pthread problems

[matty3269]

Hey everyone.

I am having a few problems with the pthread functions. I am trying to create a thread class with the following definition:

#ifndef CTHREAD_H_
#define CTHREAD_H_

#include <pthread.h>

class CThread
{
public:
	CThread();
	~CThread();

	//beginThreadExecution - start thread.
	void beginThreadExecution();

	//stopThreadExecution - stop thread.
	void stopThreadExecution();

	//threadEntryPoint - override this function for the thread task:
	virtual void threadEntryPoint();

protected:
	//m_stopRequested - see note above:
	volatile bool m_stopRequested;
private:
	volatile bool m_running;

    //start_threadStatic - Because pthread needs a static entry point,
//we define a static function here that will simply call the derived
	//static thread entry point:
    static void* start_threadStatic(void *obj);

	pthread_t* m_threadHandle;	//the thread handle.

};

#endif /* CTHREAD_H_ */ 

I keep however, getting a segfault with this function:

void CThread::beginThreadExecution()
{
	//start the thread:
	if(m_running == true)
	{
		//don't start twice:
		return;
	}

	//we are now starting the thread:
	m_running = true;
	pthread_create(m_threadHandle, 0,
			&CThread::start_threadStatic, this);
}

The problem is with the pthread_create function, I get the following output from GDB:

Program received signal SIGSEGV, Segmentation fault.
0x00f5dea0 in pthread_create@@GLIBC_2.1 () from /lib/tls/i686/cmov/libpthread.so.0

I've been scratching my head for days, does anyone have any insight?

Cheers,
Matt

[kbw]

Surely:
pthread_create(&m_threadHandle, 0, &CThread::start_threadStatic, this);

where threadHandle is:
pthread_t threadHandle;

[matty3269]

Thanks for the quick reply, your post made me realise that I forgot to allocate memory for the pthread_t object. Just incase anyone is curious the solution was:

CThread::CThread()
{
	//set default vars:
	m_running = false;

	//create a new pthread object:
	m_threadHandle = (pthread_t*)malloc(sizeof(pthread_t));
}

Thanks,
Matt

[kbw]

You don't need to allocate it, you can simply declare it as I have done. It's clearer, simpler and contributes less to memory fragmentation.

[matty3269]

I realise that by not malloc'ing it I don't have to worry about memory fragmentation, however, nearly every call within pthread requests a pointer to a pthread_t struct, therefore I find it much more clearer to just declare a pointer and then malloc that. Rather than using &m_threadHandle everywhere.

[PanGalactic]

That really makes no sense to me. You are using dynamic memory when it is not needed. You are using malloc in a C++ program. You are not checking the return of malloc. You are not initializing the pointer in the member init list. You are not using an auto_ptr, which means you have to free() inside the destructor. Why submit yourself to such a huge bug farm when kbw's method is short, simple and works?

[Galik]

I have to agree that kbw has the better solution.

If your philosophy is to let what can be auto be auto then you are asking for fewer errors.