📄 csdn_文档中心_vc++多线程下内存操作的优化.htm
字号:
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在高负荷下有上千次的上下文切换是正常的，但当计数超过</SPAN><SPAN
lang=EN-US>80,000</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">或</SPAN><SPAN
lang=EN-US>100,000</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">时，说明过多的时间都浪费在线程的切换，稍微计算一下就可以知道，如果每秒有</SPAN><SPAN
lang=EN-US>100,000</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">次线程切换，则每个线程只有</SPAN><SPAN
lang=EN-US>10</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">微秒用于运行，而</SPAN><SPAN
lang=EN-US>NT</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">上的正常的时间片长度约有</SPAN><SPAN
lang=EN-US>12</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">毫秒，是前者的上千倍。</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">图</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的性能图显示了过度的线程切换，而图</SPAN><SPAN
lang=EN-US>2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">显示了同一个进程在同样的环境下，在使用了下面提供的解决方法后的情况。图</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的情况下，系统每秒钟要进行</SPAN><SPAN
lang=EN-US>120,000</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">次线程切换，改进后，每秒钟线程切换的次数减少到</SPAN><SPAN
lang=EN-US>1,000</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">次以下。两张图都是在运行同一个测试程序时截取得，程序中同时有</SPAN><SPAN
lang=EN-US>3</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">个线程同时进行最大为</SPAN><SPAN
lang=EN-US>2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，</SPAN><SPAN
lang=EN-US>048</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">字节的堆的申请，硬件平台是一个双</SPAN><SPAN
lang=EN-US>Pentium II 450</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">机器，有</SPAN><SPAN
lang=EN-US>256MB</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">内存。</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US> <o:p></o:p></SPAN></P>
<P class=MsoNormal><B><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">解决方法</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></B></P>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">本方法要求多线程程序是用</SPAN><SPAN
lang=EN-US>VC++</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">编写的，并且是动态链接到</SPAN><SPAN
lang=EN-US>C</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">运行库的。要求</SPAN><SPAN
lang=EN-US>NT</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">系统所安装的</SPAN><SPAN
lang=EN-US>VC++</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">运行库文件</SPAN><SPAN
lang=EN-US>msvcrt.dll</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的版本号是</SPAN><SPAN
lang=EN-US>6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，所安装的</SPAN><SPAN
lang=EN-US>service pack</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的版本是</SPAN><SPAN
lang=EN-US>5</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">以上。如果程序是用</SPAN><SPAN
lang=EN-US>VC++ v6.0</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">以上版本编译的，即使多线程程序和</SPAN><SPAN
lang=EN-US>libcmt.lib</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是静态链接，本方法也可以使用。</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">当一个</SPAN><SPAN
lang=EN-US>VC++</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">程序运行时，</SPAN><SPAN
lang=EN-US>C</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">运行库被初始化，其中一项工作是确定要使用的堆管理器，</SPAN><SPAN
lang=EN-US>VC++ v6.0</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">运行库既可以使用其自己内部的堆管理函数，也可以直接调用操作系统的堆管理函数（</SPAN><SPAN
lang=EN-US>HeapAlloc()</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">系列的函数），在</SPAN><SPAN
lang=EN-US>__heap_select()</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">函数内部分执行以下三个步骤：</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN>1</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、检查操作系统的版本，如果运行于</SPAN><SPAN
lang=EN-US>NT</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，并且主版本是</SPAN><SPAN
lang=EN-US>5</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">或更高（</SPAN><SPAN
lang=EN-US>Window 2000</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">及以后版本），就使用</SPAN><SPAN
lang=EN-US>HeapAlloc()</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN>2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、查找环境变量</SPAN><SPAN
lang=EN-US>__MSVCRT_HEAP_SELECT</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，如果有，将确定使用哪个堆函数。如果其值是</SPAN><SPAN
lang=EN-US>__GLOBAL_HEAP_SELECTED</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，则会改变所有程序的行为。如果是一个可执行文件的完整路径，还要调用</SPAN><SPAN
lang=EN-US>GetModuleFileName()</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">检查是否该程序存在，至于要选择哪个堆函数还要查看逗号后面的值，</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">表示使用</SPAN><SPAN
lang=EN-US>HeapAlloc()</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，</SPAN><SPAN
lang=EN-US>2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">表示使用</SPAN><SPAN
lang=EN-US>VC++ v5</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的堆函数，</SPAN><SPAN
lang=EN-US>3</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">表示使用</SPAN><SPAN
lang=EN-US>VC++ v6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的堆函数。</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN>3</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、检测可执行文件中的链接程序标志，如果是由</SPAN><SPAN
lang=EN-US>VC++ v6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">或更高的版本创建的，就使用版本</SPAN><SPAN
lang=EN-US>6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的堆函数，否则使用版本</SPAN><SPAN
lang=EN-US>5</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的堆函数。</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">那么如何提高程序的性能？如果是和</SPAN><SPAN
lang=EN-US>msvcrt.dll</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">动态链接的，保证这个</SPAN><SPAN
lang=EN-US>dll</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是</SPAN><SPAN
lang=EN-US>1999</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">年</SPAN><SPAN
lang=EN-US>2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">月以后，并且安装的</SPAN><SPAN
lang=EN-US>service pack</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的版本是</SPAN><SPAN
lang=EN-US>5</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">或更高。如果是静态链接的，保证链接程序的版本号是</SPAN><SPAN
lang=EN-US>6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">或更高，可以用</SPAN><SPAN
lang=EN-US>quickview.exe</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">程序检查这个版本号。要改变所要运行的程序的堆函数的选取，在命令行下键入以下命令：</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal
style="TEXT-INDENT: 21pt; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><SPAN
lang=EN-US>set
__MSVCRT_HEAP_SELECT=__GLOBAL_HEAP_SELECTED,1<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">以后，所有从这个命令行运行的程序，都会继承这个环境变量的设置。这样，在堆操作时都会使用</SPAN><SPAN
lang=EN-US>HeapAlloc()</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。如果让所有的程序都使用这些速度更快的堆操作函数，运行控制面板的“系统”程序，选择“环境”，点取“系统变量”，输入变量名和值，然后按“应用”按钮关闭对话框，重新启动机器。</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">按照微软的说法，可能有一些用</SPAN><SPAN
lang=EN-US>VC++ v6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">以前版本编译程序，使用</SPAN><SPAN
lang=EN-US>VC++ v6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的堆管理器会出现一些问题。如果在进行以上设置后遇到这样的问题，可以用一个批处理文件专门为这个程序把这个设置去掉，例如：</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal
style="TEXT-INDENT: 10.5pt; mso-char-indent-count: 1.0; mso-char-indent-size: 10.5pt"><SPAN
lang=EN-US>set __MSVCRT_HEAP_SELECT=c:\program
files\myapp\myapp.exe,1 c:\bin\buggyapp.exe,2<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US> <o:p></o:p></SPAN></P>
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