79 lines
2.7 KiB
C++
79 lines
2.7 KiB
C++
/**
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* Compile
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* mpic++ MPI_Send_Recv.cpp -Wall -pedantic -Wpedantic -o MPI_Send_Recv
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* Usage
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* mpirun -n 4 ./MPI_Send_Recv
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*
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* Note: An easy way to finde the location of the `mpi.h` file is
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* mpic++ --showme:compile
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* which might be usefull to configure the intellicense.
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*/
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#include <iostream>
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#include <sstream>
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#include <mpi.h>
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/** min of two ints (fine for an example) */
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int min(int a, int b) { return a < b ? a : b; }
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int main(int argn, char* argv[]) {
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// Initialize MPI (always required)
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MPI_Init(nullptr, nullptr);
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// Allocate MPI Settings
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int mpi_size; /*< Number of processes */
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int mpi_rank; /*< This process rank (a.k.a. the MPI process ID) */
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// Set/Get MPI Settings
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MPI_Comm_size(MPI_COMM_WORLD, &mpi_size);
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MPI_Comm_rank(MPI_COMM_WORLD, &mpi_rank);
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// Write MPI info to stdout
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std::cout << "Hello World, i am rank " << mpi_rank << " of " << mpi_size
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<< " processes." << std::endl;
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// setting this to small truncates the message (Try it, works fine.)
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constexpr int max_size = 128; /*< Maximum message length */
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// Distinguish between rank 0 and the rest
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if (mpi_rank == 0) {
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// Send a different message to all other ranks
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for (int rank = 1; rank < mpi_size; ++rank) {
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// Build message
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std::ostringstream message;
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message << "Hello rank nr. " << rank;
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std::string sendbuf = message.str();
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// Send message
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MPI_Send(sendbuf.c_str(), min(max_size, sendbuf.size()),
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MPI_CHAR, rank, sendbuf.size(), MPI_COMM_WORLD);
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// Note: the tag beeing set to the string length (hacky, but :-})
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}
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// Report your done
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std::cout << "Done: rank 0 send all messages." << std::endl;
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} else {
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char recvbuf[max_size]; /*< MPI_Recv buffer, e.g. memory to write to */
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MPI_Status status; /*< MPI Status object, e.g. communication info */
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// Each rank listens for a single message from rank 0
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MPI_Recv(recvbuf, max_size,
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MPI_CHAR, 0, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
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if (status.MPI_ERROR) {
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std::cerr << "Error: Recv reported an Error?!" << std::endl;
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} else {
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// Ensure C-style string is terminated and of propper size as
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// the tag encodes the string length.
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// Should be null terminated, but better save than sorry.
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recvbuf[min(max_size - 1, status.MPI_TAG)] = '\0';
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// Print receved message to console
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std::cout << "Recv: " << recvbuf << std::endl;
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}
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}
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// Shutdown MPI (always required)
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MPI_Finalize();
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return 0;
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}
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