Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Mon, 18 May 2020 19:57:50 -0700

On 5/18/20 10:56 AM, Johnson, Andrew N. wrote:
> 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).

I listed some of the areas which would need to change the last time this topic was raised.

https://epics.anl.gov/tech-talk/2017/msg00371.php

The subsequent addition of epicsThreadMustJoin() would help to safely stop worker threads.
For libCom, the two I can think of right away are the errlog thread and the ipToAsciiProxy
thread.  Likely also the windows specific pllThread (cf. the WIN32 osdTime.cpp).  There
may be other windows specific worker threads I'm not aware of.

Some way of dealing with epicsAtExit() handlers would also be needed.

This doesn't even start on the problem of free()ing global allocations.
Though this may be tolerable.

> - Andrew
> 
> 
> On May 18, 2020, at 12:21 PM, Carsten Winkler via Tech-talk <tech-talk at aps.anl.gov <mailto: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) <http://hz-b.de/calab>.
>>
>> 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.
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System