C++ - Thread - Pointer to function!

[fantasticamir]

Guys,

I have a problem which takes me 2 days to solve so far, hope you may help me.

I have posted a thread before about it but unfortunately the problem is still there!!

http://www.thescripts.com/forum/thread647482.html

-----
the problem is simply "I do not know what is the correct syntax if I want to call a function in POSIX thread create which has an argument which is pointer to function".

class EventInterface {
   public:
     EventInterface(void (*ptToFunc)(Event *, int));
     .....
     static void * receiveEvent (void (*onMessageFunc)(Event *, int));

}
       
   EventInterface::EventInterface(void (*ptToFunc)(char *, int)){

            pthread_create( &receiveThread, NULL, EventInterface::receiveEvent, (void *) (*ptToFunc))    ?????
          ....
 
      }

   void EventInterface::receiveEvent(void (*onMessageFunc)(Event *, int)){
   .....

    onMessageFunc(notifiedEvent , subscriptionID);
    }

I really have no idea, I almost check all of possible syntaxes but they do not work...

The errors I received are basically because of the syntax faults. (mostly concerning the "invalid conversion from ....")

Thanks,

Amir.

[weaknessforcats]

Your problem is the function pointer.

For Windows, your thread function you supply to CreateThread must be:
[code=cpp]
DWORD WINAPI THreadProc(LPVO ID);
[/code]

You can write any function BUT the function must have an LPVOID argument and return a DWORD. If it doesn't, then it can't be used as a thread.

Read the pthread_create( ) documentation clearly and focus on the type of function pointer required. You may need to type cast your function to the correct type.

[fantasticamir]

Your problem is the function pointer.

For Windows, your thread function you supply to CreateThread must be:
[code=cpp]
DWORD WINAPI THreadProc(LPVO ID);
[/cpp]

You can write any function BUT the function must have an LPVOID argument and return a DWORD. If it doesn't, then it can't be used as a thread.

Read the pthread_create( ) documentation clearly and focus on the type of function pointer required. You may need to type cast your function to the correct type.

I am working with linux.

I just have one question: what is the correct syntax to call a method with function pointer as an argument in pthered_create?

[fantasticamir]

forexample when I define this like:

pthread_create( &receiveThre ad, NULL, EventInterface: :receiveEvent, (void *) (*ptToFunc))

or

pthread_create( &receiveThre ad, NULL, EventInterface: :receiveEvent, (void *) ptToFunc)


I have this error:

error: invalid conversion from 'void* (*)(void (*)(Event*, int))' to 'void* (*)(void*)'

[weaknessforcats]

pthread_create has this prototype:

[code=c]
int pthread_create( pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routin e)(void*), void *arg);

[/code]

The start routine is:

void *(*start_routin e)(void*)

That is, start_routine is a pointer to a function with a void* argunment that returns a void*.

Your function must have thisprototype.

However, this function:
[code=c]
void (*ptToFunc)(Eve nt *, int));
[/code]

does not have a void* argument and does not return a void*. So you can't use this function as a thread.

Yout could use:
[code=c]
void *MyFunction(voi d*);
[/code]

This is exactly the procedure I outlined in the Windows eaxmple. The OS function cannot accommodate just any old function. It has to be of a pre-defined format.

Inside MyFunction(void * arg) you know the arg is an Event* so it is safe to type cast the void* to an Event* and off you go.

[fantasticamir]

I guess I find a way to solve the problem.

 class EventInterface {
            public:
		typedef void (*onMessageFunction)(Event*, int);


		EventInterface(onMessageFunction);
 	
	}
	
	    EventInterface::EventInterface(onMessageFunction pt2Func){
 
                  pthread_create( &receiveThread, NULL, EventInterface::receiveEvent, (void *) pt2Func)                   *
 
        }

       void EventInterface::receiveEvent(void * arg){
	
	  onMessageFunction onMessageFunc;                               *
          onMessageFunc= (onMessageFunction) arg;		
 
          onMessageFunc(notifiedEvent , subscriptionID);
       }

However now I see some warning like:

ISO C++ forbids casting between pointer-to-function and pointer-to-object

for those lines I showed by *.

Do you have any idea?

[weaknessforcats]

Did you read Post #5??

[fantasticamir]

Did you read Post #5??

actually I read that after I post my new post!

The problem is the name of call back function is called from EventInterface constructor. so how could it be possible with your solution?!

maybe I need to read your solution more accurately.

[fantasticamir]

for those who might see this thread then... I finally come up with a syntax which WORKS!

I just wrap my pointer to function in an struct!\

class EventInterface 
{

public:

	typedef struct{
		void (*onMessageFunction)(Event*, int);
	} callBackFunc;

	EventInterface(callBackFunc);
        ...
	static void * receiveEvent (void *);

}

EventInterface::EventInterface(callBackFunc ptToFunc){
 
	pthread_create( &receiveThread, NULL, EventInterface::receiveEvent, (void *) &ptToFunc)
	
}

void * EventInterface::receiveEvent(void * arg){
	
	callBackFunc * onMessageFunc;
	onMessageFunc= (callBackFunc*) arg;

       .....

       onMessageFunc->onMessageFunction(notifiedEvent , subscriptionID);
}

[AdrianH]

for those who might see this thread then... I finally come up with a syntax which WORKS!

I just wrap my pointer to function in an struct!\

class EventInterface 
{

public:

	typedef struct{
		void (*onMessageFunction)(Event*, int);
	} callBackFunc;

	EventInterface(callBackFunc);
        ...
	static void * receiveEvent (void *);

}

EventInterface::EventInterface(callBackFunc ptToFunc){
 
	pthread_create( &receiveThread, NULL, EventInterface::receiveEvent, (void *) &ptToFunc)
	
}

void * EventInterface::receiveEvent(void * arg){
	
	callBackFunc * onMessageFunc;
	onMessageFunc= (callBackFunc*) arg;

       .....

       onMessageFunc->onMessageFunction(notifiedEvent , subscriptionID);
}

Don't do it. It will mess up. Get rid of the address operator. You are passing the address of where the callback pointer is stored on the stack.
[code=c] pthread_create( &receiveThre ad, NULL, EventInterface: :receiveEvent, (void *) ptToFunc)[/code].


Adrian