MPI 每個rank依次往下一個rank傳送訊息的迴圈
阿新 • • 發佈：2019-02-14
https://www.sharcnet.ca/help/index.php/Getting_Started_with_MPI
上面的實現之所有沒有死鎖是依賴於資料傳輸的中間buffer，也就是寫的時候直接寫到buffer，不需要等到接收端的迴應，程式碼是可以正確執行的，但是他的實現是並不是完全依賴MPI的標準，下面給出一個MPI 安全的例子#include <stdio.h> #include <mpi.h> #define BUFMAX 81 int main(int argc, char *argv[]) { char outbuf[BUFMAX], inbuf[BUFMAX]; int rank, size; int sendto, recvfrom; MPI_Status status; MPI_Init(&argc, &argv); MPI_Comm_rank(MPI_COMM_WORLD, &rank); MPI_Comm_size(MPI_COMM_WORLD, &size); sprintf(outbuf, "Hello, world! from process %d of %d", rank, size); sendto = (rank + 1) % size; recvfrom = ((rank + size) - 1) % size; MPI_Send(outbuf, BUFMAX, MPI_CHAR, sendto, 0, MPI_COMM_WORLD); MPI_Recv(inbuf, BUFMAX, MPI_CHAR, recvfrom, 0, MPI_COMM_WORLD, &status); printf("[P_%d] process %d said: \"%s\"]\n", rank, recvfrom, inbuf); MPI_Finalize(); return(0); }
#include <stdio.h> #include <mpi.h> #define BUFMAX 81 int main(int argc, char *argv[]) { char outbuf[BUFMAX], inbuf[BUFMAX]; int rank, size; int sendto, recvfrom; MPI_Status status; MPI_Init(&argc, &argv); MPI_Comm_rank(MPI_COMM_WORLD, &rank); MPI_Comm_size(MPI_COMM_WORLD, &size); sprintf(outbuf, "Hello, world! from process %d of %d", rank, size); sendto = (rank + 1) % size; recvfrom = ((rank + size) - 1) % size; if (!(rank % 2)) { MPI_Send(outbuf, BUFMAX, MPI_CHAR, sendto, 0, MPI_COMM_WORLD); MPI_Recv(inbuf, BUFMAX, MPI_CHAR, recvfrom, 0, MPI_COMM_WORLD, &status); } else { MPI_Recv(inbuf, BUFMAX, MPI_CHAR, recvfrom, 0, MPI_COMM_WORLD, &status); MPI_Send(outbuf, BUFMAX, MPI_CHAR, sendto, 0, MPI_COMM_WORLD); } printf("[P_%d] process %d said: \"%s\"]\n", rank, recvfrom, inbuf); MPI_Finalize(); return(0); }
這個例子和上面的最大的不同就是根據rank分成兩組，這兩組的接收和傳送的順序是剛好相反的，這樣如果沒有buffer，一樣可以正確的得到結果，因此是安全的。