Re: [sigc] templates and my problem

[Ulrich Eckhardt <ulrich eckhardt dominolaser com>]

Am 02.08.2012 07:51, schrieb Mohsen Pahlevanzadeh:
> Thank you so mush, i wake up now,I wrote the following function as a
> signal:
> ///////////////////////////////////////////////////
> bool NetworkSocket::isDataReady()
> {
> void *buffer;
> sockaddr_in from;
> socklen_t fromLength = sizeof( from );
>
> if (::recvfrom(this->socketFD,buffer,FRAMEBUFFER + 6, 0, (sockaddr *)&this->getSocketAddressStructureOfServer(), &fromLength ) == -1)
> {
> if (errno == EAGAIN || errno == EWOULDBLOCK)
> return false;
> }
> return true;
>
> }
> /////////////////////////////////////////////////

I don't know where you see any signalling being done here. There are 
various things wrong with your code though, like 'buffer' not being a 
buffer but an unitialized pointer, unused variables, unindented code 
(this could be the fault of your email client), confusing control flow 
(what is this true or false thing?), C-style casts in C++ code.


> When in blocking mode data is ready it can notify me that i can read
> socket...
> Then i wrote a function as slot:
> ///////////////////////////////////////////////////
> int NetworkSocket::readDatagrams(unsigned char *buffer, string
> &srcAddress, unsigned short int & srcPort)
> {
> unsigned int maximumPacketSize = FRAMEBUFFER + 6;
> int returnValue ;
> sockaddr_in from;
> socklen_t fromLength = sizeof( from );
> int receivedBytes;
>
> fromLength = sizeof(this->getSocketAddressStructureOfServer());
> receivedBytes = recvfrom( this->socketFD, buffer, maximumPacketSize, 0, (sockaddr *)&this->getSocketAddressStructureOfServer(), &fromLength );
>
> returnValue = receivedBytes;
> if ( receivedBytes <= 0 )
> returnValue = -1;
>
>
> srcAddress = inet_ntoa(this->getSocketAddressStructureOfServer().sin_addr);
> srcPort = ntohs( ( unsigned short int)this->getSocketAddressStructureOfServer().sin_port );
>
> return returnValue;
> }
> ////////////////////////////////////////////////////////

...sizeof is not a function, you only need (brackets) when applying that 
operator to a type, not to a reference. Again, lots of unused variables, 
something which you could avoid systematically by always declaring _and_ 
initializing them in the same place.


> Above functions work fine, Kjell helped and i debug my code that wrote
> in asleep, i define the following 2 lines in class body:
> /////////////////////////////
> sigc::signal<bool> ready;
> void run();
> ///////////////////////////
> the i wrote following code in constructor:
> //////////////////////////
> this->ready.connect(sigc::mem_fun(*this,&NetworkSocket::createThread));
> /////////////////////////////////////////
> Question:
> But i don't relate my signal (isDataReady()) to createThread

I'm not sure what your problem is here, if you want your function to be 
called, just do that directly or maybe indirectly by emitting the 
signal. Also, do you really want to create a thread when something is ready?


However, I think you are going about this the wrong way on a very basic 
conceptual level. Let me explain...

Example 1: The ready() signal
If there is data ready, you probably want to call it with 'true' as 
parameter. If no data is ready, do you really want to call it with false 
as parameter? My approach would have been to emit a signal with the 
received data whenever I receive the data and not emit anything when no 
data is received.

Example 2: The readDatagrams() slot
Here, you receive data which is stored in a buffer provided by the 
caller. What happens if multiple slots are connected to the same signal? 
Or if none are connected? In general, a slot/signal framework is IMHO 
most "natural" when you have one sender and multiple receivers and when 
the receiver doesn't expect any response.


I think that the approach that best suits your problem is that you start 
a thread that receives datagrams and then emits a signal with the 
received data.

{Removed dozens of lines of quoted text without any relation to the 
question.}


Good luck!

Uli


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