为什么 valgrind 说基本 SDL 程序正在泄漏内存？

Question

这是 SDL 程序：

#include <SDL/SDL.h>

int main(int argc, char** argv){


  SDL_Init(SDL_INIT_VIDEO);
  SDL_Surface* screen = SDL_SetVideoMode(640, 480, 16, SDL_HWSURFACE);
  SDL_Quit();
  return 0;

}

使用以下命令编译：

g++ -o test test.cpp -lSDL

这是 valgrind 的输出：

christian@christian-laptop:~/cpp/tetris$ valgrind --leak-check=full ./test
==3271== Memcheck, a memory error detector
==3271== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==3271== Using Valgrind-3.5.0-Debian and LibVEX; rerun with -h for copyright info
==3271== Command: ./test
==3271== 
==3271== 
==3271== HEAP SUMMARY:
==3271==     in use at exit: 91,097 bytes in 1,258 blocks
==3271==   total heap usage: 14,250 allocs, 12,992 frees, 2,615,177 bytes allocated
==3271== 
==3271== 10 bytes in 2 blocks are definitely lost in loss record 8 of 134
==3271==    at 0x4024C1C: malloc (vg_replace_malloc.c:195)
==3271==    by 0x4946F04: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4945DA1: _XimEncodeLocalICAttr (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4947195: _XimSetICValueData (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x493FDF1: _XimLocalCreateIC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4922478: XCreateIC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x407AA64: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x407BCBB: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x4069C2A: SDL_VideoInit (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x403F9D3: SDL_InitSubSystem (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x403FA36: SDL_Init (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x8048658: main (in /home/christian/cpp/tetris/test)
==3271== 
==3271== 12 bytes in 1 blocks are definitely lost in loss record 12 of 134
==3271==    at 0x4024C1C: malloc (vg_replace_malloc.c:195)
==3271==    by 0x4A3DA8D: ???
==3271==    by 0x4A3D48C: ???
==3271==    by 0x4A3D5A4: ???
==3271==    by 0x4A3DD26: ???
==3271==    by 0x4A38BC5: ???
==3271==    by 0x4A38FCD: ???
==3271==    by 0x40717DD: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x407BDCA: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x4069C2A: SDL_VideoInit (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x403F9D3: SDL_InitSubSystem (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x403FA36: SDL_Init (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271== 
==3271== 112 (8 direct, 104 indirect) bytes in 1 blocks are definitely lost in loss record 102 of 134
==3271==    at 0x4024D12: realloc (vg_replace_malloc.c:476)
==3271==    by 0x492847E: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492976D: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492AA41: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492B1A4: _XlcCreateLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x494B4FA: _XlcDefaultLoader (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4933153: _XOpenLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x49332C2: _XlcCurrentLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4933761: XSetLocaleModifiers (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x407161D: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x407AD8F: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271==    by 0x407BCBB: ??? (in /usr/lib/libSDL-1.2.so.0.11.2)
==3271== 
==3271== 112 (8 direct, 104 indirect) bytes in 1 blocks are definitely lost in loss record 103 of 134
==3271==    at 0x4024D12: realloc (vg_replace_malloc.c:476)
==3271==    by 0x492847E: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492976D: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492AA41: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x492B1A4: _XlcCreateLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x494B4FA: _XlcDefaultLoader (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4933153: _XOpenLC (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x493327D: _XrmInitParseInfo (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x4918F20: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x491AF37: XrmGetStringDatabase (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x48F8459: ??? (in /usr/lib/libX11.so.6.2.0)
==3271==    by 0x48F864E: XGetDefault (in /usr/lib/libX11.so.6.2.0)
==3271== 
==3271== LEAK SUMMARY:
==3271==    definitely lost: 38 bytes in 5 blocks
==3271==    indirectly lost: 208 bytes in 8 blocks
==3271==      possibly lost: 0 bytes in 0 blocks
==3271==    still reachable: 90,851 bytes in 1,245 blocks
==3271==         suppressed: 0 bytes in 0 blocks
==3271== Reachable blocks (those to which a pointer was found) are not shown.
==3271== To see them, rerun with: --leak-check=full --show-reachable=yes
==3271== 
==3271== For counts of detected and suppressed errors, rerun with: -v
==3271== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 93 from 14)

为什么这个基本的 SDL 程序会泄漏内存？

Answer 1

即使对于没有完整 SDL 的基本 OpenGL“hello world”程序，Valgrind 也会在 OpenGL 库深处向我发出类似的警告。这很奇怪，但我假设

• 库实现者知道他们在做什么（可能预先分配了一些他们从不费心释放的小型静态缓冲区），
• 即使他们不这样做，这也是一次性泄漏，将由当程序终止时操作系统，

并且没有因此而失去太多睡眠。

Answer 2

这对于图形 API 库（OpenGL、Vulkan 等）和窗口 API（X11、SDL 等）来说是正常的。最好的选择是使用 valgrind 抑制文件来忽略这些错误。

以下是如何使用 Linux、SDL 和 Linux 来实现这一点。 OpenGL：

假设您正在调试的程序名为“prog.out”（请记住将 prog.out 替换为程序的实际名称），

您可以像这样导出抑制信息：

valgrind --leak-check=full --show-reachable=yes --show-leak-kinds=all --error-limit=no --gen-suppressions=all --log-file=supdata.log ./prog.out

您现在可以从“supdata”中提取抑制信息.log' 使用脚本或手动。您可以使用通配符（“*”、“...”）使抑制更加通用（从而不必在每次更新代码时都更新抑制文件）。

之后，每当您调试程序时，您都会从现在开始包含抑制文件。例如，我在“linux_sdl_gl.sup”下面制作了抑制文件。当我在 Linux 上使用 SDL 和 OpenGL 进行开发时，它非常适合我。它忽略所有 OpenGL、SDL 和 X11 内置错误，以便我可以轻松找到我创建的错误。请随意在您的开发中使用它。

当我调试代码时，我使用以下对 valgrind 的调用。这使我能够找到我的抑制文件可能遗漏的任何新系统错误。

valgrind --gen-suppressions=all --suppressions=./linux_sdl_gl.sup --leak-check=full --show-leak-kinds=all ./prog.out

文件：linux_sdl_gl.sup

# Copyright (c) <'2019'> <'Alrick Grandison'>

# This software is provided 'as-is', without any express or implied
# warranty. In no event will the authors be held liable for any damages
# arising from the use of this software.

# Permission is granted to anyone to use this software for any purpose,
# including commercial applications, and to alter it and redistribute it
# freely, subject to the following restrictions:

# 1. The origin of this software must not be misrepresented; you must not
#    claim that you wrote the original software. If you use this software
#    in a product, an acknowledgment in the product documentation would be
#    appreciated but is not required.
# 2. Altered source versions must be plainly marked as such, and must not be
#    misrepresented as being the original software.
# 3. This notice may not be removed or altered from any source distribution.

{
   opengl_memcpy_addr8
   Memcheck:Addr8
   fun:memcpy@GLIBC*
   obj:/usr/lib/x86_64-linux-gnu/dri/*_dri.so
   ...
}

{
   opengl_memcpy_addr1
   Memcheck:Addr1
   fun:memcpy@GLIBC*
   obj:/usr/lib/x86_64-linux-gnu/dri/*_dri.so
   ...
}

{
   opengl_memset_addr8
   Memcheck:Addr8
   fun:memset
   obj:/usr/lib/x86_64-linux-gnu/dri/*_dri.so
   ...
}

{
   sdl_leak_reachable
   Memcheck:Leak
   match-leak-kinds: reachable
   ...
   fun:SDL_Init_REAL
   ...
}

{
   x11_leak_reachable
   Memcheck:Leak
   match-leak-kinds: reachable
   ...
   obj:/usr/lib/x86_64-linux-gnu/libX11.so.*
   ...
}

{
   sdl_leak_indirect
   Memcheck:Leak
   match-leak-kinds: indirect
   ...
   fun:SDL_Init_REAL
   ...
}

{
  sdl_leak_definite
   Memcheck:Leak
   match-leak-kinds: definite
   ...
   fun:SDL_Init_REAL
   ...
}

# OpenGL Calls DL under the Hood - Taken straight out of Valgrind --gen-suppressions
# Could overlap with non-graphics DL api calls
# But, If you are not using DL directly, then don't worry about this
{
   dl_leak_reachable
   Memcheck:Leak
   match-leak-kinds: reachable
   ...
   fun:dlopen@@GLIBC*
   ...
}

# Same as above but more generic
# Could overlap with non-graphics DL api calls
# But, If you are not using DL directly, then don't worry about this
{
   dl_leak_reachable
   Memcheck:Leak
   match-leak-kinds: reachable
   ...
   fun:_dl_*
   ...
}

{
   x11_leak_indirect
   Memcheck:Leak
   match-leak-kinds: indirect
   ...
   obj:/usr/lib/x86_64-linux-gnu/libX11.so.*
   ...
}

{
   x11_leak_definite
   Memcheck:Leak
   match-leak-kinds: definite
   ...
   obj:/usr/lib/x86_64-linux-gnu/libX11.so.*
   ...
}

{
   x11_leak_possible
   Memcheck:Leak
   match-leak-kinds: possible
   ...
   obj:/usr/lib/x86_64-linux-gnu/libX11.so.*
   ...
}

{
   opengl_leak_reachable
   Memcheck:Leak
   match-leak-kinds: reachable
   ...
   obj:/usr/lib/x86_64-linux-gnu/libGLX.so.*
   ...
}

github：valgrind 抑制代码

Answer 3

您加载的每个 SDL_Surface 都应该在调用 SDL_Quit() 之前释放。

为此，只需使用 SDL_FreeSurface(surfaceName) 来释放在内存上分配的表面。

Answer 4

SDL 的 SDL_TLSCleanup 和 SDL_TLSData 肯定存在内存泄漏问题。

事实上，SDL_TLSCleanup 永远不会被主线程调用。

Answer 5

单例几乎总是标准实现的“泄漏”。不过，这通常是可以的，因为通常您不想卸载执行诸如打印到控制台之类的操作的能力。