#include <sys/uio.h>
#include <CTransport.h>
class CTransport
{
public:
virtual void recv(void** ppData, size_t& size) = 0;
virtual void send(iovec* parts, size_t numParts) = 0;
virtual void end();
};
Transports are objects that carry data across some high level
protocol for data transport. Examples of high level protocols
are ZeroMQ (ZMQ), MPI, or event raw TCP/IP sockets.
Transports are normally bound into a
CSender or CReceiver
object.
Transport insulate the actual mechanisms of data transport from
those objects. Each concrete transport must, at a minimum
implement the recv and
send methods. In addition,
transports may implement the end method
which is used to signal for a transport used inside a
CSender that no more data will be transferred
on that transport.
virtual = 0 void recv(void** ppData, size_t& size);
Abstract interface to receive data from a concrete
transport. ppData will be
written with a pointer to the data received.
The storage pointed to must have been dynamically
allocated via the malloc()(3)
library function.
size will be written with the
number of bytes of data received. Note that all errors
should be signalled via exceptions. While not mandatory,
in many transports, a size of 0 is used to indicate end
of data. In that case, the pointer is not meaningful
and should not be freed.
virtual = 0 void send(iovec* parts, size_t numParts);
Writes a message to the peer of the transport.
See the manual pages for
writev(2) for a description of
the iovec struct.
numParts are the number of
parts in the message
This call mechanism allows messages to be built via a gather mechanism that, in some transports, can minimize the data copies needed to marshall the complete message.
Concrete transports must gaurantee that they are
done using parts buffers on
return. Thus, if zero copy, asynchronous sends are
use by the transport, the send
must block until the send has actually completed.
virtual void end();
Transports that have a mechanism to signal an end of data should implement this. The default implementation is to do nothing. One standard used to indicate an end of data condition is to send a zero length message. The underlying transport protocol must, however support this if it is to be used.