Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Mon, 18 May 2020 09:27:02 -0700

libca and especially libCom can't be completely shutdown, and therefore
can't be safely unloaded.

On 5/18/20 8:34 AM, Carsten Winkler via Tech-talk wrote:
> Hi,
> 
> for a project I need to load and unload the Channel Access context in a
> shared library. Loading is no problem but unloading. It always fails
> during ca_context_destroy() function.
> 
> Here is my demo code:
> main.cpp (most simple case for a bigger project where it's necessary to
> load and unload different shared libraries at runtime without
> terminating main application)
> ----------------------------------------------------------
> 
> #include <windows.h>
> #include <iostream>
> 
> int main()
> {
>     HINSTANCE hinstLib;
>     BOOL fFreeResult;
>     hinstLib = LoadLibrary(TEXT("myCaLib.dll"));
>     if (hinstLib == NULL) {
>         std::cout << "myCaLib.dll not found" << std::endl;
>         return 1;
>     }
>     std::cout << "library loaded; hit ENTER to unload" << std::endl;
>     getchar();
>     fFreeResult = FreeLibrary(hinstLib);
>     std::cout << "bye" << std::endl;
>     return 0;
> }
> _______________________________________________________________________
> 
> myCaLib.cpp (most simple shared library with no functions except
> creating and releasing the Channel Access context)
> --------------------------------------------------------------
> 
> #include <iostream>
> #include <cadef.h>
> #include <windows.h>
> 
> BOOLEAN WINAPI DllMain(HINSTANCE hDllHandle, DWORD nReason, LPVOID
> Reserved) {
>     switch (nReason)
>     {
>         case DLL_PROCESS_ATTACH: {
>             int32_t iResult =
> ca_context_create(ca_enable_preemptive_callback);
>             if (iResult != ECA_NORMAL) {
>                 std::cout << "Error: Could not create any instance of
> Channel Access." << std::endl;
>                 return 0;
>             }
>             std::cout << "New instance of Channel Access context." <<
> std::endl;
>             std::cout << ca_context_status(ca_current_context(), 1) <<
> std::endl;
>             break;
>         }
>         case DLL_PROCESS_DETACH: {
>             std::cout << "detach process ... " << std::endl;
>             ca_context_destroy();
>             break;
>         }
>     }
>     return 1;
> }
> _______________________________________________________________________
> 
> build at command line at Windows 7 64 bit
> --------------------------------------------------------------
> 
> %comspec% /k "C:\Program Files (x86)\Microsoft Visual
> Studio\2019\Community\VC\Auxiliary\Build\vcvars64.bat"
> 
> set base=C:\base-7.0.x            <== directory of nightly build or
> stable EPICS BASE 7.0 (built with "EPICS_HOST_ARCH=windows-x64")
> cd C:\test_case\                       <== directory of our test sources
> main.cpp and myCaLib.cpp
> 
> cl -nologo -FC -D__STDC__=0 -D_CRT_SECURE_NO_DEPRECATE
> -D_CRT_NONSTDC_NO_DEPRECATE -Ox -GL -Oy- -W3 -MD -EHsc -DEPICS_BUILD_DLL
> -DEPICS_CALL_DLL -I%base%/include/compiler/msvc
> -I%base%/include/os/WIN32 -I%base%/include -c main.cpp myCaLib.cpp
> 
> link -nologo -subsystem:windows -dll -LTCG -incremental:no -opt:ref
> -release -version:7.0 -MACHINE:X64 -libpath:%base%\lib\windows-x64
> -out:myCaLib.dll -implib:myCaLib.lib myCaLib.obj ca.lib Com.lib
> link -nologo -LTCG -incremental:no -opt:ref -release -version:7.0
> -MACHINE:X64 -out:test.exe main.obj
> 
> set path=%base%\bin\windows-x64;%path%
> test.exe
> _______________________________________________________________________
> 
> test.exe will freeze because it hangs on ca_context_destroy()
> 
> I need any solution for this case, please.
> 
> Best regards
> Carsten
> 
> 
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System