多线程无锁(lock-free) 堆的实现

堆的多线程化处理比较简单，它只有一个指向堆顶的变量需要竞争，因此我们可以很方便的用 cas 操作来完成。

/*
* Copyright (C) 2010  Chen Wang ( China )
* Email: jadedrip@gmail.com
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/
#pragma once
#include "lockfree.hpp"
#if !defined(_MSC_VER) || (_MSC_VER < 1600)
#	define nullptr NULL
#endif
namespace lichc
{
namespace lockfree
{
static_assert(sizeof(void *) == 4, "64-bit code generation is not supported.");
template< typename T >
class queue
{
public:
queue<T>()
{
_head.data=0;
}
void push( const T t )
{
data* n=new data;
n->value=t;
int64 old,x;
do{
old=_head.data;
n->next=reinterpret_cast<data*>(old);
// 高 32 位加一，这是为了处理 ABA 问题；低32位保存下一个对象的指针。
x=( old + 0x100000000LL ) & 0xFFFFFFFF00000000LL | reinterpret_cast<int32>(n);
}while( !atomic_cas( &_head, old, x ) );
}
bool pop( T& v )
{
int64 old,x;
data *olddata;
do{
old=_head.data;
if( (old & 0xFFFFFFFFLL) == 0 ) return false;
olddata=reinterpret_cast<data*>( old );
x=( old + 0x100000000LL ) & 0xFFFFFFFF00000000LL | reinterpret_cast<int32>(olddata->next);
}while( !atomic_cas( &_head, old, x ) );
v=olddata->value;
delete olddata;
return true;
}
private:
struct data
{
data* next;	// Next Node, nullptr for end.
T value;
};
private:
atomic_int64 _head;
};
};
};

代码来自我们正准备开源的 C++ 库，开发代号 lugce。

不明白什么是 lockfree 算法的可以参考我的这篇博文：http://blog.csdn.net/jadedrip/archive/2007/08/08/1731554.aspx