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

[Freddie Akeroyd - UKRI STFC via Tech-talk <tech-talk at aps.anl.gov>]

Hi Carsten,

 

It looks like caLab on Linux uses dlopen/dlsym to access the libca/libcom functions and avoids explicitly calling dlclose on these libraries – is using the same approach (via LoadLibrary / GetProcAddress) what you mean by wrapper service? I have done similar things in the past  (though not with libca/libcom), feel free to drop me a line if you need any help

 

Regards,

 

Freddie

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Carsten Winkler via Tech-talk
Sent: 18 May 2020 20:03
To: Johnson, Andrew N. <anj at anl.gov>
Cc: EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: Re: BASE 7.0.x@Windows_64 - Channel Access Context in shared library - "ca_context_destroy bug"

 

I guess the best way would be a wrapper service. Unfortunately, I have no experience with this yet.

Am 18.05.2020 um 20:46 schrieb Johnson, Andrew N.:

 

On May 18, 2020, at 1:24 PM, Carsten Winkler <carsten.winkler at helmholtz-berlin.de> wrote:

I am afraid that I have unknowingly used a glitch in the past. My simple example don't work for any EPICS Base version. But up to EPICS Base 3.14.12.8 I could unload the library by using the destructor function of a static object in my interface library.

After compiling CA Lab with EPICS Base 7, LabVIEW now freezes completely when you close a VI with CA Lab modules. This problem is new and very critical.

Could you modify the loader and your interface code so that LabView loads the CA and Com DLLs separately from your interface code? My idea is for you to avoid having to unload the CA and Com DLL's, just release all your channels and destroy your CA context, then unloading and reloading your interface code wouldn’t require reloading them?

 

- Andrew

Am 18.05.2020 um 19:56 schrieb Johnson, Andrew N.:

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

 

-- 

Complexity comes for free, simplicity you have to work for.

 

 

---

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

 

-- 

Complexity comes for free, simplicity you have to work for.

 

 

---

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

This email and any attachments are intended solely for the use of the named recipients. If you are not the intended recipient you must not use, disclose, copy or distribute this email or any of its attachments and should notify the sender immediately and delete this email from your system. UK Research and Innovation (UKRI) has taken every reasonable precaution to minimise risk of this email or any attachments containing viruses or malware but the recipient should carry out its own virus and malware checks before opening the attachments. UKRI does not accept any liability for any losses or damages which the recipient may sustain due to presence of any viruses. Opinions, conclusions or other information in this message and attachments that are not related directly to UKRI business are solely those of the author and do not represent the views of UKRI.