📄 9_2_2 用户层垃圾回收算法的实现 - 《多任务下的数据结构与算法》 - 免费试读 - book_csdn_net.htm
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*p += 1</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 13.8pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt"> }</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=4 style="LINE-HEIGHT: 13.8pt"><STRONG><SPAN
lang=EN-US>
</SPAN></STRONG><STRONG><SPAN style="FONT-FAMILY: 华康简宋">～</SPAN><SPAN
lang=EN-US>GCPtr()</SPAN></STRONG></P>
<P class=MsoNormal style="LINE-HEIGHT: 13.8pt"><STRONG><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
</SPAN></STRONG><SPAN lang=EN-US style="FONT-SIZE: 9pt">{</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 13.8pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
T *p = m_pAddr</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 13.8pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
INT *p = (INT *)m_pAddr</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">－</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt">1</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
*p</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">－</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt">= 1</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt"> }</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="MARGIN-BOTTOM: 8pt; LINE-HEIGHT: 14pt"><SPAN
lang=EN-US style="FONT-SIZE: 9pt">}</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: 华康简宋">以上编码便是使用</SPAN><SPAN
lang=EN-US>GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">类管理引用计数的一个初步实现，当然这里只是为了演示一下如何管理引用计数，并不是全部功能的实现。具体应用中还有许多操作符需要重载，将在后面进行介绍。</SPAN></P>
<H4 style="MARGIN-LEFT: 0cm"><SPAN lang=EN-US>4. </SPAN><SPAN
style="FONT-FAMILY: 黑体">构造函数和析构函数的说明</SPAN></H4>
<P class=MsoNormal><SPAN style="FONT-FAMILY: 华康简宋">可以看到在</SPAN><SPAN
lang=EN-US>GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">的构造函数中，直接由内存地址定位到存放引用计数的位置，将引用计数加</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN style="FONT-FAMILY: 华康简宋">。</SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 华康简宋; LETTER-SPACING: 0.1pt">析构函数要做的事情也很简单，就是当一个</SPAN><SPAN
lang=EN-US style="LETTER-SPACING: 0.1pt">GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋; LETTER-SPACING: 0.1pt">类型的变量释放时，直接由要释放的内存地址</SPAN><SPAN
lang=EN-US style="LETTER-SPACING: 0.1pt">(</SPAN><SPAN
style="FONT-FAMILY: 华康简宋; LETTER-SPACING: 0.1pt">已经存放到</SPAN><SPAN lang=EN-US
style="LETTER-SPACING: 0.1pt">m_pAddr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋; LETTER-SPACING: 0.1pt">中</SPAN><SPAN lang=EN-US
style="LETTER-SPACING: 0.1pt">)</SPAN><SPAN
style="FONT-FAMILY: 华康简宋; LETTER-SPACING: 0.1pt">定位到存放引用计数的位置，将引用计数减</SPAN><SPAN
lang=EN-US style="LETTER-SPACING: 0.1pt">1</SPAN><SPAN
style="FONT-FAMILY: 华康简宋; LETTER-SPACING: 0.1pt">。</SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 华康简宋">这种方法在修改引用计数时效率非常高，与哈希表相比无需查表等操作。</SPAN></P>
<H4 style="MARGIN-LEFT: 0cm"><SPAN lang=EN-US>5. </SPAN><SPAN
style="FONT-FAMILY: 黑体">需要修改引用计数的情况</SPAN></H4>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 华康简宋">实际上，不仅仅是构造函数和析构函数要修改引用计数，牵涉指针的操作基本上都需要修改引用计数，主要有以下三种情况。</SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US>1) </SPAN><SPAN
style="FONT-FAMILY: 华康简宋">当将新地址赋给</SPAN><SPAN lang=EN-US>GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">时，需要将原来地址的引用计数减</SPAN><SPAN lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">，新的地址的引用计数加</SPAN><SPAN lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">，这时需要重载运算符“</SPAN><SPAN lang=EN-US>=</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">”号。</SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US>2) </SPAN><SPAN
style="FONT-FAMILY: 华康简宋">当将一个</SPAN><SPAN lang=EN-US>GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">赋给另外一个</SPAN><SPAN lang=EN-US>GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">时，需要将等号左边的</SPAN><SPAN lang=EN-US>GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">指向的内存块的引用计数减</SPAN><SPAN lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">，等号右边的</SPAN><SPAN lang=EN-US>GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">指向的内存块的引用计数加</SPAN><SPAN lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">。</SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US>3) </SPAN><SPAN
style="FONT-FAMILY: 华康简宋">当需要对象的副本时，需要调用</SPAN><SPAN
lang=EN-US>GCPtr</SPAN><SPAN
style="FONT-FAMILY: 华康简宋">的拷贝构造函数，如将对象当作参数传递给函数，作为函数的返回值等情况都会调用拷贝构造函数。由于复制的对象是指向相同的地址，而复制对象在释放时要调用析构函数，析构函数将引用计数减</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN style="FONT-FAMILY: 华康简宋">，因此需要在拷贝函数里加</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN style="FONT-FAMILY: 华康简宋">以维持引用计数的平衡。</SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 华康简宋">下面给出这几个操作的编码，由于构造函数和析构函数等在前面已经给出，所以这里省略。</SPAN></P>
<P class=4><SPAN lang=EN-US>template <class T> class <STRONG>GCPtr
</STRONG>{</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">public</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">：</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt"> T
*m_pAddr</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt"> /* </SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">用来记住定义的指针地址便于析构函数使用</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt"> */</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">public</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">：</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt"> /*
</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">拷贝构造函数</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt"> */</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
</SPAN><STRONG><SPAN lang=EN-US style="FONT-SIZE: 9pt">GCPtr(const GCPtr
&gcPtr)</SPAN></STRONG></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><STRONG><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
</SPAN></STRONG><SPAN lang=EN-US style="FONT-SIZE: 9pt">{</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
INT *p = (INT *)gcPtr.m_pAddr</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">－</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt">1</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
*p += 1</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
m_pAddr = gcPtr.m_pAddr</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt"> }</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><STRONG><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
</SPAN></STRONG><STRONG><SPAN lang=EN-US style="FONT-SIZE: 9pt">T *operator=(T
*t) </SPAN></STRONG></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><STRONG><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
</SPAN></STRONG><SPAN lang=EN-US style="FONT-SIZE: 9pt">{</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
/* </SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">将原来指向的内存引用计数减</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt">1 */</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
INT *p = (INT *)m_pAddr</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">－</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt">1</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
*p</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">－</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt">= 1</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
m_pAddr = t</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
/* </SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">将新指向的内存的引用计数加</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt">1 */</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
p = (INT *)t</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">－</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt">1</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
*p += 1</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
return t</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt"> }</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><STRONG><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
</SPAN></STRONG><STRONG><SPAN lang=EN-US style="FONT-SIZE: 9pt">GCPtr &
operator = (GCPtr &r) </SPAN></STRONG></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><STRONG><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
</SPAN></STRONG><SPAN lang=EN-US style="FONT-SIZE: 9pt">{ </SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
/* </SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">将原来指向的内存引用计数减</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt">1 */</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
INT *p = (INT *)m_pAddr</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">－</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt">1</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
<P class=MsoNormal style="LINE-HEIGHT: 14pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt">
*p</SPAN><SPAN style="FONT-SIZE: 9pt; FONT-FAMILY: 华康简宋">－</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt">= 1</SPAN><SPAN
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体">；</SPAN></P>
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