Re: BASE 7.0.x@Windows_64 - Channel Access Context in shared library - "ca_context_destroy bug"

[Carsten Winkler via Tech-talk <tech-talk@aps.anl.gov>]

Hi Michael,

thank you for your answer. This are bad news for our community. Many users are waiting for an EPICS Base upgrade for the Open Source software CaLab (interface beween LabVIEW and EPICS).

Best reganrds
Carsten

Am 18.05.2020 um 18:27 schrieb Michael Davidsaver:

> 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
> >
> >
> > ________________________________
> >
> > Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
> >
> > Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V.
> >
> > Aufsichtsrat: Vorsitzender Dr. Volkmar Dietz, stv. Vorsitzende Dr. Jutta Koch-Unterseher
> > Geschäftsführung: Prof. Dr. Bernd Rech (Sprecher), Prof. Dr. Jan Lüning, Thomas Frederking
> >
> > Sitz Berlin, AG Charlottenburg, 89 HRB 5583
> >
> > Postadresse:
> > Hahn-Meitner-Platz 1
> > D-14109 Berlin

---

Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V.

Aufsichtsrat: Vorsitzender Dr. Volkmar Dietz, stv. Vorsitzende Dr. Jutta Koch-Unterseher
Geschäftsführung: Prof. Dr. Bernd Rech (Sprecher), Prof. Dr. Jan Lüning, Thomas Frederking

Sitz Berlin, AG Charlottenburg, 89 HRB 5583

Postadresse:
Hahn-Meitner-Platz 1
D-14109 Berlin