c++ - Valgrind 显示 std::vector<> alloc 的次数超过空闲时间，但没有内存泄漏

Question

代码相当简单:

#include <vector>
int main() {
    std::vector<int> v;
}

然后我用 Valgrind 构建并运行它:

g++ test.cc && valgrind ./a.out
==8511== Memcheck, a memory error detector
==8511== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==8511== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==8511== Command: ./a.out
==8511==
==8511==
==8511== HEAP SUMMARY:
==8511==     in use at exit: 72,704 bytes in 1 blocks
==8511==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==8511==
==8511== LEAK SUMMARY:
==8511==    definitely lost: 0 bytes in 0 blocks
==8511==    indirectly lost: 0 bytes in 0 blocks
==8511==      possibly lost: 0 bytes in 0 blocks
==8511==    still reachable: 72,704 bytes in 1 blocks
==8511==         suppressed: 0 bytes in 0 blocks
==8511== Rerun with --leak-check=full to see details of leaked memory
==8511==
==8511== For counts of detected and suppressed errors, rerun with: -v
==8511== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

问题有两个:

(1) “total heap usage”表示有1个alloc和0个free。我假设 1 alloc 是因为 std::vector 实例需要堆中的内存块。没关系;但为什么它在销毁期间不释放内存？

(2) 而且，如果它没有释放它，为什么“LEAK SUMMARY”中没有内存泄漏？

(3) 对了，每行前面的==8511==是什么意思？ (虽然我可以在手册中查找它。你不必回答这个问题)

谢谢!

Answer 1

报告的内存仍在被 C++ 运行时使用。你不必担心。 Valgrind 的常见问题解答有 an entry关于这个问题:

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.