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

["Johnson, Andrew N. via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Carsten,

I’m not aware of anything that has actually been added to libCom or libca recently to prevent a completely shutdown; are you saying that you used to be able to unload the CA library and you can’t now? I don’t believe this has ever been possible (which is probably what Michael is also going by), but I might be wrong – please let us know what version of Base you were using if and when you could do that.

If it’s your requirement that has changed we would be happy to advise someone how to work out what needs to be modified to allow the complete unloading that you’re looking for, but I can’t promise that we’ll have core developer effort available to do the actual investigation and any development needed (we all manage our own time and have our own priorities controlled by our employers, so I can’t speak for the others).

- Andrew

On May 18, 2020, at 12:21 PM, Carsten Winkler via Tech-talk <tech-talk at aps.anl.gov> wrote:

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

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