#include <CMPIFanoutTransport_mpi.h>
class CMPIFanoutTransport : public CMPITransport, public CFanoutTransport
{
public:
CMPIFanoutTransport();
CMPIFanoutTransport(MPI_Comm communicator);
virtual void recv(void** ppData, size_t& size);
virtual void send(iovec* parts, size_t numParts);
virtual void end();
static const int dataRequestTag = 2;
};
This transport provides the supplier side of mechanism to fanout
data chunks to multiple workers. Fanouts allow for worker
processes to operate in parallel on distinct chunks of data.
Clients of this data accept it using a
CMPIFanoutClientTransport class.
At a low level, the protocol used is a pull protocol. When a worker
is ready for data, it requests it by sending this rank an empty
message with a dataRequestTag (value is
2). send operations
read the next data request message and respond by sending the
requested data to the rank that sent the data request.
As each process sends a data request, it is rememebered and end of data is handled by sending end of datas as requested until all registered requestors have received the end..
CMPIFanoutTransport();
Constructs a new fanout transport using the default communicator (MPI_COMM_WORLD).
CMPIFanoutTransport(MPI_Comm communicator);
Constructs the transport using an alternate
communicator. Note that
since the transport is not point to point, there's not
a concept of the receiver rank.
virtual void recv(void** ppData, size_t& numParts);
Throws an std::logic_error
as this transport is uni-dicectional.
virtual void send(iovec* parts, size_t numParts);
Sends the message to the next requestor using the underlying transport. You can think of this as having the following pseudocode implementation:
get request message using base class recv.
get rank of request message sender after ensuring the tag is a data request tag.
set receive rank of base class.
send message using base class send.
Note that in the above pseudo code, if the
message received when getting the data request is non-empty,
or is not tagged by a dataRequestTag,
the method throws a std::logic_error
exception
Note as well that request messages from first time requestors result in the rank of the requestor being entered in a registry of clients.
virtual void end();
Sends an end to all clients. The pseudo code for this is essentially:
while the client registry is not empty:
get a data request as in send
send an end message to the requestor.
Remove the requestor from the client registry.
endwhile
Note that it's therefore important for there not to be so many workers for a small data set that some of them never get any data. If that happens, it's possible the client registry can be empty before some of those workers requested data and received end messages.
For very small data sets, it might be wise to only constitute a single worker.