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G4MPIutils.hh
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25 //
26 // Utility functions for MPI G4 interface
27 #ifndef G4MPIUTILS_HH
28 #define G4MPIUTILS_HH
29 #include <map>
30 #include <vector>
31 #include <functional>
32 #include <numeric>
33 
34 //Namespace with some utility functions for G4 MPI integration.
35 //Main utilities:
36 // G4mpi::Merge(...) : Merge results via a semi-optimized communication
37 // patterns between ranks. Note that this implementation
38 // is not topology aware. This means that MPI_Reduce and
39 // MPI_Gather are more performant. However if you cannot
40 // implement an appropriate MPI reducer or you cannot efford
41 // the memory overhead of Gather, this can be used instead of
42 // p2p communications.
43 namespace G4mpi {
44  //Simple data type representing a rank
45  typedef unsigned int rank_t;
46  //A couple of sending/receiving ranks
47  typedef std::pair<rank_t,rank_t> couple_t;
48  //This map represent, for each cycle (key) a set of communications
49  //pairs
50  typedef std::map<int,std::vector<couple_t> > commMap_t;
51 
52  //This function takes as input a vector of rank_t objects representing
53  //a communication node identified by an ID (rank:int).
54  //It returns a map of cycle:int -> vector<pairs<rank_t> >
55  //Representing a sequence of communciation cycles. At each communication cycle
56  //one or more p2p communications are established: in the pair the first element
57  //is the sender and the second element of the pair is the receiver
58  //At the end of the cycles all communications have been done to rank 0
59  //For example with 4 nodes: [0,1,2,3] we have:
60  // Cycle 0: (3->2),(1->0)
61  // Cycle 1: (2->0)
62  // With 5 nodes:
63  // Cycle 0: (4->3),(2->1)
64  // Cycle 1: (3->1)
65  // Cycle 2: (1->0)
66  // The algorithm can be used to implement a communication across mpi ranks
67  // optimizing the network trafic. Each rank (the nodes) can send/receive to another node.
68  // Once they have sent out the payload they become empty and non-active anymore.
69  commMap_t buildCommunicationMap( std::vector<rank_t>& input );
70 
71  //Performs merging to rank 0 using the provided sender, receiver and barrier functions.
72  //CommSize is the size of the communicator and myrank is the rank of the caller
73  //For example: assume a class UserMerger has two members Send(uint) and
74  // Receive(uint) and we are using a MPI::Intracomm object as
75  // communicator, then to use this function the ranks can:
76  // using std::placeholers::_1;
77  // std::function<void(unsigned int)> sender =
78  // std::bind(&Merger::Send,&mergerInst,_1);
79  // std::function<void(unsigned int)> receiver =
80  // std::bind(&Merger::Receiver,&mergerInst,_1);
81  // std::function<void(void)> barrier =
82  // std::bind(&MPI::Intracomm::Barrier,&commInst);
83  // G4mpi::Merge(sender,receiver,barrier,commSize,myrank);
84  void Merge( std::function<void(unsigned int)> senderF ,
85  std::function<void(unsigned int)> receiverF ,
86  std::function<void(void)> barrierF ,
87  unsigned int commSize , unsigned int myrank);
88  //Type representing a merging functions
89  typedef std::function<void(std::function<void(unsigned int)>,
90  std::function<void(unsigned int)>,
91  std::function<void(void)>,
92  unsigned int, unsigned int)>
94 }
95 
96 #endif //G4MPIUTILS_HH
unsigned int rank_t
Definition: G4MPIutils.hh:45
G4double(* function)(G4double)
std::pair< rank_t, rank_t > couple_t
Definition: G4MPIutils.hh:47
commMap_t buildCommunicationMap(std::vector< rank_t > &input)
Definition: G4MPIutils.cc:37
typedef int(XMLCALL *XML_NotStandaloneHandler)(void *userData)
void Merge(std::function< void(unsigned int)> senderF, std::function< void(unsigned int)> receiverF, std::function< void(void)> barrierF, unsigned int commSize, unsigned int myrank)
Definition: G4MPIutils.cc:161
std::map< int, std::vector< couple_t > > commMap_t
Definition: G4MPIutils.hh:50
std::function< void(std::function< void(unsigned int)>, std::function< void(unsigned int)>, std::function< void(void)>, unsigned int, unsigned int)> mergerHandler_t
Definition: G4MPIutils.hh:93