[RESOLVED] Critical section

[juanpast]

Hi again.

Now I'm trying to write a example of critical sections but it's not work. why?

NOTE: main function only call Inicio function.

#define NTHREADS 500
#define MAXCADENA 10
#define MAXTIMESLEEP 50

CRITICAL_SECTION CriticalSection_Cadena;

void Inicio (void);
char sCadena[MAXCADENA];
int nNumero;

int Aleatorio(int nMin, int nMax) {
	UINT nNumero;	
	rand_s(&nNumero);
	int nRes = (UINT)((double)nNumero / (double) UINT_MAX * (double)nMax) + nMin;	
	return nRes;
}

void WINAPI fx(void) {	
	EnterCriticalSection(&CriticalSection_Cadena);

		char c = Aleatorio(48, 90); // del 48 al 90 las letras
		int nPos = Aleatorio(0, (MAXCADENA-1));	
		sCadena[nPos] = c;	
		nNumero = c;
	
	LeaveCriticalSection(&CriticalSection_Cadena);
}

void Inicio (void) {

	srand(time(NULL));	
	memset(sCadena, '-', sizeof(char) * MAXCADENA);

	void (WINAPI *vfx[NTHREADS])(); // matriz de NTHREADS de punteros a funciones	
	// Creamos las funciones
	for(int i=0;i<NTHREADS;i++) {
		vfx[i] = fx;
	}

	InitializeCriticalSection(&CriticalSection_Cadena);

	HANDLE vhThread[NTHREADS];
	// Abro los hilos
	for(int i=0;i<NTHREADS;i++) {
		vhThread[i] = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)vfx[i], NULL, 0, 0);		
	}

	WaitForMultipleObjects(NTHREADS, vhThread,  TRUE, INFINITE);
	sCadena[MAXCADENA-1] = '\0';	

	for(int i=0;i<NTHREADS;i++) {
		CloseHandle(vhThread[i]);
	}

	DeleteCriticalSection(&CriticalSection_Cadena); 

	MessageBox(NULL, sCadena, "Cadena", MB_OK);	
}

[ninja9578]

Show us the code for EnterCriticalSection / LeaveCriticalSection... Did you write them or did you get them from somewhere? I recommend using one of the more common thread libraries, pthread is the one I think most widely used, but Boost's is more C++ oriented. I do believe that std::thread will start becoming fairly standard in the next few years though. I'm quite sure it's very based on Boost.

[Paul McKenzie]

Hi again.

Now I'm trying to write a example of critical sections but it's not work. why?

Please describe what you mean by "does not work".

Regards,

Paul McKenzie

[Paul McKenzie]

What threading library is this? I recommend using one of the more common ones, pthread is the one I think most widely used, but Boost's is more C++ oriented.

It's Windows. Probably should have posted in the Windows API forum.

Regards,

Paul McKenzie

[juanpast]

I created few threads. Now I create 500 threads and the program crass.

I change the code and use the Critical Section. This is my code now:

#define NTHREADS 500
#define MAXCADENA 10
#define MAXTIMESLEEP 50

CRITICAL_SECTION CriticalSection_Cadena;

void Inicio (void);
char sCadena[MAXCADENA];
int nNumero;
int nHilosEsperan;

inline int Aleatorio(int nMin, int nMax) {
	UINT nNumero;	
	rand_s(&nNumero);
	int nRes = (UINT) ((double)nNumero / (((double) UINT_MAX + nMin ) * (double)nMax) + nMin);
	return nRes;
}

void WINAPI fx(void) {	
	if(TryEnterCriticalSection(&CriticalSection_Cadena) != 0) {		
		char c = Aleatorio(48, 90); // del 48 al 90 las letras
		int nPos = Aleatorio(0, (MAXCADENA-1));	
		sCadena[nPos] = c;	
		nNumero = c;
	} else {
		Sleep(Aleatorio(0,10));
		nHilosEsperan++;
		fx();
	}
	LeaveCriticalSection(&CriticalSection_Cadena);
}

void Inicio (void) {	
	
	srand(time(NULL));	
	memset(sCadena, '-', sizeof(char) * MAXCADENA);

	void (WINAPI *vfx[NTHREADS])(); // matriz de NTHREADS de punteros a funciones	
	// Creamos las funciones
	for(int i=0;i<NTHREADS;i++) {
		vfx[i] = fx;
	}

	nHilosEsperan = 0;

	InitializeCriticalSection(&CriticalSection_Cadena);

	HANDLE vhThread[NTHREADS];
	// Abro los hilos
	for(int i=0;i<NTHREADS;i++) {
		vhThread[i] = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)vfx[i], NULL, 0, 0);		
	}

	WaitForMultipleObjects(NTHREADS, vhThread,  TRUE, INFINITE);
	sCadena[MAXCADENA-1] = '\0';	

	for(int i=0;i<NTHREADS;i++) {
		CloseHandle(vhThread[i]);
	}

	DeleteCriticalSection(&CriticalSection_Cadena); 

	MessageBox(NULL, sCadena, "Cadena", MB_OK);	
}

Is fine the code remarks in bold type?

[nuzzle]

Now I create 500 threads and the program crass.

Do you get a stack overflow?

I would suspect the recursive call to fx within fx. Try and replace it with an equivalent loop.

[juanpast]

No, access violation as i want.

As you suggest I change the code, now is that:

void WINAPI fxCriticalSection(void) {	
	while (TryEnterCriticalSection(&CriticalSection_Cadena) == 0) {		
		Sleep(Aleatorio(0,10));
		nHilosEsperan++;
	}

	char c = Aleatorio(97, 122); // del 97 al 122 las letras
	int nPos = Aleatorio(0, (MAXCADENA-1));	
	sCadena[nPos] = c;	
	nNumero = c;
	
	LeaveCriticalSection(&CriticalSection_Cadena);
}

It works fine.

Thank you for your suggest.

Best regards, Toño.

[nuzzle]

It works fine.

Glad it worked. The bug was probably a stack overflow that manifested itself as an access violation.

The more threads you started the more threads were likely to be refused access to the critical section and the bigger the chance some thread made too many recursive calls causing the stack to overflow.