LabVIEW + C-DLL: Access violation (0xC0000005) at EIP = 0x00000000

Question

Information: LabVIEW: 2019 Version: 19.0.1 (32-bit) Operating system: Windows 64-bit

Labview crashes completely after an indefinite time. I call three functions of the C-DLL. I loop through all the functions of the DLL over and over again. After about 2 minutes to an hour Labview crashes without reason.

Calling of OpenConnection():

Calling of QueryOpenConnectionStatus():

Calling of CloseConnection():

Type definition of TConnectionResult

Follow the given Headerfile.h

#ifndef __epMCOMLib_h_
#define __epMCOMLib_h_
#include <stdint.h>
#include <stddef.h>
#define DLLIMPORT __declspec(dllimport) 
#pragma pack (push,1)


typedef struct {
  uint16_t DLLFailureCode;
  uint8_t ConnectionStatus;
  uint32_t SystemFailureCode;
} TConnectionResult;
                                                                                         
#pragma pack (pop)


#ifdef __cplusplus
extern "C" {
#endif

DLLIMPORT uint16_t __cdecl OpenConnection(uint8_t            PortType, 
                                          char *             PortName, 
                                          uint32_t OnConnectSucces,
                                          uint32_t *         Handle);
                                          
DLLIMPORT void __cdecl QueryOpenConnectionStatus(uint32_t Handle,
                                                 TConnectionResult * Result); 

DLLIMPORT uint16_t __cdecl CloseConnection(uint32_t Handle);

                                                     
#ifdef __cplusplus
} // extern "C"
#endif

#endif //#ifndef __epMCOMLib_h_

The DLL works perfectly. For this I integrated the DLL in Python ,LabWindows/CVI, C++ and Delphi. There is no crash in these programming languages!

Can anyone give me any useful tips on how to further isolate or eliminate the error. Even if a function of the DLL has been executed and the DLL is then closed, it still causes a crash. As if it's still in memory. It feels like looking for a needle in a haystack.

Answer 1

Run the thread on the UI thread instead of any thread!

In the log file of the DLL I could see that the thread is attached and detached. I suspect this is causing a memory violation. Since Labview is shot down by its called DLL.