符设置成私有// uncomment if you need copying and assignment//// AtomicIntegerT(const AtomicIntegerT& that)//   : value_(that.get())// {}//// AtomicIntegerT& operator=(const AtomicIntegerT& that)// {//   getAndSet(that.get());//   return *this;// }//返回value_，原子性操作T get(){return __sync_val_compare_and_swap(&value_, 0, 0);}//先获取后加，返回value_，之后把value_+x，原子性操作T getAndAdd(T x){return __sync_fetch_and_add(&value_, x);}//先加后获取，返回value_+x，原子性操作T addAndGet(T x){return getAndAdd(x) + x;}//自增1，先增后获取，返回value_+1T incrementAndGet(){return addAndGet(1);}//自减1，先减后获取，返回value_-1T decrementAndGet(){return addAndGet(-1);}//先获取后加，返回value_，之后把value_+xvoid add(T x){getAndAdd(x);}//自增1，先增后获取，返回value_+1void increment(){incrementAndGet();}//自减1，先减后获取，返回value_-1void decrement(){decrementAndGet();}//返回原来的value_，并将其设置为newValueT getAndSet(T newValue){return __sync_lock_test_and_set(&value_, newValue);}private://volatile的作用： 作为指令关键字，确保本条指令不会因编译器的优化而省略，且要求每次直接读值。简单地说就是防止编译器对代码进行优化//当要求使用volatile 声明的变量的值的时候，系统总是重新从它所在的内存读取数据，而不是使用保存在寄存器中的备份。即使它前面的指令刚刚从该处读取过数据。而且读取的数据立刻被保存//多线程编程时很重要volatile T value_;
};
}typedef detail::AtomicIntegerT<int32_t> AtomicInt32;
typedef detail::AtomicIntegerT<int64_t> AtomicInt64;
}#endif  // MUDUO_BASE_ATOMIC_H

Types模板类

两个转换模板：

//隐式转换，将from类型转换成to类型
template<typename To, typename From>
inline To implicit_cast(From const &f) {return f;
}

//向下转换，基类from指针转换为派生类to指针
template<typename To, typename From>    
inline To down_cast(From* f) {                   if (false) {implicit_cast<From*, To>(0);}#if !defined(NDEBUG) && !defined(GOOGLE_PROTOBUF_NO_RTTI)assert(f == NULL || dynamic_cast<To>(f) != NULL); 
#endifreturn static_cast<To>(f);
}}

Types.h

#ifndef MUDUO_BASE_TYPES_H
#define MUDUO_BASE_TYPES_H#include <stdint.h>
#ifdef MUDUO_STD_STRING
#include <string>
#else  // !MUDUO_STD_STRING
#include <ext/vstring.h>
#include <ext/vstring_fwd.h>
#endif///
/// The most common stuffs.
///
namespace muduo
{#ifdef MUDUO_STD_STRING
using std::string;
#else  // !MUDUO_STD_STRING
typedef __gnu_cxx::__sso_string string;
#endif// Taken from google-protobuf stubs/common.h
//
// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// http://code.google.com/p/protobuf/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.// Author: kenton@google.com (Kenton Varda) and others
//
// Contains basic types and utilities used by the rest of the library.//
// Use implicit_cast as a safe version of static_cast or const_cast
// for upcasting in the type hierarchy (i.e. casting a pointer to Foo
// to a pointer to SuperclassOfFoo or casting a pointer to Foo to
// a const pointer to Foo).
// When you use implicit_cast, the compiler checks that the cast is safe.
// Such explicit implicit_casts are necessary in surprisingly many
// situations where C++ demands an exact type match instead of an
// argument type convertable to a target type.
//
// The From type can be inferred, so the preferred syntax for using
// implicit_cast is the same as for static_cast etc.:
//
//   implicit_cast<ToType>(expr)
//
// implicit_cast would have been part of the C++ standard library,
// but the proposal was submitted too late.  It will probably make
// its way into the language in the future.//隐式转换，将from类型转换成to类型
template<typename To, typename From>
inline To implicit_cast(From const &f) {return f;
}// When you upcast (that is, cast a pointer from type Foo to type
// SuperclassOfFoo), it's fine to use implicit_cast<>, since upcasts
// always succeed.  When you downcast (that is, cast a pointer from
// type Foo to type SubclassOfFoo), static_cast<> isn't safe, because
// how do you know the pointer is really of type SubclassOfFoo?  It
// could be a bare Foo, or of type DifferentSubclassOfFoo.  Thus,
// when you downcast, you should use this macro.  In debug mode, we
// use dynamic_cast<> to double-check the downcast is legal (we die
// if it's not).  In normal mode, we do the efficient static_cast<>
// instead.  Thus, it's important to test in debug mode to make sure
// the cast is legal!
//    This is the only place in the code we should use dynamic_cast<>.
// In particular, you SHOULDN'T be using dynamic_cast<> in order to
// do RTTI (eg code like this:
//    if (dynamic_cast<Subclass1>(foo)) HandleASubclass1Object(foo);
//    if (dynamic_cast<Subclass2>(foo)) HandleASubclass2Object(foo);
// You should design the code some other way not to need this.//向下转换，基类from指针转换为派生类to指针
template<typename To, typename From>     // use like this: down_cast<T*>(foo);
inline To down_cast(From* f) {                   // so we only accept pointers// Ensures that To is a sub-type of From *.  This test is here only// for compile-time type checking, and has no overhead in an// optimized build at run-time, as it will be optimized away// completely.if (false) {implicit_cast<From*, To>(0);}#if !defined(NDEBUG) && !defined(GOOGLE_PROTOBUF_NO_RTTI)assert(f == NULL || dynamic_cast<To>(f) != NULL);  // RTTI: debug mode only!
#endifreturn static_cast<To>(f);
}}#endif

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