我试图找到数组中所有给定数字的总和。我必须以相同的大小拆分数组并发送到每个进程并计算总和。稍后将每个进程的计算总和发送回根进程以获得最终答案。实际上，我知道我可以使用MPI_Scatter。但我的问题是，如果我的列表在奇数。例如，我有一个包含13元素的数组，然后我有3个进程。因此，默认情况下，MPI_Scatter会将数组除以3并保留最后一个元素。基本上，它将仅计算12个元素的总和。我刚使用MPI_Scatter时的输出：
myid = 0 total = 6
myid = 1 total = 22
myid = 2 total = 38
results from all processors_= 66
size= 13
所以，我打算使用MPI_Scatter和MPI_Send。所以我可以得到最后一个元素并通过MPI_Send发送并计算它，并在root进程中接收。但我遇到问题..我的代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mpi.h>
/* globals */
int numnodes, myid, mpi_err;
int last_core;
int n;
int last_elements[];
#define mpi_root 0
/* end globals */
void init_it(int *argc, char ***argv);
void init_it(int *argc, char ***argv) {
mpi_err = MPI_Init(argc, argv);
mpi_err = MPI_Comm_size( MPI_COMM_WORLD, &numnodes );
mpi_err = MPI_Comm_rank(MPI_COMM_WORLD, &myid);
}
int main(int argc, char *argv[]) {
int *myray, *send_ray, *back_ray;
int count;
int size, mysize, i, k, j, total;
MPI_Status status;
init_it(&argc, &argv);
/* each processor will get count elements from the root */
count = 4;
myray = (int*)malloc(count * sizeof(int));
size = (count * numnodes) + 1;
send_ray = (int*)malloc(size * sizeof(int));
back_ray = (int*)malloc(numnodes * sizeof(int));
last_core = numnodes - 1;
/* create the data to be sent on the root */
if(myid == mpi_root){
for(i = 0; i < size; i++)
{
send_ray[i] = i;
}
}
/* send different data to each processor */
mpi_err = MPI_Scatter( send_ray, count, MPI_INT,
myray, count, MPI_INT,
mpi_root, MPI_COMM_WORLD);
if(myid == mpi_root) {
n = 1;
memcpy(last_elements, &send_ray[size-n], n * sizeof(int));
//Send the last numbers to the last core through send command
MPI_Send(last_elements, n, MPI_INT, last_core, 99, MPI_COMM_WORLD);
}
/* each processor does a local sum */
total = 0;
for(i = 0; i < count; i++)
total = total + myray[i];
//total = total + send_ray[size-1];
printf("myid= %d total= %d\n", myid, total);
if(myid == last_core)
{
printf("Last core\n");
MPI_Recv(last_elements, n, MPI_INT, 0, 99, MPI_COMM_WORLD, &status);
}
/* send the local sums back to the root */
mpi_err = MPI_Gather(&total, 1, MPI_INT,
back_ray, 1, MPI_INT,
mpi_root, MPI_COMM_WORLD);
/* the root prints the global sum */
if(myid == mpi_root){
total=0;
for(i = 0; i < numnodes; i++)
total = total + back_ray[i];
printf("results from all processors_= %d \n", total);
printf("size= %d \n ", size);
}
mpi_err = MPI_Finalize();
}
输出：
myid = 0 total = 6
myid = 1 total = 22
myid = 2 total = 38
Last core
[ubuntu:11884] *** An error occurred in MPI_Recv
[ubuntu:11884] *** on communicator MPI_COMM_WORLD
[ubuntu:11884] *** MPI_ERR_TRUNCATE: message truncated
[ubuntu:11884] *** MPI_ERRORS_ARE_FATAL: your MPI job will now abort
--------------------------------------------------------------------------
mpiexec has exited due to process rank 2 with PID 11884 on
node ubuntu exiting improperly. There are two reasons this could occur:
1. this process did not call "init" before exiting, but others in
the job did. This can cause a job to hang indefinitely while it waits
for all processes to call "init". By rule, if one process calls "init",
then ALL processes must call "init" prior to termination.
2. this process called "init", but exited without calling "finalize".
By rule, all processes that call "init" MUST call "finalize" prior to
exiting or it will be considered an "abnormal termination"
This may have caused other processes in the application to be
terminated by signals sent by mpiexec (as reported here).
我知道我做错了。如果你能指出我，我将不胜感激。
答案 0 :(得分：0)
您的last_elements数组没有指定大小。 MPI_Recv错误输出，因为没有空间放置它正在发送的项目。您的代码缺少last_elements的malloc。
答案 1 :(得分：0)
我可能很晚才回答，但也许其他人可以得到帮助。
请查看以下代码
# include <cstdlib>
# include <iostream>
# include <iomanip>
# include <ctime>
# include <mpi.h>
using namespace std;
int main ( int argc, char *argv[] );
void timestamp ( );
//****************************************************************************80
int main ( int argc, char *argv[] )
//****************************************************************************80
{
int *a;
int dest;
float factor;
int global;
int i;
int id;
int ierr;
int n;
int npart;
int p;
int source;
int start;
MPI_Status status;
int tag;
int tag_target = 1;
int tag_size = 2;
int tag_data = 3;
int tag_found = 4;
int tag_done = 5;
int target;
int workers_done;
int x;
//
// Initialize MPI.
//
ierr = MPI_Init ( &argc, &argv );
//
// Get this processes's rank.
//
ierr = MPI_Comm_rank ( MPI_COMM_WORLD, &id );
//
// Find out how many processes are available.
//
ierr = MPI_Comm_size ( MPI_COMM_WORLD, &p );
if ( id == 0 )
{
timestamp ( );
cout << "\n";
cout << "SEARCH - Master process:\n";
cout << " C++ version\n";
cout << " An example MPI program to search an array.\n";
cout << "\n";
cout << " Compiled on " << __DATE__ << " at " << __TIME__ << ".\n";
cout << "\n";
cout << " The number of processes is " << p << "\n";
}
cout << "\n";
cout << "Process " << id << " is active.\n";
//
// Have the master process generate the target and data. In a more
// realistic application, the data might be in a file which the master
// process would read. Here, the master process decides.
//
if ( id == 0 )
{
//
// Pick the number of data items per process, and set the total.
//
factor = ( float ) rand ( ) / ( float ) RAND_MAX;
npart = 50 + ( int ) ( factor * 100.0E+00 );
n = npart * p;
cout << "\n";
cout << "SEARCH - Master process:\n";
cout << " The number of data items per process is " << npart << "\n";
cout << " The total number of data items is " << n << ".\n";
//
// Now allocate the master copy of A, fill it with values, and pick
// a value for the target.
//
a = new int[n];
factor = ( float ) n / 10.0E+00 ;
for ( i = 0; i < n; i++ )
{
a[i] = ( int ) ( factor * ( float ) rand ( ) / ( float ) RAND_MAX );
}
target = a[n/2];
cout << " The target value is " << target << ".\n";
//
// The worker processes need to have the target value, the number of data items,
// and their individual chunk of the data vector.
//
for ( i = 1; i <= p-1; i++ )
{
dest = i;
tag = tag_target;
ierr = MPI_Send ( &target, 1, MPI_INT, dest, tag, MPI_COMM_WORLD );
tag = tag_size;
ierr = MPI_Send ( &npart, 1, MPI_INT, dest, tag, MPI_COMM_WORLD );
start = ( i - 1 ) * npart;
tag = tag_data;
ierr = MPI_Send ( a+start, npart, MPI_INT, dest, tag,
MPI_COMM_WORLD );
}
//
// Now the master process simply waits for each worker process to report that
// it is done.
//
workers_done = 0;
while ( workers_done < p-1 )
{
ierr = MPI_Recv ( &x, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG,
MPI_COMM_WORLD, &status );
source = status.MPI_SOURCE;
tag = status.MPI_TAG;
if ( tag == tag_done )
{
workers_done = workers_done + 1;
}
else if ( tag == tag_found )
{
cout << "P" << source << " " << x << " " << a[x] << "\n";
}
else
{
cout << " Master process received message with unknown tag = "
<< tag << ".\n";
}
}
//
// The master process can throw away A now.
//
delete [] a;
}
//
// Each worker process expects to receive the target value, the number of data
// items, and the data vector.
//
else
{
source = 0;
tag = tag_target;
ierr = MPI_Recv ( &target, 1, MPI_INT, source, tag, MPI_COMM_WORLD,
&status );
source = master;
tag = tag_size;
ierr = MPI_Recv ( &npart, 1, MPI_INT, source, tag, MPI_COMM_WORLD,
&status );
a = new int[npart];
source = 0;
tag = tag_data;
ierr = MPI_Recv ( a, npart, MPI_INT, source, tag, MPI_COMM_WORLD,
&status );
//
// The worker simply checks each entry to see if it is equal to the target
// value.
//
for ( i = 0; i < npart; i++ )
{
if ( a[i] == target )
{
global = ( id - 1 ) * npart + i;
dest = 0;
tag = tag_found;
ierr = MPI_Send ( &global, 1, MPI_INT, dest, tag, MPI_COMM_WORLD );
}
}
//
// When the worker is finished with the loop, it sends a dummy data value with
// the tag "TAG_DONE" indicating that it is done.
//
dest = 0;
tag = tag_done;
ierr = MPI_Send ( &target, 1, MPI_INT, dest, tag, MPI_COMM_WORLD );
delete [] ( a );
}
//
// Terminate MPI.
//
MPI_Finalize ( );
//
// Terminate.
//
if ( id == 0 )
{
cout << "\n";
cout << "SEARCH - Master process:\n";
cout << " Normal end of execution.\n";
cout << "\n";
timestamp ( );
}
return 0;
}
//****************************************************************************80
void timestamp ( )
//****************************************************************************80
{
# define TIME_SIZE 40
static char time_buffer[TIME_SIZE];
const struct std::tm *tm_ptr;
size_t len;
std::time_t now;
now = std::time ( NULL );
tm_ptr = std::localtime ( &now );
len = std::strftime ( time_buffer, TIME_SIZE, "%d %B %Y %I:%M:%S %p", tm_ptr );
std::cout << time_buffer << "\n";
return;
# undef TIME_SIZE
}
，输出为：
SEARCH - Master process:
A program using MPI, to search an array.
Compiled on jan 14 2018 at 11:21:45.
The number of processes is 4
Process 0 is active.
SEARCH - Master process:
The number of data items per process is 101
The total number of data items is 404.
The target value is 14.
P3 202 14
P2 145 14
P2 178 14
P2 180 14
P3 211 14
P3 240 14
P3 266 14
P3 295 14
P1 12 14
P1 23 14
P1 36 14
P1 71 14
SEARCH - Master process:
Normal end of execution.
Process 1 is active.
Process 2 is active.
Process 3 is active.