C++内存泄露排查

内存泄漏是指程序动态分配的内存未能及时释放，导致系统内存逐渐耗尽，最终可能造成程序崩溃或性能下降。在C++中，内存泄漏通常发生在使用new或malloc等分配内存的操作时，但没有正确地使用delete或free来释放这块内存。

在日常开发过程中，为了避免内存泄露，一般都用智能指针去自动管理内存，避免忘记释放。

1.内存泄露动态分析工具——Valgrind

Valgrind是运行在linux上的程序分析工具，它包含很多小工具： memcheck(内存泄露检查工具)等

1.1 安装Valgrind

下载链接：https://valgrind.org/downloads/current.html#current

1.2 Valgrind简单上手和分析

参考:Linux 性能分析valgrind（一）之memcheck使用

命令(以下程序均可以使用此命令)：

valgrind --log-file=valgrind.log --tool=memcheck --leak-check=full --show-leak-kinds=all ./your_program
# --log-file: 报告文件名。如果没有指定，输出到stderr
# --tool=memcheck: 指定Valgrind使用的工具，Valgrind是一个工具集，包括Memcheck、Cachegrind、Callgrind等多个工具，memcheck是缺省项。
# --leak-check: 指定如何报告内存泄漏（memcheck能检查多种内存使用错误，内存泄漏是其中常见的一种），可选值有:
#  	- no 不报告
#  	- summary 显示简要信息，有多少个内存泄漏。summary是缺省值。
#  	- yes 和 full 显示每个泄漏的内存在哪里分配。
# --show-leak-kinds: 指定显示内存泄漏的类型的组合。类型包括definite, indirect, possible,reachable。也可以指定all或none。[缺省值](https://www.zhihu.com/search?q=缺省值&search_source=Entity&hybrid_search_source=Entity&hybrid_search_extra={"sourceType"%3A"article"%2C"sourceId"%3A92074597})是definite,possible。 运行一段时间后想停止进程不要kill掉，需要ctrl + c来结束，输出的log会在上述命令中的valgrind.log中。

程序1（C程序）：使用未初始化的内存

#include <stdio.h>
#include <stdlib.h> 

int main(void)
{
    char *p; 

    char c = *p; 

    printf("\n [%c]\n",c); 

    return 0;
}

Valgrind重点结果信息：使用未初始化的变量，无效的读( 读取没有分配地址空间的区域数据 )

==73374== Use of uninitialised value of size 8
==73374==    at 0x400513: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)
==73374== 
==73374== Invalid read of size 1
==73374==    at 0x400513: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)
==73374==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

程序2（C程序）：在内存被释放后进行读/写

#include <stdio.h>
#include <stdlib.h> 

int main(void)
{
    char *p = malloc(1);
    *p = 'a'; 

    char c = *p; 

    printf("\n [%c]\n",c); 

    free(p);
    c = *p;
    return 0;
}

Valgrind重点结果信息:

==74181== Invalid read of size 1
==74181==    at 0x4005E3: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)
==74181==  Address 0x520a040 is 0 bytes inside a block of size 1 free'd
==74181==    at 0x4C3195F: free (vg_replace_malloc.c:872)
==74181==    by 0x4005DE: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)
==74181==  Block was alloc'd at
==74181==    at 0x4C2F075: malloc (vg_replace_malloc.c:381)
==74181==    by 0x4005A8: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)

程序3（C程序）: 内存泄露

#include <stdio.h>
#include <stdlib.h> 

int main(void)
{
    char *p = malloc(1);
    *p = 'a'; 

    char c = *p; 

    printf("\n [%c]\n",c); 

    return 0;
}

Valgrind重点结果信息：直接泄露

==74814== 1 bytes in 1 blocks are definitely lost in loss record 1 of 1
==74814==    at 0x4C2F075: malloc (vg_replace_malloc.c:381)
==74814==    by 0x400558: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)

程序4（C++程序）：不匹配使用malloc free 和 new delete

#include <stdio.h>
#include <stdlib.h>
#include<iostream> 

int main(void)
{
    char *p = (char*)malloc(1);
    *p = 'a'; 

    char c = *p; 

    printf("\n [%c]\n",c);
    delete p;
    return 0;
}

Valgrind重点结果信息:

==75341==    by 0x400683: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)
==75341==  Address 0x5b20c80 is 0 bytes inside a block of size 1 alloc'd
==75341==    at 0x4C2F075: malloc (vg_replace_malloc.c:381)
==75341==    by 0x400648: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)

程序5（C程序）：两次释放内存

#include <stdio.h>
#include <stdlib.h> 

int main(void)
{
    char *p = (char*)malloc(1);
    *p = 'a'; 

    char c = *p;
    printf("\n [%c]\n",c);
    free(p);
    free(p);
    return 0;
}

Valgrind重点结果信息:

==76126== Invalid free() / delete / delete[] / realloc()
==76126==    at 0x4C3195F: free (vg_replace_malloc.c:872)
==76126==    by 0x4005EA: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)
==76126==  Address 0x520a040 is 0 bytes inside a block of size 1 free'd
==76126==    at 0x4C3195F: free (vg_replace_malloc.c:872)
==76126==    by 0x4005DE: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)
==76126==  Block was alloc'd at
==76126==    at 0x4C2F075: malloc (vg_replace_malloc.c:381)
==76126==    by 0x4005A8: main (in /home/bossdog/3Growup/valgrind/test1/a.exe)

1.3 官方手册

官方手册

2.实际问题分析

struct image_u8
{
    const int32_t width;
    const int32_t height;
    const int32_t stride;

    uint8_t *buf;
};

std::shared_ptr<image_u8> image;

image.reset(new image_u8(
            { frame_out.stFrameInfo.nWidth,
              frame_out.stFrameInfo.nHeight,
              frame_out.stFrameInfo.nWidth,
              new uint8_t[frame_out.stFrameInfo.nWidth * frame_out.stFrameInfo.nHeight * sizeof(uint8_t)] }));
              
image.reset();