std :: map clear（）在调试器中的性能？ [英] std::map clear() performance in debugger?

问题描述

附带的，微不足道的测试程序测试排空一个简单std :: map的性能。使用MSVC 2008和2010，从命令提示符执行调试构建将需要<30秒，但是在调试器中执行时，差不多3分钟。对clear（）的调用是完全负责的。如果我进入调试器，callstack将始终指向HeapFree。

问题：为什么有巨大差异？我可以以某种方式更改调试堆设置，以便在调试器中执行时会很快？

The attached, trivial, test program tests the performance of emptying a simple std::map. Using MSVC 2008 and 2010, the debug build will take <30seconds when executed from a command prompt but almost 3 minutes when executed from within the debugger. The call to clear() is entirely responsible for the difference. If I break into the debugger the callstack will always point to HeapFree.
Question: Why the huge difference? Can I somehow change debug heap settings so it'll be fast when executed in the debugger?

#include <map>

int
main ( int, char )
{
    std::map< time_t, double > test;
    for ( int i = 0; i < 1000000; ++i )
    {
        test[i] = i / 3.14;
    }
    test.clear();
    return 0;
}

推荐答案

尝试设置环境变量_NO_DEBUG_HEAP = 1在程序的初始环境中。这将禁用Windows的内部调试堆，这可能会使调试内存损坏问题变得更加困难。

Trying setting the environment variable _NO_DEBUG_HEAP=1 in the program's initial environment. This disables Windows' internal debug heap, which might make it harder to debug memory corruption problems.

这个知识库文章提到标志，如果程序在没有该环境变量的调试器中运行，您可以推断默认（低碎片堆）是禁用的。另见博客文章，该文章讨论调试堆如何减缓程序3-5次。

This KB article mentions the flag, and you can infer that the default (low-fragmentation heap) is disabled if the program is run in a debugger without that environment variable. See also this blog post, which discusses how the debug heap can slow down their program by 3-5 times.

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