Mutex, semaphore, fork, threads and other Win32/posix services in WinCC C-scripts.

Hi Fran

I, particularly,never tested this functions in the WinCC, but is possible the use of API of Windowsto use the semaphore, mutex, critical sections, events and others to synchronize threads. You can use theses API functions inside actions scripts writing in CANSI, using #pragma() directive.

But, you know that these functions be used in multi-threadprograms, and when they are used, should be taken very care, because a minimal error can be cause dead locks .

Well, imagine that you really need to use these API, and you create a mutex, then you will save a handle to mutex where? In a external variable of WinCC scope? In a tag?

Imagine that you lost the handle to mutex and don't release him, and you use a WaitForSingleObject(m_hMutex, INFINITE), you will create a dead lock in a system thatcan'tbe locked.

Always that I needed to use this API, I encapsulated her in a DLL and then I called the API by exported functions of DLL. Don't forget that other user will accomplish maintenance in those systems, and mainly, the C instructions in the WinCC will be interpreted, so, the performance of scripts will also be slow. If you make with other thread, you will have an increase of performance.

And today, I try don't use this API. Almost always the WinCC has a other option that can help in the same way.

I hope to have helped,I can trypost a function using mutex, but I never made this.

Hi Fran,

If you use Mutex to synchronize this programs, you can use this:

m_hMutex = CreateMutex( NULL, TRUE, "MyUniqueMutexIdInOS");
if(GetLastError() == ERROR_ALREADY_EXISTS){
//this mutex already has created
}
And use the wait function, in that way:
if (WaitForSingleObject(m_hMutex, 5000) == WAIT_TIMEOUT){
ReleaseMutex(m_hMutex);
CloseHandle(m_hMutex);
}

Well, As I had said, I never tested this inside of scripts of WinCC. I always used this API inside functions of DLLs calls in the scripts of WinCC.

I will try to test its problem in my system.

Tosee the manual of C ANSI for WinCC. See the the link below:
http://support.automation.siemens.com/WW/view/en/1405195, chapter 4 - WinCC C - Course.

The Siemens supplies a tool called ODK, that documents the API of WinCC. Maybe, be better you try to do that you need , calling the API of WinCC, without using Windows API for multithread.

Hi Fran

I tested the Mutex's functions in the WinCC 6.0 SP3, and I didn't find problems. Inclusive, I tested the TIMEOUT situation. In my test, I created a action to running with intervals of 1s, and she don't was locked in any case.

See the sources files of my test. Sorry the zip file of project has 1.8MB.