C ++映射性能 - Linux（30秒）和Windows（30分钟）！ [英] C++ map performance - Linux (30 sec) vs Windows (30 mins) !

问题描述

我需要处理文件列表。不应为同一文件重复处理操作。我使用的代码是 -

  using namespace std; 
 
 vector< File *> gInputFileList; //可以包含重复，文件有成员sFilename 
 map< string，File *> gProcessedFileList; // using map to avoid linear search costs 
 
 void processFile（File * pFile）
 {
 File * pProcessedFile = gProcessedFileList [pFile-> sFilename]; 
 if（pProcessedFile！= NULL）
 return; // Already processed 
 
 foo（pFile）; // foo（）是为每个文件执行的操作
 gProcessedFileList [pFile-> sFilename] = pFile; 
} 
 
 void main（）
 {
 size_t n = gInputFileList.size（）; //使用数组语法（迭代器语法也提供相同的性能）
 for（size_t i = 0; i  processFile（gInputFileList [i]）; 
} 
} 
  

代码可以正常工作， p>

我的问题是，当输入大小为1000时，在Windows / Visual Studio 2008 Express上需要30分钟 - 半小时。对于相同的输入，在Linux / gcc上运行只需要40秒！

可能是什么问题？当单独使用时，动作foo（）只需要很短的时间来执行。我应该使用像vector :: reserve为地图吗？

$ b 1.它打开文件
2.将其读入内存
3.关闭文件
4.内存中的文件内容被解析
5.构建令牌列表;我正在使用一个向量。

每当我中断程序时（运行程序时使用1000+个文件输入集）：调用堆栈显示程序在std中间： ：vector add。

解决方案

在Microsoft Visual Studio中，访问标准C ++库以防止多线程问题在Debug构建。这可能导致大的性能命中。例如，我们的完整测试代码在Linux / gcc上运行50分钟，而在Windows VC ++ 2008上需要5个小时。请注意，在使用非调试Visual C ++运行时在发布模式下编译时，此性能命中不存在。

I need to process a list of files. The processing action should not be repeated for the same file. The code I am using for this is -

using namespace std;

vector<File*> gInputFileList; //Can contain duplicates, File has member sFilename
map<string, File*> gProcessedFileList; //Using map to avoid linear search costs

void processFile(File* pFile)
{
    File* pProcessedFile = gProcessedFileList[pFile->sFilename];
    if(pProcessedFile != NULL)
        return; //Already processed

    foo(pFile); //foo() is the action to do for each file
    gProcessedFileList[pFile->sFilename] = pFile;
}

void main()
{
    size_t n= gInputFileList.size(); //Using array syntax (iterator syntax also gives identical performance)
    for(size_t i=0; i<n; i++){
        processFile(gInputFileList[i]);
    }
}

The code works correctly, but...

My problem is that when the input size is 1000, it takes 30 minutes - HALF AN HOUR - on Windows/Visual Studio 2008 Express. For the same input, it takes only 40 seconds to run on Linux/gcc!

What could be the problem? The action foo() takes only a very short time to execute, when used separately. Should I be using something like vector::reserve for the map?

EDIT, EXTRA INFORMATION

What foo() does is: 1. it opens the file 2. reads it into memory 3. closes the file 4. the contents of the file in memory is parsed 5. it builds a list of tokens; I'm using a vector for that.

Whenever I break the program (while running the program with the 1000+ files input set): the call-stack shows that the program is in the middle of a std::vector add.

解决方案

In the Microsoft Visual Studio, there's a global lock when accessing the Standard C++ Library to protect from multi threading issue in Debug builds. This can cause big performance hits. For instance, our full test code runs on Linux/gcc in 50 minutes, whereas it needs 5 hours on Windows VC++2008. Note that this performance hit does not exist when compiling in Release mode, using the non-debug Visual C++ runtime.

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