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51 lines
2.1 KiB
C++
51 lines
2.1 KiB
C++
#include <mpi.h>
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#include <iostream>
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/*
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MPI_Gather(
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const void* sendbuf, //the element to send
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int sendcount, //number of element to send
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MPI_Datatype sendtype, //type of element
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void* recvbuf, //buffer to receive
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int recvcount, //number of elements to receive from each process
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MPI_Datatype recvtype, //type of element
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int root, //rank of the process that have to receive
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MPI_Comm comm //communicator
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)
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*/
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int main(int argc, char* argv[])
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{
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int sendbuf[4] = {1,2,3,4};
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MPI_Init(&argc, &argv); //Initialize the MPI environment //TODO perche qui non (NULL, NULL) ??
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int world_size;
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MPI_Comm_size(MPI_COMM_WORLD, &world_size); //Get the number of processes
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int recvbuf[4*world_size];
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int world_rank;
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MPI_Comm_rank(MPI_COMM_WORLD, &world_rank); //Get the number of process
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//MPI_Gather(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype, root, comm)
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MPI_Gather(sendbuf, 3, MPI_INT, recvbuf, 4, MPI_INT, 1, MPI_COMM_WORLD);
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/*Il sendcount non puo esere maggiore della dimensione del sendbuffer ma puo essere minore, tuttavia
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il processo root si aspetta di ricevere tutto il buffer di partenza. Per questo motivo oltre a dimensionare
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il recvbuf in modo appropriato bisogna ricordare che il processo root disporra in questo modo i dati che
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riceve: [expectedFrom0-0, expectedFrom0-1, expectedFrom0-2, expectedFrom0-3, expectedFrom1-0, ...] supponendo un sendbuf da 4.
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Se vengono inviati meno dati dell'originale, supponiamo 3, allora la parte expectedFrom*-3 risultera' casualmente riempita.
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Il processo root riceve anche i dati che si manda da solo come se facesse parte dei senders.*/
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if(world_rank == 1)
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{
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std::cout << "Process (rank " << world_rank+1 << "/" << world_size << ") recived:" << std::endl;
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for (int i=0; i<4*world_size; i++)
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{
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std::cout << " " << recvbuf[i] << " ";
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}
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std::cout << std::endl;
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}
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MPI_Finalize(); //Clean up the MPI environment
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return 0;
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} |