Memory leak on Windows, when unloading FFmpeg dlls

[seveneleven]

I built a dll (VC++, Win32), that uses FFmpeg for video processing and is used by several applications.

Each time this dll is loaded/freed (using Windows API: LoadLibrary/FreeLibrary), it leaks around 20KB (given that, in this way, FFmpeg dlls are also loaded/unloaded):

'Demo.exe' (Win32): Loaded 'C:\Windows\SysWOW64\avcodec-57.dll'. Module was built without symbols.
'Demo.exe' (Win32): Loaded 'C:\Windows\SysWOW64\avutil-55.dll'. Module was built without symbols.
'Demo.exe' (Win32): Loaded 'C:\Windows\SysWOW64\swresample-2.dll'. Module was built without symbols.
'Demo.exe' (Win32): Unloaded 'C:\Windows\SysWOW64\avcodec-57.dll'
'Demo.exe' (Win32): Unloaded 'C:\Windows\SysWOW64\swresample-2.dll'
'Demo.exe' (Win32): Unloaded 'C:\Windows\SysWOW64\avutil-55.dll'

On a Windows 7 Machine, I observed leaks of ~20KB each "load/unload". On Windows 10 it ranges from 4KB to 20KB (16KB at the most).

Except for the latest build, this issue can be reproduced with 3.0.1, 3.0, 2.8.6, 2.8.3.
In 0.8.7 it worked fine.

This is all the 'dll code' to reproduce it.

extern "C" 
{
    #include <libavcodec\avcodec.h>
    #pragma comment(lib, "avcodec.lib")
}

void __stdcall proveIssue()
{
    int v = avcodec_version();
}

Removing the line with avcodec_version would fix it, because no FFmpeg dlls would be linked.

[Carl Eugen Hoyos]

A leak report would need valgrind output (or an equivalent report like DrMemory) but I think this is a duplicate of several tickets including #3194.

[seveneleven]

I don't think this is a duplicate (at least not of #3194): This leak occurs by only loading and unloading FFmpeg dlls during runtime. There is nothing else to do, like calling avcodec_*() functions for example.

Demo.exe loads Demo.dll (LoadLibrary("Demo.dll")), thus loading avcodec-57.dll etc.
When Demo.dll gets freed (FreeLibrary()) immediately thereafter, it will cause the leak.

[Carl Eugen Hoyos]

Then please provide the output of a memory debugger as required for every leak report.

[Carl Eugen Hoyos]

Please reopen this ticket if you can provide the necessary information.