为什么Valgrind说明我的std :: map< T，T&产生内存泄漏？ [英] Why is Valgrind stating that my implementation of std::map<T, T> produces a memory leak?

问题描述

Valgrind正在输出以下内容：

Valgrind is outputting the following:

==14446== 2,976 (176 direct, 2,800 indirect) bytes in 2 blocks are definitely lost in loss record 23 of 33
==14446==    at 0x4C2506C: operator new(unsigned long) (in /usr/lib64/valgrind/amd64-linux/vgpreload_memcheck.so)
==14446==    by 0x41C487: __gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> > >::allocate(unsigned long, void const*) (new_allocator.h:92)
==14446==    by 0x41C4AB: std::_Rb_tree<unsigned, std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn>, std::_Select1st<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> >, std::less<unsigned>, std::allocator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> > >::_M_get_node() (stl_tree.h:357)
==14446==    by 0x41C915: std::_Rb_tree<unsigned, std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn>, std::_Select1st<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> >, std::less<unsigned>, std::allocator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> > >::_M_create_node(std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> const&) (stl_tree.h:366)
==14446==    by 0x5036E9A: std::_Rb_tree<unsigned, std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn>, std::_Select1st<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> >, std::less<unsigned>, std::allocator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> > >::_M_insert_(std::_Rb_tree_node_base const*, std::_Rb_tree_node_base const*, std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> const&) (stl_tree.h:852)
==14446==    by 0x5037027: std::_Rb_tree<unsigned, std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn>, std::_Select1st<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> >, std::less<unsigned>, std::allocator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> > >::_M_insert_unique(std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> const&) (stl_tree.h:1148)
==14446==    by 0x5037227: std::_Rb_tree<unsigned, std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn>, std::_Select1st<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> >, std::less<unsigned>, std::allocator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> > >::_M_insert_unique_(std::_Rb_tree_const_iterator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> >, std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> const&) (stl_tree.h:1188)
==14446==    by 0x50375CD: std::map<unsigned, vimrid::imaging::ImageMatrixColumn, std::less<unsigned>, std::allocator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> > >::insert(std::_Rb_tree_iterator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> >, std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> const&) (stl_map.h:496)
==14446==    by 0x50376DE: std::map<unsigned, vimrid::imaging::ImageMatrixColumn, std::less<unsigned>, std::allocator<std::pair<unsigned const, vimrid::imaging::ImageMatrixColumn> > >::operator[](unsigned const&) (stl_map.h:419)
==14446==    by 0x5036A43: vimrid::imaging::ImageMatrixRow::operator[](unsigned) (ImageMatrixRow.cpp:10)
==14446==    by 0x5034BBB: vimrid::imaging::ImageMatrix::_getRotatedCopy(double, vimrid::imaging::ImageMatrix&) (ImageMatrix.cpp:151)
==14446==    by 0x503350A: vimrid::imaging::processing::ImageFilter& vimrid::imaging::ImageMatrix::GetRotatedCopy<vimrid::imaging::processing::ImageFilter>(double) (ImageMatrix.h:48)

这可能意味着什么？

//ImageMatrixRow.cpp:8-11
ImageMatrixColumn &ImageMatrixRow::operator[](VUInt32 columnIndex)
{
    return columns[columnIndex];
}

//ImageMatrix.cpp:151
target[x][y][0] = source[roundX][roundY][0];

//ImageMatrix.h:48
return *(T*)&_getRotatedCopy(degrees, CopyDimensions());

推荐答案

这可能是因为一个池分配器。从Valgrind常见问题：

It's probably because of a pool allocator. From Valgrind FAQ:

我的程序使用C ++ STL和
字符串类。 Valgrind报告
'仍然可达内存泄漏
涉及这些类在
程序的退出，但应该有
无。

My program uses the C++ STL and string classes. Valgrind reports 'still reachable' memory leaks involving these classes at the exit of the program, but there should be none.

首先：放松，它可能不是
a的错误，而是一个功能。许多
实现的C ++标准
库使用自己的内存池
分配器。内存相当多的
的破坏对象不是
立即释放并返回给
的操作系统，但保存在池中的
以后重新使用。池
在
程序的exit（）处未释放的事实导致Valgrind将此
内存报告为仍可访问。
行为不是在
exit（）释放池，但可以称为
库的bug。

First of all: relax, it's probably not a bug, but a feature. Many implementations of the C++ standard libraries use their own memory pool allocators. Memory for quite a number of destructed objects is not immediately freed and given back to the OS, but kept in the pool(s) for later re-use. The fact that the pools are not freed at the exit() of the program cause Valgrind to report this memory as still reachable. The behaviour not to free pools at the exit() could be called a bug of the library though.

阅读更多：
Valgrind Faq

我可能是错了，因为我很匆忙，我不能分析你的代码。

I may be wrong, as I'm in a hurry and I can't analyse your code.

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