Hello, Sorry to post this long, stupid and simple question. I found that some time MPI_Barrier cannot stop all the process. I try to write a simple test program to create data_struct shown below: #include <stdlib.h> #include <stdio.h> #include "mpi.h" typedef struct { int a; char b; int c; int d; } foo; int main(int argc, char *argv[]) { int rank, size; int i; foo x; MPI_Init(&argc, &argv); MPI_Comm_size(MPI_COMM_WORLD, &size); MPI_Comm_rank(MPI_COMM_WORLD, &rank); char processor_name[MPI_MAX_PROCESSOR_NAME]; int name_len; MPI_Get_processor_name(processor_name, &name_len); printf("-- processor %s, rank %d out of %d processors\n", processor_name, rank, size); * MPI_Barrier(MPI_COMM_WORLD);* int count=4; MPI_Datatype testtype; MPI_Datatype types[4] = {MPI_INT, MPI_CHAR, MPI_INT, MPI_DOUBLE}; int len[4] = {1, 1, 1, 1}; MPI_Aint disp[4]; long int base; MPI_Address(&x, disp); MPI_Address(&(x.a), disp+1); MPI_Address(&(x.b), disp+2); MPI_Address(&(x.c), disp+3); base = disp[0]; for(i=0; i<4; i++) disp[i] -= base; MPI_Type_struct(count, len, disp, types, &testtype); MPI_Type_commit(&testtype); if(rank == 0){ x.a = 2; x.b = 0; x.c = 10; x.d = 3; } printf("rank %d(before): x value is %d, %d, %d, %d\n", rank, x.a, x.b, x.c, x.d); *MPI_Barrier(MPI_COMM_WORLD);* MPI_Bcast(&x, 1, testtype, 0, MPI_COMM_WORLD); printf("rank %d(after): x value is %d, %d, %d, %d\n", rank, x.a, x.b, x.c, x.d); MPI_Finalize(); return 0; } the output should be looks like: -- processor iocfccd3.aps.anl.gov, rank 0 out of 4 processors -- processor iocfccd3.aps.anl.gov, rank 3 out of 4 processors -- processor iocfccd3.aps.anl.gov, rank 1 out of 4 processors -- processor iocfccd3.aps.anl.gov, rank 2 out of 4 processors rank 0(before): x value is 2, 0, 10, 3 rank 1(before): x value is 1197535864, -1, 4994901, 0 rank 2(before): x value is 1591464488, -1, 4994901, 0 rank 3(before): x value is 1851622184, -1, 4994901, 0 rank 0(after): x value is 2, 0, 10, 3 rank 3(after): x value is 2, 0, 10, 3 rank 1(after): x value is 2, 0, 10, 3 rank 2(after): x value is 2, 0, 10, 3 but some time is shows as: -- processor iocfccd3.aps.anl.gov, rank 0 out of 4 processors rank 0(before): x value is 2, 0, 10, 3 rank 0(after): x value is 2, 0, 10, 3 -- processor iocfccd3.aps.anl.gov, rank 1 out of 4 processors rank 1(before): x value is -464731256, -1, 4994901, 0 rank 1(after): x value is 2, 0, 10, 3 -- processor iocfccd3.aps.anl.gov, rank 2 out of 4 processors rank 2(before): x value is 1863042488, -1, 4994901, 0 rank 2(after): x value is 2, 0, 10, 3 -- processor iocfccd3.aps.anl.gov, rank 3 out of 4 processors rank 3(before): x value is 1721065144, -1, 4994901, 0 rank 3(after): x value is 2, 0, 10, 3 or -- processor iocfccd3.aps.anl.gov, rank 0 out of 4 processors -- processor iocfccd3.aps.anl.gov, rank 1 out of 4 processors rank 1(before): x value is -1883169624, -1, 4994901, 0 -- processor iocfccd3.aps.anl.gov, rank 2 out of 4 processors rank 2(before): x value is -451256152, -1, 4994901, 0 -- processor iocfccd3.aps.anl.gov, rank 3 out of 4 processors rank 3(before): x value is 1715067240, -1, 4994901, 0 rank 0(before): x value is 2, 0, 10, 3 rank 0(after): x value is 2, 0, 10, 3 rank 1(after): x value is 2, 0, 10, 3 rank 2(after): x value is 2, 0, 10, 3 rank 3(after): x value is 2, 0, 10, 3 it is all randomly, I am not sure where is the problem. The second issue is I use MPI_Datatype to create a MPI struct for broadcast. However, as the program shown above, if I change the struct: typedef struct { int a; char b; int c; *int d;* } foo; as typedef struct { int a; char b; int c; *double d*; } foo; I found the result is: -- processor ephesus.ece.iit.edu, rank 1 out of 4 processors -- processor ephesus.ece.iit.edu, rank 2 out of 4 processors -- processor ephesus.ece.iit.edu, rank 3 out of 4 processors -- processor ephesus.ece.iit.edu, rank 0 out of 4 processors rank 0(before): x value is 2, 0, 10, 3.250000 rank 3(before): x value is 0, 0, 547474368, 0.000000 rank 1(before): x value is 0, 0, 547474368, 0.000000 rank 2(before): x value is 0, 0, 547474368, 0.000000 rank 0(after): x value is 2, 0, 10, 3.250000 *rank 2(after): x value is 2, 0, 10, 0.000000 <- should be 3.25 rank 3(after): x value is 2, 0, 10, 0.000000 <- should be 3.25 rank 1(after): x value is 2, 0, 10, 0.000000** <- should be 3.25 * Do you have any clues on why this happened? Thanks a lot! -- Best Regards, Sufeng Niu ECASP lab, ECE department, Illinois Institute of Technology Tel: 312-731-7219