Experimental Physics and
Industrial Control System

Freddie Akeroyd - UKRI STFC via Tech-talk <tech-talk at aps.anl.gov> · Tue, 19 May 2020 17:18:10 +0000

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