Segmentation Fault or compilation error?

[Jacob Ensien]

Hi, i have a very weird fatal exception happening very rarely on my application (compiled under gcc - Ubuntu linux)

it seems that this this function :

bool GetConnect( ) {return m_Connected;}

causes a Segmentation Fault sometimes (not all the times)

No the instance of the class is not deleted when i call that function.
I tried declaring m_Connected as volatile bool m_Connected but still the error happens.
several different threads also access the function that calls this function.

bool CPDC :: CBoolExpr(Clients *client)
{
	if(!client)
	{
		return false;
	}
	
	if(client->m_Deleting) // before we delete our instance of Clients* we set this flag. the instance is deleted 240 seconds later.
	{
		
		return false;
	}
	
	if( !client->m_Socket )
	{
	    return false;
	}
	
	cout << "CBE4" << endl;
	if( !client->m_Socket->GetConnected() )
	{
		return false;
	}

	cout << "CBE5" << endl;
	if(client->m_Socket->HasError() )
	{
		return false;
	}

	cout << "CBEE" << endl;
	return true;
}

it always crashes when it outputs CBE4.
to make sure that another thread doesnt crash the application i also tried creating the other threads in completely different timings. It crashes every time on the same line. Although it makes no sense at all..

Did i miss anything?

[strongdrink]

Try to set up an environment that ALWAYS crashes where the problem is, and then run it through GDB.
(If you haven't used gdb, here is a basic run through)

compile your code in debug mode

in the console

gdb PROGRAM_NAME
...
(gdb) run

This will run your program... keep running it until it gives a segmentation fault.

When there is a segfault.. run

backtrace

This will help you track whether it's your code or a bad version of stdlib

[kbw]

If you can set up an environment where is ALWAYS crashes, you're already 75% of the way there.

You seem to have an interesting shut down mechanism. That client Deleting business looks very odd. Can I assume that you have a number of race conditions within the app that have been causing other crashes and you've taken such measures to "fix" them?

[Jacob Ensien]

the application crashes within 24 hours.

it takes 1 hour to 24 hours (depends on server traffic)

			CTCPSocket *NewSocket = pdcc->m_CTCPS->Accept( (fd_set *)&fd );

			if( NewSocket )
			{
				NewSocket->SetNoDelay(true);
				Clients *client = new Clients(NewSocket, pdcc);
				client->m_Identified = false;
				client->m_Chat = pdcc->m_DefaultChat;
				CONSOLE_Print("[SERVER] New client has connected to the server [ " + NewSocket->GetIPString( ) + "].");
				m_Clients.push_back(client);
			}

client connects to the server...

	for(vector<Clients*> :: iterator i = m_Clients.begin( ); i != m_Clients.end( );)
	{
		if( (*i)->m_Socket && (*i)->m_Socket->GetConnected( ) && !(*i)->m_Socket->HasError( ) )
		{
			(*i)->m_Socket->SetFD(&fd, &send_fd, &nfds);
			nfds++;
			i++;
		}
		else
		{
			cout << "[PROXY] A client connection was lost." << endl;
			CleanUpUser((*i));
			i = m_Clients.erase( i );
		}
	}

client connection lost

void CPDC :: CleanUpUser(Clients *client)
{
	client->m_DeleteTime = GetTime();
	client->m_Deleting = true;
	m_ClientsDeleting.push_back(client);

}

dereferrencing the instance safely later

	for(vector<Clients*> :: iterator i = m_ClientsDeleting.begin( ); i != m_ClientsDeleting.end( ); )
	{
		if( (*i) )
		{
			if( GetTime() - (*i)->m_DeleteTime >= 240 )
			{
				delete *i;
				i = m_ClientsDeleting.erase( i );
			}
			else
				i++;
			}
		else
			i = m_ClientsDeleting.erase( i );
	}

seg fault happens on the CBoolExpr( ) function that validates the Client
i use that whenever a client sends a 'special' package and when the client disconnects ( we got chat channels that remove Clients if their delete flag is on. )

    for(vector<CChat*> :: iterator i = m_ChatRooms.begin( ); i != m_ChatRooms.end( );)
	{
		if(!(*i))
			i = m_ChatRooms.erase( i );
		else
		{
			for(vector<Clients*> :: iterator j = (*i)->m_Users.begin( ); j != (*i)->m_Users.end( );)
			{
				if( !CBoolExpr( (*j) ) )
				{
					Event_UserLeft2( (*j), (*i) );
					j = (*i)->m_Users.erase( j );
				}
				else
					j++;
			}
			
			i++;
				
		}
	}

although i think i fixed it by making that function where we see the segmentation fault to 'non-virtual' and 'volatile' (it was a virtual bool function)

if that's the case... then it means that virtual and multi-threading can not work together.

[strongdrink]

Ok, try setting up a local server/client system that crashes instantly

[Jacob Ensien]

server is still up since yesterday night, so i guess that was it? ^^

virtual functions and multiple threads accessing it = segmentation fault?

first time i see such thing...

[kbw]

that virtual and multi-threading can not work together.

Not true at all.