On 2 Oct 2003 13:47:49 -0700,
mp********@hotm ail.com (MPowell) wrote:
Well, I can fix the errors in the code, but you'll have to explain
what the code is meant to do. What do you want to do with the messages
that you receive? Do you need to perform some action depending on the
type of message you receive?
Consider
The below doesn't answer the question, a couple of paragraphs of text
might.
#define ID_ERROR_MASK 0x08 // #defined at top of the translation unit
#define ID_MASK 0x07 // #defined at top of the translation unit
int _msg2_header_er ror_count = 0;
int _msg1_header_er ror_count = 0;
int _msg2_message_i ndex = 0;
int _msg1_message_i ndex = 0;
// lots more
struct _MSG2_STATUS // here for demo and lots more of these
{
// for simplicity strip out 'stuff'.
unsigned int idx : 1;
unsigned int ldx : 32;
} MSG2_STATUS;
MSG2_STATUS _msg2_message[ 2 ]; // for double buffering
I now finally understand what you mean by double buffering - you want
to keep the last two messages of each type.
// lots more
The Create function will look at the msg_id (which it does) then check
for error.
if (msg_id & ID_ERROR_MASK) == 0 )
{
// if no error look at msg_type
MSG_HEADER msg_type =
(((( msg_id >> 4 ) & ID_MASK ) <<3 )) | ( msg_id &
ID_MASK );
Lets suppose now the msg_type maps to MSG2_STATUS defined above
switch (msg_type)
{
case _msg2_status: //got a status 2 message
// double buffer it
i = _msg2_message_i ndex ^ 1;
memcpy( &_msg2_messa ge[i], buffer, sizeof(MSG2_STA TUS) );
_msg2_message_i ndex ^= 1;
_msg2_message_r eady = TRUE;
break;
case _msg1_status: //got a status 1 message
// double buffer it
i = _msg1_message_i ndex ^ 1;
memcpy( &_msg1_messa ge[i], buffer, sizeof(MSG1_STA TUS) );
_msg1_message_i ndex ^= 1;
_msg1_message_r eady = TRUE;
break;
// and so on
default:
break;
The above code doesn't really do anything. Instead, you should
probably just add the message to a queue and signal a condition
variable on that queue so that another thread whose job is to process
these messages can do so.
}
else
{
switch( msg_id )
{
case _msg2_header_er ror: //got a status 2 message
_msg2_header_er ror_count++;
printf (" msg2_header_err or = &d ", msg2_header_err or);
break;
case _msg1_header_er ror: //got a status 2 message
_msg1_header_er ror_count++;
// I suspect it'd be prudent to pass in the counters and
have values returend by the ++ ostream approach
printf (" msg1_header_err or = &d ", msg1_header_err or);
break;
// and so on
default:
break;
}
}
So now, double buffer the data,increment a counter, then set a flag -
for no errors. For errors, increment an error counter. The current
template style approach is certainly more elegant
Yes, since all messages can be treated the same - no switch
statements. Polymorphism is the important thing here though -
templates are just an implementation detail.
A separate function within the class should retrieve the most current
double buffer data.
Does this operate in the same thread? It might be good to put it in
another thread.
I suspect (assuming i understand templates) eachbuffered data will be 'pushed' into a container/holder/??
Seems like a good idea.
and whennecessary (a 120hz processing rountine retrieves the latest) retrieved
via a call to some function with the template parameter being the
appropriate struct.
Yes, something like that. You could use the visitor pattern as Gianni
suggested.
Lastly, the individual structs form a part of an overall struct. ie
struct OVERALL
{
MSG1_TYPE msg1;
MSG2_TYPE msg2;
lots more.
}
A separate function will retrieve the 'overall'.
Now I'm confused - aren't the messages separate? What *are* these
messages? What do they signify? Where do they come from? Some hardware
device? How are you meant to react to different messages? Why is there
more than one message type?
In essence, a template to 'get' the data and hold data for the
requestor
> CMDBase* Create(unsigned char const* buffer)
> {
> //MSG_HEADER* msg_id = reinterpret_cas t<MSG_HEADER*>( buffer);
> MSG_HEADER* msg_id; // only here because reinterpret_cas t error
>complaint
>
> //insert error checking!
> return (m_creators[msg_id->source])(buffer);
> }
The above function should go more like this:
CMDBase* Create(unsigned char const* buffer)
{
MSG_HEADER const* msg_id = reinterpret_cas t<MSG_HEADER
const*>(buffer) ;
map_t::const_it erator i = m_creators.find (msg_id->source);
map_t error ??
Whoops, that's meant to be a typedef for the map type that you need to
add to your class definition. e.g.
typedef std::map<int, Creator*> map_t;
Following is some complete compileable code that might help. It
basically shows how to enqueue all messages onto a queue, and how you
might go about processing those messages. If you might need different
processors for the messages in different circumstances, then the
visitor pattern might be appropriate. This is rather a lot to take in
if you are quite new to C++, but I hope it helps in any case.
#include <iostream>
#include <map>
#include <queue>
using namespace std;
//message queue
class CMDBase;
queue<CMDBase*> CMDQueue;
enum MSG_ID
{
msg1_cmd = 0,
msg1_status = 1,
msg2_status = 2
};
struct MSG_HEADER
{
MSG_ID source;
unsigned int msg_length : 12;
unsigned int count : 4;
};
struct MSG2_STATUS
{
MSG_HEADER header;
unsigned int idx : 1;
unsigned int jdx : 3;
unsigned int kdx : 4;
unsigned int spare : 24;
unsigned int ldx : 32;
};
struct MSG1_STATUS
{
MSG_HEADER header;
unsigned int idx : 1;
unsigned int jdx : 3;
unsigned int kdx : 4;
unsigned int spare : 8;
};
struct MSG1_CMD
{
MSG_HEADER header;
unsigned int idx : 1;
unsigned int jdx : 3;
};
class CMDProcessor
{
public:
void process(MSG2_ST ATUS& msg)
{
std::cout << "MSG2_STATU S processed\n";
}
void process(MSG1_ST ATUS& msg)
{
std::cout << "MSG1_STATU S processed\n";
}
void process(MSG1_CM D& cmd)
{
std::cout << "MSG1_CMD processed\n";
}
};
class CMDBase
{
public:
virtual ~CMDBase(){}
virtual void process(CMDProc essor* processor) = 0;
};
template <class CMD>
class CMDHolder: public CMDBase
{
public:
CMDHolder(unsig ned char const* buffer)
{
memcpy(&m_CMDSt ruct, buffer, sizeof m_CMDStruct);
}
virtual void process(CMDProc essor* processor)
{
processor->process(m_CMDS truct);
}
private:
CMD m_CMDStruct;
};
class CMDFactory
{
public:
static CMDFactory& instance()
{
static CMDFactory fact;
return fact;
}
// Register the creator
template <class T> void Register(int Id)
{
m_creators[Id] = CMDCreator<CMDH older<T> >;
}
// unregister creator
bool Unregister( const int& Id )
{
return m_creators.eras e( Id ) == 1;
}
CMDBase* Create(unsigned char const* buffer)
{
MSG_HEADER const* msg_id = reinterpret_cas t<MSG_HEADER
const*>(buffer) ;
map_t::const_it erator i = m_creators.find (msg_id->source);
if (i == m_creators.end( ))
{
throw runtime_error(" Invalid source");
}
else
{
//call create function through pointer.
return (i->second)(buffer );
}
}
private:
typedef CMDBase* (*CMDCreator_t) (unsigned char const*);
template <class T>
static CMDBase* CMDCreator(unsi gned char const* buffer)
{
return new T(buffer);
}
typedef std::map<int, CMDCreator_t> map_t;
map_t m_creators;
};
void register_types( )
{
CMDFactory::ins tance().Registe r<MSG1_CMD>(0) ;
CMDFactory::ins tance().Registe r<MSG1_STATUS>( 1);
CMDFactory::ins tance().Registe r<MSG2_STATUS>( 2);
}
size_t ReadData(unsign ed char* buffer, size_t size)
{
//generate sample data
static bool doMsg1 = false;
void* data;
size_t actualSize;
MSG1_STATUS msg1 = {};
MSG2_STATUS msg2 = {};
if (doMsg1)
{
msg1.header.sou rce = msg1_status;
data = &msg1;
actualSize = sizeof msg1;
}
else
{
msg2.header.sou rce = msg2_status;
data = &msg2;
actualSize = sizeof msg2;
}
if (size < actualSize)
throw runtime_error(" buffer too short");
memcpy(buffer, data, actualSize);
doMsg1 = !doMsg1;
return actualSize;
}
CMDProcessor processor;
void processQueue()
{
while (!CMDQueue.empt y())
{
CMDBase* cmd = CMDQueue.front( );
CMDQueue.pop();
cmd->process(&proce ssor);
delete cmd;
}
}
void fillQueue()
{
unsigned char buffer[512];
ReadData(buffer , 512);
CMDBase* newCommand = CMDFactory::ins tance().Create( buffer);
CMDQueue.push(n ewCommand);
}
int main ( void )
{
register_types( );
for (int i = 0; i < 5; ++i)
{
fillQueue();
processQueue();
}
return EXIT_SUCCESS;
}
