#ifndef BUFFEREXCHANGE_DEFINED

#include "base.h"


//
// Swap data buffers with a specified set of peer ranks.
//
template <class T> class BufferExchange
{
	protected:
	
		IntVec ranks;
		std::vector<MPI_Request> recv_reqs, send_reqs;
		IntVec recv_lengths, send_lengths; // temporary, used in FullExchange() - don't rely on these for anything else!
		
		int full_exchange_length_tag, full_exchange_buffer_tag, exchange_tag;
		
		int _wait( std::vector<MPI_Request> &reqs );
		void _waitall( std::vector<MPI_Request> &reqs );

	public:
	
		// ensure the data buffers are publically accessible.
		std::vector< std::vector<T> > recv_buffers, send_buffers;
				
		BufferExchange();
		~BufferExchange();
		
		//
		// Resets the internal state to reflect a new set of peer ranks.
		//
		void Clear( IntVec &_ranks );
		
		//
		// For when we don't know the sizes of recv_buffers, but we know the sizes of send_buffers.
		// This is a fully blocking method, it won't return until all comms complete.
		//
		void FullExchange();

		//
		// Nonblocking; assumes the lengths of the receive and send buffers are correct.
		//
		void PostRecvs();
		void PostSends();

		//
		// Blocking wait on ALL receives  / sends to complete.
		//
		void WaitRecvs();
		void WaitSends();
		
		//
		// Blocking wait on any complete operation. Return index into buffer arrays (NOT MPI RANKS!)
		// of a completed recv/send.
		// Return -1 where all outstanding operations are complete.
		//
		int WaitRecv();
		int WaitSend();
		
		//
		// Blocks until all cancellations have completed.
		//
		void CancelRecvs();
};

#define BUFFEREXCHANGE_DEFINED
#endif